Configuring Dynamic List Next Hop

 

The routing table on a remote PE has a next hop entry for Ethernet segment identifier (ESI) routes with multiple next-hop elements for multihomed PE devices. For EVPN active-active multihoming device, the ESI route points to two next hop elements. Prior to dynamic list next hop, the routing protocol process (rpd) removed the next-hop entry for the ESI route when the link between the CE device and a multihome PE device goes down. The rpd would then create a new next hop entry for the ESI causing mass MAC route withdrawals and additions.

Starting in Junos OS Release 17.4R1, Junos OS supports the dynamic list next-hop feature in an EVPN network. Now when the link between the CE device and a multihomed PE device goes down, rather than removing the entire next hop and creating a new next hop for the ESI , the rpd removes the affected next hop element from the dynamic list next-hop entry for the ESI route. Dynamic list next hop provides the benefit of reducing mass MAC route withdrawals, improving the device performance, and reducing network convergence time.

To enable the dynamic list next-hop feature, include the dynamic-list-next-hop statement in the [edit routing-options forwarding-table] hierarchy.

Note

If you are performing an unified in-service software upgrade (ISSU) to upgrade your device from a Junos OS release prior to Junos OS Release 17.4R1, you must upgrade both the master Routing Engine and the backup Routing Engine before enabling the dynamic list next-hop feature.

To disable the dynamic list next-hop feature when it is enabled, use the delete routing-options forwarding-table dynamic-list-next-hop statement.

To display the next-hop elements from the Routing Engine’s forwarding table, use the show route label and show route forwarding-table commands.

The following sample output from the show route label detail command shows two indirect next hops for an ESI with the dynamic list next-hop feature enabled.

user@host> show route label 299952 detail

The following sample output from the show route forwarding table command shows two next-hop entries for a destination with a multihomed route.

user@host> show route forwarding-table label 299952 extensive

The following sample shows the show route forwarding table command output after one of the PE devices has been disabled. It shows one next-hop element and one empty next-hop element.

user@host> show route forwarding-table label 299952 extensive