MS-PW routing — pseudowire routing

The following sections describe the end-to-end solution with BGP PW-routing, assuming appropriate platforms are used for various functions.

Each S-PE and T-PE has a pseudowire routing table that contains a reference to the T-LDP session to use to signal to a set of next-hop S-PEs to reach a specific T-PE (or the T-PE if that is the next hop). For VLLs, this table contains aggregated AII Type 2 FECs and may be populated with routes that are learned through MP-BGP or that are statically configured.

MP-BGP is used to automatically distribute T-PE prefixes using the new MS-PW NLRI, or static routes can be used. The MS-PW NLRI is composed of a length, an 8-byte RD, a 4-byte global ID, a 4-byte local prefix, and (optionally) a 4-byte AC ID. Support for the MS-PW address family is configured in CLI under config>router>bgp>family ms-pw.

MS-PW routing parameters are configured in the config>service>pw-routing context.

To enable support for dynamic MS-PWs on a 7210 SAS node to be used as a T-PE or S-PE, a single, globally unique, S-PE ID, known as the S-PE address, is first configured under config>service>pw-routing on each 7210 SAS to be used as a T-PE or S-PE. The S-PE address has the format global-id:prefix. It is not possible to configure any local prefixes used for pseudowire routing or to configure spoke-SDPs using dynamic MS-PWs at a T-PE unless an S-PE address has already been configured. The S-PE address is used as the address of a node used to populate the switching point TLV in the LDP label mapping message and the pseudowire status notification sent for faults at an S-PE.

Each T-PE is also be configured with the following parameters:

1. Global ID

   This is a 4-byte identifier that uniquely identifies an operator or the local network.

2. Local prefix

   One or more local (Layer 2) prefixes (up to a maximum of 16), which are formatted in the style of a 4-octet IPv4 address. A local prefix identifies a T-PE or S-PE in the PW routing domain.

3. For each local prefix, at least one 8-byte route distinguisher (RD) can be configured. It is also possible to configure an optional BGP community attribute.

For each local prefix, BGP then advertises each global-id:prefix and unique RD and community pseudowire using the MS-PW NLRI, based on the aggregated FEC129 AII Type 2 and the Layer 2 VPN/PW routing AFI/SAFI 25/6, to each T-PE/S-PE that is a T-LDP neighbor, subject to local BGP policies.

The dynamic advertisement of each of these pseudowire routes is enabled for each prefix and RD, using the advertise-bgp command.

An export policy is also required to export MS-PW routes in MP-BGP. This can be done using a default policy, such as the following:

*A:lin-123>config>router>policy-options# info
----------------------------------------------
            policy-statement "ms-pw"
                default-action accept
                exit
            exit
----------------------------------------------

However, the preceding would export all routes. Nokia recommends enabling filtering per-family, as follows:

*A:lin-123>config>router>policy-options# info
----------------------------------------------
            policy-statement "to-mspw"
                entry 1
                    from
                        family ms-pw
                    exit
                    action accept
                    exit
                exit
            exit
----------------------------------------------

The following command is then added in the config>router>bgp context:

export "to-mspw"

The local-preference parameter for iBGP and BGP communities can be configured under such a policy.