implicit null

Unanswered Question
Jul 27th, 2008

i need to know when PHP is performed does router imposes any label on the packet or not.



I have this problem too.
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lee.reade Mon, 07/28/2008 - 00:04

Hi Shivlu,

When doing PenUltimate Hop Popping (PHP) the top label is popped off, and no label is imposed into the packet.

This means that if there a single label on the packet, after PHP, the packet will be forwarded based on the FIB table, ie routed, if there is two labels on the packet, as you would have in an MPLS VPN environment, then the packet will be forwarded using the LFIB matching on the last remaining label.

Explicit Null, label value 0, can be used so that instead of using popping off the top label, a null label can be added so that QOS information can be retained. When using explicit null, you would have two labels in an MPLS VPN environment.



shivlu jain Mon, 07/28/2008 - 22:22

thanks. It means during the use of explicit null label can mtu create the problems.




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