Subject: Re: MPLS and fragmentation...

From: [email-masked]
Date: Thu, 14 Dec 2000 15:46:25 -0500

Eric Gray wrote:

> Consider this.  You are about to discard a packet
> because it is to large.  Who cares if you do this on the
> slow path?

I see at least 2 issues...

1) If you need to fragment the packet rather than discard it
Doing this in the slow path can result in packet re-ordering w.r.t.
subsequent smaller packets processed in the fast path.
Is this acceptable?

2) If you need to send an ICMP message back to the source.
How fast must the slow path be in order to handle all of the
concurrent PMTUD's being performed by the many TCP flows
passing through a core link? I.e. What percentage of the packets will
be performing PMTUD and have the DF bit set, requiring the generation
of an ICMP message?

Keith Schuettpelz

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From: Dan Tappan <[email-masked]>
Date: Thu, 14 Dec 2000 16:15:05 -0500

>be performing PMTUD and have the DF bit set, requiring the generation

Both good questions. Why do you think they apply differently to a labeled 
IP datagram as compared to an unlabeled datagram?

(In other words: this is a red herring. There are implementation techniques 
for avoiding, or mitigating, those effects. Which can be applied in either 
case. And it would be a rathole to discuss them here)