Technical Documentation

Configuring the Layer 2 Circuit Neighbor Address and Virtual Circuit Identifier

After you enable the PE router interfaces with the proper encapsulations, you then configure Layer 2 circuits (also referred to as VCs) between two or more PE router neighbors. To configure a Layer 2 circuit, include the l2circuit statement at the [edit protocols] hierarchy level.

Each Layer 2 circuit is represented by a logical interface on the local PE router, the IP address of the remote PE router neighbor, and a virtual circuit identifier. The logical interface connects the local PE router to the local CE router. The loopback address and router ID of the PE neighbor is commonly the neighbor’s IP address. This address is also the destination end-point of the LSP tunnel, which transports the Layer 2 circuit to the neighbor. The virtual circuit ID uniquely identifies the VC to a specific neighbor.

This combination of logical interface, neighbor address, and virtual circuit ID is used to map a particular LDP forwarding equivalence class (FEC) received from a specific neighbor to a local VC. The egress label is added to a table and is used for sending traffic on that VC between the CE routers.

Both ends of a Layer 2 circuit must use the same Layer 2 technology because the Layer 2 encapsulation type is carried in the LDP FEC. The encapsulation type from a received FEC is matched against the local encapsulation type of the VC. If there is a mismatch, the VC is not established.

To add the IP address of the remote PE router neighbor into a Layer 2 circuit, include the neighbor ip-address statement at the [edit protocols l2circuit] hierarchy level. To map the remote neighbor to the local interface that connects to the CE router, include the interface statement at the [edit protocols l2circuit neighbor ip-address] hierarchy level. To select the identifier for the virtual circuit, include the virtual-circuit-identifier statement at the [edit protocols l2circuit neighbor ip-address interface interface-name] hierarchy level. To disable default control word processing, include the no-control-word statement at the [edit protocols l2circuit neighbor ip-address interface interface-name] hierarchy level. Finally, to assign the Layer 2 circuit to a community, include the community community-namestatement at the [edit protocols l2circuit neighbor ip-address interface interface-name] hierarchy level.

Note: On M Series routers only, if you include the control-word statement at the [edit protocols l2circuit neighbor address interface interface-name] hierarchy level (the default setting for Layer 2 circuits), the software cannot rewrite MPLS EXP bits.

[edit]protocols {l2circuit {traceoptions {file name [replace] [size size] [files files ] [nostamp];flag (error | topology | nlri | connections | route) [detail];}neighbor ip-address {interface interface-name {virtual-circuit-id identifier;no-control-word;community community-name;}}}}

You do not need to specify the encapsulation type at the [edit protocols l2circuit] hierarchy level because it is already specified in the interface configuration.


Published: 2010-04-15