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dhcpd.conf(5)							 dhcpd.conf(5)

NAME
       dhcpd.conf - dhcpd configuration file

DESCRIPTION
       The  dhcpd.conf	file contains configuration information for dhcpd, the
       Internet Systems Consortium DHCP Server.

       The dhcpd.conf file is a free-form ASCII text file.  It	is  parsed  by
       the  recursive-descent  parser  built into dhcpd.  The file may contain
       extra tabs and newlines for formatting purposes.	 Keywords in the  file
       are  case-insensitive.  Comments may be placed anywhere within the file
       (except within quotes).	Comments begin with the # character and end at
       the end of the line.

       The file essentially consists of a list of statements.  Statements fall
       into two broad categories - parameters and declarations.

       Parameter statements either say how to do something (e.g., how  long  a
       lease  to  offer),  whether to do something (e.g., should dhcpd provide
       addresses to unknown clients), or what parameters  to  provide  to  the
       client (e.g., use gateway 220.177.244.7).

       Declarations  are  used	to  describe  the  topology of the network, to
       describe clients on the network,	 to  provide  addresses	 that  can  be
       assigned	 to  clients,  or to apply a group of parameters to a group of
       declarations.  In any group of parameters and declarations, all parame‐
       ters  must  be  specified before any declarations which depend on those
       parameters may be specified.

       Declarations about network topology include the shared-network and  the
       subnet  declarations.   If  clients  on	a  subnet  are	to be assigned
       addresses dynamically, a range declaration must appear within the  sub‐
       net  declaration.   For	clients with statically assigned addresses, or
       for installations where only known clients will be  served,  each  such
       client  must  have a host declaration.  If parameters are to be applied
       to a group of declarations which are not related strictly on a per-sub‐
       net basis, the group declaration can be used.

       For  every  subnet  which will be served, and for every subnet to which
       the dhcp server is connected, there must	 be  one  subnet  declaration,
       which  tells  dhcpd how to recognize that an address is on that subnet.
       A subnet declaration is required for each subnet even if	 no  addresses
       will be dynamically allocated on that subnet.

       Some  installations  have  physical  networks on which more than one IP
       subnet operates.	 For example, if there is a site-wide requirement that
       8-bit  subnet  masks  be	 used, but a department with a single physical
       ethernet network expands to the point where it has more than 254 nodes,
       it may be necessary to run two 8-bit subnets on the same ethernet until
       such time as a new physical network can be added.  In  this  case,  the
       subnet  declarations  for  these	 two  networks	must  be enclosed in a
       shared-network declaration.

       Note that even when the shared-network declaration is absent, an	 empty
       one  is	created	 by  the  server to contain the subnet (and any scoped
       parameters included in the subnet).  For practical purposes, this means
       that  "stateless"  DHCP	clients,  which are not tied to addresses (and
       therefore subnets) will receive	the  same  configuration  as  stateful
       ones.

       Some  sites  may	 have  departments which have clients on more than one
       subnet, but it may be desirable to offer those clients a uniform set of
       parameters  which  are  different than what would be offered to clients
       from other departments on the same subnet.  For clients which  will  be
       declared	 explicitly  with host declarations, these declarations can be
       enclosed in a group declaration along with  the	parameters  which  are
       common to that department.  For clients whose addresses will be dynami‐
       cally assigned, class declarations and conditional declarations may  be
       used  to	 group	parameter  assignments based on information the client
       sends.

       When a client is to be booted, its boot parameters  are	determined  by
       consulting that client's host declaration (if any), and then consulting
       any class declarations matching the client, followed by the pool,  sub‐
       net  and shared-network declarations for the IP address assigned to the
       client.	Each of these declarations itself  appears  within  a  lexical
       scope,  and  all	 declarations at less specific lexical scopes are also
       consulted for client option declarations.  Scopes are never  considered
       twice,  and  if	parameters  are	 declared  in more than one scope, the
       parameter declared in the most specific scope is the one that is used.

       When dhcpd tries to find a host declaration  for	 a  client,  it	 first
       looks for a host declaration which has a fixed-address declaration that
       lists an IP address that is valid for the subnet or shared  network  on
       which  the  client  is  booting.	 If it doesn't find any such entry, it
       tries to find an entry which has no fixed-address declaration.

EXAMPLES
       A typical dhcpd.conf file will look something like this:

       global parameters...

       subnet 204.254.239.0 netmask 255.255.255.224 {
	 subnet-specific parameters...
	 range 204.254.239.10 204.254.239.30;
       }

       subnet 204.254.239.32 netmask 255.255.255.224 {
	 subnet-specific parameters...
	 range 204.254.239.42 204.254.239.62;
       }

       subnet 204.254.239.64 netmask 255.255.255.224 {
	 subnet-specific parameters...
	 range 204.254.239.74 204.254.239.94;
       }

       group {
	 group-specific parameters...
	 host zappo.test.isc.org {
	   host-specific parameters...
	 }
	 host beppo.test.isc.org {
	   host-specific parameters...
	 }
	 host harpo.test.isc.org {
	   host-specific parameters...
	 }
       }

				      Figure 1

       Notice that at the beginning of the file, there's a  place  for	global
       parameters.  These might be things like the organization's domain name,
       the addresses of the name servers (if they are  common  to  the	entire
       organization), and so on.  So, for example:

	    option domain-name "isc.org";
	    option domain-name-servers ns1.isc.org, ns2.isc.org;

				      Figure 2

       As  you	can see in Figure 2, you can specify host addresses in parame‐
       ters using their domain names rather than their numeric	IP  addresses.
       If  a given hostname resolves to more than one IP address (for example,
       if that host has two ethernet interfaces), then	where  possible,  both
       addresses are supplied to the client.

       The  most obvious reason for having subnet-specific parameters as shown
       in Figure 1 is that each subnet, of necessity, has its own router.   So
       for the first subnet, for example, there should be something like:

	    option routers 204.254.239.1;

       Note  that  the	address	 here  is  specified numerically.  This is not
       required - if you have a different domain name for  each	 interface  on
       your  router, it's perfectly legitimate to use the domain name for that
       interface instead of the numeric address.  However, in many cases there
       may  be only one domain name for all of a router's IP addresses, and it
       would not be appropriate to use that name here.

       In Figure 1 there is also a  group  statement,  which  provides	common
       parameters  for	a set of three hosts - zappo, beppo and harpo.	As you
       can see, these hosts are all in the test.isc.org domain,	 so  it	 might
       make  sense  for a group-specific parameter to override the domain name
       supplied to these hosts:

	    option domain-name "test.isc.org";

       Also, given the domain they're in, these are  probably  test  machines.
       If we wanted to test the DHCP leasing mechanism, we might set the lease
       timeout somewhat shorter than the default:

	    max-lease-time 120;
	    default-lease-time 120;

       You may have noticed that while some parameters start with  the	option
       keyword, some do not.  Parameters starting with the option keyword cor‐
       respond to actual DHCP options, while parameters that do not start with
       the  option  keyword  either  control  the  behavior of the DHCP server
       (e.g., how long a lease dhcpd will give out), or specify client parame‐
       ters  that  are not optional in the DHCP protocol (for example, server-
       name and filename).

       In Figure 1, each  host	had  host-specific  parameters.	  These	 could
       include	such  things  as  the  hostname	 option, the name of a file to
       upload (the filename parameter) and the	address	 of  the  server  from
       which  to upload the file (the next-server parameter).  In general, any
       parameter can appear anywhere that parameters are allowed, and will  be
       applied according to the scope in which the parameter appears.

       Imagine that you have a site with a lot of NCD X-Terminals.  These ter‐
       minals come in a variety of models, and you want to  specify  the  boot
       files  for each model.  One way to do this would be to have host decla‐
       rations for each server and group them by model:

       group {
	 filename "Xncd19r";
	 next-server ncd-booter;

	 host ncd1 { hardware ethernet 0:c0:c3:49:2b:57; }
	 host ncd4 { hardware ethernet 0:c0:c3:80:fc:32; }
	 host ncd8 { hardware ethernet 0:c0:c3:22:46:81; }
       }

       group {
	 filename "Xncd19c";
	 next-server ncd-booter;

	 host ncd2 { hardware ethernet 0:c0:c3:88:2d:81; }
	 host ncd3 { hardware ethernet 0:c0:c3:00:14:11; }
       }

       group {
	 filename "XncdHMX";
	 next-server ncd-booter;

	 host ncd1 { hardware ethernet 0:c0:c3:11:90:23; }
	 host ncd4 { hardware ethernet 0:c0:c3:91:a7:8; }
	 host ncd8 { hardware ethernet 0:c0:c3:cc:a:8f; }
       }

ADDRESS POOLS
       The pool and pool6 declarations can  be	used  to  specify  a  pool  of
       addresses  that	will  be  treated  differently	than  another  pool of
       addresses, even on the same network segment or  subnet.	 For  example,
       you  may	 want to provide a large set of addresses that can be assigned
       to DHCP clients that are registered to your DHCP server, while  provid‐
       ing  a  smaller set of addresses, possibly with short lease times, that
       are available for unknown clients.  If you have a firewall, you may  be
       able to arrange for addresses from one pool to be allowed access to the
       Internet, while addresses in another pool  are  not,  thus  encouraging
       users  to  register their DHCP clients.	To do this, you would set up a
       pair of pool declarations:

       subnet 10.0.0.0 netmask 255.255.255.0 {
	 option routers 10.0.0.254;

	 # Unknown clients get this pool.
	 pool {
	   option domain-name-servers bogus.example.com;
	   max-lease-time 300;
	   range 10.0.0.200 10.0.0.253;
	   allow unknown-clients;
	 }

	 # Known clients get this pool.
	 pool {
	   option domain-name-servers ns1.example.com, ns2.example.com;
	   max-lease-time 28800;
	   range 10.0.0.5 10.0.0.199;
	   deny unknown-clients;
	 }
       }

       It is also possible to set up entirely different subnets for known  and
       unknown	clients - address pools exist at the level of shared networks,
       so address ranges within pool declarations can be on different subnets.

       As you can see in the preceding example, pools can  have	 permit	 lists
       that  control  which  clients  are allowed access to the pool and which
       aren't.	Each entry in a pool's permit  list  is	 introduced  with  the
       allow  or  deny	keyword.  If a pool has a permit list, then only those
       clients that match specific entries on the permit list will be eligible
       to  be  assigned	 addresses  from the pool.  If a pool has a deny list,
       then only those clients that do not match any entries on the deny  list
       will  be	 eligible.    If  both permit and deny lists exist for a pool,
       then only clients that match the permit list and do not match the  deny
       list will be allowed access.

       The  pool6  declaration is similar to the pool6 declaration.  Currently
       it is only allowed  within  a  subnet6  declaration,  and  may  not  be
       included	 directly in a shared network declaration.  In addition to the
       range6 statement it allows the prefix6 statement to be  included.   You
       may  include  range6  statements for both NA and TA and prefixy6 state‐
       ments in a single pool6 statement.

DYNAMIC ADDRESS ALLOCATION
       Address allocation is actually only done when a client is in  the  INIT
       state and has sent a DHCPDISCOVER message.  If the client thinks it has
       a valid lease and sends a DHCPREQUEST to initiate or renew that	lease,
       the server has only three choices - it can ignore the DHCPREQUEST, send
       a DHCPNAK to tell the client it should stop using the address, or  send
       a  DHCPACK,  telling  the  client to go ahead and use the address for a
       while.

       If the server finds the address the  client  is	requesting,  and  that
       address is available to the client, the server will send a DHCPACK.  If
       the address is no longer available, or the client  isn't	 permitted  to
       have  it,  the server will send a DHCPNAK.  If the server knows nothing
       about the address, it will remain silent, unless the address is	incor‐
       rect  for the network segment to which the client has been attached and
       the server is authoritative for that network segment, in which case the
       server  will  send  a  DHCPNAK  even  though  it doesn't know about the
       address.

       There may be a host declaration matching the  client's  identification.
       If  that	 host  declaration  contains  a fixed-address declaration that
       lists an IP address that is valid for the network segment to which  the
       client  is  connected.	In  this  case,	 the DHCP server will never do
       dynamic address allocation.  In this case, the client  is  required  to
       take  the  address  specified  in  the host declaration.	 If the client
       sends a DHCPREQUEST for some other address,  the	 server	 will  respond
       with a DHCPNAK.

       When  the  DHCP	server allocates a new address for a client (remember,
       this only happens if the client has  sent  a  DHCPDISCOVER),  it	 first
       looks  to see if the client already has a valid lease on an IP address,
       or if there is an old IP address the client had before that hasn't  yet
       been  reassigned.   In that case, the server will take that address and
       check it to see if the client is still permitted to  use	 it.   If  the
       client  is  no  longer  permitted  to use it, the lease is freed if the
       server thought it was still in use - the fact that the client has  sent
       a  DHCPDISCOVER proves to the server that the client is no longer using
       the lease.

       If no existing lease is found, or if the client is forbidden to receive
       the  existing  lease,  then the server will look in the list of address
       pools for the network segment to which the client  is  attached	for  a
       lease  that is not in use and that the client is permitted to have.  It
       looks through each pool declaration in sequence (all range declarations
       that appear outside of pool declarations are grouped into a single pool
       with no permit list).  If the permit  list  for	the  pool  allows  the
       client  to be allocated an address from that pool, the pool is examined
       to see if there is an address available.	 If so,	 then  the  client  is
       tentatively assigned that address.  Otherwise, the next pool is tested.
       If no addresses are found that  can  be	assigned  to  the  client,  no
       response is sent to the client.

       If  an  address is found that the client is permitted to have, and that
       has never been assigned to any client before, the  address  is  immedi‐
       ately allocated to the client.  If the address is available for alloca‐
       tion but has been previously assigned to a different client, the server
       will  keep looking in hopes of finding an address that has never before
       been assigned to a client.

       The DHCP server generates the list of available	IP  addresses  from  a
       hash  table.   This means that the addresses are not sorted in any par‐
       ticular order, and so it is not possible to predict the order in	 which
       the DHCP server will allocate IP addresses.  Users of previous versions
       of the ISC DHCP server may have become accustomed to  the  DHCP	server
       allocating  IP addresses in ascending order, but this is no longer pos‐
       sible, and there is no way to configure this behavior with version 3 of
       the ISC DHCP server.

IP ADDRESS CONFLICT PREVENTION
       The  DHCP  server  checks IP addresses to see if they are in use before
       allocating them to clients.  It does  this  by  sending	an  ICMP  Echo
       request	message	 to  the  IP address being allocated.  If no ICMP Echo
       reply is received within a second, the address is assumed to  be	 free.
       This  is	 only done for leases that have been specified in range state‐
       ments, and only when the lease is thought by the DHCP server to be free
       -  i.e.,	 the DHCP server or its failover peer has not listed the lease
       as in use.

       If a response is received to an ICMP  Echo  request,  the  DHCP	server
       assumes	that there is a configuration error - the IP address is in use
       by some host on the network that is not a DHCP client.	It  marks  the
       address as abandoned, and will not assign it to clients.

       If  a  DHCP  client tries to get an IP address, but none are available,
       but there are abandoned IP addresses, then the DHCP server will attempt
       to  reclaim  an abandoned IP address.  It marks one IP address as free,
       and then does the same ICMP Echo request	 check	described  previously.
       If there is no answer to the ICMP Echo request, the address is assigned
       to the client.

       The DHCP server does not cycle through abandoned IP  addresses  if  the
       first  IP  address  it tries to reclaim is free.	 Rather, when the next
       DHCPDISCOVER comes in from the client, it will attempt a new allocation
       using  the  same method described here, and will typically try a new IP
       address.

DHCP FAILOVER
       This version of the ISC DHCP server supports the DHCP failover protocol
       as  documented  in draft-ietf-dhc-failover-12.txt.  This is not a final
       protocol document, and we have not done interoperability	 testing  with
       other vendors' implementations of this protocol, so you must not assume
       that this implementation conforms to the standard.  If you wish to  use
       the  failover  protocol, make sure that both failover peers are running
       the same version of the ISC DHCP server.

       The failover protocol allows two DHCP servers (and no more than two) to
       share  a	 common address pool.  Each server will have about half of the
       available IP addresses in the pool at any given	time  for  allocation.
       If one server fails, the other server will continue to renew leases out
       of the pool, and will allocate new addresses out of the roughly half of
       available  addresses  that  it  had  when communications with the other
       server were lost.

       It is possible during a prolonged failure to tell the remaining	server
       that  the other server is down, in which case the remaining server will
       (over time) reclaim all the addresses the other	server	had  available
       for  allocation,	 and  begin to reuse them.  This is called putting the
       server into the PARTNER-DOWN state.

       You can put the server into the PARTNER-DOWN state either by using  the
       omshell	(1)  command  or  by  stopping	the  server,  editing the last
       failover state declaration  in  the  lease  file,  and  restarting  the
       server.	If you use this last method, change the "my state" line to:

       failover peer name state {
       my state partner-down;.
       peer state state at date;
       }

       It is only required to change "my state" as shown above.

       When the other server comes back online, it should automatically detect
       that it has been offline and request a complete update from the	server
       that  was running in the PARTNER-DOWN state, and then both servers will
       resume processing together.

       It is possible to get into a dangerous situation: if you put one server
       into  the PARTNER-DOWN state, and then *that* server goes down, and the
       other server comes back up, the other server will  not  know  that  the
       first  server  was  in  the PARTNER-DOWN state, and may issue addresses
       previously issued by the other server to different  clients,  resulting
       in  IP  address	conflicts.   Before putting a server into PARTNER-DOWN
       state, therefore, make sure that the  other  server  will  not  restart
       automatically.

       The  failover  protocol	defines	 a primary server role and a secondary
       server role.  There are some differences in how	primaries  and	secon‐
       daries  act, but most of the differences simply have to do with provid‐
       ing a way for each peer to behave in the opposite way from  the	other.
       So one server must be configured as primary, and the other must be con‐
       figured as secondary, and it doesn't  matter  too  much	which  one  is
       which.

FAILOVER STARTUP
       When  a	server	starts	that  has not previously communicated with its
       failover peer, it must establish communications with its failover  peer
       and  synchronize	 with it before it can serve clients.  This can happen
       either because you have just configured your DHCP  servers  to  perform
       failover	 for  the  first time, or because one of your failover servers
       has failed catastrophically and lost its database.

       The initial recovery process  is	 designed  to  ensure  that  when  one
       failover	 peer  loses  its database and then resynchronizes, any leases
       that the failed server gave out before it failed will be honored.  When
       the  failed  server starts up, it notices that it has no saved failover
       state, and attempts to contact its peer.

       When it has established contact, it asks the peer for a	complete  copy
       its  peer's lease database.  The peer then sends its complete database,
       and sends a message indicating that it is done.	The failed server then
       waits until MCLT has passed, and once MCLT has passed both servers make
       the transition back into normal operation.  This waiting period ensures
       that  any leases the failed server may have given out while out of con‐
       tact with its partner will have expired.

       While the failed server is recovering, its partner remains in the part‐
       ner-down state, which means that it is serving all clients.  The failed
       server provides no service at all to DHCP clients until it has made the
       transition into normal operation.

       In  the case where both servers detect that they have never before com‐
       municated with their partner, they both come up in this recovery	 state
       and follow the procedure we have just described.	 In this case, no ser‐
       vice will be provided to DHCP clients until MCLT has expired.

CONFIGURING FAILOVER
       In order to configure failover, you need to write  a  peer  declaration
       that  configures the failover protocol, and you need to write peer ref‐
       erences in each pool declaration for which you  want  to	 do  failover.
       You  do	not  have to do failover for all pools on a given network seg‐
       ment.   You must not tell one server it's doing failover on a  particu‐
       lar  address  pool and tell the other it is not.	 You must not have any
       common address pools on which you are not doing failover.  A pool  dec‐
       laration that utilizes failover would look like this:

       pool {
	    failover peer "foo";
	    pool specific parameters
       };

       The   server currently  does very  little  sanity checking,  so if  you
       configure it wrong, it will just	 fail in odd ways.  I would  recommend
       therefore  that you either do  failover or don't do failover, but don't
       do any mixed pools.  Also,  use the same master configuration file  for
       both   servers,	and  have  a  separate file  that  contains  the  peer
       declaration and includes the master file.  This will help you to	 avoid
       configuration   mismatches.  As our  implementation evolves,  this will
       become  less of	a  problem.  A	basic  sample dhcpd.conf  file for   a
       primary server might look like this:

       failover peer "foo" {
	 primary;
	 address anthrax.rc.vix.com;
	 port 519;
	 peer address trantor.rc.vix.com;
	 peer port 520;
	 max-response-delay 60;
	 max-unacked-updates 10;
	 mclt 3600;
	 split 128;
	 load balance max seconds 3;
       }

       include "/etc/dhcpd.master";

       The statements in the peer declaration are as follows:

       The primary and secondary statements

	 [ primary | secondary ];

	 This  determines  whether  the	 server	 is  primary  or secondary, as
	 described earlier under DHCP FAILOVER.

       The address statement

	 address address;

	 The address statement declares the IP address or DNS  name  on	 which
	 the  server should listen for connections from its failover peer, and
	 also the value to use for the DHCP Failover Protocol  server  identi‐
	 fier.	 Because  this	value  is used as an identifier, it may not be
	 omitted.

       The peer address statement

	 peer address address;

	 The peer address statement declares the IP address  or	 DNS  name  to
	 which	the  server  should  connect  to  reach	 its failover peer for
	 failover messages.

       The port statement

	 port port-number;

	 The port statement declares the TCP port on which the	server	should
	 listen for connections from its failover peer.	 This statement may be
	 omitted, in which case the IANA assigned port number 647 will be used
	 by default.

       The peer port statement

	 peer port port-number;

	 The  peer  port  statement  declares the TCP port to which the server
	 should connect to reach its  failover	peer  for  failover  messages.
	 This  statement  may be omitted, in which case the IANA assigned port
	 number 647 will be used by default.

       The max-response-delay statement

	 max-response-delay seconds;

	 The max-response-delay statement tells the DHCP server how many  sec‐
	 onds  may  pass  without  receiving  a message from its failover peer
	 before it assumes that connection has failed.	This number should  be
	 small enough that a transient network failure that breaks the connec‐
	 tion will not result in the servers being out of communication for  a
	 long  time,  but large enough that the server isn't constantly making
	 and breaking connections.  This parameter must be specified.

       The max-unacked-updates statement

	 max-unacked-updates count;

	 The max-unacked-updates statement tells the remote  DHCP  server  how
	 many BNDUPD messages it can send before it receives a BNDACK from the
	 local system.	We don't have enough  operational  experience  to  say
	 what  a good value for this is, but 10 seems to work.	This parameter
	 must be specified.

       The mclt statement

	 mclt seconds;

	 The mclt statement defines the Maximum Client Lead Time.  It must  be
	 specified  on the primary, and may not be specified on the secondary.
	 This is the length of time for which a lease may be renewed by either
	 failover peer without contacting the other.  The longer you set this,
	 the longer it	will  take  for	 the  running  server  to  recover  IP
	 addresses  after moving into PARTNER-DOWN state.  The shorter you set
	 it, the more load your servers will experience when they are not com‐
	 municating.   A  value of something like 3600 is probably reasonable,
	 but again bear in mind that we have no	 real  operational  experience
	 with this.

       The split statement

	 split index;

	 The  split statement specifies the split between the primary and sec‐
	 ondary for the purposes of load balancing.  Whenever a client makes a
	 DHCP  request,	 the DHCP server runs a hash on the client identifica‐
	 tion, resulting in value from 0 to 255.  This is  used	 as  an	 index
	 into  a  256 bit field.  If the bit at that index is set, the primary
	 is responsible.  If the bit at that index is not set,	the  secondary
	 is  responsible.   The split value determines how many of the leading
	 bits are set to one.  So, in practice, higher split values will cause
	 the  primary  to  serve more clients than the secondary.  Lower split
	 values, the converse.	Legal values are between 0 and 255,  of	 which
	 the most reasonable is 128.

       The hba statement

	 hba colon-separated-hex-list;

	 The  hba  statement  specifies the split between the primary and sec‐
	 ondary as a bitmap rather than a cutoff, which	 theoretically	allows
	 for  finer-grained  control.	In practice, there is probably no need
	 for such fine-grained control, however.  An example hba statement:

	   hba ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:
	       00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00;

	 This is equivalent to a split 128;  statement,	 and  identical.   The
	 following two examples are also equivalent to a split of 128, but are
	 not identical:

	   hba aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:
	       aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa;

	   hba 55:55:55:55:55:55:55:55:55:55:55:55:55:55:55:55:
	       55:55:55:55:55:55:55:55:55:55:55:55:55:55:55:55;

	 They are equivalent, because half the bits are set to 0, half are set
	 to  1	(0xa and 0x5 are 1010 and 0101 binary respectively) and conse‐
	 quently this would roughly divide the	clients	 equally  between  the
	 servers.  They are not identical, because the actual peers this would
	 load balance to each server are different for each example.

	 You must only have split or hba defined, never both.  For most cases,
	 the  fine-grained  control that hba offers isn't necessary, and split
	 should be used.

       The load balance max seconds statement

	 load balance max seconds seconds;

	 This statement allows you to configure a cutoff after which load bal‐
	 ancing	 is  disabled.	 The  cutoff is based on the number of seconds
	 since the client sent its first DHCPDISCOVER or DHCPREQUEST  message,
	 and only works with clients that correctly implement the secs field -
	 fortunately most clients do.  We recommend setting this to  something
	 like 3 or 5.  The effect of this is that if one of the failover peers
	 gets into a state where it is responding to failover messages but not
	 responding to some client requests, the other failover peer will take
	 over its client load automatically as the clients retry.

       The auto-partner-down statement

	 auto-partner-down seconds;

	 This statement instructs the server to initiate a  timed  delay  upon
	 entering the communications-interrupted state (any situation of being
	 out-of-contact with the remote failover peer).	 At the conclusion  of
	 the  timer,  the  server  will	 automatically	enter the partner-down
	 state.	 This permits the server to allocate leases from the partner's
	 free  lease  pool after an STOS+MCLT timer expires, which can be dan‐
	 gerous if the partner is in fact  operating  at  the  time  (the  two
	 servers will give conflicting bindings).

	 Think	very carefully before enabling this feature.  The partner-down
	 and communications-interrupted states	are  intentionally  segregated
	 because there do exist situations where a failover server can fail to
	 communicate with its peer, but still has the ability to  receive  and
	 reply to requests from DHCP clients.  In general, this feature should
	 only be used in those deployments  where  the	failover  servers  are
	 directly  connected  to one another, such as by a dedicated hardwired
	 link ("a heartbeat cable").

	 A  zero  value	 disables  the	auto-partner-down  feature  (also  the
	 default),  and	 any  positive	value indicates the time in seconds to
	 wait before automatically entering partner-down.

       The Failover pool balance statements.

	  max-lease-misbalance percentage;
	  max-lease-ownership percentage;
	  min-balance seconds;
	  max-balance seconds;

	 This version of the DHCP Server evaluates pool balance on a schedule,
	 rather	 than  on demand as leases are allocated.  The latter approach
	 proved to be slightly klunky when pool misbalanced reach total	 satu‐
	 ration	 —  when  any server ran out of leases to assign, it also lost
	 its ability to notice it had run dry.

	 In order to understand pool balance, some elements of	its  operation
	 first	need  to  be  defined.	 First,	 there are ´free´ and ´backup´
	 leases.  Both of these	 are  referred	to  as	´free  state  leases´.
	 ´free´	 and  ´backup´	are  ´the free states´ for the purpose of this
	 document.  The difference is that only the primary may allocate  from
	 ´free´	 leases	 unless under special circumstances, and only the sec‐
	 ondary may allocate ´backup´ leases.

	 When pool balance is performed, the only plausible expectation is  to
	 provide  a  50/50  split  of  the  free  state leases between the two
	 servers.  This is because no one can predict which server will	 fail,
	 regardless  of the relative load placed upon the two servers, so giv‐
	 ing each server half the leases gives both servers the same amount of
	 ´failure  endurance´.	 Therefore,  there  is no way to configure any
	 different behaviour, outside of  some	very  small  windows  we  will
	 describe shortly.

	 The  first  thing  calculated	on  any	 pool  balance	run is a value
	 referred to as ´lts´, or "Leases To Send".  This, simply, is the dif‐
	 ference  in the count of free and backup leases, divided by two.  For
	 the secondary, it is the difference in the backup  and	 free  leases,
	 divided  by  two.   The resulting value is signed: if it is positive,
	 the local server is expected to hand out leases  to  retain  a	 50/50
	 balance.   If	it  is	negative, the remote server would need to send
	 leases to balance the pool.  Once the lts  value  reaches  zero,  the
	 pool  is perfectly balanced (give or take one lease in the case of an
	 odd number of total free state leases).

	 The current approach is still	something  of  a  hybrid  of  the  old
	 approach,  marked  by the presence of the max-lease-misbalance state‐
	 ment.	This parameter configures what used to be a 10% fixed value in
	 previous  versions:  if lts is less than free+backup * max-lease-mis‐
	 balance percent, then the server will skip balancing a given pool (it
	 won't	bother	moving	any  leases,  even  if some leases "should" be
	 moved).  The meaning of this value is also somewhat overloaded,  how‐
	 ever,	in  that  it also governs the estimation of when to attempt to
	 balance the pool (which may then also be skipped over).   The	oldest
	 leases	 in  the  free	and backup states are examined.	 The time they
	 have resided in their respective queues is used  as  an  estimate  to
	 indicate how much time it is probable it would take before the leases
	 at the top of the list would be consumed (and thus, how long it would
	 take  to  use all leases in that state).  This percentage is directly
	 multiplied by this time, and fit into the schedule if it falls within
	 the  min-balance  and	max-balance  configured values.	 The scheduled
	 pool check time is only moved in a downwards direction, it  is	 never
	 increased.  Lastly, if the lts is more than double this number in the
	 negative direction, the local server  will  ´panic´  and  transmit  a
	 Failover  protocol POOLREQ message, in the hopes that the remote sys‐
	 tem will be woken up into action.

	 Once the lts value exceeds  the  max-lease-misbalance	percentage  of
	 total	free  state leases as described above, leases are moved to the
	 remote server.	 This is done in two passes.

	 In the first pass, only leases whose most recent bound	 client	 would
	 have been served by the remote server - according to the Load Balance
	 Algorithm (see above split and hba configuration  statements)	-  are
	 given	away  to  the  peer.  This first pass will happily continue to
	 give away leases, decrementing the lts value by one for  each,	 until
	 the  lts value has reached the negative of the total number of leases
	 multiplied by the max-lease-ownership percentage.  So it  is  through
	 this  value that you can permit a small misbalance of the lease pools
	 - for the purpose of giving the peer  more  than  a  50/50  share  of
	 leases	 in  the hopes that their clients might some day return and be
	 allocated by the peer (operating normally).  This process is referred
	 to  as	 ´MAC  Address	Affinity´,  but	 this is somewhat misnamed: it
	 applies equally to DHCP Client Identifier options.   Note  also  that
	 affinity  is  applied to leases when they enter the state ´free´ from
	 ´expired´ or ´released´.  In this case also, leases will not be moved
	 from free to backup if the secondary already has more than its share.

	 The  second  pass  is	only  entered  into if the first pass fails to
	 reduce the lts underneath the total number of free state leases  mul‐
	 tiplied  by  the  max-lease-ownership	percentage.  In this pass, the
	 oldest leases are given over to the peer without second thought about
	 the  Load  Balance  Algorithm, and this continues until the lts falls
	 under this value.  In this way, the local server  will	 also  happily
	 keep  a  small percentage of the leases that would normally load bal‐
	 ance to itself.

	 So, the  max-lease-misbalance	value  acts  as	 a  behavioural	 gate.
	 Smaller values will cause more leases to transition states to balance
	 the pools over time, higher values will decrease the amount of change
	 (but may lead to pool starvation if there's a run on leases).

	 The  max-lease-ownership  value  permits a small (percentage) skew in
	 the lease balance of a percentage of the total number of  free	 state
	 leases.

	 Finally,  the	min-balance and max-balance make certain that a sched‐
	 uled rebalance event happens within a reasonable timeframe (not to be
	 thrown off by, for example, a 7 year old free lease).

	 Plausible  values  for	 the percentages lie between 0 and 100, inclu‐
	 sive, but values over 50 are indistinguishable from one another (once
	 lts  exceeds  50% of the free state leases, one server must therefore
	 have 100% of the leases in its respective free state).	 It is	recom‐
	 mended	 to  select a max-lease-ownership value that is lower than the
	 value selected for the max-lease-misbalance value.   max-lease-owner‐
	 ship defaults to 10, and max-lease-misbalance defaults to 15.

	 Plausible values for the min-balance and max-balance times also range
	 from 0 to (2^32)-1 (or the limit of your  local  time_t  value),  but
	 default  to  values 60 and 3600 respectively (to place balance events
	 between 1 minute and 1 hour).

CLIENT CLASSING
       Clients can be separated into classes, and treated differently  depend‐
       ing on what class they are in.  This separation can be done either with
       a conditional statement, or with a match	 statement  within  the	 class
       declaration.   It is possible to specify a limit on the total number of
       clients within a particular class or subclass that may hold  leases  at
       one  time, and it is possible to specify automatic subclassing based on
       the contents of the client packet.

       Classing support for DHCPv6 clients was addded in  4.3.0.   It  follows
       the  same  rules	 as for DHCPv4 except that support for billing classes
       has not been added yet.

       To add clients to classes based	on  conditional	 evaluation,  you  can
       specify a matching expression in the class statement:

       class "ras-clients" {
	 match if substring (option dhcp-client-identifier, 1, 3) = "RAS";
       }

       Note  that  whether  you use matching expressions or add statements (or
       both) to classify clients, you must always write	 a  class  declaration
       for any class that you use.  If there will be no match statement and no
       in-scope statements for a class, the declaration should look like this:

       class "ras-clients" {
       }

SUBCLASSES
       In addition to classes, it is possible to declare subclasses.   A  sub‐
       class is a class with the same name as a regular class, but with a spe‐
       cific submatch expression which is hashed for quick matching.  This  is
       essentially  a  speed  hack  - the main difference between five classes
       with match expressions and one class with five subclasses  is  that  it
       will be quicker to find the subclasses.	Subclasses work as follows:

       class "allocation-class-1" {
	 match pick-first-value (option dhcp-client-identifier, hardware);
       }

       class "allocation-class-2" {
	 match pick-first-value (option dhcp-client-identifier, hardware);
       }

       subclass "allocation-class-1" 1:8:0:2b:4c:39:ad;
       subclass "allocation-class-2" 1:8:0:2b:a9:cc:e3;
       subclass "allocation-class-1" 1:0:0:c4:aa:29:44;

       subnet 10.0.0.0 netmask 255.255.255.0 {
	 pool {
	   allow members of "allocation-class-1";
	   range 10.0.0.11 10.0.0.50;
	 }
	 pool {
	   allow members of "allocation-class-2";
	   range 10.0.0.51 10.0.0.100;
	 }
       }

       The data following the class name in the subclass declaration is a con‐
       stant value to use in matching the  match  expression  for  the	class.
       When class matching is done, the server will evaluate the match expres‐
       sion and then look the result up in the hash  table.   If  it  finds  a
       match, the client is considered a member of both the class and the sub‐
       class.

       Subclasses can be declared with or without scope.  In the  above	 exam‐
       ple,  the  sole purpose of the subclass is to allow some clients access
       to one address pool, while other clients are given access to the	 other
       pool,  so these subclasses are declared without scopes.	If part of the
       purpose of the subclass were to define different parameter  values  for
       some clients, you might want to declare some subclasses with scopes.

       In  the above example, if you had a single client that needed some con‐
       figuration parameters, while most didn't, you might write the following
       subclass declaration for that client:

       subclass "allocation-class-2" 1:08:00:2b:a1:11:31 {
	 option root-path "samsara:/var/diskless/alphapc";
	 filename "/tftpboot/netbsd.alphapc-diskless";
       }

       In  this	 example,  we've  used subclassing as a way to control address
       allocation on a per-client basis.  However, it's also possible  to  use
       subclassing  in ways that are not specific to clients - for example, to
       use the value of the vendor-class-identifier option to  determine  what
       values  to  send in the vendor-encapsulated-options option.  An example
       of this is shown under the VENDOR  ENCAPSULATED	OPTIONS	 head  in  the
       dhcp-options(5) manual page.

PER-CLASS LIMITS ON DYNAMIC ADDRESS ALLOCATION
       You may specify a limit to the number of clients in a class that can be
       assigned leases.	 The effect of this will be to make it difficult for a
       new  client  in	a  class  to get an address.  Once a class with such a
       limit has reached its limit, the only way a new client  in  that	 class
       can  get	 a  lease  is  for an existing client to relinquish its lease,
       either by letting it  expire,  or  by  sending  a  DHCPRELEASE  packet.
       Classes with lease limits are specified as follows:

       class "limited-1" {
	 lease limit 4;
       }

       This will produce a class in which a maximum of four members may hold a
       lease at one time.

SPAWNING CLASSES
       It is possible to declare a spawning class.   A	spawning  class	 is  a
       class  that  automatically produces subclasses based on what the client
       sends.  The reason that spawning classes were created was  to  make  it
       possible	 to  create  lease-limited classes on the fly.	The envisioned
       application is a cable-modem environment where the ISP wishes  to  pro‐
       vide  clients  at  a particular site with more than one IP address, but
       does not wish to provide such clients with their own subnet,  nor  give
       them  an	 unlimited  number of IP addresses from the network segment to
       which they are connected.

       Many cable modem head-end systems can be	 configured  to	 add  a	 Relay
       Agent Information option to DHCP packets when relaying them to the DHCP
       server.	These systems typically add a circuit ID or remote  ID	option
       that uniquely identifies the customer site.  To take advantage of this,
       you can write a class declaration as follows:

       class "customer" {
	 spawn with option agent.circuit-id;
	 lease limit 4;
       }

       Now whenever a request comes in from a customer site,  the  circuit  ID
       option  will  be checked against the class´s hash table.	 If a subclass
       is found that matches the circuit ID, the client will be classified  in
       that  subclass and treated accordingly.	If no subclass is found match‐
       ing the circuit ID, a new  one  will  be	 created  and  logged  in  the
       dhcpd.leases file, and the client will be classified in this new class.
       Once the client has been classified, it will be	treated	 according  to
       the  rules  of the class, including, in this case, being subject to the
       per-site limit of four leases.

       The use of the subclass spawning mechanism is not restricted  to	 relay
       agent  options  - this particular example is given only because it is a
       fairly straightforward one.

COMBINING MATCH, MATCH IF AND SPAWN WITH
       In some cases, it may be useful to  use	one  expression	 to  assign  a
       client  to a particular class, and a second expression to put it into a
       subclass of that class.	This can be done by combining the match if and
       spawn with statements, or the match if and match statements.  For exam‐
       ple:

       class "jr-cable-modems" {
	 match if option dhcp-vendor-identifier = "jrcm";
	 spawn with option agent.circuit-id;
	 lease limit 4;
       }

       class "dv-dsl-modems" {
	 match if option dhcp-vendor-identifier = "dvdsl";
	 spawn with option agent.circuit-id;
	 lease limit 16;
       }

       This allows you to have two classes that both have the same spawn  with
       expression without getting the clients in the two classes confused with
       each other.

DYNAMIC DNS UPDATES
       The DHCP server has the ability to dynamically update the  Domain  Name
       System.	 Within	 the  configuration files, you can define how you want
       the Domain Name System to be updated.  These updates are RFC 2136  com‐
       pliant  so  any DNS server supporting RFC 2136 should be able to accept
       updates from the DHCP server.

       There are two DNS schemes implemented.  The interim option is based  on
       draft  revisions	 of  the  DDNS	documents while the standard option is
       based on the RFCs for DHCP-DNS interaction and DHCIDs.  A third option,
       ad-hoc,	was  deprecated	 and  has now been removed from the code base.
       The DHCP server must be configured to use one of the two currently-sup‐
       ported methods, or not to do DNS updates.

       New  installations  should use the standard option. Older installations
       may want to continue using the interim option for backwards compatibil‐
       ity  with the DNS database until the database can be updated.  This can
       be done with the ddns-update-style configuration parameter.

THE DNS UPDATE SCHEME
       the interim and standard DNS update schemes operate mostly according to
       work  from  the	IETF.	The interim version was based on the drafts in
       progress at the time while the standard is based on the completed RFCs.
       The standard RFCs are:

			    RFC 4701 (updated by RF5494)
				      RFC 4702
				      RFC 4703

       And the corresponding drafts were:

			  draft-ietf-dnsext-dhcid-rr-??.txt
			  draft-ietf-dhc-fqdn-option-??.txt
			draft-ietf-dhc-ddns-resolution-??.txt

       The  basic framework for the two schemes is similar with the main mate‐
       rial difference being that a DHCID RR is used in the  standard  version
       while the interim versions uses a TXT RR.  The format of the TXT record
       bears a resemblance to the DHCID RR but it is not  equivalent  (MD5  vs
       SHA2, field length differences etc).

       In these two schemes the DHCP server does not necessarily always update
       both the A and the PTR records.	The FQDN option includes a flag which,
       when sent by the client, indicates that the client wishes to update its
       own A record.  In that case, the server can  be	configured  either  to
       honor  the  client´s  intentions or ignore them.	 This is done with the
       statement  allow	 client-updates;  or  the  statement  ignore   client-
       updates;.  By default, client updates are allowed.

       If the server is configured to allow client updates, then if the client
       sends a fully-qualified domain name in the FQDN option, the server will
       use  that  name	the  client  sent in the FQDN option to update the PTR
       record.	For example, let us say that the client is a visitor from  the
       "radish.org"  domain,  whose  hostname is "jschmoe".  The server is for
       the "example.org" domain.  The DHCP client indicates in the FQDN option
       that  its  FQDN	is  "jschmoe.radish.org.".   It also indicates that it
       wants to update its own A record.  The DHCP server therefore  does  not
       attempt	to  set	 up  an A record for the client, but does set up a PTR
       record for the IP address that  it  assigns  the	 client,  pointing  at
       jschmoe.radish.org.   Once  the	DHCP  client has an IP address, it can
       update its own A record, assuming that the "radish.org" DNS server will
       allow it to do so.

       If  the	server	is  configured	not to allow client updates, or if the
       client doesn´t want to do its own update, the server will simply choose
       a  name	for the client from either the fqdn option (if present) or the
       hostname option (if present).  It will use its own domain name for  the
       client.	 It will then update both the A and PTR record, using the name
       that it chose for the client.  If the client  sends  a  fully-qualified
       domain  name in the fqdn option, the server uses only the leftmost part
       of the domain name  -  in  the  example	above,	"jschmoe"  instead  of
       "jschmoe.radish.org".

       Further,	 if  the  ignore  client-updates;  directive is used, then the
       server will in addition send a response in the DHCP packet,  using  the
       FQDN  Option, that implies to the client that it should perform its own
       updates if it chooses to do so.	With deny client-updates;, a  response
       is sent which indicates the client may not perform updates.

       Also,  if the use-host-decl-names configuration option is enabled, then
       the host declaration´s hostname will be used in place of	 the  hostname
       option, and the same rules will apply as described above.

       Both  the  standard  and interim options also include a method to allow
       more than one DHCP server to update the DNS database  without  acciden‐
       tally deleting A records that shouldn´t be deleted nor failing to add A
       records that should be added.  For the standard option the method works
       as follows:

       When  the  DHCP	server	issues a client a new lease, it creates a text
       string that is an SHA hash over the DHCP client´s  identification  (see
       RFCs  4701 & 4702 for details).	The update attempts to add an A record
       with the name the server chose and a DHCID record containing the hashed
       identifier  string  (hashid).   If  this update succeeds, the server is
       done.

       If the update fails because the A record already exists, then the  DHCP
       server  attempts	 to  add the A record with the prerequisite that there
       must be a DHCID record in the same name as the new A record,  and  that
       DHCID  record´s	contents must be equal to hashid.  If this update suc‐
       ceeds, then the client has its A record and PTR record.	If  it	fails,
       then  the  name	the client has been assigned (or requested) is in use,
       and can´t be used by the client.	 At this point the DHCP	 server	 gives
       up  trying to do a DNS update for the client until the client chooses a
       new name.

       The server also does not update very aggressively.   Because  each  DNS
       update involves a round trip to the DNS server, there is a cost associ‐
       ated with doing updates even if they do not  actually  modify  the  DNS
       database.   So the DHCP server tracks whether or not it has updated the
       record in the past (this information is stored on the lease)  and  does
       not attempt to update records that it thinks it has already updated.

       This  can  lead	to cases where the DHCP server adds a record, and then
       the record is deleted through some  other  mechanism,  but  the	server
       never  again  updates  the  DNS	because	 it thinks the data is already
       there.  In this case the data can be removed  from  the	lease  through
       operator	 intervention,	and  once  this has been done, the DNS will be
       updated the next time the client renews.

       The interim DNS update scheme was written before the RFCs  were	final‐
       ized  and  does	not  quite follow them.	 The RFCs call for a new DHCID
       RRtype while he interim DNS update scheme uses a TXT record.  In	 addi‐
       tion  the  ddns-resolution  draft  called  for the DHCP server to put a
       DHCID RR on the PTR record, but the interim update method does  not  do
       this.  In the final RFC this requirement was relaxed such that a server
       may add a DHCID RR to the PTR record.

DYNAMIC DNS UPDATE SECURITY
       When you set your DNS server up to allow updates from the DHCP  server,
       you  may	 be  exposing  it to unauthorized updates.  To avoid this, you
       should use TSIG signatures -  a	method	of  cryptographically  signing
       updates	using a shared secret key.  As long as you protect the secrecy
       of this key, your updates should also be secure.	 Note,	however,  that
       the  DHCP  protocol  itself  provides no security, and that clients can
       therefore provide information to the DHCP server which the DHCP	server
       will  then  use	in  its updates, with the constraints described previ‐
       ously.

       The DNS server must be configured to allow updates for  any  zone  that
       the DHCP server will be updating.  For example, let us say that clients
       in  the	sneedville.edu	domain	will  be  assigned  addresses  on  the
       10.10.17.0/24  subnet.	In  that case, you will need a key declaration
       for the TSIG key you will be using, and also two	 zone  declarations  -
       one  for the zone containing A records that will be updates and one for
       the zone containing PTR records - for ISC BIND, something like this:

       key DHCP_UPDATER {
	 algorithm HMAC-MD5.SIG-ALG.REG.INT;
	 secret pRP5FapFoJ95JEL06sv4PQ==;
       };

       zone "example.org" {
	    type master;
	    file "example.org.db";
	    allow-update { key DHCP_UPDATER; };
       };

       zone "17.10.10.in-addr.arpa" {
	    type master;
	    file "10.10.17.db";
	    allow-update { key DHCP_UPDATER; };
       };

       You will also have to configure your DHCP server to do updates to these
       zones.	To  do	so,  you  need	to  add	 something  like  this to your
       dhcpd.conf file:

       key DHCP_UPDATER {
	 algorithm HMAC-MD5.SIG-ALG.REG.INT;
	 secret pRP5FapFoJ95JEL06sv4PQ==;
       };

       zone EXAMPLE.ORG. {
	 primary 127.0.0.1;
	 key DHCP_UPDATER;
       }

       zone 17.127.10.in-addr.arpa. {
	 primary 127.0.0.1;
	 key DHCP_UPDATER;
       }

       The primary statement specifies the IP address of the name server whose
       zone  information  is to be updated.  In addition to the primary state‐
       ment there are also the primary6 , secondary and secondary6 statements.
       The  primary6  statement specifies an IPv6 address for the name server.
       The secondaries provide for additional addresses for name servers to be
       used  if	 the primary does not respond.	The number of name servers the
       DDNS code will attempt to use before giving up is limited and  is  cur‐
       rently set to three.

       Note that the zone declarations have to correspond to authority records
       in your name server - in the above example, there must be an SOA record
       for  "example.org."  and for "17.10.10.in-addr.arpa.".  For example, if
       there were a subdomain "foo.example.org"	 with  no  separate  SOA,  you
       could not write a zone declaration for "foo.example.org."  Also keep in
       mind that zone names in your DHCP configuration should end  in  a  ".";
       this  is	 the  preferred syntax.	 If you do not end your zone name in a
       ".", the DHCP server will figure it out.	 Also note that	 in  the  DHCP
       configuration,  zone  names  are not encapsulated in quotes where there
       are in the DNS configuration.

       You should choose your own secret key, of course.  The ISC BIND 9  dis‐
       tribution  comes	 with  a  program  for	generating  secret keys called
       dnssec-keygen.  If you are using BIND 9´s dnssec-keygen, the above  key
       would be created as follows:

	    dnssec-keygen -a HMAC-MD5 -b 128 -n USER DHCP_UPDATER

       You  may	 wish to enable logging of DNS updates on your DNS server.  To
       do so, you might write a logging statement like the following:

       logging {
	    channel update_debug {
		 file "/var/log/update-debug.log";
		 severity  debug 3;
		 print-category yes;
		 print-severity yes;
		 print-time	yes;
	    };
	    channel security_info    {
		 file "/var/log/named-auth.info";
		 severity  info;
		 print-category yes;
		 print-severity yes;
		 print-time	yes;
	    };

	    category update { update_debug; };
	    category security { security_info; };
       };

       You  must  create  the  /var/log/named-auth.info	 and  /var/log/update-
       debug.log  files before starting the name server.  For more information
       on configuring ISC BIND, consult the documentation that accompanies it.

REFERENCE: EVENTS
       There are three kinds of events that can happen regarding a lease,  and
       it  is  possible	 to  declare  statements  that occur when any of these
       events happen.  These events are the commit event, when the server  has
       made  a	commitment  of a certain lease to a client, the release event,
       when the client has released the server from its	 commitment,  and  the
       expiry event, when the commitment expires.

       To  declare  a  set of statements to execute when an event happens, you
       must use the on statement, followed by the name of the event,  followed
       by  a  series of statements to execute when the event happens, enclosed
       in braces.

REFERENCE: DECLARATIONS
       The include statement

	include "filename";

       The include statement is used to read in a named file, and process  the
       contents of that file as though it were entered in place of the include
       statement.

       The shared-network statement

	shared-network name {
	  [ parameters ]
	  [ declarations ]
	}

       The shared-network statement is used to inform  the  DHCP  server  that
       some  IP subnets actually share the same physical network.  Any subnets
       in a shared network should be declared within a	shared-network	state‐
       ment.   Parameters  specified  in  the shared-network statement will be
       used when booting clients on those subnets unless  parameters  provided
       at  the	subnet or host level override them.  If any subnet in a shared
       network has addresses available for dynamic allocation, those addresses
       are  collected  into a common pool for that shared network and assigned
       to clients as needed.  There is no way to distinguish on	 which	subnet
       of a shared network a client should boot.

       Name  should be the name of the shared network.	This name is used when
       printing debugging messages, so it should be descriptive for the shared
       network.	 The name may have the syntax of a valid domain name (although
       it will never be used as such),	or  it	may  be	 any  arbitrary	 name,
       enclosed in quotes.

       The subnet statement

	subnet subnet-number netmask netmask {
	  [ parameters ]
	  [ declarations ]
	}

       The  subnet  statement is used to provide dhcpd with enough information
       to tell whether or not an IP address is on that subnet.	It may also be
       used   to  provide  subnet-specific  parameters	and  to	 specify  what
       addresses may be dynamically allocated to clients booting on that  sub‐
       net.  Such addresses are specified using the range declaration.

       The subnet-number should be an IP address or domain name which resolves
       to the subnet number of the subnet being described.  The netmask should
       be  an  IP  address or domain name which resolves to the subnet mask of
       the subnet being described.  The subnet number, together with the  net‐
       mask,  are  sufficient  to determine whether any given IP address is on
       the specified subnet.

       Although a netmask must be given with every subnet declaration,	it  is
       recommended  that if there is any variance in subnet masks at a site, a
       subnet-mask option statement be used in each subnet declaration to  set
       the  desired  subnet  mask, since any subnet-mask option statement will
       override the subnet mask declared in the subnet statement.

       The subnet6 statement

	subnet6 subnet6-number {
	  [ parameters ]
	  [ declarations ]
	}

       The subnet6 statement is used to provide dhcpd with enough  information
       to tell whether or not an IPv6 address is on that subnet6.  It may also
       be used to provide  subnet-specific  parameters	and  to	 specify  what
       addresses  may be dynamically allocated to clients booting on that sub‐
       net.

       The subnet6-number should be an IPv6 network identifier,	 specified  as
       ip6-address/bits.

       The range statement

       range [ dynamic-bootp ] low-address [ high-address];

       For  any	 subnet on which addresses will be assigned dynamically, there
       must be at least one range statement.  The range	 statement  gives  the
       lowest  and  highest  IP addresses in a range.  All IP addresses in the
       range should be in the subnet in which the range statement is declared.
       The  dynamic-bootp  flag may be specified if addresses in the specified
       range may be dynamically assigned to BOOTP  clients  as	well  as  DHCP
       clients.	  When	specifying a single address, high-address can be omit‐
       ted.

       The range6 statement

       range6 low-address high-address;
       range6 subnet6-number;
       range6 subnet6-number temporary;
       range6 address temporary;

       For any IPv6 subnet6 on which addresses will be	assigned  dynamically,
       there  must  be at least one range6 statement. The range6 statement can
       either be the lowest and highest IPv6 addresses in  a  range6,  or  use
       CIDR  notation,	specified as ip6-address/bits. All IP addresses in the
       range6 should be in the	subnet6	 in  which  the	 range6	 statement  is
       declared.

       The  temporary  variant makes the prefix (by default on 64 bits) avail‐
       able for temporary (RFC 4941) addresses. A new address  per  prefix  in
       the  shared  network  is computed at each request with an IA_TA option.
       Release and Confirm ignores temporary addresses.

       Any IPv6 addresses given to hosts with fixed-address6 are excluded from
       the range6, as are IPv6 addresses on the server itself.

       The prefix6 statement

       prefix6 low-address high-address / bits;

       The  prefix6 is the range6 equivalent for Prefix Delegation (RFC 3633).
       Prefixes of bits length are  assigned  between  low-address  and	 high-
       address.

       Any  IPv6  prefixes  given to static entries (hosts) with fixed-prefix6
       are excluded from the prefix6.

       This statement is currently global but it should have a	shared-network
       scope.

       The host statement

	host hostname {
	  [ parameters ]
	  [ declarations ]
	}

       The host declaration provides a scope in which to provide configuration
       information about a specific client, and also provides a way to	assign
       a  client a fixed address.  The host declaration provides a way for the
       DHCP server to identify a DHCP or BOOTP	client,	 and  also  a  way  to
       assign the client a static IP address.

       If  it  is  desirable to be able to boot a DHCP or BOOTP client on more
       than one subnet with fixed addresses, more  than	 one  address  may  be
       specified  in  the  fixed-address  declaration,	or  more than one host
       statement may be specified matching the same client.

       If client-specific boot parameters must change based on the network  to
       which the client is attached, then multiple host declarations should be
       used.  The host declarations will only match a client if one  of	 their
       fixed-address  statements  is  viable on the subnet (or shared network)
       where the client is attached.  Conversely, for a	 host  declaration  to
       match  a client being allocated a dynamic address, it must not have any
       fixed-address statements.  You may therefore need  a  mixture  of  host
       declarations  for  any  given client...some having fixed-address state‐
       ments, others without.

       hostname should be a name identifying the host.	If a  hostname	option
       is not specified for the host, hostname is used.

       Host declarations are matched to actual DHCP or BOOTP clients by match‐
       ing the dhcp-client-identifier option specified in the host declaration
       to  the	one supplied by the client, or, if the host declaration or the
       client does not provide a dhcp-client-identifier	 option,  by  matching
       the  hardware parameter in the host declaration to the network hardware
       address supplied by the client.	BOOTP clients do not normally  provide
       a  dhcp-client-identifier, so the hardware address must be used for all
       clients that may boot using the BOOTP protocol.

       DHCPv6 servers can use the host-identifier option parameter in the host
       declaration,  and  specify  any	option	with a fixed value to identify
       hosts.

       Please be aware that only the  dhcp-client-identifier  option  and  the
       hardware	 address can be used to match a host declaration, or the host-
       identifier option parameter for DHCPv6 servers.	For example, it is not
       possible	 to  match  a host declaration to a host-name option.  This is
       because the host-name option cannot be guaranteed to be unique for  any
       given client, whereas both the hardware address and dhcp-client-identi‐
       fier option are at least theoretically guaranteed to  be	 unique	 to  a
       given client.

       The group statement

	group {
	  [ parameters ]
	  [ declarations ]
	}

       The group statement is used simply to apply one or more parameters to a
       group of declarations.  It can be used to group hosts, shared networks,
       subnets, or even other groups.

REFERENCE: ALLOW AND DENY
       The  allow  and	deny statements can be used to control the response of
       the DHCP server to various sorts of requests.  The allow and deny  key‐
       words  actually have different meanings depending on the context.  In a
       pool context, these keywords can be used to set	up  access  lists  for
       address	allocation pools.  In other contexts, the keywords simply con‐
       trol general server behavior with respect to clients  based  on	scope.
       In  a  non-pool context, the ignore keyword can be used in place of the
       deny keyword to prevent logging of denied requests.

ALLOW DENY AND IGNORE IN SCOPE
       The following usages of allow and deny will work in any scope, although
       it is not recommended that they be used in pool declarations.

       The unknown-clients keyword

	allow unknown-clients;
	deny unknown-clients;
	ignore unknown-clients;

       The unknown-clients flag is used to tell dhcpd whether or not to dynam‐
       ically assign addresses to unknown clients.  Dynamic address assignment
       to  unknown clients is allowed by default.  An unknown client is simply
       a client that has no host declaration.

       The use of this option  is  now	deprecated.   If  you  are  trying  to
       restrict	 access	 on your network to known clients, you should use deny
       unknown-clients; inside of your address pool, as	 described  under  the
       heading ALLOW AND DENY WITHIN POOL DECLARATIONS.

       The bootp keyword

	allow bootp;
	deny bootp;
	ignore bootp;

       The bootp flag is used to tell dhcpd whether or not to respond to bootp
       queries.	 Bootp queries are allowed by default.

       The booting keyword

	allow booting;
	deny booting;
	ignore booting;

       The booting flag is used to tell dhcpd whether or  not  to  respond  to
       queries	from  a particular client.  This keyword only has meaning when
       it appears in a host declaration.  By default, booting is allowed,  but
       if it is disabled for a particular client, then that client will not be
       able to get an address from the DHCP server.

       The duplicates keyword

	allow duplicates;
	deny duplicates;

       Host declarations can match client messages based on  the  DHCP	Client
       Identifier  option  or  based on the client's network hardware type and
       MAC address.  If the MAC address is used,  the  host  declaration  will
       match  any  client  with that MAC address - even clients with different
       client identifiers.  This doesn't normally happen, but is possible when
       one  computer  has more than one operating system installed on it - for
       example, Microsoft Windows and NetBSD or Linux.

       The duplicates flag tells the DHCP server that if a request is received
       from  a	client that matches the MAC address of a host declaration, any
       other leases matching that MAC  address	should	be  discarded  by  the
       server,	even  if  the UID is not the same.  This is a violation of the
       DHCP protocol, but can prevent clients whose client identifiers	change
       regularly  from	holding	 many  leases  at  the same time.  By default,
       duplicates are allowed.

       The declines keyword

	allow declines;
	deny declines;
	ignore declines;

       The DHCPDECLINE message is used by DHCP clients to  indicate  that  the
       lease  the server has offered is not valid.  When the server receives a
       DHCPDECLINE  for	 a  particular	address,  it  normally	abandons  that
       address,	 assuming that some unauthorized system is using it.  Unfortu‐
       nately, a malicious or buggy client can,	 using	DHCPDECLINE  messages,
       completely  exhaust the DHCP server's allocation pool.  The server will
       reclaim these leases, but while the client is running through the pool,
       it  may	cause serious thrashing in the DNS, and it will also cause the
       DHCP server to forget old DHCP client address allocations.

       The declines flag tells the DHCP server whether or not to honor DHCPDE‐
       CLINE  messages.	 If it is set to deny or ignore in a particular scope,
       the DHCP server will not respond to DHCPDECLINE messages.

       The client-updates keyword

	allow client-updates;
	deny client-updates;

       The client-updates flag tells the DHCP server whether or not  to	 honor
       the  client's  intention to do its own update of its A record.  This is
       only relevant when doing interim DNS updates.   See  the	 documentation
       under the heading THE INTERIM DNS UPDATE SCHEME for details.

       The leasequery keyword

	allow leasequery;
	deny leasequery;

       The leasequery flag tells the DHCP server whether or not to answer DHC‐
       PLEASEQUERY packets. The answer to  a  DHCPLEASEQUERY  packet  includes
       information about a specific lease, such as when it was issued and when
       it will expire. By default, the server will not respond to these	 pack‐
       ets.

ALLOW AND DENY WITHIN POOL DECLARATIONS
       The  uses  of the allow and deny keywords shown in the previous section
       work pretty much the same way whether the client is sending a  DHCPDIS‐
       COVER  or  a  DHCPREQUEST message - an address will be allocated to the
       client (either the old address it's requesting, or a new	 address)  and
       then  that address will be tested to see if it's okay to let the client
       have it.	 If the client requested it, and it's  not  okay,  the	server
       will  send  a  DHCPNAK  message.	 Otherwise, the server will simply not
       respond to the client.  If it is	 okay  to  give	 the  address  to  the
       client, the server will send a DHCPACK message.

       The  primary  motivation	 behind	 pool  declarations is to have address
       allocation pools whose allocation policies are different.  A client may
       be denied access to one pool, but allowed access to another pool on the
       same network segment.  In order for this to work, access control has to
       be  done	 during	 address  allocation,  not after address allocation is
       done.

       When a DHCPREQUEST message is processed, address allocation simply con‐
       sists  of looking up the address the client is requesting and seeing if
       it's still available for the client.  If it is, then  the  DHCP	server
       checks  both  the  address  pool permit lists and the relevant in-scope
       allow and deny statements to see if it's okay to give the lease to  the
       client.	 In the case of a DHCPDISCOVER message, the allocation process
       is done as described previously in the ADDRESS ALLOCATION section.

       When declaring permit lists for address allocation pools, the following
       syntaxes are recognized following the allow or deny keywords:

	known-clients;

       If  specified, this statement either allows or prevents allocation from
       this pool to any client that has a host declaration (i.e.,  is  known).
       A  client  is known if it has a host declaration in any scope, not just
       the current scope.

	unknown-clients;

       If specified, this statement either allows or prevents allocation  from
       this  pool  to  any  client  that has no host declaration (i.e., is not
       known).

	members of "class";

       If specified, this statement either allows or prevents allocation  from
       this pool to any client that is a member of the named class.

	dynamic bootp clients;

       If  specified, this statement either allows or prevents allocation from
       this pool to any bootp client.

	authenticated clients;

       If specified, this statement either allows or prevents allocation  from
       this  pool  to  any  client  that has been authenticated using the DHCP
       authentication protocol.	 This is not yet supported.

	unauthenticated clients;

       If specified, this statement either allows or prevents allocation  from
       this  pool to any client that has not been authenticated using the DHCP
       authentication protocol.	 This is not yet supported.

	all clients;

       If specified, this statement either allows or prevents allocation  from
       this  pool  to  all clients.  This can be used when you want to write a
       pool declaration for some reason, but hold it in reserve, or  when  you
       want  to	 renumber  your	 network  quickly, and thus want the server to
       force all clients that have been allocated addresses from this pool  to
       obtain new addresses immediately when they next renew.

	after time;

       If  specified, this statement either allows or prevents allocation from
       this pool after a given date. This can be used when you	want  to  move
       clients	from one pool to another. The server adjusts the regular lease
       time so that the latest expiry time is  at  the	given  time+min-lease-
       time.   A short min-lease-time enforces a step change, whereas a longer
       min-lease-time allows for a gradual  change.   time  is	either	second
       since  epoch,  or  a  UTC  time string e.g.  4 2007/08/24 09:14:32 or a
       string with time zone offset in	seconds	 e.g.  4  2007/08/24  11:14:32
       -7200

REFERENCE: PARAMETERS
       The adaptive-lease-time-threshold statement

	 adaptive-lease-time-threshold percentage;

	 When  the  number  of	allocated leases within a pool rises above the
	 percentage given in this statement, the  DHCP	server	decreases  the
	 lease	length for new clients within this pool to min-lease-time sec‐
	 onds. Clients renewing an already valid (long) leases	get  at	 least
	 the  remaining	 time  from the current lease. Since the leases expire
	 faster, the server may either recover	more  quickly  or  avoid  pool
	 exhaustion  entirely.	Once the number of allocated leases drop below
	 the threshold, the server reverts back to normal lease times.	 Valid
	 percentages are between 1 and 99.

       The always-broadcast statement

	 always-broadcast flag;

	 The  DHCP  and BOOTP protocols both require DHCP and BOOTP clients to
	 set the broadcast bit in the flags field of the BOOTP message header.
	 Unfortunately, some DHCP and BOOTP clients do not do this, and there‐
	 fore may not receive responses from the DHCP server.  The DHCP server
	 can  be  made to always broadcast its responses to clients by setting
	 this flag to ´on´ for the relevant scope; relevant  scopes  would  be
	 inside	 a  conditional statement, as a parameter for a class, or as a
	 parameter for a host declaration.  To avoid creating excess broadcast
	 traffic  on  your  network, we recommend that you restrict the use of
	 this option to as few clients as possible.  For example,  the	Micro‐
	 soft  DHCP client is known not to have this problem, as are the Open‐
	 Transport and ISC DHCP clients.

       The always-reply-rfc1048 statement

	 always-reply-rfc1048 flag;

	 Some BOOTP clients expect RFC1048-style responses, but do not	follow
	 RFC1048  when	sending their requests.	 You can tell that a client is
	 having this problem if it is not getting the options you have config‐
	 ured  for  it	and  if	 you  see in the server log the message "(non-
	 rfc1048)" printed with each BOOTREQUEST that is logged.

	 If you want to send rfc1048 options to such a client, you can set the
	 always-reply-rfc1048  option  in  that client's host declaration, and
	 the DHCP server will respond with an  RFC-1048-style  vendor  options
	 field.	  This	flag  can  be  set  in	any scope, and will affect all
	 clients covered by that scope.

       The authoritative statement

	 authoritative;

	 not authoritative;

	 The DHCP server will normally assume that the configuration  informa‐
	 tion  about a given network segment is not known to be correct and is
	 not authoritative.  This is so that if a naive user installs  a  DHCP
	 server	 not fully understanding how to configure it, it does not send
	 spurious DHCPNAK messages to clients  that  have  obtained  addresses
	 from a legitimate DHCP server on the network.

	 Network  administrators  setting  up  authoritative  DHCP servers for
	 their networks should always write authoritative; at the top of their
	 configuration file to indicate that the DHCP server should send DHCP‐
	 NAK messages to misconfigured clients.	 If this is not done,  clients
	 will  be  unable  to  get a correct IP address after changing subnets
	 until their old lease has expired, which  could  take	quite  a  long
	 time.

	 Usually,  writing  authoritative; at the top level of the file should
	 be sufficient.	 However, if a DHCP server is to be set up so that  it
	 is aware of some networks for which it is authoritative and some net‐
	 works for which it is not, it may  be	more  appropriate  to  declare
	 authority on a per-network-segment basis.

	 Note  that the most specific scope for which the concept of authority
	 makes any sense is the physical network segment -  either  a  shared-
	 network  statement or a subnet statement that is not contained within
	 a shared-network statement.  It is not meaningful to specify that the
	 server is authoritative for some subnets within a shared network, but
	 not authoritative for others, nor is it meaningful  to	 specify  that
	 the  server  is authoritative for some host declarations and not oth‐
	 ers.

       The boot-unknown-clients statement

	 boot-unknown-clients flag;

	 If the boot-unknown-clients statement is present and has a  value  of
	 false	or  off,  then	clients for which there is no host declaration
	 will not be allowed to obtain IP addresses.  If this statement is not
	 present  or has a value of true or on, then clients without host dec‐
	 larations will be allowed to obtain IP addresses, as  long  as	 those
	 addresses  are	 not  restricted  by  allow and deny statements within
	 their pool declarations.

       The db-time-format statement

	 db-time-format [ default | local ] ;

	 The DHCP server software  outputs  several  timestamps	 when  writing
	 leases	 to  persistent storage.  This configuration parameter selects
	 one of two output formats.  The default format prints the day,	 date,
	 and  time  in	UTC, while the local format prints the system seconds-
	 since-epoch, and helpfully provides the day and time  in  the	system
	 timezone  in  a comment.  The time formats are described in detail in
	 the dhcpd.leases(5) manpage.

       The ddns-hostname statement

	 ddns-hostname name;

	 The name parameter should be the hostname that will be used  in  set‐
	 ting up the client's A and PTR records.  If no ddns-hostname is spec‐
	 ified in scope, then the server will derive  the  hostname  automati‐
	 cally,	 using	an  algorithm  that  varies  for each of the different
	 update methods.

       The ddns-domainname statement

	 ddns-domainname name;

	 The name parameter should be the domain name that will be appended to
	 the client's hostname to form a fully-qualified domain-name (FQDN).

       The dns-local-address4 and dns-local-address6 statements

	 ddns-local-address4 address;

	 ddns-local-address6 address;

	 The  address  parameter  should be the local IPv4 or IPv6 address the
	 server should use as  the  from  address  when	 sending  DDNS	update
	 requests.

       The ddns-rev-domainname statement

	 ddns-rev-domainname name;

	 The name parameter should be the domain name that will be appended to
	 the client's reversed IP address to produce a name  for  use  in  the
	 client's  PTR	record.	  By default, this is "in-addr.arpa.", but the
	 default can be overridden here.

	 The reversed IP address to which this	domain	name  is  appended  is
	 always	 the  IP  address  of  the  client,  in	 dotted quad notation,
	 reversed - for example, if the IP address assigned to the  client  is
	 10.17.92.74,  then  the  reversed  IP	address	 is 74.92.17.10.  So a
	 client with that IP address would, by default, be given a PTR	record
	 of 10.17.92.74.in-addr.arpa.

       The ddns-update-style parameter

	 ddns-update-style style;

	 The  style  parameter	must be one of standard, interim or none.  The
	 ddns-update-style statement is only meaningful in the outer  scope  -
	 it  is	 evaluated once after reading the dhcpd.conf file, rather than
	 each time a client is assigned an IP address, so there is no  way  to
	 use different DNS update styles for different clients. The default is
	 none.

       The ddns-updates statement

	  ddns-updates flag;

	 The ddns-updates parameter controls whether or not  the  server  will
	 attempt  to  do  a DNS update when a lease is confirmed.  Set this to
	 off if the server should not attempt to do updates within  a  certain
	 scope.	  The ddns-updates parameter is on by default.	To disable DNS
	 updates in all scopes, it is preferable to use the  ddns-update-style
	 statement, setting the style to none.

       The default-lease-time statement

	 default-lease-time time;

	 Time should be the length in seconds that will be assigned to a lease
	 if the client requesting the lease does not ask for a specific	 expi‐
	 ration	 time.	 This is used for both DHCPv4 and DHCPv6 leases (it is
	 also known as the "valid lifetime" in DHCPv6).	 The default is	 43200
	 seconds.

       The delayed-ack and max-ack-delay statements

	 delayed-ack count;

	 max-ack-delay microseconds;

	 Count should be an integer value from zero to 2^16-1, and defaults to
	 28.  The count represents how many DHCPv4  replies  maximum  will  be
	 queued	 pending transmission until after a database commit event.  If
	 this number is reached, a database commit event  (commonly  resulting
	 in  fsync() and representing a performance penalty) will be made, and
	 the reply packets will be transmitted in a  batch  afterwards.	  This
	 preserves  the	 RFC2131  direction  that  "stable storage" be updated
	 prior to replying to clients.	Should the  DHCPv4  sockets  "go  dry"
	 (select()  returns  immediately  with no read sockets), the commit is
	 made and any queued packets are transmitted.

	 Similarly, microseconds indicates how many microseconds are permitted
	 to  pass  inbetween queuing a packet pending an fsync, and performing
	 the fsync.  Valid values range from 0	to  2^32-1,  and  defaults  to
	 250,000 (1/4 of a second).

	 Please	 note  that  as	 delayed-ack  is  currently  experimental, the
	 delayed-ack feature is not  compiled  in  by  default,	 but  must  be
	 enabled at compile time with ´./configure --enable-delayed-ack´.

       The dhcp-cache-threshold statement

	 dhcp-cache-threshold percentage;

	 The  dhcp-cache-threshold  statement takes one integer parameter with
	 allowed values between 0 and 100. The default value is 25 (25% of the
	 lease	time).	This  parameter	 expresses the percentage of the total
	 lease time, measured from the	beginning,  during  which  a  client's
	 attempt  to  renew  its  lease	 will  result  in  getting the already
	 assigned lease, rather than an extended lease.

	 Clients that attempt renewal  frequently  can	cause  the  server  to
	 update	 and  write the database frequently resulting in a performance
	 impact on the server.	The dhcp-cache-threshold  statement  instructs
	 the DHCP server to avoid updating leases too frequently thus avoiding
	 this behavior.	 Instead the server assigns the	 same  lease  with  no
	 modifications	except	for CLTT (Client Last Transmission Time) which
	 does not require disk operations. This feature applies to IPv4 only.

       The do-forward-updates statement

	 do-forward-updates flag;

	 The do-forward-updates statement instructs  the  DHCP	server	as  to
	 whether it should attempt to update a DHCP client´s A record when the
	 client acquires or renews a lease.   This  statement  has  no	effect
	 unless	 DNS  updates  are  enabled.   Forward	updates are enabled by
	 default.  If this statement is used to disable forward	 updates,  the
	 DHCP  server  will never attempt to update the client´s A record, and
	 will only ever attempt to update  the	client´s  PTR  record  if  the
	 client supplies an FQDN that should be placed in the PTR record using
	 the fqdn option.  If forward updates are  enabled,  the  DHCP	server
	 will still honor the setting of the client-updates flag.

       The dont-use-fsync statement

	 dont-use-fsync flag;

	 The  dont-use-fsync  statement instructs the DHCP server if it should
	 call fsync() when writing leases to the lease file.  By  default  and
	 if  the flag is set to false the server will call fsync().  Suppress‐
	 ing the call to fsync() may increase the performance  of  the	server
	 but  it also adds a risk that a lease will not be properly written to
	 the disk after it has been issued to a client and before  the	server
	 stops.	  This	can lead to duplicate leases being issued to different
	 clients.  Using this option is not recommended.

       The dynamic-bootp-lease-cutoff statement

	 dynamic-bootp-lease-cutoff date;

	 The dynamic-bootp-lease-cutoff statement sets the ending time for all
	 leases	 assigned dynamically to BOOTP clients.	 Because BOOTP clients
	 do not have any way of renewing leases, and  don't  know  that	 their
	 leases	 could expire, by default dhcpd assigns infinite leases to all
	 BOOTP clients.	 However, it may make sense in some situations to  set
	 a cutoff date for all BOOTP leases - for example, the end of a school
	 term, or the time at night when a facility is closed and all machines
	 are required to be powered off.

	 Date  should be the date on which all assigned BOOTP leases will end.
	 The date is specified in the form:

				 W YYYY/MM/DD HH:MM:SS

	 W is the day of the week expressed as a number from zero (Sunday)  to
	 six  (Saturday).  YYYY is the year, including the century.  MM is the
	 month expressed as a number from 1 to 12.   DD	 is  the  day  of  the
	 month,	 counting from 1.  HH is the hour, from zero to 23.  MM is the
	 minute and SS is the second.  The time is always in Coordinated  Uni‐
	 versal Time (UTC), not local time.

       The dynamic-bootp-lease-length statement

	 dynamic-bootp-lease-length length;

	 The dynamic-bootp-lease-length statement is used to set the length of
	 leases dynamically assigned to BOOTP clients.	At some sites, it  may
	 be  possible to assume that a lease is no longer in use if its holder
	 has not used BOOTP or DHCP to get its address within a	 certain  time
	 period.   The	period	is specified in length as a number of seconds.
	 If a client reboots using BOOTP during the timeout period, the	 lease
	 duration  is reset to length, so a BOOTP client that boots frequently
	 enough will never lose its lease.  Needless to	 say,  this  parameter
	 should be adjusted with extreme caution.

       The filename statement

	 filename "filename";

	 The filename statement can be used to specify the name of the initial
	 boot file which is to be loaded by a client.  The filename should  be
	 a filename recognizable to whatever file transfer protocol the client
	 can be expected to use to load the file.

       The fixed-address declaration

	 fixed-address address [, address ... ];

	 The fixed-address declaration is used to assign one or more fixed  IP
	 addresses  to a client.  It should only appear in a host declaration.
	 If more than one address is supplied, then when the client boots,  it
	 will be assigned the address that corresponds to the network on which
	 it is booting.	 If none of the addresses in the fixed-address	state‐
	 ment are valid for the network to which the client is connected, that
	 client will not match the host	 declaration  containing  that	fixed-
	 address  declaration.	 Each address in the fixed-address declaration
	 should be either an IP address or a domain name that resolves to  one
	 or more IP addresses.

       The fixed-address6 declaration

	 fixed-address6 ip6-address ;

	 The  fixed-address6  declaration  is  used  to	 assign	 a  fixed IPv6
	 addresses to a client.	 It should only appear in a host declaration.

       The get-lease-hostnames statement

	 get-lease-hostnames flag;

	 The get-lease-hostnames statement is used to tell  dhcpd  whether  or
	 not  to  look	up  the domain name corresponding to the IP address of
	 each address in the lease pool and use	 that  address	for  the  DHCP
	 hostname  option.   If flag is true, then this lookup is done for all
	 addresses in the current scope.  By default, or if flag is false,  no
	 lookups are done.

       The hardware statement

	 hardware hardware-type hardware-address;

	 In  order  for	 a BOOTP client to be recognized, its network hardware
	 address must be declared using a hardware clause in the  host	state‐
	 ment.	 hardware-type	must be the name of a physical hardware inter‐
	 face type.  Currently, only the ethernet  and	token-ring  types  are
	 recognized,  although	support	 for a fddi hardware type (and others)
	 would also be desirable.  The hardware-address should	be  a  set  of
	 hexadecimal  octets  (numbers from 0 through ff) separated by colons.
	 The hardware statement may also be used for DHCP clients.

       The host-identifier option statement

	 host-identifier option option-name option-data;

	 or

	 host-identifier v6relopt number option-name option-data;

	 This identifies a DHCPv6 client in a host statement.  option-name  is
	 any  option,  and  option-data	 is  the value for the option that the
	 client will send. The option-data must be a constant value.   In  the
	 v6relopts  case the additional number is the relay to examine for the
	 specified option name and value.  The values are the same as for  the
	 v6relay  option.  0 is a no-op, 1 is the relay closest to the client,
	 2 the next one in and so on.  Values that are larger than the maximum
	 number	 of  relays  (currently	 32) indicate the relay closest to the
	 server independent of number.

       The ignore-client-uids statement

	 ignore-client-uids flag;

	 If the ignore-client-uids statement is present and  has  a  value  of
	 true or on, the UID for clients will not be recorded.	If this state‐
	 ment is not present or has a value of false or off, then client  UIDs
	 will be recorded.

       The infinite-is-reserved statement

	 infinite-is-reserved flag;

	 ISC DHCP now supports ´reserved´ leases.  See the section on RESERVED
	 LEASES below.	If this flag is	 on,  the  server  will	 automatically
	 reserve  leases  allocated  to	 clients  which	 requested an infinite
	 (0xffffffff) lease-time.

	 The default is off.

       The lease-file-name statement

	 lease-file-name name;

	 Name should be the name of the DHCP server's lease file.  By default,
	 this  is DBDIR/dhcpd.leases.  This statement must appear in the outer
	 scope of the configuration file - if it appears in some other	scope,
	 it  will have no effect.  Furthermore, it has no effect if overridden
	 by the -lf flag or the PATH_DHCPD_DB environment variable.

       The limit-addrs-per-ia statement

	 limit-addrs-per-ia number;

	 By default, the DHCPv6 server will limit clients to one IAADDR per IA
	 option,  meaning  one address.	 If you wish to permit clients to hang
	 onto multiple addresses at a time, configure a larger number here.

	 Note that there is no present	method	to  configure  the  server  to
	 forcibly  configure the client with one IP address per each subnet on
	 a shared network.  This is left to future work.

       The dhcpv6-lease-file-name statement

	 dhcpv6-lease-file-name name;

	 Name is the name of the lease file to use if and only if  the	server
	 is  running in DHCPv6 mode.  By default, this is DBDIR/dhcpd6.leases.
	 This statement, like lease-file-name, must appear in the outer	 scope
	 of the configuration file.  It has no effect if overridden by the -lf
	 flag or the PATH_DHCPD6_DB environment	 variable.   If	 dhcpv6-lease-
	 file-name  is not specified, but lease-file-name is, the latter value
	 will be used.

       The local-port statement

	 local-port port;

	 This statement causes the DHCP server to listen for DHCP requests  on
	 the UDP port specified in port, rather than on port 67.

       The local-address statement

	 local-address address;

	 This  statement  causes  the  DHCP server to listen for DHCP requests
	 sent to the specified address,	 rather	 than  requests	 sent  to  all
	 addresses.  Since serving directly attached DHCP clients implies that
	 the server must respond to requests sent to the all-ones IP  address,
	 this  option  cannot be used if clients are on directly attached net‐
	 works; it is only  realistically  useful  for	a  server  whose  only
	 clients are reached via unicasts, such as via DHCP relay agents.

	 Note:	 This  statement  is only effective if the server was compiled
	 using the USE_SOCKETS #define statement, which is default on a	 small
	 number	 of  operating	systems, and must be explicitly chosen at com‐
	 pile-time for all others.  You can be sure if your server is compiled
	 with USE_SOCKETS if you see lines of this format at startup:

	  Listening on Socket/eth0

	 Note  also  that since this bind()s all DHCP sockets to the specified
	 address, that only one address may be supported  in  a	 daemon	 at  a
	 given time.

       The log-facility statement

	 log-facility facility;

	 This statement causes the DHCP server to do all of its logging on the
	 specified log facility once the dhcpd.conf file has  been  read.   By
	 default  the  DHCP  server logs to the daemon facility.  Possible log
	 facilities include auth, authpriv,  cron,  daemon,  ftp,  kern,  lpr,
	 mail,	mark,  news,  ntp,  security,  syslog,	user, uucp, and local0
	 through local7.  Not all of these facilities  are  available  on  all
	 systems,  and	there  may be other facilities available on other sys‐
	 tems.

	 In addition to setting this value, you may need to modify  your  sys‐
	 log.conf  file to configure logging of the DHCP server.  For example,
	 you might add a line like this:

	      local7.debug /var/log/dhcpd.log

	 The syntax of the syslog.conf file may be different on some operating
	 systems  -  consult  the  syslog.conf manual page to be sure.	To get
	 syslog to start logging to the new file, you must  first  create  the
	 file  with correct ownership and permissions (usually, the same owner
	 and permissions of your /var/log/messages or  /usr/adm/messages  file
	 should	 be  fine) and send a SIGHUP to syslogd.  Some systems support
	 log rollover using a shell script  or	program	 called	 newsyslog  or
	 logrotate, and you may be able to configure this as well so that your
	 log file doesn't grow uncontrollably.

	 Because the log-facility setting  is  controlled  by  the  dhcpd.conf
	 file,	log  messages  printed	while  parsing	the dhcpd.conf file or
	 before parsing it are logged to the default log facility.  To prevent
	 this,	see  the  README  file	included with this distribution, which
	 describes BUG: where is that mentioned in README?  how to change  the
	 default  log  facility.  When this parameter is used, the DHCP server
	 prints its startup message a second time after parsing the configura‐
	 tion file, so that the log will be as complete as possible.

       The max-lease-time statement

	 max-lease-time time;

	 Time should be the maximum length in seconds that will be assigned to
	 a lease.  If not defined, the default maximum lease  time  is	86400.
	 The only exception to this is that Dynamic BOOTP lease lengths, which
	 are not specified by the client, are not limited by this maximum.

       The min-lease-time statement

	 min-lease-time time;

	 Time should be the minimum length in seconds that will be assigned to
	 a  lease.   The  default  is the minimum of 300 seconds or max-lease-
	 time.

       The min-secs statement

	 min-secs seconds;

	 Seconds should be the minimum number of seconds since a client	 began
	 trying	 to acquire a new lease before the DHCP server will respond to
	 its request.  The number of seconds  is  based	 on  what  the	client
	 reports, and the maximum value that the client can report is 255 sec‐
	 onds.	Generally, setting this to one will result in the DHCP	server
	 not  responding  to the client's first request, but always responding
	 to its second request.

	 This can be used to set up a secondary DHCP server which never offers
	 an  address  to  a  client  until the primary server has been given a
	 chance to do so.  If the primary server is down, the client will bind
	 to  the secondary server, but otherwise clients should always bind to
	 the primary.  Note that this does not, by itself,  permit  a  primary
	 server and a secondary server to share a pool of dynamically-allocat‐
	 able addresses.

       The next-server statement

	 next-server server-name;

	 The next-server statement is used to specify the host address of  the
	 server	 from  which  the initial boot file (specified in the filename
	 statement) is to be loaded.   Server-name  should  be	a  numeric  IP
	 address or a domain name.

       The omapi-port statement

	 omapi-port port;

	 The  omapi-port  statement causes the DHCP server to listen for OMAPI
	 connections on the specified port.  This  statement  is  required  to
	 enable	 the  OMAPI  protocol, which is used to examine and modify the
	 state of the DHCP server as it is running.

       The one-lease-per-client statement

	 one-lease-per-client flag;

	 If this flag is enabled, whenever a client sends a DHCPREQUEST for  a
	 particular lease, the server will automatically free any other leases
	 the client holds.  This presumes that when the client sends a DHCPRE‐
	 QUEST,	 it has forgotten any lease not mentioned in the DHCPREQUEST -
	 i.e., the client has only a single network interface and it does  not
	 remember leases it's holding on networks to which it is not currently
	 attached.  Neither of these assumptions are guaranteed	 or  provable,
	 so we urge caution in the use of this statement.

       The pid-file-name statement

	 pid-file-name name;

	 Name  should  be the name of the DHCP server's process ID file.  This
	 is the file in which the DHCP server's process ID is stored when  the
	 server	 starts.   By  default,	 this  is  RUNDIR/dhcpd.pid.  Like the
	 lease-file-name statement, this statement must appear	in  the	 outer
	 scope	of  the configuration file.  It has no effect if overridden by
	 the -pf flag or the PATH_DHCPD_PID environment variable.

	 The dhcpv6-pid-file-name statement

	    dhcpv6-pid-file-name name;

	    Name is the name of the pid file to use if and only if the	server
	    is	running in DHCPv6 mode.	 By default, this is DBDIR/dhcpd6.pid.
	    This statement, like pid-file-name, must appear in the outer scope
	    of	the configuration file.	 It has no effect if overridden by the
	    -pf	 flag  or  the	PATH_DHCPD6_PID	 environment   variable.    If
	    dhcpv6-pid-file-name  is  not specified, but pid-file-name is, the
	    latter value will be used.

	 The ping-check statement

	    ping-check flag;

	    When the DHCP server is considering dynamically allocating	an  IP
	    address  to a client, it first sends an ICMP Echo request (a ping)
	    to the address being assigned.  It waits for a second, and	if  no
	    ICMP  Echo	response has been heard, it assigns the address.  If a
	    response is heard, the lease is abandoned, and the server does not
	    respond to the client.

	    This  ping check introduces a default one-second delay in respond‐
	    ing to DHCPDISCOVER messages, which can  be	 a  problem  for  some
	    clients.   The default delay of one second may be configured using
	    the ping-timeout parameter.	 The ping-check configuration  parame‐
	    ter	 can  be  used to control checking - if its value is false, no
	    ping check is done.

	 The ping-timeout statement

	    ping-timeout seconds;

	    If the DHCP server determined it should send an ICMP echo  request
	    (a	ping)  because	the ping-check statement is true, ping-timeout
	    allows you to configure how many seconds the  DHCP	server	should
	    wait  for  an  ICMP	 Echo  response	 to  be heard, if no ICMP Echo
	    response has been received before the timeout expires, it  assigns
	    the	 address.  If a response is heard, the lease is abandoned, and
	    the server does not respond to the client.	If no  value  is  set,
	    ping-timeout defaults to 1 second.

	 The preferred-lifetime statement

	    preferred-lifetime seconds;

	    IPv6  addresses have ´valid´ and ´preferred´ lifetimes.  The valid
	    lifetime determines at what point at lease might be said  to  have
	    expired,  and  is  no  longer useable.  A preferred lifetime is an
	    advisory condition to help applications move off  of  the  address
	    and onto currently valid addresses (should there still be any open
	    TCP sockets or similar).

	    The preferred lifetime defaults to the renew+rebind timers, or 3/4
	    the default lease time if none were specified.

	 The remote-port statement

	    remote-port port;

	    This  statement  causes the DHCP server to transmit DHCP responses
	    to DHCP clients upon the UDP port specified in port,  rather  than
	    on	port 68.  In the event that the UDP response is transmitted to
	    a DHCP Relay, the server generally uses the local-port  configura‐
	    tion  value.   Should  the	DHCP  Relay  happen to be addressed as
	    127.0.0.1, however, the DHCP Server transmits its response to  the
	    remote-port	 configuration	value.	 This is generally only useful
	    for testing purposes, and this configuration value	should	gener‐
	    ally not be used.

	 The server-identifier statement

	    server-identifier hostname;

	    The	 server-identifier  statement  can be used to define the value
	    that is sent in the DHCP Server  Identifier	 option	 for  a	 given
	    scope.   The  value	 specified  must be an IP address for the DHCP
	    server, and must be reachable by all clients served by a  particu‐
	    lar scope.

	    The	 use  of  the server-identifier statement is not recommended -
	    the only reason to use it is to  force  a  value  other  than  the
	    default  value  to	be  sent  on occasions where the default value
	    would be incorrect.	 The default value is  the  first  IP  address
	    associated	with  the  physical  network  interface	 on  which the
	    request arrived.

	    The usual case where the server-identifier statement needs	to  be
	    sent  is  when  a physical interface has more than one IP address,
	    and the one being sent by default isn't appropriate	 for  some  or
	    all clients served by that interface.  Another common case is when
	    an alias is defined for the purpose	 of  having  a	consistent  IP
	    address  for  the  DHCP server, and it is desired that the clients
	    use this IP address when contacting the server.

	    Supplying a value for the dhcp-server-identifier option is equiva‐
	    lent to using the server-identifier statement.

	 The server-duid statement

	    server-duid LLT [ hardware-type timestamp hardware-address ] ;

	    server-duid EN enterprise-number enterprise-identifier ;

	    server-duid LL [ hardware-type hardware-address ] ;

	    The server-duid statement configures the server DUID. You may pick
	    either LLT (link local address plus time), EN (enterprise), or  LL
	    (link local).

	    If you choose LLT or LL, you may specify the exact contents of the
	    DUID.  Otherwise the server will generate a DUID of the  specified
	    type.

	    If	you  choose EN, you must include the enterprise number and the
	    enterprise-identifier.

	    The default server-duid type is LLT.

	 The server-name statement

	    server-name name ;

	    The server-name statement can be used to inform the client of  the
	    name  of  the server from which it is booting.  Name should be the
	    name that will be provided to the client.

	 The site-option-space statement

	    site-option-space name ;

	    The site-option-space statement can be used to determine from what
	    option  space  site-local options will be taken.  This can be used
	    in much the same way as the vendor-option-space statement.	 Site-
	    local  options  in	DHCP are those options whose numeric codes are
	    greater than 224.  These options are  intended  for	 site-specific
	    uses, but are frequently used by vendors of embedded hardware that
	    contains DHCP clients.  Because site-specific  options  are	 allo‐
	    cated  on  an ad hoc basis, it is quite possible that one vendor's
	    DHCP client might use the same option code that  another  vendor's
	    client uses, for different purposes.  The site-option-space option
	    can be used to assign a different set of site-specific options for
	    each  such vendor, using conditional evaluation (see dhcp-eval (5)
	    for details).

	 The stash-agent-options statement

	    stash-agent-options flag;

	    If the stash-agent-options parameter is true for a	given  client,
	    the	 server	 will  record the relay agent information options sent
	    during the client's initial DHCPREQUEST message  when  the	client
	    was	 in  the  SELECTING  state  and behave as if those options are
	    included in all subsequent DHCPREQUEST messages sent in the RENEW‐
	    ING	 state.	 This works around a problem with relay agent informa‐
	    tion options, which is that they usually not appear in DHCPREQUEST
	    messages  sent  by	the client in the RENEWING state, because such
	    messages are unicast directly to the server and not sent through a
	    relay agent.

	 The update-conflict-detection statement

	    update-conflict-detection flag;

	    If	the  update-conflict-detection	parameter  is true, the server
	    will perform standard  DHCID  multiple-client,  one-name  conflict
	    detection.	 If  the parameter has been set false, the server will
	    skip this check and instead simply tear down any previous bindings
	    to install the new binding without question.  The default is true.

	 The update-optimization statement

	    update-optimization flag;

	    If	the update-optimization parameter is false for a given client,
	    the server will attempt a DNS update for that client each time the
	    client  renews  its	 lease,	 rather than only attempting an update
	    when it appears to be necessary.  This will allow the DNS to  heal
	    from  database  inconsistencies  more easily, but the cost is that
	    the DHCP server must do many more DNS updates.  We recommend leav‐
	    ing	 this  option enabled, which is the default.  This option only
	    affects the behavior of the interim DNS update scheme, and has  no
	    effect  on the ad-hoc DNS update scheme.  If this parameter is not
	    specified, or is true, the DHCP server will only update  when  the
	    client  information changes, the client gets a different lease, or
	    the client's lease expires.

	 The update-static-leases statement

	    update-static-leases flag;

	    The update-static-leases flag, if enabled, causes the DHCP	server
	    to	do  DNS	 updates  for  clients even if those clients are being
	    assigned their IP address using a fixed-address statement  -  that
	    is,	 the client is being given a static assignment.	 This can only
	    work with the interim DNS update scheme.  It  is  not  recommended
	    because  the  DHCP	server	has no way to tell that the update has
	    been done, and therefore will not delete the record when it is not
	    in	use.   Also,  the server must attempt the update each time the
	    client renews its lease, which could have  a  significant  perfor‐
	    mance  impact in environments that place heavy demands on the DHCP
	    server.

	 The use-host-decl-names statement

	    use-host-decl-names flag;

	    If the use-host-decl-names parameter is true  in  a	 given	scope,
	    then  for  every host declaration within that scope, the name pro‐
	    vided for the host declaration will be supplied to the  client  as
	    its hostname.  So, for example,

		group {
		  use-host-decl-names on;

		  host joe {
		    hardware ethernet 08:00:2b:4c:29:32;
		    fixed-address joe.fugue.com;
		  }
		}

	    is equivalent to

		  host joe {
		    hardware ethernet 08:00:2b:4c:29:32;
		    fixed-address joe.fugue.com;
		    option host-name "joe";
		  }

	    An option host-name statement within a host declaration will over‐
	    ride the use of the name in the host declaration.

	    It should be noted here that most DHCP clients  completely	ignore
	    the	 host-name option sent by the DHCP server, and there is no way
	    to configure them not to do this.  So you generally have a	choice
	    of	either	not  having  any hostname to client IP address mapping
	    that the client will recognize,  or	 doing	DNS  updates.	It  is
	    beyond  the	 scope	of  this document to describe how to make this
	    determination.

	 The use-lease-addr-for-default-route statement

	    use-lease-addr-for-default-route flag;

	    If the use-lease-addr-for-default-route parameter  is  true	 in  a
	    given  scope,  then	 instead of sending the value specified in the
	    routers option (or sending no value at all), the IP address of the
	    lease  being  assigned  is	sent  to  the client.  This supposedly
	    causes Win95 machines to ARP for all IP addresses,	which  can  be
	    helpful  if	 your  router is configured for proxy ARP.  The use of
	    this feature is not recommended, because it won't  work  for  many
	    DHCP clients.

	 The vendor-option-space statement

	    vendor-option-space string;

	    The	 vendor-option-space  parameter	 determines  from  what option
	    space vendor options are taken.  The  use  of  this	 configuration
	    parameter  is  illustrated	in the dhcp-options(5) manual page, in
	    the VENDOR ENCAPSULATED OPTIONS section.

SETTING PARAMETER VALUES USING EXPRESSIONS
       Sometimes it's helpful to be able to set the value  of  a  DHCP	server
       parameter  based	 on  some value that the client has sent.  To do this,
       you can	use  expression	 evaluation.   The  dhcp-eval(5)  manual  page
       describes how to write expressions.  To assign the result of an evalua‐
       tion to an option, define the option as follows:

	 my-parameter = expression ;

       For example:

	 ddns-hostname = binary-to-ascii (16, 8, "-",
					  substring (hardware, 1, 6));

RESERVED LEASES
       It's often useful to allocate a single address to a single  client,  in
       approximate  perpetuity.	  Host	statements  with fixed-address clauses
       exist to a certain extent to  serve  this  purpose,  but	 because  host
       statements  are	intended  to  approximate ´static configuration´, they
       suffer from not being referenced in a littany of other Server Services,
       such as dynamic DNS, failover, ´on events´ and so forth.

       If  a  standard	dynamic	 lease, as from any range statement, is marked
       ´reserved´, then the server will only allocate this lease to the client
       it is identified by (be that by client identifier or hardware address).

       In practice, this means that the lease follows the normal state engine,
       enters ACTIVE state when the client is bound  to	 it,  expires,	or  is
       released,  and  any  events or services that would normally be supplied
       during these events are processed normally, as with any	other  dynamic
       lease.	The  only  difference  is that failover servers treat reserved
       leases as special when they enter the FREE  or  BACKUP  states  -  each
       server  applies the lease into the state it may allocate from - and the
       leases are not placed on the queue for  allocation  to  other  clients.
       Instead	they  may  only	 be ´found´ by client identity.	 The result is
       that the lease is only offered to the returning client.

       Care should probably be taken to ensure that the client	only  has  one
       lease within a given subnet that it is identified by.

       Leases  may  be	set  ´reserved´	 either	 through OMAPI, or through the
       ´infinite-is-reserved´ configuration option (if this is	applicable  to
       your environment and mixture of clients).

       It  should  also be noted that leases marked ´reserved´ are effectively
       treated the same as leases marked ´bootp´.

REFERENCE: OPTION STATEMENTS
       DHCP option statements are documented  in  the  dhcp-options(5)	manual
       page.

REFERENCE: EXPRESSIONS
       Expressions used in DHCP option statements and elsewhere are documented
       in the dhcp-eval(5) manual page.

SEE ALSO
       dhcpd(8),  dhcpd.leases(5),  dhcp-options(5),  dhcp-eval(5),   RFC2132,
       RFC2131.

AUTHOR
       dhcpd.conf(5) is maintained by ISC.  Information about Internet Systems
       Consortium can be found at https://www.isc.org.

								 dhcpd.conf(5)
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