Issues with SNMP monitoring over a GRE tunnel.

Brian Christopher Raaen mailing-lists at
Wed Nov 5 15:59:50 UTC 2014

I have two different customers where I am unable to monitor their networks
due to GRE MTU issues.  This is monitoring cable modems so I can't change
the MTU of the end device.  The problem I am having is that the modems are
producing frames that appear to be larger than some kind of MTU limit in
the system (we do not control the customer routers in either case).  One
that I am looking at is dropping anything larger than 1472, and I have let
to tune down on the other one.  In one case the customer endpoint is a
Cisco ASR1K router and the other is a ASR9K.  because these are UDP packets
I can't use a mss to clamp things down.  Also I have been unable to
replicate the issue in my lab, so I can't send them a list of commands to
help fix the issue on their end.

Brian Christopher Raaen
Network Architect

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