At 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

View Answer

Answer: B

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". Hope this helps.