Each NHG is modeled as a single NHLFE. The following are the specifics of the data path operation:
Forwarding over the primary or backup next hop is modeled as a swap operation from the binding label to an implicit-null label over multiple outgoing interfaces (multiple NHLFEs) corresponding to the resolved next hops of the indirect route.
Packets of flows are sprayed over the resolved next hops of an NHG with resolution of type indirect as a one-level ECMP spraying. See Spraying of packets in a MPLS forwarding policy.
An NHG of resolution type indirect uses a single NHLFE and does not support uniform failover. It has CPM program only the active, the primary or backup, and the indirect next hop at any point in time.
Within an NHG, the primary next hop is the preferred active path in the absence of any failure of the NHG of resolution type indirect.
The forwarding database tracks the primary or backup next hop in the routing table. A route delete of the primary indirect next hop causes CPM to program the backup indirect next hop in the data path.
A route modify of the indirect primary or backup next hop causes CPM to update its resolved next hops and to update the data path if it is the active indirect next hop.
When the primary indirect next hop is restored and is added back into the routing table, CPM waits for an amount of time equal to the user programmed revert-timer before updating the data path. However, if the backup indirect next hop fails while the timer is running, CPM updates the data path immediately.