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

Nick Hilliard nick at
Fri Sep 30 15:24:01 UTC 2011

On 30/09/2011 15:45, Christopher Morrow wrote:
> traceroute could certainly be handled in the fastpath.

which traceroute?  icmp?  udp?  tcp?  Traceroute is not a single protocol.

> what is that limit? from a single port? from a single linecard? from a
> chassis? how about we remove complexity here and just deal with this
> in the fastpath?

on a pfc3, the mls rate limiters deal with handling all punts from the
chassis to the RP.  It's difficult to handle this in any other way.

> My point in calling this all 'stupid' is that by now we all have been
> burned by this sort of behavior, vendors have heard from all of us
> that 'this is really not a good answer', enough is enough please stop
> doing this.

"This is a Hard Problem".  There is a balance to be drawn between hardware
complexity, cost and lifecycle.  In the case of the PFC3, we're talking
about hardware which was released in 2000 - 11 years ago.  The ipv6
fragment punting problem was fixed in the pfc3c, which was released in
2003.  I'm aware that cisco is still selling the pfc3b, but they really
only push the rsp720 for internet stuff (if they're pushing the 6500/7600
line at all).


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