Most switches (not specifically familiar with the ME series) will compensate for dot1q tags by transparently allowing packets of MTU+dot1q tag size. This is not usually true for mpls (again not directly familiar with the ME series) that being said the mpls header is exactly 4 bytes which seems to be your ceiling so I'd say you were right.
2011/7/12 Leigh Harrison <[email protected]> > All, > > I have inherited a network which I feel is having MTU issues, but I cannot > be sure and would like a second opinion. > > There is a legacy layer 2 network which has had an mpls network built over > it. A link between two of the data centres is a dark fibre between two > Cisco 3750E switches running on the ten gig ports with a variety of vlans > passing over a dot1q trunk. Both of these switches are pretty much out of > the box and have a standard system mtu of 1500. > > Connected to these 3750E switches are a set of Cisco ME3600X switches that > are talking mpls to each other via an SVI, over a vlan on the trunk between > the 3750E switches. Sending packets of 1496 bytes over the mpls works just > fine, but when I push 1497, it doesn't work - hence my thoughts of an MTU > issue. > > Have we fallen into a silly trap or is there a straightforward solution? > Is this an MTU problem or am I clutching at straws? > > Thanks in advance, > > Leigh > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
