If you have a point-to-point link but the encapsulations aren’t the same, the link will never
come up. Figure 1 shows one link with PPP and one with HDLC.
FIGURE 1 Mismatched WAN encapsulations
Look at router Pod1R1 in this output:
Pod1R1#sh int s0/0
Serial0/0 is up, line protocol is down
Hardware is PowerQUICC Serial
Internet address is 10.0.1.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 254/255, txload 1/255, rxload 1/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
LCP REQsent
Closed: IPCP, CDPCP
The serial interface is down and LCP is sending requests but will never receive any responses because router Pod1R2 is using the HDLC encapsulation. To fix this problem, you would have to go to router Pod1R2 and configure the PPP encapsulation on the serial interface. One more thing even though the usernames are configured and they’re wrong, it doesn’t matter because the command ppp authentication chap isn’t used under the serial interface configuration and the username command isn’t relevant in this example.
come up. Figure 1 shows one link with PPP and one with HDLC.
FIGURE 1 Mismatched WAN encapsulations
Pod1R1#sh int s0/0
Serial0/0 is up, line protocol is down
Hardware is PowerQUICC Serial
Internet address is 10.0.1.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 254/255, txload 1/255, rxload 1/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
LCP REQsent
Closed: IPCP, CDPCP
The serial interface is down and LCP is sending requests but will never receive any responses because router Pod1R2 is using the HDLC encapsulation. To fix this problem, you would have to go to router Pod1R2 and configure the PPP encapsulation on the serial interface. One more thing even though the usernames are configured and they’re wrong, it doesn’t matter because the command ppp authentication chap isn’t used under the serial interface configuration and the username command isn’t relevant in this example.
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