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New Member

MTU can not be set on port

I have a 6509 switch that we just upgraded to a Sup720 module, put in a WS-X6548-GE-45AF module, and configured. So far everything is working except for setting the MTU on the ports on the gigabit blade to greater then 1500.

When I log onto an interface (say GI1/47) and issue the mtu 9216 command I get a response saying that the MTU is not settable for this interface. Everything I am reading tells me it should be. Any ideas where this comes from?

I am runnng in Native mode and have tried to see if there is a system-wide mtu setting. I found one (do not remember where) and set it to 9216. This did not help. HAs anyone run into this and have you resolved this?



Re: MTU can not be set on port


I suppose it will be in default mode of mtu. ie) jumbo frame will be disabled.

It will display default mtu size

show system jumbomtu

Enable jumbo frame and try,

MTU size of 9216 is consider to be jumbo frame so you should use "system jumbomtu" command.

system jumbomtu mtu-size

mtu-size = valid values are from 1500 to 9216 bytes.

I hope it will clear ur doubt,

Rate if it does,


New Member

Re: MTU can not be set on port

Got that far before. The show system jumbomtu does not work on The IOS version of the CLI, but the command system jumbomtu 9216 worked well enough. Even though I have enetered that command I still get the "not settable" message. I guess I'll check to verify the Gigabit blade supports it, though I think it would be ludicrous for it not to.

New Member

Re: MTU can not be set on port

The new blade does not support jumbo packet sizes over 1516. Go figure. The largest packet size I can ping is 1472, which seems normal and better then the 1422 I was seeign before.

Thanks for all the help