Re: 6to4 anycast IP as source address / PTR record

[David Malone <dwmalone@maths.tcd.ie>]

On Wed, Jan 30, 2008 at 06:33:23PM -0600, Kevin Day wrote:
> http://www.ops.ietf.org/lists/v6ops/v6ops.2004/msg00253.html  -- "As  
> an anycast address, 192.88.99.1 should probably not appear as a source  
> address, however for reasons related to both operational and software  
> it does."

I think the reasons that I had in mind when I wrote this were:

	1) Some 6to4 client implementations would only accept packets
	back from the IP of the configured relay (presumeably the
	code was basically tunnel code that hadn't been fully
	6to4ised).

	2) For some people it was hard to get approved software
	versions that supported both 6to4 and IPv4 anycast, so
	relays were set up that just had 6to4 support and so generated
	packets sourced from 192.88.99.1.

Since then (as Pekka comments) other issues like stateful firewalls
have come up which make your life easier if your relay answers with
192.88.99.1 as a source IP. Note, if you run a public relay, you
need your BGP peers to accept packets from you with a source in
192.88.99.0/24, which has caused some 6to4 connectivity problems.

	David.