Troubleshooting Serial Links

This final major section discusses how to isolate and find the root cause of problems related to topics covered earlier in this chapter. Also, this section does not attempt to repeat the IP troubleshooting coverage in Parts II and III of this book, but it does point out some of the possible symptoms on a serial link when a Layer 3 subnet mismatch occurs on opposite ends of a serial link, which prevents the routers from routing packets over the serial link.

A simple ping command can determine whether a serial link can or cannot forward IP packets. A ping of the other router’s serial IP address—for example, a working ping 192.168.2.2 command on R1 in Figure 12-11, the figure used for both the HDLC and PPP configuration ...

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