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Configuring Many Shim Interfaces with the Same Peer, VC Type, and VC ID

The mpls-relay command enables you to specify the peer and the VC ID explicitly. The VC type is either automatically determined by the layer 2 interface type or you explicitly configure the VC type with the relay-format keyword in the mpls-relay command.

For example, the following commands create a single layer 2 circuit to the remote peer 10.9.1.3. Load balancing is established on two shim interfaces, fastEthernet 2/0.1 and fastEthernet 3/0.1. The VC type is determined by the layer 2 interface type.



host1(config)#interface fast 2/0.1 

host1(config-subif)#vlan id 1 

host1(config-subif)#mpls-relay 10.9.1.3 200001 

host1(config-subif)#exit 

host1(config)#interface fast 3/0.1 

host1(config-subif)#vlan id 1 

host1(config-subif)#mpls-relay 10.9.1.3 200001

In this example, the router advertises a single label, 53, to the remote peer, 10.9.1.3, and receives a single label, 55, from the peer, resulting in the following forwarding table:

host1:# show mpls forwarding brief
Platform label space
In Label  Owner                                 Action
-------- -------- -------------------------------------------------------
53       ldp      l2transport to FastEthernet3/0.1
                  l2transport to FastEthernet2/0.1
L2transport
     Interface        Owner                      Action
-------------------- -------- -------------------------------------------------
FastEthernet2/0.1    ldp      swap to 55, push 42 on ATM5/0.1, nbr 10.10.11.5
FastEthernet3/0.1    ldp      swap to 55, push 42 on ATM5/0.1, nbr 10.10.11.5

Traffic that arrives on either interface, 2/0.1 or 3/0.1, is forwarded to the remote peer with the same label stack (55, 42). Traffic from the remote peer with label 53 is forwarded to one of the two shim interfaces; the ECMP algorithm determines which of the two shim interfaces receives the traffic.

In the case of a local cross-connects configuration, the following commands illustrate how a three-way cross-connect is created when 10.9.1.2 is a local address:



host1(config)#interface atm 6/0.101 point-to-point 

host1(config-subif)#mpls-relay 10.9.1.2 600001 

host1(config-subif)#exit 

host1(config)#interface atm 6/2.101 point-to-point 

host1(config-subif)#mpls-relay 10.9.1.2 600001 

host1(config-subif)#exit 

host1(config)#interface atm 6/2.103 point-to-point 

host1(config-subif)#mpls-relay 10.9.1.2 600001

This configuration results in the following forwarding table:

host1:two# show mpls forwarding brief
Platform label space
…
L2transport
     Interface        Owner                                            Action
-------------------- -------- -------------------------------------------------------------------
ATM6/0.101           ldp      l2transport to ATM6/2.101
                              l2transport to ATM6/2.103
ATM6/2.101           ldp      l2transport to ATM6/0.101
                              l2transport to ATM6/2.103
ATM6/2.103           ldp      l2transport to ATM6/0.101
                              l2transport to ATM6/2.101

Traffic that arrives on interface 6/0.101 is forwarded by means of ECMP to both interface 6/2.101 and interface 6/2.103. Traffic that arrives on interface 6/2.101 is forwarded by means of ECMP to interface 6/0.101 and interface 6/2.103. Traffic that arrives on interface 6/2.103 is forwarded by means of ECMP to interface 6/0.101 and 6/2.101.

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