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MPLS 101 - Missing something

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Hi all

 

I am having a problem understanding an issue I have and in particular the verification of the issue.

 

The setup I have is based on the INE R&S topology but I have constructed a diagram which you can find here:

 

https://www.lucidchart.com/documents/view/4beb-20d4-52149a0e-98dc-29fb0a004143

 

R4 and R6 have a GRE tunnel between them with static routes pointing to a next hop which is the other end of the Tunnel. VPNv4 peerings are esatblished via the Loopbacks and custoemr routes are exchanged.

 

Now I can fix the issue in a number of ways:

 

  1. enable mpls and mpls ip on Tunnel 0

  2. change the BGP peerings to peer using the tunnel end points and use mpls bgp forwarding on Tunnel 0

  3. Reset the next hop information to be the tunnel end points using mpls bgp forwarding on the Tunnel

 

There are pssoible other resolutions but I want to focus on point 1) Enabling mpls ip on the tunnel interface.

 

My understanding is that without this I cannot send a labeled packet on this interface but how do I see that it is 'broken' using verification commands?

 

My standard verification went like this:

 

Rack1R4#sh ip cef vrf VPN_A 212.18.0.0 de

212.18.0.0/24, epoch 0

recursive via 150.1.6.6 label 47

recursive via 141.1.46.6 unusable: no label

 

Rack1R4#sh ip cef 150.1.6.6 de

150.1.6.0/24, epoch 0

local label info: global/27

recursive via 141.1.46.6

attached to Tunnel0

 

Rack1R4#sh ip cef 141.1.46.6 det

141.1.46.0/24, epoch 0, flags attached, connected, cover dependents, need deagg

Covered dependent prefixes: 3

need deagg: 3

attached to Tunnel0

 

1) However when I enable mpls ip on the tunnel interface my customer pings start working but nothing in the above verification changes so what additional verification should I be looking at?

 

2) Why when I am peering via a loopback does the mpls bgp forwarding not allow me to send labeled packets using the labels I learnt from VPNv4 yet it does when they peer directy or I modify next hop?

 

 

 

Nick


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