MTU size

Unanswered Question
Feb 18th, 2009
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One of my remote location connected to my core switch through MPLS, in port gi3/8 and the MTU sige is 1500 bytes only.

When I tried to ping to remote location with packet sige 5000 also its taking.

My question is if the MTU is 1500 only then how it can take still 5000.



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ccannon88567 Wed, 02/18/2009 - 04:07
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Are you trying this with a "Don't Fragment" offset in the ICMP packet?

Giuseppe Larosa Wed, 02/18/2009 - 05:38
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Hello Naidu,

as Carlton has noted a 5000 byte icmp packet is fragmented to be sent out.

the correct test is with 1500 byte and DF bit set.

in your CE device an MTU of 1500 byte is correct because it receives and sends IP packets without any MPLS label.

It is the service provider that needs to update its mtu settings

Hope to help



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