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TTL and MTU Faiulures on Cisco7609

Hello all

Running show mls statistic on a Cisco 7609 I get the follwing output form one of the modules

Errors

MAC/IP length inconsistencies : 18

Short IP packets received : 0

IP header checksum errors : 35

TTLfailures : 27831123

MTUfailures : 7998775

Is it normal to have so many TTL and MTU failures? What is the true meaning of this failures and how can we troubleshoot in order to minimize them?

Your feedback will be appreciated.

1 REPLY
Cisco Employee

Re: TTL and MTU Faiulures on Cisco7609

This might be normal depending on how long the switch has been running.

The TTL failures counter is incremented every time a received packet TTL reaches 0.

The MTU failure counter is incremented every time a received packet size exceeds the outbound interface MTU but can't be fragmented due to the DF bit being set in the ip header.

There is not much you can do to prevent these counters from incrementing.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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