Panasonic NN46240-710 - Manual (Page 96)

Nortel Secure Router 8000 Series
Troubleshooting - VPN___________ 3 BGP/MPLS IP VPN troubleshooting
3.3.2 CEs cannot communicate
Fault symptom
Figure 3-6 BGP/MPLS VPN networking diagram
Loopback 1
PE1
Loopback 1
PE2
P1 P2
CE1 CE2
The BGP/MPLS VPN service is configured in the network as shown in Figure 3-6. CE1 and
CE2 belong to the same VPN. After the configuration, CE1 cannot successfully ping CE2.
Fault analysis
CQ NOTE
Consider the configuration of PE2 as an example. The configuration of PE1 is similar to that of PE2, and is
not covered in this chapter.
Use the display bgp peer command on PE2 to check the IBGP peer relationship between PE2
and PE1. The IBGP peer relationship is not set up successfully.
Query the distribution of labels, and find that P2 distributes a label of 3 to the previous hop P1.
In normal cases, PE2 distributes a label less than 16 to the previous hop P2, and P2 distributes a
label larger than 16 to the previous hop P1. Then it can be determined that the error lies in
incorrect judgment of hops.
A router judges whether it is the egress node of the LSP because a direct route exists to the
outbound interface of the IBGP session. Check the routing table on P2. Find that a direct route
to PE2 exists, the endpoint of IBGP.
Check the configuration and find that the loopback interface is not specified by using the peer
peer-ip-address connect-interface loopback interface-number command as the outbound
interface of the local IBGP peer session.
If the outbound interface is not specified for the local IBGP session, the default is the outbound
interface of data streams. Because the outbound interface of data streams connects P2 directly;
P2 considers itself as the egress node of the LSP. The P2 mistakenly distributes a label with a
value less than 16 to P1, which causes the label at the stack bottom to pop up ahead of schedule
and results in interworking failure.
Currently, the Secure Router 8000 Series, by default, distributes labels only for the route with a
32-bit mask. This type of configuration error can cause another phenomenon where the public
network route or private network route has no corresponding LSPs.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 3-17