[cisco-bba] MTU challenges on Cisco 7206VXR

Frank Bulk - iNAME frnkblk at iname.com
Wed Mar 12 16:13:07 EDT 2008

We're mostly PPPoA over an OC-3, but we do have some PPPoE over the OC-3,
and about ~150 customers using PPPoE coming in on NPE-400's Ethernet port.
We have a Cisco 7206VXR with 12.2(26).

We've had a few reports about the last two years, as we added PPPoE support,
that large packets don't get through.  The answer was always to lower the
MTU to 1400 on their CPE (mostly SonicWall, some WatchGuard) and the problem
was solved.

We have an existing customer moving from PPPoA to PPPoE coming in on the
OC-3with a new consultant and he's pretty sure that "it should just work".
What's odd is that the ~150 PPPoE customers coming in over the Ethernet port
and we haven't had any PPPoE issues.  So I'm guessing something may be
configured on the ATM interface that's not an issue on the Ethernet

Has anyone run into this problem, and if so, is there something I can do on
our BRAS to resolve this?



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