Anyone know the answer to this question....

[eggedd2k]

Been doing a lot of online practice tests.

One question that has come up a few times is below however I cannot find an answer for it:

...The Serial line shows UP and protocol shows as UP however the router cannot be contacted via a Ping test.

What layer is the problem likely to be on?

A. Physical
B. Data Link
C. Network
D. Transport

I chose Physical.

 

[dopehead]

Well, since up/up means that it has seen data on the port i would say routing issue ie. C.Network


Network Systems Engineer
CCNA/CQS/CCSP/Infosec

 

[Lundah]

I would agree with you there. The thing to keep in mind is that a Cisco Router is a layer 3 device, therefore when you look at an interface it wants tell you right away what states layer 1 and 2 are in for the interface. Hence, you get an up/up, up/down, or down/down when you look at the "show interface" results. First it will check the physical layer (are there bits on the wire), then the data-link layer (can I understand the bits on the wire). Once those are up, it's all router (Layer 3) config issues that will affect connectivity.

 

[melampus]

They're correct. Ping is layer 3 (Network). I remember seeing that question when I did my CCNA. I'm sure it's in my book somewhere.

 

[rocketlauncher]

Right on Layer 3, network, subnet mask, gateway misconfiguration.

 

[mgodinez]

Dear Greater Cisco Intellect,

I too think it's layer 3, as ICMP echo requests are defined at this layer.

Regards,

Mike Godinez
Seattle, WA

Sunny!!!

 

[Axis911]

Hey.

I think your answer is right cos of many reasons. i know some times when you go deep in to CCNA every one tends to forget the basics. well i am not one of them.....

Anyway the reason the answer to your question is Physical Layer is coz the ping test is the most basic test and it will only look if the physical media is functioning correctly there for the answer for it is **** PHYSICAL****

unless you do a telnet which checks all 7 layers of the OSI model which is also know to be the most compleat test, well that is not relavent to this topic anyway..

Good Luck

Regards

Axis 911

 

[Lundah]

Not exactly. If the router interface is "up and up", then we already know the physical layer is there (i.e., the cable is good). The "Cisco" correct answer is Network, since the "up and up" covers the first two layers. The port is connected and has a good signal, but there's no routed path to the far end.

 

[lgarner]

... the ping test is the most basic test and it will only look if the physical media is functioning ..." ?

Ping uses ICMP, which is part of IP. IP is a layer-3 protocol. Other layer 3 protocols have ping-like functions also.

Remember, when you ping a device, you are trying to connect to its IP address. Ping doesn't even consider the layer 1 and layer 2 topologies. The physical and data-link parts can be working just fine and ping may still fail.