When faced with a troubleshooting ticket involving MPLS you need to clear the basics first to ensure that everything is working from a Label Distribution perspective.
- First establish IGP connectivity between all the routers.
- Can you ping all the loopbacks?
- Are there /32 loopbacks configured on every router and advertised into IGP?
- Is CEF enabled?
- Is MPLS IP enabled on the required interfaces?
- Have the routers discovered any LDP neighbors?
I have put together this quick list of commands that I would run on each router to quicky verify that Label Distribution is working
sh run | inc ip cef
sh run | inc mpls ip
sh mpls interface
sh mpls ldp disco
sh mpls ldp neigh
When applied to a router in a working MPLS Core the output should look like below
R21#sh run | inc mpls ip mpls ip mpls ip mpls ip mpls ip R21#sh run | inc ip cef ip cef R21#sh run | inc mpls ip R21#sh mpls interface Interface IP Tunnel Operational FastEthernet0/0 Yes (ldp) No Yes FastEthernet0/1 Yes (ldp) No Yes FastEthernet1/0 Yes (ldp) No Yes FastEthernet2/0 Yes (ldp) No Yes R21#sh mpls ldp neigh Peer LDP Ident: 22.22.22.22:0; Local LDP Ident 21.21.21.21:0 TCP connection: 22.22.22.22.24740 - 21.21.21.21.646 State: Oper; Msgs sent/rcvd: 294/292; Downstream Up time: 04:02:51 LDP discovery sources: FastEthernet0/1, Src IP addr: 172.16.1.2 Addresses bound to peer LDP Ident: 172.16.1.0 172.16.1.2 22.22.22.22 Peer LDP Ident: 172.16.1.9:0; Local LDP Ident 21.21.21.21:0 TCP connection: 172.16.1.9.51621 - 21.21.21.21.646 State: Oper; Msgs sent/rcvd: 210/213; Downstream Up time: 02:48:22 LDP discovery sources: FastEthernet1/0, Src IP addr: 172.16.1.9 Addresses bound to peer LDP Ident: 172.16.1.9 24.24.24.24 172.16.1.10 Peer LDP Ident: 26.26.26.26:0; Local LDP Ident 21.21.21.21:0 TCP connection: 26.26.26.26.43548 - 21.21.21.21.646 State: Oper; Msgs sent/rcvd: 118/119; Downstream Up time: 01:27:44 LDP discovery sources: FastEthernet2/0, Src IP addr: 172.16.1.15 Addresses bound to peer LDP Ident: 172.16.1.15 26.26.26.26 172.16.1.13 Peer LDP Ident: 23.23.23.23:0; Local LDP Ident 21.21.21.21:0 TCP connection: 23.23.23.23.62234 - 21.21.21.21.646 State: Oper; Msgs sent/rcvd: 28/28; Downstream Up time: 00:11:03 LDP discovery sources: FastEthernet0/0, Src IP addr: 172.16.1.4 Addresses bound to peer LDP Ident: 172.16.1.4 23.23.23.23 172.16.1.6 R21#sh run | inc ip cef ip cef R21#sh run | inc mpls ip R21#sh mpls interface Interface IP Tunnel Operational FastEthernet0/0 Yes (ldp) No Yes FastEthernet0/1 Yes (ldp) No Yes FastEthernet1/0 Yes (ldp) No Yes FastEthernet2/0 Yes (ldp) No Yes R21#sh mpls ldp disco Local LDP Identifier: 21.21.21.21:0 Discovery Sources: Interfaces: FastEthernet0/0 (ldp): xmit/recv LDP Id: 23.23.23.23:0 FastEthernet0/1 (ldp): xmit/recv LDP Id: 22.22.22.22:0 FastEthernet1/0 (ldp): xmit/recv LDP Id: 172.16.1.9:0; no host route FastEthernet2/0 (ldp): xmit/recv LDP Id: 26.26.26.26:0
This LDP Troubleshooting was taken from an MPLS L3VPN Tutorial which I posted here – MPLS L3VPN Configuration Tutorial –
