Thanks Sandip. I was wondering what the behavior would be if a packet arrives with let's say labels 100 and 18, with 18 being the top-of-stack label? It technically matches on this entry, right? now what will be the outgoing label(s) look like?

Hello,

Up to my knowledge.

If the router is a LER it will pop lable 18 and will check the purpose of the other label in the stack whether it is a VPN label or TE label and deliver it accordingly.

If the rotuer is a LSR it will swap the label 18 with the label as per the LFIB and forward it accordingly.

Regards

Thanveer

Hi Mohammad,

I think the MPLS entry, regardless of where/how the router is deployed should determine the behavior. Based on the information in this entry, does a incomming packet with labels {X, 18} go out as {X, 120, 35} or just {120, 35}? 

Thanks

Peyman

Hello,

As an example we are running vrf at R2 for R1 and Vrf for R5 at R4.

R1---->vrfR2---->R3---->R4vrf---->R5

If R1 wnats to reach R4,

R2 and R3 have a vpnv4 enabled ,think that X is an MPLS label  in the label stack and 18 being VPNV4 label at R2{X,18} then R3 swaps it to Y as per the LFIB and then sends it to R4. then R4 checks it and POPS the label Y and finds the VPNV4 label and then it takes the decission as per the label to send the ip traffic to proper vrf instance.

Hope you understand

Thanks for you example. I understand this case. Now imagine you are in a carrier network with 2 layers of MPLS and a VPN label (a total of 3 labels)

I am going to modify your example as follows:

R1---->vrfR2---->[R3---->[  R4  ]--->R5]---->R6vrf---->R7

where R3 and R5 have an MPLS+VPN label and R4 has 2 MPLS + 1 VPN label.

Now if R3 has the MPLS entry 18-->{35,120}  that I should at the beginign of this discussion; and it receives a packet with [VPN label, 18] it should send the packet out with three labels: [VPN label, 120, 35], right? In that case how the router knows the full label stack? IMO, it should only know the top two outgoing labels and can only show them in the output of 'show mpls forwarding-table detail'. therefore, 'label stack' part of the output only refers to the top of the stack, not all the stack.