This feature enables class-based forwarding (CBF) over IGP shortcuts. When the class-forwarding command is enabled, the following types of packets are forwarded based on their forwarding class:
packets of BGP prefixes
packets that are CPM-originated for the IPv4, IPv6, or both IPv4 and IPv6 families that have been enabled over IGP shortcuts using the igp-shortcut CLI context in one or more IGP instances
The SR OS CBF implementation supports spraying of packets over a maximum of six forwarding sets of ECMP LSPs. The user must define a class-forwarding policy object in MPLS to configure the mapping of FCs to the forwarding sets. Then, the user assigns the CBF policy name and set ID to each MPLS LSP that is used in IGP shortcuts.
When a BGP IPv4 or IPv6 prefix is resolved, the FC of the packet, is used to look up the forwarding set ID. Then, a modulo operation is performed on the tunnel next-hops of this set ID only, to spray packets of this FC. The data path concurrently implements, CBF and ECMP within the tunnels of each set ID.
CPM-originated packets on the router, including control plane and OAM packets, are forwarded over a single LSP from the set of LSPs that the packet's FC is mapped to, as per the CBF configuration.