shim6 @ NANOG

Iljitsch van Beijnum iljitsch at
Sun Mar 5 14:51:12 UTC 2006

On 5-mrt-2006, at 12:09, Ian Dickinson wrote:

> As an irrelevent aside, when someone comes up with a way to  
> firewall/acl
> shim6, how much breaks?

The idea is that there will be a shim6 header that can do two things:  
carry shim6 signalling and carry data packets with rewritten  
addresses after a rehoming. Since data packets with rewritten  
addresses can only occur after there have been shim6 signalling  
packets on the same path, filtering out packets with the shim6 header  
on the initially chosen path makes it impossible for the shim state  
to be created so there is no multihoming. If shim packets are allowed  
on the initially chosen path but not on the backup path, shim6 (un) 
reachability detection won't work over the backup path so the backup  
path will be considered broken and won't be used.

In other words: you fall back to single homing without ill effects.

Of course having a TCP session or the like change addresses halfway  
through the session may throw stateful firewalls a bit.

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