[c-nsp] MPLS T.E Autoroute problem

[Oliver Boehmer (oboehmer)]

> 
> I have strange behaviour with MPLS T.E with autoroute
> 
> Topology
> 
> R4 (AS100)
> |
> |
> R1-------R2-------R3-------R5 -----> (AS 200)
> |-----Tun13---------|
> 
> both AS200 runs OSPF (single area) and Tunnel13 on R1 is between
R1-Lo0 and
> R3-Lo0 and as shown R5 is reachable from R3
> 
> the problem is when enabling autoroute
> 
> and in LFIB , R5-Lo0 is reachable over the tunnel with untagged label
and
> R3-Lo0 has Pop label so any VPN traffic sourced on R4 and destinted to
CE
> connected to R5 will be routed to R1 which removes ALL  labels and
forward
> it out the tunnel and it will be dropped on R3 and never reaches it is
> destination
> 
> by disabling autoroute
> 
> R5 is still reachable via R3 BUT LFIB has label assigned other than
untag
> and traffic flow seamlessly
> 
> enabling MPLS over the tunnel didn't fix the problem
> 
> is there any feature or command i can use so routes reachable over
tunnel
> and behind tunnel tailend can have a label other than untag ?
 
well, first of all you absolutely need LDP/MPLS enabled on the tunnel,
otherwise R1 (head) has no information about R3's label advertised to
reach R5. So please enable LDP on the tunnel and check the LDP adjacency
between R1 and R3, as well as the label bindings. You should see a label
for R5's lo0 on R1. Haven't looked at it in a while, but you might need
"mpls ldp discovery targeted-hello accept" on R3 for R1's directed
request to be accepted.

BTW: When you disable autoroute, R1 will NOT reach R5 via the tunnel, it
will use the LDP-built LSP across R2, as seen by

> R1#sh mpls forwarding-table 20.1.5.5
> Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
> tag    tag or VC   or Tunnel Id      switched   interface
> 115    211         20.1.5.5/32       0          Fa0/0.12   20.1.12.2

no [T] in the output.

	oli