(Loose) uRPF vs. non-announced IXP space

[Gert Doering]

Hi,

On Wed, Feb 08, 2012 at 01:01:24PM +0100, Thomas Schmid wrote:
> On 08.02.2012 12:55, Bernhard Schmidt wrote:
> > FYI, I've been informed that there has been a similar problem on the
> > RIPE ipv6-wg mailinglist last June. Start here:
> >
> > http://www.ripe.net/ripe/mail/archives/ipv6-wg/2011-July/001839.html
> >
> > There has not been a clear solution in this thread either.
> 
> that's a real pain, especially since IXPs are the internet's MTU 
> bottlenecks.

Actually, if the *IXP* is the MTU bottleneck, this is not a problem
at all - as the last router *before* the IXP would source the ICMP
packet, and not the router after the IXP mesh.

In this case, it's the first router *after* the IXP, which sends
back the ICMP packet using the IXP interface as egress, thus using
the uRPF-filtered source address.

>  From my point of view RFC 5963 should be updated to recommend the 
> global announcement
> of IX prefixes for IPv6 or - as already mentioned - an alternative would 
> be to source the
> ICMP messages from a public address instead.

Vendors providing uRPF implementations that cannot be configured to
add exceptions, like "permit all ICMP packet too big" are part of the
problem.

Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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