0 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. Chapter 23: Frame Relay Local IP addresses mapped to remote DLCIs will not be locally available if the remote router fails or the PVC becomes unavailable. In this ex- ample, 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. 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 configuration 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 you've seen, having a physical interface for each PVC is not beneficial for cost reasons. For example, with the network in Figure 23-11, each PVC terminates into a single interface. If you ran a routing protocol on these routers, Router B would advertise 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 pro- tocol 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, subinterfaces allow you to configure virtual interfaces for each PVC. These virtual in- terfaces 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 subinterfaces can have only one DLCI active on them, while multipoint sub