trbleshoot when interface and protocol are up

mguy

<sub>I'm unsure how to go abouts with this problem

"At which OSI layer should you begin troubleshooting if you cannot ping the remote router, but the interface on the router that connects the remote router reports that the interface and protocol are up?"

A: OSI Layer 3


There are other variations of this question; like if interface is up and protocol is down or something like that. How to solve these problems?
Help!</sub>

craigaaron

if i remember the interface is the physical part so e.g right cables are plugged in at OSI layer 1 and the protocol is part of layer 2/3 so like checking the clock speeds for a dce interface or dte.

but i find with most of theses working on the real lab helps to test ideas

osJoe

Your interface is up and working, layer 1 is good. Line protocol is up and running, layer 2 is good. Next up is to check layer 3 for any issues relating to routing/ IP addresses.

SteveO86

Remember pinging an IP is testing Layer 3 of OSI.

It will just come in time. As mentioned before:

Down/Down - Usually points to a Physical issues something is either not plugged in or their is a cabling issue.
Admin Down/Down - Interface is shutdown
Up/Down - Could be an encapsulation issue, or some type of layer 2 problem (DLCI or so forth.)
Up/Up - Usually means the interface is working if the IP/Routing information is correct at layer 3.

mguy

SteveO86 wrote: »

Remember pinging an IP is testing Layer 3 of OSI.

It will just come in time. As mentioned before:

Down/Down - Usually points to a Physical issues something is either not plugged in or their is a cabling issue.
Admin Down/Down - Interface is shutdown
Up/Down - Could be an encapsulation issue, or some type of layer 2 problem (DLCI or so forth.)
Up/Up - Usually means the interface is working if the IP/Routing information is correct at layer 3.

This layered troubleshooting is a tricky concept for beginners like me, but thanks everyone!

From what I gathered:

Interface = Physical Layer
"Line" Protocol = Above Physical Layer

fsanyee

when you troubleshoot, you should use OSI

Roguetadhg

Also though, sometimes following the OSI layered approach isn't always the most reasonable-worldly approach.

Most people when they've been on the production floor and troubleshooted errors usually knows what things look like. What the feel of the network tends to be. Networks tend to have "days" or times when things react differently. It's living, for the most part.

"My computer doesn't work" usually means to me is that the user didn't log off sometime in a week, and the sever updated and got locked off the network. Or someone didn't want to sit beside someone else, and unplugged the computer / ethernet cables.

Ya know. Non-network issues :P