IGP Shortcut Binding Construct

The SR OS tunnel-next-hop construct binds IP prefixes to IPv4 IGP shortcuts on a per-prefix family basis.

The following details the behavior of the construct.

• The construct supports the IPv4 and IPv6 families. It allows each family to resolve independently to either an IGP shortcut next hop using the unicast RTM or to the IP next hop using the multicast RTM.

• The advertise-tunnel-link (forwarding adjacency) takes priority over igp-shortcut if both CLI options are enabled. This is overall and not per family.

• The following commands are enabled based on the following relative priorities (from highest to lowest):

  • advertise-tunnel-link (IPv4 family with OSPFv2, IPv4, and IPv6 families with IS-IS MT=0 and IPv6 family in MT=2, no support in OSPFv3)

  • igp-shortcut (IPv4 family in OSPFv2, IPv6 family in OSPFv3, IPv4 and IPv6 families in IS-IS MT=0 and IPv6 family in MT=2)

  • ldp-over-rsvp (IPv4 FECs only)

  More details can be found in Table 1.

• No default behavior exists for IPv4 prefixes to automatically resolve to RSVP LSPs used as IGP shortcut by enabling the igp-shortcut context only. The IPv4 family must be enabled and the resolution-filter set to the value of rsvp which selects the RSVP-TE tunnel type.

• A [no] shutdown command under the igp-shortcut context enforces that the IGP shortcut context cannot be enabled unless at least one family is configured under the tunnel-next-hop node to a value other than resolution disabled, which is the default value for all families and that a tunnel type is selected if the resolution is set to filter.

• To disable IGP shortcuts globally, shutdown the igp-shortcut context.

• When computing the backup next hop of an IPv4 or IPv6 prefix, LFA considers the IP links and tunnels of the selected tunnel type which are the result of the configuration of the tunnel-next-hop for the IPv4 or IPv6 prefix family.

The resolution outcome for each of the IPv4 and IPv6 prefix families is summarized in Table 1. The description and behavior of the SRv4 and SRv6 families are described in SR Shortest Path Tunnel Over RSVP-TE IGP Shortcut Feature Configuration. The description and behavior of the sr-te resolution option using SR-TE IGP shortcuts are described in IPv4 IGP Shortcuts using SR-TE LSP Feature Configuration.