, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 112/112/112 ms Notice the ping time compared with the previous example, where the remote side was pinged. Pinging yourself will take twice as long as pinging the remote side. Local IP addresses mapped to remote DLCIs will not be locally avail- able should the remote router fail, or the PVC become unavailable. In this example, should Router B fail, Router A will no longer be able to ping its own SO/O IP address, though Router A will still be able to communicate with Router C. Configuring Frame Relay As a matter of best practice, I like to always map my DLCIs to IP addresses, even if the router can do it reliably on its own. Placing the DLCI information in the configu- ration makes the config easier to read and troubleshoot. Frame-Relay Subinterfaces Sometimes, having two PVCs terminating on a single interface is not what you want, but, as we've seen, having a physical interface for each PVC is not beneficial for cost reasons. For example, with the network in Figure 22-11, each PVC terminates into a single interface. If you ran a routing protocol on these routers, Router B would adver- tise itself, but Router A would not advertise this route out to Router C because of the split-horizon rule. Splitting the PVCs into separate interfaces would allow the routing protocol to advertise the route, because the split-horizon rule would no longer apply. Cisco routers have a feature called subinterfaces that solves this problem. In a nutshell, you're able to configure virtual interfaces for each PVC. These virtual inter- faces are named after the physical interfaces on which they are found. For example, a subinterface derived from SO/O might be called SO/0.100. The subinterface number is user-definable, and can be within the range of 1 to 4,294,967,293. I like to name subinterfaces according to the DLCIs mapped to them. There are two types of subinterfaces: point-to-point and multipoint. Point-to-point