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Community Member

MPLS confusion !

Hi guys. I have configured a very simple scenario.

R1---------R2---------R3

I have configured a loopback on R1 and advertised to others via rip. then i ran mpls. On R1 why i cant see my directly connected interfaces ?? same is on R2 and R3 !! they are surely advertising implicit null label dont they ? then why directly connected interfaces are not being showed as untagged ?

Kindly guide me

3 REPLIES
Cisco Employee

Re: MPLS confusion !

Hi,

I guess you are looking at "show mpls forwarding-table". The output will only contain labels assigned to networks, where packets could be forwarded to by cef. Packets to connected networks are punted, hence do not show up. To see the imp-null labels please use "show mpls ldp binding", which displays the LIB. It contains all the locally assigned labels plus the ones learned through LDP for every network including the connected ones.

Hope this helps!

Regards,

Martin

Community Member

Re: MPLS confusion !

Dear Sir, what did you mean by punted ? if the packet is for directly connected interface, doesnt router still does a cef lookup ?

Cisco Employee

Re: MPLS confusion !

Hi,

Punted means the packets are processed by the Router CPU because the destination address is one of its local addresses.

But you're right there is still a CEF lookup before the packet is sent to the CPU

On R2 for example, you don't see its local network in the MPLS forwarding table because there is nothing to forward (the LSP simply stops here).

But on R1, you should see R2-R3 link in its forwarding table with a pop label as outgoing label. Same thing from R3 and R1-R2 link

HTH

Laurent.

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