Cisco 7600 PFC3B(XL) and IPv6 packets with fragmentation header

Mikael Abrahamsson swmike at
Fri Sep 30 05:07:50 UTC 2011

Just thought I'd share some operational info.

PFC3B will by default punt IPv6 packets with fragmentation header to RP 
and route them there, with the obvious performance penalty this incurs.

Workaround is to change this behaviour, meaning ACLs won't work for 
packets with fragmentation header anymore:

   #platform ipv6 acl fragment hardware ?
     drop     Drop IPv6 fragments at hardware
     forward  Forward IPv6 fragments at hardware

PFC3C is supposed to not be affected.

A lot of Teredo and 6to4 traffic has fragmentation headers, so this 
actually is a real problem. We discovered this at our Teredo relay 
upstream router.

Mikael Abrahamsson    email: swmike at

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