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Creating and Deploying a Multisegment Pseudowire


A pseudowire is a Layer 2 circuit or service that emulates the essential attributes of a telecommunications service, such as a T1 line, over an MPLS packet-switched network (PSN). The pseudowire is intended to provide only the minimum necessary functionality to emulate the wire with the required resiliency requirements for the given service definition.

When a pseudowire originates and terminates on the edge of the same PSN, the pseudowire label is unchanged between the originating and terminating provider edge (T-PE) devices. This is called a single-segment pseudowire (SS-PW). Figure 1 illustrates an SS-PW established between two PE routers. The pseudowires between the PE1 and PE2 routers are located within the same autonomous system (AS).

Figure 1: L2VPN Pseudowire
L2VPN Pseudowire

In cases where it is impossible to establish a single pseudowire from a local to a remote PE, either because it is unfeasible or undesirable to establish a single control plane between the two PEs, a multisegment pseudowire (MS-PW) is used.

An MS-PW is a set of two or more contiguous SS-PWs that are made to function as a single point-to-point pseudowire. It is also known as switched pseudowire. MS-PWs can go across different regions or network domains. A region can be considered as an interior gateway protocol (IGP) area or a Border Gateway Protocol (BGP) autonomous system that belongs to the same or different administrative domain. An MS-PW spans multiple cores or ASs of the same or different carrier networks. A Layer 2 VPN MS-PW can include up to 254 pseudowire segments.

Figure 2 illustrates a set of two or more pseudowire segments that function as a single pseudowire. The end routers are called terminating PE (T-PE) routers, and the switching routers are called stitching PE (S-PE) routers. The S-PE router terminates the tunnels of the preceding and succeeding pseudowire segments in an MS-PW. The S-PE router can switch the control and data planes of the preceding and succeeding pseudowire segments of the MS-PW. An MS-PW is declared to be up when all the single-segment pseudowires are up.

Figure 2: Multisegment Pseudowire
Multisegment Pseudowire

Typically, there can be three types of MS-PW setups:

  • Static configuration of pseudowire

  • LDP using Forwarding Equivalence Class (FEC) 128—The FEC 128 MS-PW behaves the same as a basic Label Distribution Protocol (LDP) pseudowire. In an FEC 128 MS-PW, the intermediate segments terminate on a logical interface and stitching of two segments is done by peering the logical interfaces. In this setup, you have to select each transit router to configure segments. Stitching is done at transit routers for traffic to move from one segment to another segment. You can use a logical tunnel (lt) or interworking (iw) interface on the intermediate segments.

  • Generalized FEC 129—The FEC 129 MS-PW uses LDP as the signaling protocol and BGP as a discovery protocol ( you need to enable MS-PW auto-discovery on BGP). For the FEC 129 MS-PW, you don’t need to identify each transit router between the source and destination devices. You just have to select the source and destination devices and BGP dynamically finds all the segments between them. For the dynamic MS-PW with FEC 129, there is a requirement for the identifiers of attachment circuits to be globally unique, for the purposes of reachability and manageability of the pseudowire. Thus, individual globally unique addresses are allocated to all the attachment circuits and S-PEs that make up the MS-PW. The attachment circuit used for MS-PW based on FEC 129 consists of following fields.

    In the case of a dynamically placed MS-PW,

    • Global ID – Global identification, which is usually the AS number.

    • Prefix – IPv4 address, which is usually the router ID (Connectivity Services Director uses the Loopback Address).

    • AC_ID – Local attachment circuit, which is a user-configurable value (Connectivity Services Director uses the last part of Route Target, which is an integer and is unique for a given AS number).


Junos OS does not support:

  • Switching between static pseudowire segments

  • Switching between FEC 128 and FEC 129 segments

  • Multi-homing support for FEC 129

  • Instance type evpn-vpws under BGP signalling protocol

Therefore, we will only discuss MS-PW for FEC 128 and FEC 129 in the following documentation.

Pre-configuration before creating FEC 129 Multisegment Pseudowire Service

There are no prerequisites for creating an FEC 128 MS-PW. For FEC 129 MS-PW, you need to add the following configuration to the devices that act as the endpoints of the MS-PW:

where, ibgp is the BGP group name.

Procedure to Create and Deploy and FEC 128 and FEC 129 Multisegment Pseudowire Service

The following procedure describes how to create MS-PW. The difference in settigns for FEC-128 and FEC-129 are highlighted:

To create and deploy an FEC 128 or FEC 129 MS-PW service and deploy it:

  1. Create an E-Line service definition—see Creating a Multisegment Pseudowire Service Definition.
  2. In the Build mode of the Network Services > Connectivity task pane, select Service Design > Manage Service Definitions. Select the service definition you created in Step 1 and click Publish.

    The service definition is published and the State of the service definition changes to Published in the Manage Service Definitions page.

  3. Create an E-Line service order—Creating an E-Line Multisegment Pseudowire Service Order.
  4. Deploy the E-Line service order.
    1. Click the Deploy icon in the Service View of the Connectivity Services Director banner. The functionalities that you can configure in this mode are displayed in the task pane. From the Manage Network Services > Connectivity task pane, select Service Provisioning > Deploy Services.

      The Manage Network Services page appears in the top part of the right pane, which displays all of the configured services. The Manage Service Orders page appears in the bottom part of the right pane, which displays all of the service orders associated with a service.

    2. In the Manage Service Orders page, select the E-Line service order you created in Step 2.

    3. Select the Deploy now option button at the top of the page and click OK.

    The service order is deployed. The Deployment State of the service order changes from Pending to Active in the Manage Network Services > Connectivity page.

    To see the progress of the service order deployment, click the Deploy icon in the Service View of the Connectivity Services Director banner. From the Tasks pane, select View Deployment Jobs. The CSD Deployment Jobs page appears displaying the deployment jobs.

Modifying a multisegment pseudowire— When a service order is based on a service definition that you created in the Service Design workflow in step 1, you can edit only those parameters of a service that were marked as Editable in Service Order in the service definition. The other attributes can be updated only in the service definition or service template.