Path: utzoo!attcan!uunet!lll-winken!lll-ncis!helios.ee.lbl.gov!pasteur!ucbvax!LANL.GOV!mws%beta
From: mws%beta@LANL.GOV (Mitchel W Sukalski)
Newsgroups: comp.protocols.tcp-ip
Subject: connection between ARP and ICMP...
Message-ID: <8901052354.AA05731@beta.lanl.gov>
Date: 5 Jan 89 23:54:48 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 35


I'm in a slight dilemma here, and I was wondering if anybody out in
netland can help me?  I'm looking for documentation (RFCs, IENs, etc.)
that validates the behavior I'm going to describe.

I have a router with two network interfaces.  I'm trying to connect from
machine A, on one of the networks, to machine B, on the other network.
The router does not have an ARP entry for machine B, and when it receives
the first packet from machine A, it sends a "host unreachable" destination
unreachable ICMP message to machine A.  Simultaneously, it generates
an ARP request for machine B.

Some of the folks I have talked to have stated that it is the duty of 
the receiving machine, machine A in this case, to ignore the host
unreachable messages and use a timeout mechanism instead (reporting the
error condition upon timeout, perhaps).  As I see it, that makes sense
for an active connection (to avoid reacting to a transient network problem),
but upon opening a connection, an application, such as telnet,
should take heed of the error immediately and let the user take
the necessary recovery action.

In any case, I have been unable to find any documentation that says the
above behavior is within specification.  I have found ample statements to
the effect that the packet can be dropped, and an ARP request generated;
then, it is up to the transport protocol to resend the packet.  If the
ARP module has not gotten a reply, then the router could send a host
unreachable message.

I'd appreciate any insights or references.

Thanks in advance,

Mitch Sukalski
Communications Group, C-4
Los Alamos National Laboratory