To enable the next-hop resolution of unlabeled IPv4 routes using tunnels in the tunnel table of the router, it is necessary to add family ipv4 under the config>router>bgp>next-hop-resolution>shortcut-tunnel context. The family ipv4 context, provides commands to specify the resolution mode (any, disabled or filter) and set of tunnel types that are eligible for use when filter mode (resolution filter) is selected.
If the resolution mode is set to disabled, the next hops of unlabeled IPv4 routes can only be resolved by route table lookup.
If there are multiple tunnels in the tunnel table that are allowed by resolution any or resolution filter mode and that can resolve the BGP next-hop, the selection of the resolving tunnel is determined by factors such as route color, admin-tag-policy, tunnel-table preference, and LDP FEC prefix length.
If disallow-igp is enabled and no resolving tunnel is found in the tunnel table, no attempt is made to resolve the IPv4 BGP route using route table lookup.
The available tunneling options for IPv4 shortcuts are as follows:
bgp
This refers to IPv4 and IPv6 tunnels created by receiving BGP label-unicast IPv4 routes for /32 IPv4 prefixes and BGP label-unicast IPv6 routes for /128 IPv6 prefixes. The installation of BGP-LU IPv6 tunnels in TTM requires executing the disable-explicit-null command or configuring explicit-null false in MD-CLI.
ldp
This refers to LDP FEC prefixes imported into the tunnel table. For resolution purposes, BGP selects the LDP FEC that is the longest-prefix-match (LPM) of the BGP next-hop address.
rsvp
This refers to RSVP tunnels in tunnel-table. This option allows BGP to use the best metric RSVP LSP to the address of the BGP next-hop. This address can correspond to the system interface or to another loopback interface of the remote BGP router. In the case of multiple RSVP LSPs with the same lowest metric, BGP selects the LSP with the lowest tunnel-id.
sr-isis
This refers to segment routing tunnels (shortest path) to destinations reachable by the IS-IS protocol. This option allows BGP to use the segment routing tunnel in tunnel-table submitted by the lowest preference IS-IS instance or, in case of a tie, the lowest numbered IS-IS instance.
sr-ospf
This refers to segment routing tunnels (shortest path) to destinations reachable by the OSPF protocol. This option allows BGP to use the segment routing tunnel in the tunnel table submitted by the lowest preference OSPF instance or (in case of a tie) the lowest numbered OSPF instance.
sr-policy
This refers to segment routing policies that are statically configured in the local router or learned via BGP routes (AFI 1/SAFI 73). For BGP to resolve the next-hop of an IPv4 route using an sr-policy the highest numbered color-extended community attached to the IPv4 route must match the color of the SR policy and if the CO bits of this color-extended community have the value 00 the BGP next-hop of the route must exactly match the endpoint of the SR policy.
sr-te
This refers to traffic engineered (TE) segment routing tunnels. This option allows BGP to use the best metric SR-TE tunnel to the address of the BGP next-hop. In the case of multiple SR-TE tunnels with the same lowest metric, BGP selects the tunnel with the lowest tunnel-id.