IPv6 uRPF operation

IPv6 uRPF does not check multicast packets.

Figure 214 shows how IPv6 uRPF works.

1. IPv6 uRPF checks whether the received packet carries a multicast destination address:

   • If yes, IPv6 uRPF permits the packet.

   • If no, IPv6 uRPF proceeds to step 2.

2. IPv6 uRPF checks whether the source address matches a unicast route:

   • If yes, IPv6 uRPF proceeds to step 3.

   • If no, IPv6 uRPF proceeds to step 6. A non-unicast source address matches a non-unicast route.

3. IPv6 uRPF checks whether the matching route is to the host itself:

   • If yes, the output interface of the matching route is an InLoop interface. IPv6 uRPF checks whether the receiving interface of the packet is an InLoop interface. If yes, IPv6 uRPF permits the packet. If no, IPv6 uRPF proceeds to step 6. If the source address is a link-local address and is the receiving interface address, also proceeds to step 6.

   • If no, IPv6 uRPF proceeds to step 4.

4. IPv6 uRPF checks whether the receiving interface matches the output interface of the matching FIB entry:

   • If yes, IPv6 uRPF proceeds to step 5.

   • If no, IPv6 uRPF checks whether the check mode is loose. If yes, it proceeds to step 5. If no, it proceeds to step 6.

5. IPv6 uRPF checks whether the matching route is a default route:

   • If yes, IPv6 uRPF checks whether the allow-default-route keyword is configured to allow using the default route. If yes, the packet is forwarded. If no, IPv6 uRPF proceeds to step 6.

   • If no, the packet is forwarded.

6. IPv6 uRPF checks whether the packet is permitted by the IPv6 ACL:

   • If yes, the packet is forwarded (such a packet is displayed in the uRPF information as a "suppressed drop").

   • If no, the packet is discarded.