arp man page on IRIX

Man page or keyword search:  
man Server   31559 pages
apropos Keyword Search (all sections)
Output format
IRIX logo
[printable version]



ARP(7P)								       ARP(7P)

NAME
     arp - Address Resolution Protocol

DESCRIPTION
     ARP is a protocol that provides a dynamic mapping from an IP address to
     the corresponding physical network address. The 32-bit IP addresses only
     make sense to the TCP/IP protocol suite. A physical network such as an
     Ethernet or a token ring has it own addressing scheme (often 48-bit
     addresses) to which any network layer using the physical network must
     conform.  Two machines on a given physical network can communicate only
     if they know each other's physical network address. ARP provides a
     mapping between the two different forms of addresses.

     ARP caches IP-physical address mappings.  When an interface requests a
     mapping for an address not in the cache, ARP queues the message which
     requires the mapping and broadcasts a message on the associated network
     requesting the address mapping.  If a response is provided, the new
     mapping is cached and any pending message is transmitted.	Each address
     mapping has a timer associated with it and completed address mappings are
     aged after 20 minutes.  The timer is reset each time the address mapping
     is updated by a SIOCSARP ioctl call or by the reception of an appropriate
     ARP message.  This timer value is not configurable.  ARP will queue at
     most one packet while waiting for a mapping request to be responded to;
     only the most recently ``transmitted'' packet is kept.

     To facilitate communications with systems which do not use ARP, ioctls
     are provided to enter and delete entries in the IP-to-physical address
     tables.  Usage:

	  #include <sys/ioctl.h>
	  #include <sys/socket.h>
	  #include <net/if.h>
	  struct arpreq arpreq;

	  ioctl(s, SIOCSARP, (caddr_t)&arpreq);
	  ioctl(s, SIOCGARP, (caddr_t)&arpreq);
	  ioctl(s, SIOCDARP, (caddr_t)&arpreq);

     Each ioctl takes the same structure as an argument.  SIOCSARP sets an ARP
     entry, SIOCGARP gets an ARP entry, and SIOCDARP deletes an ARP entry.
     These ioctls may be applied to any socket descriptor s, but only by the
     super-user.  The arpreq structure contains:

     /* ARP ioctl request */
     struct arpreq {
	  struct sockaddr     arp_pa;	     /* protocol address */
	  struct sockaddr     arp_ha;	     /* hardware address */
	  int	    arp_flags;	   /* flags */
     };
     /*	 arp_flags field values */
     #define   ATF_COM	      0x02 /* completed entry (arp_ha valid) */
     #define   ATF_PERM	      0x04 /* permanent entry */

									Page 1

ARP(7P)								       ARP(7P)

     #define   ATF_PUBL	      0x08 /* publish (respond for other host) */
     #define   ATF_USETRAILERS	   0x10 /* send trailer packets to host */

     The address family for the arp_pa sockaddr must be AF_INET; for the
     arp_ha sockaddr it must be AF_UNSPEC.  The only flag bits which may be
     written are ATF_PERM, ATF_PUBL and ATF_USETRAILERS.  ATF_PERM causes the
     entry to be permanent if the ioctl call succeeds.	The peculiar nature of
     the ARP tables may cause the ioctl to fail if more than 8 (permanent)
     Internet host addresses hash to the same slot.  ATF_PUBL specifies that
     the ARP code should respond to ARP requests for the indicated host coming
     from other machines.  This allows a host to act as an ``ARP server,''
     which may be useful in convincing an ARP-only machine to talk to a non-
     ARP machine.

     ARP is also used to negotiate the use of trailer IP encapsulations;
     trailers are an alternate encapsulation used to allow efficient packet
     alignment for large packets despite variable-sized headers.  Hosts which
     wish to receive trailer encapsulations so indicate by sending gratuitous
     ARP translation replies along with replies to IP requests; they are also
     sent in reply to IP translation replies.  The negotiation is thus fully
     symmetrical, in that either or both hosts may request trailers.  The
     ATF_USETRAILERS flag is used to record the receipt of such a reply, and
     enables the transmission of trailer packets to that host.

     ARP watches passively for hosts impersonating the local host (i.e. a host
     which responds to an ARP mapping request for the local host's address).

DIAGNOSTICS
     The following messages can appear on the console:
     arp: host with ether address %x:%x:%x:%x:%x:%x is using my IP address
     x.x.x.x
     ARP has discovered another host on the local network which responds to
     mapping requests for its own Internet address.
     arp: ether address is broadcast for IP address x.x.x.x
     ARP has discovered another host on the local network which maps that
     host's IP address onto the ethernet broadcast address.

SEE ALSO
     inet(7F), arp(1M), ifconfig(1M), intro(3)
     ``An Ethernet Address Resolution Protocol,'' RFC826, Dave Plummer,
     Network Information Center, SRI.
     ``Trailer Encapsulations,'' RFC893, S.J. Leffler and M.J. Karels, Network
     Information Center, SRI.

									Page 2

[top]

List of man pages available for IRIX

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net