In a next-hop static route, only the next-hop IPv6 address is specified. The output interface is derived from the next hop. For instance, in Figure 1, three next-hop static routes are configured on R1.
As with IPv4, before any packet is forwarded by the router, the routing table process must resolve the route to determine the exit interface to use to forward the packet. The route resolvability process will vary depending upon the type of forwarding mechanism being used by the router. CEF (Cisco Express Forwarding) is the default behavior on most platforms running IOS 12.0 or later.
Figure 2 details the basic packet forwarding route resolvability process in the routing table for R1 without the use of CEF. When a packet is destined for the 2001:DB8:ACAD:3::/64 network, R1:
1. Looks for a match in the routing table and finds that it has to forward the packets to the next-hop IPv6 address 2001:DB8:ACAD:4::2. Every route that references only a next-hop IPv6 address and does not reference an exit interface must have the next-hop IPv6 address resolved using another route in the routing table with an exit interface.
2. R1 must now determine how to reach 2001:DB8:ACAD:4::2; therefore, it searches a second time looking for a match. In this case, the IPv6 address matches the route for the directly connected network 2001:DB8:ACAD:4::/64 with the exit interface Serial 0/0/0. This lookup tells the routing table process that this packet is forwarded out of that interface.
Therefore, it actually takes two routing table lookup processes to forward any packet to the 2001:DB8:ACAD:3::/64 network. When the router has to perform multiple lookups in the routing table before forwarding a packet, it is performing a process known as a recursive lookup.
A recursive static IPv6 route is valid (that is, it is a candidate for insertion in the routing table) only when the specified next hop resolves, either directly or indirectly, to a valid exit interface.
Use the Syntax Checker in Figure 3 and Figure 4 to configure next-hop static IPv6 routes.