Figure 12 shows a sample configuration that illustrates the next-hop verification feature. In this example, two Fast Ethernet interfaces are configured between a remote system and an E-series router: Fast Ethernet interface 4/0 and Fast Ethernet interface 4/1. At any given time, only one of these interfaces forwards IP traffic, even though the associated layer 2 interfaces may be up concurrently.
On the E-series router, Fast Ethernet interfaces 4/0 and 4/1 are configured as unnumbered IP interfaces. In addition, each interface has an RTR probe configured as an echo type that sends requests over the interface to determine its availability. RTR 10 sends requests over Fast Ethernet interface 4/0, and RTR 11 sends requests over Fast Ethernet interface 4/1.
In this example, both RTR 10 and RTR 11 use the IP address of the remote system (10.1.1.2) as the target address. When you configure multiple RTR entries to use the same target address, you must set the receive-interface attribute to specify the interface on which the probe expects to receive responses. (See Step 4c in the next section, Configuring RTR Next-Hop Verification.) This action enables the router to map incoming responses to the proper RTR entry, even when multiple RTR entries have the same target address.
Figure 12: Sample Configuration for Next-Hop Verification
The ip route command is issued for each interface with the verify rtr and last-resort keywords to establish the necessary static routes. (See Steps 6 and 7 in the next section, Configuring RTR Next-Hop Verification.) This command causes the results described in Table 7, based on the status of the associated RTR operations.
Table 7: Next-Hop Verification Results for Sample Configuration
The next section, Configuring RTR Next-Hop Verification, provides instructions for configuring the example shown in Figure 12.
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