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Viewing, Saving, and Erasing Configurations

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F I G U R E 4 . 7 The show controllers command

Router R1 has a DTE connection—the default for all Cisco routers. Routers R1 and R2

can’t communicate. Check out the output of the show controllers s0/0 command here:

R1#sh controllers serial 0/0

HD unit 0, idb = 0x1229E4, driver structure at 0x127E70

buffer size 1524 HD unit 0, V.35 DCE cable

cpb = 0xE2, eda = 0x4140, cda = 0x4000

The show controllers s0/0 command shows that the interface is a V.35 DCE cable. This

means that R1 needs to provide clocking of the line to router R2. Basically, the interface has

the wrong label on the cable on the R1 router’s serial interface. But if you add clocking on the

R1 router’s serial interface, the network should come right up.

Let’s check out another issue, shown in Figure 4.8, that you can solve by using the show

controllers command. Again, routers R1 and R2 can’t communicate.

F I G U R E 4 . 8 The show controllers command used with the show ip interface command

Here’s the output of R1’s show controllers s0/0 command and show ip interface s0/0:

R1#sh controllers s0/0

HD unit 0, idb = 0x1229E4, driver structure at 0x127E70

buffer size 1524 HD unit 0,

DTE V.35 clocks stopped

cpb = 0xE2, eda = 0x4140, cda = 0x4000

R1#sh ip interface s0/0

Serial0/0 is up, line protocol is down

Internet address is 192.168.10.2/24

Broadcast address is 255.255.255.255

If you use the show controllers command and the show ip interface command, you’ll

see that router R1 isn’t receiving clocking of the line. This network is a nonproduction network,

R1 R2

DTE

DCE

R1 R2

S0/0

47020.book Page 235 Wednesday, January 2, 2008 4:31 PM

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Cisco 2501 - Router - EN Bedienungsanleitung Seite 57