Troubleshooting guide

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ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 8 Troubleshooting Tag and MPLS Switching Connections
Troubleshooting MPLS VPN
172.20.42.0/24
in label: imp-null
out label: imp-null lsr: 222.2.1.1:0
out label: imp-null lsr: 111.0.1.18:0
200.1.0.0/16
in label: 18
222.2.1.1/32
in label: 19
out label: imp-null lsr: 222.2.1.1:0 inuse
out label: 21 lsr: 111.0.1.18:0
222.2.1.2/32
in label: 20
out label: 19 lsr: 222.2.1.1:0
out label: imp-null lsr: 111.0.1.18:0 inuse
222.2.1.3/32
in label: imp-null
out label: 21 lsr: 222.2.1.1:0
out label: 22 lsr: 111.0.1.18:0
This display contains label bindings for 111.0.1.X/30 networks that are the interfaces for each Label
Switch Router (LSR). Notice there are multiple labels for each LSR. Each label corresponds to a
different path. For example, the connection to the Loopback 0 interface 222.2.1.1/32 on the 8540-PE1
switch router uses the following labels:
• in label 19
• out label 22 to LSR interface 111.0.1.18 on the 8540-PE2 switch router
Troubleshooting MPLS VPN
This section provides troubleshooting steps for MPLS Virtual Private Networks (VPNs) over ATM
connections.
When used with MPLS, the VPN allows several sites to interconnect transparently through a service
provider network. One service provider network can support several different IP VPNs. Each of these
appears to its users as a private network, separate from all other networks. Within a VPN, each site can
send IP packets to any other site in the same VPN.
Each VPN is associated with one or more VPN routing or forwarding instances (VRFs). A VRF consists
of an IP routing table, a derived Cisco Express Forwarding (CEF) table, and a set of interfaces that use
this forwarding table.
The ATM switch router maintains a separate routing and CEF table for each VRF. This prevents
information from being sent outside the VPN, and allows the same subnet to be used in several VPNs
without causing duplicate IP address problems.
The ATM switch router distributes the VPN routing information using the MP-BGP extended
communities.