[c-nsp] q-in-q mtu

[Antonio Querubin]

A new carrier will be handing us customer connections as q-in-q vlans. 
However, during our initial network validation we noticed what seem like 
possible MTU issues.  Pings work fine but HTTP connections to various 
sites is flakey - more so for IPv4 than IPv6 oddly enough.

The customer circuit is terminated on a q-in-q sub-interface of a 
FastEthernet interface on our Cisco 7206VXR.  We interconnect with the 
carrier's Ciena switches through our HP Procurve 4000M switches:

7206VXR --- HP 4000M --- HP 4000M --- Ciena switches ... --- customer

Our HP switches use an MTU of 1514.  The default MTU on our 7206 
sub-interfaces is 1500.  The MTU of the physical FastEthernet is 1500.

Existing single dot1q sub-interfaces on the 7206VXR have been working fine 
for years using the default MTU for both IPv4 and IPv6.  It's just the new 
q-in-q sub-interface that exhibits problems.  Will we need to drop the MTU 
on every q-in-q sub-interface?

Are there other things we need to check?

Antonio Querubin
808-545-5282 x3003
e-mail/xmpp:  tony at lava.net