When ECMP is enabled, some routes may have multiple equal-cost next-hops in the forwarding table. When an IP packet matches such a route, the next-hop selection is typically based on a hash algorithm that tries to load balance traffic across all the next-hops while keeping all packets of a flow on the same path. The QPPB configuration model described in Associating an FC and priority with a route allows different QoS information to be associated with the different ECMP next-hops of a route. The forwarding-class and priority of a packet matching an ECMP route is based on the next-hop used to forward the packet.
When Edge PIC [1] is enabled, some BGP routes may have a backup next-hop in the forwarding table, as well as the one or more primary next-hops representing the equal-cost best paths allowed by the ECMP/multipath configuration. When an IP packet matches such a route, a reachable primary next-hop is selected (based on the hash result) but if all the primary next-hops are unreachable, the backup next-hop is used. The QPPB configuration model described in Associating an FC and priority with a route allows the forwarding-class and priority associated with the backup path to be different from the QoS characteristics of the equal-cost best paths. The forwarding class and priority of a packet forwarded on the backup path is based on the fc and priority of the backup route.