Routing Jumbo Frames

[david_genton]

Has anyone attempted to route with jumbo frames ?? I am curious as to the EXACT behavior encountered when attempted. Will the router fragment the jumbo frame ? Will a router even accept a jumbo frame from a 6509 since the MSFC does not support it ??

[murabi]

Jumbo frames are supported on the CAT 6K in 6.1(1) and 12.1(1)E but are dependent on the line cards being used.

http://www.cisco.com/warp/public/473/148.html

[DAVE GENTON]

Yes I am aware of the support, but my question is what happens when the jumbo frame leaves it's support LAN ?? Will the router fragment it, or throw it away as a jumbo ??

d-

[DALE FRANCIS]

I have never tried to route them, however knowing IOS it seems as tho they would be processed switched by the MSFC and thus leads me to believe it will fragment the frame, hence the warning on CCO about a significant degrade in performance.

But with saying that from 12.1(2) and NOTE a MSFC2, you can set the MTU size on the VLAN interface and this "supports" Jumbo frame routing. As you can imagine if you have other VLAN interfaces that are set at the standard MTU and the packet has to traverse this interface then fragmentation will take place unless the DF bit is set.

Refer to CCO for support is IOS

http://www.cisco.com/en/US/partner/products/hw/switches/ps700/prod_release_note09186a00800fbca0.html#xtocid19

This is from CCO:

The Multilayer Switching Feature Card (MSFC) and Multilayer Switch Module (MSM) do not support jumbo frame routing; if jumbo frames are sent to these routers, router performance is significantly degraded. The Gigabit Switch Router (GSR) does support jumbo frames.

[DAVE GENTON]

Yea, I read that and I guess if I think it thru that would answer my question. I was looking for what ANOTHER router would do with it, but with an MSFC he would get it before the WAN side router anyways, which should just be receiving fragments from the MSFC, which I am scared would be terribly slow.

thanks for waking me up this morning,

Dave