Cisco MPLS VPN Troubleshooting: VRF, BGP and Labels

MPLS VPN faults can hide in four different places — the VRF definition, the MP-BGP control plane, the PE-CE routing protocol or the label forwarding plane — and guessing which one wastes hours. This article adapts the official Cisco troubleshooting methodology for the classic three-route-reflector MPLS VPN topology into a step-by-step command sequence that walks you from VRF verification to an end-to-end VRF-aware ping.

Step 1: Validate the VRF Configuration

show ip vrf [vrf-name]
show ip vrf detail vrf-name

Confirm the VRF exists with the correct route distinguisher and import/export route targets. Remember that VRF names are case sensitive: Customer_A is not customer_a. A missing VRF or wrong RT here breaks everything downstream.

Step 2: Check the VPNv4 BGP Control Plane

show ip bgp vpnv4 all
show ip bgp vpnv4 vrf Customer_A
show ip bgp vpnv4 all tags

Verify the VPNv4 table contains the customer routes and that labels are assigned. If the VPNv4 table is empty, the problem is MP-BGP: check show ip bgp neighbors for session state and address-family activation between PEs and the route reflectors.

Step 3: Validate PE-CE Routing

If the customer runs a protocol other than BGP at the PE-CE edge, apply the traditional show commands within the VRF context — for example show ip rip database vrf [vrf-name], or OSPF/EIGRP equivalents scoped to the VRF. Missing routes here indicate redistribution or filtering issues on the PE.

Step 4: Test with VRF-Aware Tools

ping vrf Customer_A 10.1.1.14
traceroute vrf Customer_A 10.1.1.14 source 10.1.1.1

Use VRF-aware ping/traceroute to prove connectivity from the PE into the customer site. When tracerouting across the MPLS backbone, the absence of core router hops is normal if the backbone does not propagate IP TTL — configure mpls ip propagate-ttl if you need hop-by-hop visibility. For related control-plane issues, see BGP neighbor flapping root causes and the VXLAN MP-BGP EVPN design guide.

原文链接：https://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/13734-mpls-vpn-tsh.html