we have had issues with MTU problems but usually on the client computers
across slow links.

You mention that a normal ping doesn't help - and you would be correct.
However, try this:

ping 123.456.789.001 -f -l 1500

The -f checks for fragmentation requirement
The -l of course is length of packet sent

If the response is normal then the MTU is good.
If it isn't good, ping will respond with something like:
Fragmentation required but df flag set.

So you try the ping again with a smaller packet, say 1400 - until the ping
doesn't fragment anymore.

Kevin Wigle, CD
CCSP, CCDP, CCNP, MCSE 2003
Security+, ITProject+, ISSP
MCTS Windows Vista Configuration


-----Original Message-----
From: [email protected]
[mailto:[EMAIL PROTECTED] On Behalf Of Konowal, Ed
Sent: September-19-08 11:40 AM
To: InterMapper Discussion
Subject: [IM-Talk] Anyone have MTU problems?

We have a infrequent but recurring problem with our telco.  Every few
weeks they seem to screw something up and we have an MTU problem, which
we have to convience them is their problem.

My problem is, I don't have a tool to scan all my sites with 1500 byte
packets.  Does anyone else have this problem?  Anyone have a solution?

When it's just an MTU problem, you can't see it with normal pings or
even SNMP.  To me my network looks good... Until a site calls to tell me
it's not working.

Ed Konowal
Network Operations Supervisor
Lee County School District
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