Message "output packet too big" and then two interfaces goes down.

[luizsergiosantos]

There is router that I saw a few times in the log the message "Output packet size of 1504 bytes too big", just after it two interfaces goes down. The IOS version is 12.2(25). Is it a hardware problem or it would be better to update the IOS version first?

[Giuseppe Larosa]

Hello Luiz,

"Output packet size of 1504 bytes too big"

you have an interface with MTU 1500 and a bigger packet should be sent out of it.

Are you deploying MPLS ?

An ip packet of 1500 byte + 4 byte MPLS header makes a 1504 byte PDU that cannot be handled without increasing the MTU.

I've seen this message when deploying MPLS in a network.

depending on the IOS version and platform you could be able to increase the interface MTU or not

try

int fx/y

mtu 1508

I agree the ports shouldn't go down and so I would start to consider an IOS upgrade

Hope to help

Giuseppe