[comp.protocols.tcp-ip] self-referential arp?

roy@alanine.phri.nyu.edu (Roy Smith) (04/19/91)

	Does it make any sense for something to arp for its own ethernet
address?  This is some tcpdump output from a Kinetics FastPath I'm trying
to configure to use KIP/IPTalk:

13:18:44.62  wombat.phri.nyu.edu.16513 > 128.122.136.160.at-nbp: udp 43
13:18:44.62  arp who-has 128.122.136.160 tell 128.122.136.160
13:18:45.66  wombat.phri.nyu.edu.16513 > 128.122.136.160.at-nbp: udp 43
13:18:45.66  arp who-has 128.122.136.160 tell 128.122.136.160
13:18:46.68  wombat.phri.nyu.edu.16513 > 128.122.136.160.at-nbp: udp 43
13:18:46.68  arp who-has 128.122.136.160 tell 128.122.136.160
13:18:47.70  wombat.phri.nyu.edu.16513 > 128.122.136.160.at-nbp: udp 43
13:18:47.70  arp who-has 128.122.136.160 tell 128.122.136.160
13:18:48.72  wombat.phri.nyu.edu.16514 > 128.122.136.160.at-nbp: udp 43
13:18:48.72  128.122.136.160.16514 > wombat.phri.nyu.edu.at-nbp: udp 43
13:18:48.78  wombat.phri.nyu.edu.at-nbp > 128.122.136.160.16513: udp 43
13:18:48.78  128.122.136.160.at-nbp > wombat.phri.nyu.edu.16513: udp 43

	What do the "arp who-has 128.122.136.160 tell 128.122.136.160"
packets mean?  This is the kbox asking for its own ethernet address.  Is
that normal, or something I might have configured wrong, or a bug in the
gateway code?
--
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy
"Arcane?  Did you say arcane?  It wouldn't be Unix if it wasn't arcane!"

barmar@think.com (Barry Margolin) (04/19/91)

In article <1991Apr18.181504.21390@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes:
>	Does it make any sense for something to arp for its own ethernet
>address?

Many systems do this when they first boot.  If it gets a reply, it means
that someone configured two hosts with the same address, and it can then
display an error message.

However, this doesn't seem to be what was happening in your case, because
it ARPs for itself whenever it receives the at-nbp packet.  My guess is
that it's a configuration problem.



--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar