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Configuring the FAT Flow Label for FEC 128 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) 128 virtual private wire service (VPWS) pseudowires for load-balancing MPLS traffic.

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 128 VPWS pseudowires by including the flow-label-transmit and flow-label-receive configuration statements at the [edit protocols l2circuit neighbor neighbor-id 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.

Alternatively, you can configure the following statements at the [edit protocols l2circuit neighbor neighbor-id interface interface-name] hierarchy level:

  • flow-label-transmit-static to statically push the flow label on the pseudowire packets sent to the remote provider edge (PE) router.

  • flow-label-receive-static to statically pop the flow label on the pseudowire packets received from the remote PE router.

Before you begin:

  1. Configure the device interfaces and enable MPLS on all the interfaces.

  2. Configure MPLS and an LSP to the remote PE router.

  3. Configure OSPF and IS-IS.

  4. Configure LDP on the loopback interface and the PE interface connecting to the P (transit) router.

To configure the FAT flow label for an FEC 128-signaled VPLS pseudowire, on the ingress PE router:

  1. Configure the neighbors for the Layer 2 circuit.

    All the Layer 2 circuits using a particular remote PE router designated for remote CE routers are listed under the neighbor statement. Each neighbor is identified by its IP address and is usually the end-point destination for the label-switched path (LSP) tunnel transporting the Layer 2 circuit.

  2. Configure the interface for the Layer 2 circuit neighbor and a unique identifier for the Layer 2 circuit.
  3. Note

    You can only configure one of the following pairs of statements:

    • flow-label-transmit and flow-label-receive or,

    • flow-label-transmit-static and flow-label-receive-static

    Configure the router to signal the capability to push the flow label in the transmit direction to the remote PE router.
  4. Alternatively, configure the flow-label-transmit-static statement to statically push the flow label on the pseudowire packets sent to the remote PE router.

    If the incoming pseudowire packet is not marked with the flow label, the packet is dropped by the egress PE router.

  5. Configure the router to signal the capability to pop the flow label in the receive direction to the remote egress PE router.
  6. Alternatively, configure the flow-label-receive-static statement to pop the flow label on the pseudowire packets received from the remote PE router.

    The ingress PE router inserts the flow label in the pseudowire packet, irrespective of the information exchanged in the signaling plane. If the egress PE router cannot handle the pseudowire packet marked with the flow label, the packet is dropped.

  7. Verify and commit the configuration.

    For example:

    OR:

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