IPv6 uRPF check modes

IPv6 uRPF supports strict and loose check modes.

• Strict IPv6 uRPF check—To pass strict IPv6 uRPF check, the source address of a packet and the receiving interface must match the destination address and output interface of an IPv6 FIB entry. In some scenarios (for example, asymmetrical routing), strict IPv6 uRPF might discard valid packets. Strict IPv6 uRPF is often deployed between a PE and a CE.

• Loose IPv6 uRPF check—To pass loose IPv6 uRPF check, the source address of a packet must match the destination address of an IPv6 FIB entry. Loose IPv6 uRPF can avoid discarding valid packets, but might let go attack packets. Loose IPv6 uRPF is often deployed between ISPs, especially in asymmetrical routing.