[c-nsp] GRE/MPLS

[Timothy Arnold]

Hi,

I've got to terminate a remote site in to a customer's VRF using a GRE tunnel. The tunnel comes up and I can ping across the tunnel and I can also reach other hosts in the same VRF on the PE router that the tunnel terminates. However I cannot reach any hosts on other PE routers. For example, the traffic path is as follows

CE---GRE---PE-1---PE-2---FIREWALL

I don't see any ICMP packets hitting the firewall.

However, other hosts on PE1 are able to reach the firewall without any issues. The GRE tunnel on PE-1 is in the correct VRF

interface Tunnel1
 ip vrf forwarding XXX
 ip address 172.31.255.45 255.255.255.252
 ip mtu 1460
 tunnel source Loopback0
 tunnel destination xxx.xxx.xxx.xxx
end

ON PE-1, I can see the correct route

Routing entry for 10.200.0.0/24
  Known via "bgp 20547", distance 200, metric 0, type internal
  Redistributing via ospf 2
  Advertised by ospf 2 metric-type 1 subnets
  Last update from xxx.xxx.xxx.xxx 7w0d ago
  Routing Descriptor Blocks:
  * xxx.xxx.xxx.xxx (default), from xxx.xxx.xxx.xxx, 7w0d ago
      Route metric is 0, traffic share count is 1
      AS Hops 0
      MPLS Required

I can see the forwarding table is correct and goes out of the right interface towards PE-2

Local  Outgoing      Prefix            Bytes Label   Outgoing   Next Hop
Label  Label or VC   or Tunnel Id      Switched      interface
None   143           10.200.0.0/24[V]  0             Gi1/1.5    xxx.xxx.xxx.xxx

And PE-2 has the correct local label and will remove it.

143    No Label      10.200.0.0/24[V]  0             Vl2055     172.31.255.49

It is strange how it only occurs with the GRE tunnel. Anyone have any suggestions on how I can troubleshoot this further?

Thanks
Tim


Timothy Arnold
Senior Engineer, Network & Security Group, UKSolutions

Telephone: 0845 004 1333, option 2
Email: timothy.arnold at uksolutions.co.uk
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