MPLS question

Answered Question
Feb 24th, 2009

I have a question about the "show mpls ip binding" command.

r2#show mpls ip binding

5.5.5.0/24

in label: 17

out label: imp-null lsr: 10.0.0.1:0 inuse

6.6.6.0/24

in label: 18

out label: 17 lsr: 10.0.0.1:0 inuse

10.0.0.0/24

in label: imp-null

out label: imp-null lsr: 10.0.0.1:0

10.0.1.0/24

in label: imp-null

out label: 16 lsr: 10.0.0.1:0

10.9.9.0/24

in label: 16

out label: imp-null lsr: 10.0.0.1:0 inuse

is the subnet 5.5.5.0/24 the destination network, or is 10.0.0.1 the destination from 5.5.5.0?

Thanks,

John

I have this problem too.
0 votes
Correct Answer by Edison Ortiz about 7 years 9 months ago

No, 10.0.0.1 seems to be the adjacent router on the path towards 5.5.5.0/24.

The packet is coming in as label in R2 (label 17) and leaving as an IPv4 towards 10.0.0.1

10.0.0.1 receives this packet as a regular IPv4 packet and performs the necessary routing on it.

The imp-null is a way for 10.0.0.1 to tell R2 to pop the top label and send the packet as IPv4.

HTH,

__

Edison.

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Edison Ortiz Tue, 02/24/2009 - 15:02

5.5.5.0/24 is on 10.0.0.1 IPv4's routing table. A PHP was sent from this router to R2.

HTH,

__

Edison.

John Blakley Tue, 02/24/2009 - 15:03

Can you expand on your answer a little Edison? From the way that I'm reading your response, it seems as though the "show mpls ip binding" was done on the 10.0.0.1 router. Is this correct?

John

Correct Answer
Edison Ortiz Tue, 02/24/2009 - 15:08

No, 10.0.0.1 seems to be the adjacent router on the path towards 5.5.5.0/24.

The packet is coming in as label in R2 (label 17) and leaving as an IPv4 towards 10.0.0.1

10.0.0.1 receives this packet as a regular IPv4 packet and performs the necessary routing on it.

The imp-null is a way for 10.0.0.1 to tell R2 to pop the top label and send the packet as IPv4.

HTH,

__

Edison.

ajay.manam Wed, 02/25/2009 - 06:19

hi john,

here the network 10.0.0.1 is the network which is owned by #r2

here we can say 5.5.5.0 is destination,

in any mpls enabled router it assigns label to each and every route , but it does not assign any label to it's own routes , simply it assigns imp-null

thanks and regards

............ Ajay krishna

John Blakley Wed, 02/25/2009 - 06:40

Ajay,

I was under the impression that imp-null had nothing to do with the routers "own routes", but it was when PHP was in effect. The imp-null value is CoS value 3, and it tells the router to pop the label before it gets to its next hop which is the edge LSR. The edge LSR won't have to do two lookups when PHP is in effect. It only has to look up in its routing table on how to send the packet.

Am I wrong?

Thanks,

John

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