[c-nsp] q-in-q mtu

[David Freedman]

Problem is the DEC chip found on PA-FE-TX , it has a hard limit of 1530
PDU (i.e on the wire, with headers), IOS prevented you changing the mtu
on the interface (which is usually the SDU, i.e without the ethernet
frame overhead) because it was so close to the edge, but with advent of
"tag-switching mtu" you were allowed to "bleed" into this space,
in later releases they abandoned tag-switching mtu in favour of just
letting the user configure the mtu directly up to the 1530 limit (but
woe betide you if you configured it 1530 as this is the assumed SDU and
hence had a PDU >1530!)

Dave.

Antonio Querubin wrote:
> On Thu, 21 Oct 2010, Christophe Lucas wrote:
> 
>> You could be able to set mtu higher than 1500, so that you can handle
>> q-in-q frames.
> 
> 1500 is the highest MTU the router will accept for configuration on its
> FastEthernet interfaces.  It doesn't have any GigabitEthernet interfaces.
> 
>> <off topic>
>> I am interested in what kind of router are terminating your Q-in-Q vlan ?
>> </off>
> 
> It's a 7206VXR running IOS 12.4.
> 
> Antonio Querubin
> 808-545-5282 x3003
> e-mail/xmpp:  tony at lava.net
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
> 


-- 


David Freedman
Group Network Engineering
Claranet Group