[nsp] Re: increased Ethernet MTU on 7200

[Rainer]

Stefan Stefanov wrote:
> Been through this pain some time ago....
> 
> On IO-2FE you can have 1528 bytes of max MTU. To achieve this you have
> to create a 802.1q vlan sub-interface. Without this you are bound to
> 1524 bytes.
> 
> This should be sufficient for MPLS + ATOM over FastEthernet in most
> cases (1500 bytes customer MTU with Frame Relay, HDLC and 802.1q
> encapsulations).
> 
> On this controller you can see the maximum MTU with the show contr fa0/0
> and search for max_mtu:
> 
> rtr>sh controllers fa0/1 | inc max_mtu
>   max_mtu=1528
> 
> Hope this helps.

indeed that's a very good hint.

Do I get this right that max_mtu includes the Ethernet header - leaving
(max_mtu - 24) Byte for IP?

Hmm, even with "encap dot1q 2 native" the MTU is stuck at 1500. Is there
another trick to increase it to 1504? Does this need a certain IOS? Or
do I have to ignore the output from "sh int"?  

Otherwise I assume that this makes the box only accept the larger
frames, but will stick to standard sized frames when sending.

> On ??, 2003-05-27 at 11:37, Rainer wrote:
> > is it possible to increase the MTU on any Ethernet interface available
> > for 7200 routers? Searching cisco.com or googling around didn't turn up
> > anything helpful.
> > 
> > So far I had no luck with io-2fe, io-1fe-tx-isl and pa-1fa-tx-isl.



Rainer

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