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ROUTE(8)		   Linux Programmer's Manual		      ROUTE(8)

NAME
       route - show / manipulate the IP routing table

SYNOPSIS
       route [-CFvnee]

       route  [-v]  [-A	 family]  add [-net|-host] target [netmask Nm] [gw Gw]
	      [metric N] [mss M] [window W]  [irtt  I]	[reject]  [mod]	 [dyn]
	      [reinstate] [[dev] If]

       route  [-v]  [-A	 family]  del [-net|-host] target [gw Gw] [netmask Nm]
	      [metric N] [[dev] If]

       route  [-V] [--version] [-h] [--help]

DESCRIPTION
       Route manipulates the kernel's IP routing tables.  Its primary  use  is
       to  set up static routes to specific hosts or networks via an interface
       after it has been configured with the ifconfig(8) program.

       When the add or del  options  are  used,	 route	modifies  the  routing
       tables.	 Without these options, route displays the current contents of
       the routing tables.

OPTIONS
       -A family
	      use the specified address family (eg `inet'; use `route  --help'
	      for a full list).

       -F     operate  on the kernel's FIB (Forwarding Information Base) rout‐
	      ing table.  This is the default.

       -C     operate on the kernel's routing cache.

       -v     select verbose operation.

       -n     show numerical addresses instead of trying to determine symbolic
	      host  names.  This  is useful if you are trying to determine why
	      the route to your nameserver has vanished.

       -e     use netstat(8)-format for displaying  the	 routing  table.   -ee
	      will  generate  a	 very  long  line with all parameters from the
	      routing table.

       del    delete a route.

       add    add a new route.

       target the destination network or host. You can provide IP addresses in
	      dotted decimal or host/network names.

       -net   the target is a network.

       -host  the target is a host.

       netmask NM
	      when adding a network route, the netmask to be used.

       gw GW  route  packets  via a gateway.  NOTE: The specified gateway must
	      be reachable first. This usually means that you have to set up a
	      static  route  to	 the  gateway  beforehand.  If you specify the
	      address of one of your local interfaces,	it  will  be  used  to
	      decide about the interface to which the packets should be routed
	      to. This is a BSDism compatibility hack.

       metric M
	      set the metric field in the routing table (used by routing  dae‐
	      mons) to M.

       mss M  set the TCP Maximum Segment Size (MSS) for connections over this
	      route to M bytes.	 The default is the device MTU minus  headers,
	      or  a  lower  MTU when path mtu discovery occurred. This setting
	      can be used to force smaller TCP packets on the other  end  when
	      path  mtu discovery does not work (usually because of misconfig‐
	      ured firewalls that block ICMP Fragmentation Needed)

       window W
	      set the TCP window size for connections over  this  route	 to  W
	      bytes.  This  is	typically only used on AX.25 networks and with
	      drivers unable to handle back to back frames.

       irtt I set the initial round trip time (irtt) for TCP connections  over
	      this  route  to I milliseconds (1-12000). This is typically only
	      used on AX.25 networks. If omitted the RFC 1122 default of 300ms
	      is used.

       reject install  a  blocking  route,  which will force a route lookup to
	      fail.  This is for example used  to  mask	 out  networks	before
	      using the default route.	This is NOT for firewalling.

       mod, dyn, reinstate
	      install  a  dynamic or modified route. These flags are for diag‐
	      nostic purposes, and are generally only set by routing daemons.

       dev If force the route to be associated with the specified  device,  as
	      the kernel will otherwise try to determine the device on its own
	      (by checking already existing routes and device  specifications,
	      and  where  the  route is added to). In most normal networks you
	      won't need this.

	      If dev If is the last option on the command line, the  word  dev
	      may  be omitted, as it's the default. Otherwise the order of the
	      route modifiers (metric - netmask - gw - dev) doesn't matter.

EXAMPLES
       route add -net 127.0.0.0 netmask 255.0.0.0 dev lo
	      adds the normal loopback	entry,	using  netmask	255.0.0.0  and
	      associated with the "lo" device (assuming this device was previ‐
	      ously set up correctly with ifconfig(8)).

       route add -net 192.56.76.0 netmask 255.255.255.0 dev eth0
	      adds a route to the local network 192.56.76.x via	 "eth0".   The
	      word "dev" can be omitted here.

       route del default
	      deletes the current default route, which is labeled "default" or
	      0.0.0.0 in the destination field of the current routing table.

       route add default gw mango-gw
	      adds a default route (which will	be  used  if  no  other	 route
	      matches).	  All  packets	using  this  route  will  be gatewayed
	      through "mango-gw". The device which will actually be  used  for
	      that  route  depends on how we can reach "mango-gw" - the static
	      route to "mango-gw" will have to be set up before.

       route add ipx4 sl0
	      Adds the route to the "ipx4" host via the SLIP interface (assum‐
	      ing that "ipx4" is the SLIP host).

       route add -net 192.57.66.0 netmask 255.255.255.0 gw ipx4
	      This  command adds the net "192.57.66.x" to be gatewayed through
	      the former route to the SLIP interface.

       route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0
	      This is an obscure one documented so people know how to  do  it.
	      This  sets  all  of  the class D (multicast) IP routes to go via
	      "eth0". This is the correct normal  configuration	 line  with  a
	      multicasting kernel.

       route add -net 10.0.0.0 netmask 255.0.0.0 reject
	      This   installs  a  rejecting  route  for	 the  private  network
	      "10.x.x.x."

OUTPUT
       The output of the kernel routing table is organized  in	the  following
       columns

       Destination
	      The destination network or destination host.

       Gateway
	      The gateway address or '*' if none set.

       Genmask
	      The  netmask  for	 the  destination net; '255.255.255.255' for a
	      host destination and '0.0.0.0' for the default route.

       Flags  Possible flags include
	      U (route is up)
	      H (target is a host)
	      G (use gateway)
	      R (reinstate route for dynamic routing)
	      D (dynamically installed by daemon or redirect)
	      M (modified from routing daemon or redirect)
	      A (installed by addrconf)
	      C (cache entry)
	      !	 (reject route)

       Metric The 'distance' to the target (usually counted in	hops).	It  is
	      not  used	 by  recent kernels, but may be needed by routing dae‐
	      mons.

       Ref    Number of references to this route. (Not used in the Linux  ker‐
	      nel.)

       Use    Count  of lookups for the route.	Depending on the use of -F and
	      -C this will be either route cache misses (-F) or hits (-C).

       Iface  Interface to which packets for this route will be sent.

       MSS    Default maximum segment  size  for  TCP  connections  over  this
	      route.

       Window Default window size for TCP connections over this route.

       irtt   Initial  RTT  (Round  Trip  Time). The kernel uses this to guess
	      about the best TCP protocol parameters without waiting on	 (pos‐
	      sibly slow) answers.

       HH (cached only)
	      The  number  of  ARP entries and cached routes that refer to the
	      hardware header cache for the cached route. This will be -1 if a
	      hardware	address	 is not needed for the interface of the cached
	      route (e.g. lo).

       Arp (cached only)
	      Whether or not the hardware address for the cached route	is  up
	      to date.

FILES
       /proc/net/ipv6_route
       /proc/net/route
       /proc/net/rt_cache

SEE ALSO
       ifconfig(8), netstat(8), arp(8), rarp(8)

HISTORY
       Route  for  Linux  was  originally  written  by	Fred  N.   van Kempen,
       <waltje@uwalt.nl.mugnet.org> and then modified by Johannes  Stille  and
       Linus  Torvalds for pl15. Alan Cox added the mss and window options for
       Linux 1.1.22. irtt support and merged with netstat  from	 Bernd	Ecken‐
       fels.

AUTHOR
       Currently  maintained  by Phil Blundell <Philip.Blundell@pobox.com> and
       Bernd Eckenfels <net-tools@lina.inka.de>.

net-tools			  2007-12-02			      ROUTE(8)
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