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

Simon Leinen simon.leinen at
Sat Oct 1 19:36:18 UTC 2011

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

Router processing is only dependent on noticing that TTL is expiring,
and being able to return an ICMP message (including a "quote" of part of
the original packet) to the sender.

>> 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.

If the rate limit is done "in hardware" (which one should hope), then it
would be more natural to do it on a per-PFC/DFC basis.  So on a box with
DFCs on all linecards, it would be per linecard, not per chassis.

Maybe someone who knows for sure can decide.

>> 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.

Um, no, in 2000 there was no PFC3.  That came out (on the Supervisor
720) in March 2003.

> The ipv6 fragment punting problem was fixed in the pfc3c, which was
> released in 2003.

The PFC 3C was announced (with the RSP720) in December 2006.

> 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).

See Janos' reply, the Catalyst 6500 seems alive and kicking with the
Supervisor 2T.

The 7600 is a somewhat different story.  As far as I see, all
development is going into feature-rich ES+ cards and a few relatively
narrow applications such as mobile backhaul and FTTH aggregation(?).

We have been using the 7600 as a cheap fast IPv4/IPv6 (and later also
MPLS) backbone router.  According to Cisco we should probably move "up"
to the ASR9000 or CRS-3, but I'm tempted to "downgrade" to Catalyst 6500
with Sup-2T (until we need 100G :-).

More information about the NANOG mailing list