Networking - IOS and Security Device Manager - Discussion

Discussion :: IOS and Security Device Manager - IOS and Security Device Manager (Q.No.5)

5. 

What layer of the OSI model would you assume the problem is in if you type show interface serial 1 and receive the following message? "Serial1 is down, line protocol is down."

[A]. Physical layer
[B]. Data Link layer
[C]. Network layer
[D]. None. It is a router problem.

Answer: Option A

Explanation:

If you see that a serial interface and the protocol are both down, then you have a Physical layer problem. If you see serial1 is up, line protocol is down, then you are not receiving (Data Link) keepalives from the remote end.

Eswar said: (Mar 26, 2016)  
The serial link is available in routers, so routers available in the network layer, then how it is in a physical layer?

Subu said: (Apr 3, 2016)  
Serial link is used to transfer the signals from router to router so signals, voltages are part of the physical layer.

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