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

Unanswered Question
Oct 2nd, 2008
User Badges:

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?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Thu, 10/02/2008 - 22:59
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

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


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



This Discussion