MPLS and Giants

Unanswered Question

On point to point links in our MPLS network I'm seeing anywhere from 100 million to a billion "giants" on the interface/day. Is this acceptable in an mpls network with a 9214 mtu. Are the giants discarded or fragmented? A Cisco TAC recommendation was "do not use the mpls mtu command." Something about it being quick fix for some bug that had some unpredictable side effects. I'm confused and need some clarification.

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Giuseppe Larosa Mon, 01/26/2009 - 00:36
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Hello Andrew,

if you have set the interface mtu to 9214 bytes there is a chance to have baby giants that are frames with a 4 byte MPLS header.

This can count as giants but they are still handled correctly.

I have seen this in the past on GE interfaces of GSR or C7507 but they were not a real issue.

Frames were correctly received but giants counters was incrementing over time.


Actually if your network had discarded one billion of giant frames you should have had complains or application problems.

Setting mpls mtu can be a solution but my understanding is that it is platform dependent (when to use mpls mtu or not)


Hope to help

Giuseppe


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