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Configuring Remote LFA Backup over LDP Tunnels in an IS-IS Network

The primary goal of a remote loop-free alternate (LFA) is to increase backup coverage for IS-IS routes and provide protection especially for Layer 1 metro-rings. The existing LDP implemented for the MPLS tunnel setup can be reused for protection of IS-IS networks and subsequent LDP destinations. The IS-IS protocol creates a dynamic LDP tunnel to reach the remote LFA node from the point of local repair (PLR). The PLR uses this remote LFA backup path when the primary link fails.

Before you configure remote LFA over LDP tunnels in an IS-IS network, you must do the following:

  1. Enable LDP on the loopback interface.

    Configure a loopback interface because an LDP targeted adjacency cannot be formed without a loopback interface. LDP targeted adjacency is essential for determining remote LFA backup paths.

  2. Make sure that remote LFA allows asymmetric remote neighbor discovery—that is, it must send periodic targeted hello messages to the router that initiated the remote neighbor for LDP auto-targeted adjacency.

  3. Configure link protection or node-link protection on the PLR.

To configure remote LFA backup over LDP tunnels in an IS-IS network:

  1. Enable remote LFA backup to determine the backup next hop using dynamic LDP label-switched path.
  2. (Optional) Include the node-link-degradation statement even if node-link protection is not configured for a given interface.

    The device uses the configured link protection LFA as the backup for the primary link.

  3. Enable automatically targeted LDP sessions using the loopback addresses between the PLR and the remote LFA node.
  4. Specify a time interval for which the targeted LDP sessions are kept up even after the remote LFA node goes down.

    For example, to set a teardown delay value of 60 seconds:

  5. Specify the maximum number of automatically targeted LDP sessions to optimize memory usage.

    For example, to set a maximum sessions allowed to 20:

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