Configure a Directly Connected Static IPv6 Route
When configuring a static route on point-to-point networks, an alternative to using the next-hop IPv6 address is to specify the exit interface. This is an alternative used in older IOSs or whenever CEF is disabled, to avoid the recursive lookup problem.
For instance, in Figure 1, three directly connected static routes are configured on R1 using the exit interface.
The IPv6 routing table for R1 in Figure 2 shows that when a packet is destined for the 2001:DB8:ACAD:3::/64 network, R1 looks for a match in the routing table and finds that it can forward the packet out of its Serial 0/0/0 interface. No other lookups are required.
Notice how the routing table looks different for the route configured with an exit interface than the route configured with a recursive entry.
Configuring a directly connected static route with an exit interface allows the routing table to resolve the exit interface in a single search instead of two searches. Recall that with the use of the CEF forwarding mechanism, static routes with an exit interface are considered unnecessary. A single lookup is performed using a combination of the FIB and adjacency table stored in the data plane.
Use the Syntax Checker in Figure 3 and Figure 4 to configure directly connected static IPv6 routes.
Configure a Fully Specified Static IPv6 Route
In a fully specified static route, both the output interface and the next-hop IPv6 address are specified. Similar to fully specified static routes used with IPv4, this would be used if CEF were not enabled on the router and the exit interface was on a multi-access network. With CEF, a static route using only a next-hop IPv6 address would be the preferred method even when the exit interface is a multi-access network.
Unlike IPv4, there is a situation in IPv6 when a fully specified static route must be used. If the IPv6 static route uses an IPv6 link-local address as the next-hop address, a fully specified static route including the exit interface must be used. Figure 1 shows an example of a fully qualified IPv6 static route using an IPv6 link-local address as the next-hop address.
The reason a fully specified static route must be used is because IPv6 link-local addresses are not contained in the IPv6 routing table. Link-local addresses are only unique on a given link or network. The next-hop link-local address may be a valid address on multiple networks connected to the router. Therefore, it is necessary that the exit interface be included.
In Figure 1, a fully specified static route is configured using R2’s link-local address as the next-hop address. Notice that IOS requires that an exit interface be specified.
Figure 2 shows the IPv6 routing table entry for this route. Notice that both the next-hop link-local address and the exit interface are included.
Use the Syntax Checker in Figure 3 to configure fully specified static IPv6 routes on R2 to reach R1’s LAN using a link-local address.