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Configuring the FAT Flow Label for FEC 129 VPWS Pseudowires for Load-Balancing MPLS Traffic

This topic shows how to configure flow-aware transport of pseudowires (FAT) flow labels for forwarding equivalence class (FEC) 129 virtual private wire service (VPWS) pseudowires.

Before you begin:

  1. Configure the device interfaces and enable MPLS on all core-facing interfaces.

  2. Configure CCC encapsulation and the CCC address family for interfaces configured as members of the FEC 129 VPWS instance.

  3. Configure MPLS and an LSP to the remote provider edge (PE) router.

  4. Configure the BGP sessions on the PE devices with the BGP autodiscovery-only address family to allow exchange of the autodiscovery routes.

  5. Configure an IGP such as IS-IS or OSPF.

  6. Configure LDP on the loopback interface and the core-facing interface.

  7. Configure the autonomous system (AS) number.

FAT flow labels enable load-balancing of MPLS packets across equal-cost multipath (ECMP) paths or link aggregation groups (LAGs) without the need for deep packet inspection of the payload. FAT flow labels can be used for LDP-signaled FEC 128 and FEC 129 pseudowires for virtual private LAN service (VPLS) and VPWS networks.

You can configure FAT flow labels to be signaled by LDP on FEC 129 VPWS pseudowires (Layer 2 circuits) by including the flow-label-transmit and flow-label-receive configuration statements at the [edit routing-instances instance-name protocols l2vpn site name] or the [edit routing-instances instance-name protocols l2vpn site name interface interface-name] hierarchy level. This configuration sets the T bit and R bit advertisement to 1 (the default being 0) in the Sub-TLV field, which is one of the interface parameters of the FEC for the LDP label-mapping message header. These statements signal the pushing and popping of the load-balancing label to the routing peers in the control plane.

To configure the FAT flow label for an FEC 129 VPWS pseudowire, on the ingress PE router:

  1. Configure the VPWS routing instance.

    LDP listens for routes from instance.l2vpn.0 for any instance configured for FEC 129 VPWS. These routes are identified by the instance-type l2vpn statement in the routing instance and the presence of the l2vpn-id statement.

    Because VPWS is a point-to-point service, FEC 129 VPWS routing instances are configured as instance-type l2vpn. As with FEC 129 VPLS, FEC 129 VPWS uses the l2vpn-id statement to define the Layer 2 VPN of which the routing instance is a member. The presence of the l2vpn-id statement designates that FEC 129 LDP-signaling is used for the routing instance.

  2. Configure the device to signal the capability to push the flow label in the transmit direction to the remote PE router.
  3. Configure the device to signal the capability to pop the flow label in the receive direction to the remote PE router.
  4. Alternatively, configure the flow-label-transmit and flow-label-receive statements directly within the site. When configured within the site, the defined parameters affect any pseudowire originating from that site. When configured under an interface within the site, the defined parameters affect that single specific pseudowire. This enables you to manipulate the parameters across all pseudowires associated with a particular local site in one place in the configuration.
  5. Verify and commit the configuration.

    For example:

  6. Repeat the configuration on the remote egress PE router.

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