Verifying PPP Encapsulation

Okay—now that PPP encapsulation is enabled, let me show you how to verify that it’s up and running. First, let’s take a look at a figure of a sample network. Figure 1 shows two routers connected with either a point-to-point serial or ISDN connection.

FIGURE 1 PPP authentication example

You can start verifying the configuration with the show interface command:

Pod1R1#sh int s0/0
Serial0/0 is up, line protocol is up
Hardware is PowerQUICC Serial
Internet address is 10.0.1.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 239/255, txload 1/255, rxload 1/255
Encapsulation PPP
loopback not set
Keepalive set (10 sec)
LCP Open
Open: IPCP, CDPCP
[output cut]

Notice that the sixth line lists encapsulation as PPP and the eighth line shows that the LCP is open. This means that it has negotiated the session establishment and all is good! The ninth line tells us that NCP is listening for the protocols IP and CDP.

But what will you see if everything isn’t perfect? I’m going to type in the configuration shown in Figure 1.1 and find out.

FIGURE 1.1 Failed PPP authentication

Okay—what’s wrong here? Take a look at the usernames and passwords. Do you see the problem now? That’s right, the C is capitalized on the Pod1R2 username command found in the configuration of router Pod1R1. This is wrong because the usernames and passwords are case sensitive, remember? Let’s take a look at the show interface command and see what happens:

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 243/255, txload 1/255, rxload 1/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
LCP Closed
Closed: IPCP, CDPCP

First, notice in the first line of output that Serial0/0 is up, line protocol is down.This is because there are no keepalives coming from the remote router. Next, notice that the LCP is closed because the authentication failed.