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

Christopher Morrow morrowc.lists at
Fri Sep 30 14:45:54 UTC 2011

On Fri, Sep 30, 2011 at 10:26 AM, Saku Ytti <saku at> wrote:
> explained. And probably issues I'm not aware of. Unsure if blind forwarding is
> best option. But I'm all for giving operator options, but calling it stupid
> that vendors punt something is misguided.

after this long, yes... this is just dumb, there's no reason that the
default should be punt. There are cases (you've brought up a few)
where it's required today because of design limitations, there really
shouldn't be cases like this anymore. this isn't our first rodeo,
'lessons learned' and all that...

>> I really think zero limit is the right limit... (for a large number of
>> deployments)
> Traceroute would also break. Unpoliced punting certainly is extremely unwise,

traceroute could certainly be handled in the fastpath.

> but punting to a level that does not introduce significant CPU load, should be
> safest default.

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?

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.


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