Re: Problems with AT&T

[<bdragon () gweep net>]

> If someone can identify what you are actually seeing, I'll check into
> it.
> If you are experiencing drops or slow traces, only through the core,
> there is an issue with excessive de-prioritization of ICMP control
> message with a particular router type (vendcor) in the core. End to end
> data flow has not seemed to be affected but trace and ping core
> latencies are looking very wierd. I've been asking customers to use
> trace only for path detail and to use end to end ping for any
> performance data.=20
>
> Yes, the core is MPLS enabled. Diffserv acted on only at the edges
> though.=20
>
> Michelle

It could certainly be customers who have broken themselves. I've heard
lots of stories about people who do PMTUD but simultaneously filter
ICMP Can't Frag messages.

As soon as the Path MTU drops below whatever their local box is (usually
1500) they "break" although due to their own screwed up config.

Since MPLS adds additional overhead, dropping the MTU, I'ld seriously
consider this as a possible reason.

The major problems are:
1) identifying broken customers
2) convincing customers that they are broken when they "haven't changed
anything"
3) getting them to actually change

Some folks just put off the problem until later by moving to MTUs > 1500.
The only benefit to this is that hopefully when the customer next breaks
it is as a direct result of them having "changed something" which gets
you over the hurdle of convincing some person that their filtering of all
ICMP isn't just stupid, but is also broken.