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New Member

help with mtu size

I know basic IOS stuff, but I have no idea.

I have a 2620 with a standard T1 CSU/DSU WIC card.

Can the FastEthernet and Serial interfaces be configured with an mtu size of 9000?



Re: help with mtu size


They can not be configured for this MTU. On WAN interfaces you will have a maximum value of 4470 Bytes, which are possible.

The 9216 Bytes are possible on GigabitEthernet interfaces. Regarding your FE interface: it depends on the hardware in use. You can try to set it to 4470 as well, and see whether it will be accepted and better test, if it is working.

Generally I would only recommend to adjust your MTU to values larer than 1500 Bytes, if there are networking requirements behind. Usually they come from other LAN equipment wich is capable of setting larger MTU.

Be aware however, that you might get into troubles, when accessing the Internet, because there you will have a max of 1500 Bytes. Once path MTU discovery fails you might get connection timeouts and connectivity problems with some Web servers out there.

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: help with mtu size


Here is the scenario... IP SAN on Catalyst 2970 is using jumbo frame size of 9000. Replication of SAN array needs to happen on a T1.

I can't seem to figure out how to make that happen (even on different hardware), and I have not found any documentation that states a maximum MTU size.

New Member

Re: help with mtu size

I confirmed with a friend that the 9000 byte size should not be a factor.

sorry...another feeble question: Can the FastEthernet port on a 2620 do jumbo?


Re: help with mtu size


I'm afraid the FE port on the 2620 does not support jumbo frames.

Hope that helps - pls rate the post if it does.



New Member

Re: help with mtu size

Thanks for the info on the 2620.

Any ideas on how to fragment the packets?

Is there a gigabit WIC card for the 2620?

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