Subject: [Tsvwg] Re: TCP and ICMP soft-errors in IPv4/6 environments

From: Bill Sommerfeld <[email-masked]>
Date: Thu, 30 Oct 2003 16:22:44 -0500

> Has this been discussed in the transport area?  Is there something to be 
> done about this, e.g. a BCP document discussing this practice and 
> suggesting ICMP DU's are OK when establishing connections -- or something 
> else?

Maybe the right answer here is a "slewed parallel" connection
establishment; start with one address, and if you get a soft error or
a RTO-sized timeout, try a second, third, fourth, etc., connection,
but leave the prior ones open in the event they complete successfully.

Soft errors wouldn't kill the first connection -- they'd just be a a
hint to try another connection in parallel.

This should probably be buried in a library routine so that
applications don't have to reinvent this wheel.

					- Bill

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From: Pekka Savola <[email-masked]>
Date: Thu, 30 Oct 2003 22:14:24 +0200 (EET)

Hi,

(Targeted at Transport area, v6ops is there just to keep v6ops in the
loop, this has already been discussed there at some length..)

With dual-stack IPv4/6 deployments, when a TCP connection is tried to both
an IPv6 and IPv4 address, these are done in serial w/ a getaddrinfo loop
(in the typical case).  If the first destination is unreachable (e.g.
resulting in a host unreachable ICMPv6 message).  

The old host requirements document states that TCP MUST NOT abort
connections on such soft errors. However, this poses some problems in
current deployments where multiple addresses are tried sequentially, as
summarized above.

This is discussed more in section 2.3 of:

http://www.ietf.org/internet-drafts/draft-ietf-v6ops-v6onbydefault-00.txt

Pekka
 Writing as v6ops co-chair

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings