Port flapping due to MTU mismatch

[fibernet570]

Hi,

We have some legacy Cisco 6513 switches with the backbone (16-port GBIC blade) MTU set to 1500.  It has a WS-X6148A-GE-TX blade as well, MTU set to 9K.

Now we have a customer sending MTU of 1546, their copper interface terminating on WS-6148A keeps flapping.  Does the flapping have something to do with the backbone set to 1500?  We cant set the backbone to 9K at this moment since it may be intrusive (reuire a reboot).

-Mn

[Alejandro Zuniga]

Hi,

It is possible to have interface flapping caused by MTU mismatches but only if the receiving port is the one with the lower MTU as this can cause input errors and others, increasing the MTU only increases the interface's capabilities for the traffic's size.

Since you have a 6500 you can change the MTU size on the go, this platform does not require a reload.

Here is a good document about this on different platforms:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c1

I hope it helps

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