Home » Cisco » 100-101 » Which OSI layer should the administrator begin troubleshooting?
A network administrator cannot connect to a remote router by using SSH. Part of the show interfaces command is shown.
router#show interfaces
Serial0/1/0 is up, line protocol is down
At which OSI layer should the administrator begin troubleshooting?
A. physical
B. data link
C. network
D. transport
Correct Answer: B
Explanation/Reference:
Explanation:
https://learningnetwork.cisco.com/thread/12389
I think the indication here is “Serial 0 is up, line protocol is down”. What causes this indication? Correct me if I am wrong. When you have this indication, a cable unplugged is not a correct answer. If you check the output of your “show interface serial 0” command again, you should notice it as “Serial 0 is down, line protocol is down. Under the “show ip int brief” you should see status = down and protocol = down as opposed to up, down. Because you disconnected the cable, layer 1 will go down, which is indicated by the serial 0 down status. The line protocol status is for layer 2. So, a cable unplugged is not a correct answer to “Serial 0 is up, line protocol is down”. Up/down means that the physical layer is OK, but there is a problem with the data link link (line protocol).
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