Cisco Cisco IOS Software Release 12.0(13)S7

To enable Unicast RPF for IPv6 in strict checking mode on a Cisco 12000 series Internet router, use the 
ipv6 verify unicast source reachable-via rx command in interface configuration mode. To disable 
Unicast RPF, use the no form of this command.

This command has no arguments or keywords.

Unicast RPF is disabled.

Interface configuration

Use the ipv6 verify unicast source reachable-via rx command to enable the Unicast RPF for 
IPv6 feature in strict checking mode.

Starting in Cisco IOS Release 12.0(31)S, the Cisco 12000 series Internet router supports both the ipv6 
verify unicast reverse-path and ipv6 verify unicast source reachable-via rx commands to enable 
Unicast RPF to be compatible with Cisco IOS Release 12.3T and 12.2S software.

The Unicast RPF feature verifies that the source IPv6 address exists in the routing table and that the 
source IPv6 address is reachable by a path through the input interface.

When Unicast RPF is enabled on an interface, the router examines all packets received on that 
interface. The router checks to make sure that the source address appears in the routing table and 
matches the interface on which the packet was received. Unicast RPF is an input feature and is 
applied only on the input interface of a router at the upstream end of a connection.

The Unicast Reverse Path Forwarding feature performs a reverse lookup in the CEF table to see if 
any packet received at a router interface has arrived on a path identified as a best return paths to the 
source of the packet. The feature does this by performing a reverse lookup in the CEF table.

If Unicast RPF does not find a reverse path for the packet, Unicast RPF drops the packet.

12.0(31)S

This command was introduced on the 10G Engine 5 SPA Interface 
Processor in the Cisco 12000 series Internet router.