[c-nsp] more mpls, mtu, etc., questions

[Alex Rubenstein]

So, I've run into another issue related to the earlier dicusscion of MTU, 
and MPLS.

We have a 7206, with a C7200-I/O-GE+E. The interface is running dot1q, and 
has two vlan subint's facing the core, and some vlan subints facing 
customers.

For the core facing subints, I'd like to run jumbo, 4470 or larger. I do 
this by typing "mtu 4470" on interface gi0/0.

However, when I try to make a customer facing vlan subint, it won't come 
up because of a MTU mismatch (the far end router has a MTU of 1500). I try 
to change the mtu on the subint facing the customer, and

xxxx.zzz(config-subif)#mtu 1500
% Sub-interface GigabitEthernet0/0.324 does not support user settable mtu

So, to solve this problem for the immediate term, I have set the mtu of 
gi0/0 to 1500, but tag-switching mtu to 4470. This allows for it to come 
up, and work.

However, this doesn't allow for l2tpv3 connections to work, because of the 
mtu of 1500 on the physical interface.

Juniper allows this by having per-subinterface settings of each type 
of MTU.

Any thoughts on this?



-- 
Alex Rubenstein, AR97, K2AHR, alex at nac.net, latency, Al Reuben
Net Access Corporation, 800-NET-ME-36, http://www.nac.net