Fault Symptom
Three PEs are configured with BGP/MPLS VPN services. Traffic from a CE is balanced between PE1 and PE2. PE2 is connected to PE1, and PE1 is connected to PE3 over a Metropolitan Area Network (MAN). After the configurations, PE1 learns the route to the network segment 10.1.2.0, and the BGP VPNv4 routing table of PE2 contains this route entry, but the VPN instance routing table of PE2 does not.
Fault Analysis
1. Run the display bgp vpnv4 all routing-table command on PE2 to view BGP VPNv4 routes. PE2 has learned the route to the network segment 10.1.2.0 but the route is not optimal.
Network NextHop MED LocPrf PrefVal Community
*> 1.1.1.0/24 1.1.1.1 0 0 no-export
* 1.1.1.2/32 1.1.1.1 0 0 no-export
*i 10.1.2.0/24 10.1.1.1 100 0 no-export
2. Run the display ip routing-table vpn-instance vpn1 10.1.2.0 verbose command on PE2 to view the routing table of the VPN instance.
Routing Table : vpn1
Summary Count : 1
Destination: 10.1.2.0/24
Protocol: BGP Process ID: 0
Preference: 255 Cost: 0
NextHop: 10.1.1.1 Interface: NULL0
RelayNextHop: 0.0.0.0 Neighbour: 10.1.1.1
Label: 109568 Tunnel ID: 0x0
SecTunnel ID: 0x0
BkNextHop: 0.0.0.0 BkInterface:
BkLabel: NULL Tunnel ID: 0x0
SecTunnel ID: 0x0
State: Inactive Adv WaitQ Age: 22h35m37s
The preceding routing information shows that the outbound interface of the next hop is Null0, and thus packets are discarded.
If VPNv4 routes are used to forward traffic, LSP labels of the public network will be added to the routes. Before adding a VPNv4 route to the routing table of a VPN instance, the system checks whether the route contains a corresponding LSP label of the public network. If no such LSP label corresponding to the VPNv4 route exists, the route will not be added to the routing table.
3. Run the display mpls lsp command on PE2. No route to 10.1.1.1 is displayed, indicating that no neighbor relationship has been established between PE1 and PE2.
Procedure
1. Run the system-view command on PE1 to enter the system view.
2. Run the mpls command to enable MPLS and enter the MPLS view.
3. Run the quit command to return to the system view.
4. Run the mpls ldp command to enable LDP globally and enter the MPLS LDP view.
5. (Optional) Run the lsr-id lsr-id command to set the LSR ID for the LDP instance.
6. Run the quit command to return to the system view.
7. Run the interface interface-type interface-number command to enter the view of the interface connecting PE1 to the peer.
8. Run the mpls command to enable MPLS on this interface.
9. Run the mpls ldp command to enable LDP on this interface.
Perform all the preceding operations on PE2. After the operations, PE1 will have learned the route to the network segment 10.1.2.0 and both the BGP VPNv4 routing table of PE2 and the routing table of the VPN instance have routes to the network segment 10.1.2.0. The fault is rectified.
Summary
If VPNv4 routes are used to forward traffic, LSP labels of the public network will be added to the routes. Before adding a VPNv4 route to the routing table of a VPN instance, the system checks whether the route contains a corresponding LSP label of the public network. If there is no such LSP label corresponding to the VPNv4 route, the route will not be added to the routing table.
