Router Configuration Help

[fitzhue]

Hello everyone, I have a question for all the router configuration guru's of AT. I'm having problems configuring a 3 router, 3 workstation, 1 switch topology in Cisco class. I am almost positive I am doing everything right. All the routers are 2501 series routers.

Router_A is hooked up to Router_B via s0->s1. Router_B is hooked up to Router_C via s0->s1 as well. I configure all the interfaces on the routers just fine including clockrates on the DCE cables. I configure all the ethernet addresses just fine and i make sure to double check that the ip addresses are right. But i still have some interfaces that don't want to ping. I configure each router the same but obviously taking into consideration the different ip addresses. Some interfaces will ping fine and others won't. I can ping 2 out of the 3 workstations.

Does anyone have a clue as to why some interfaces will ping while others wont? Does anyone have a checklist maybe to make sure i'm doing everything right? Even some sort of website, maybe on the cisco site because i couldn't find anything, that shows how to do all of this correctly would be extremely beneficial. Let me know if there's any other information I can provide as this problem has been bothering me for almost a week.

P.S. my teacher isn't exactly the greatest at configuring routers either as he just graduated from sem2 a few weeks ago.

Thanks in advance.

 

[tjaisv]

Which routing protocol did you configure? RIPv2? Check to make sure you correctly configured and enabled it.

Tell us exactly which routers are unpingable, and where they're unpingable from.

Also, if you can, post for us a print-out of your config file.

 

[fitzhue]

Ok, i dont remember all of the interfaces specifically off hand, but ill get that info tomorrow. thanks

 

[fitzhue]

alright well i figured out that the reason that its not working is that the line protocol for two of the serial ports are not up. the net admin at my school said that the encapsulation was different and he changed it. anyone know of what he might've done?

 

[Fatt]

The cables that you use to connect serial ports have a DCE end and a DTE end.

It's common for beginners to lose track of what end is what.

If you have 3 routers daisy chained A-B-C you probably chose B to apply the clockrates to. Make sure that B has DCE ends plugged into it.
.
Now, do an ERASE START, turn the router on and off (quicker than typing reload) and make sure you don't let it do any of the autostart things it wants to try and do as it finishes booting.

You chould now have a clean router.

enter your IP addresses, your clock rates, and bring up the ports with a NO SHUT command. You know, do your basic, minimum config to get started.

Now...
at the "config" prompt, enter ROUTER RIP, hit enter, then enter VER 2 and hit enter again.

That insures that if you are using VLSM, it will work.

Add your networks and ping every interface from each router. Also, telnet from one end to the other.

If that all works, you are good to go and you can now enter more advanced configs.

You don't have to worry about RIP and OSPF (for instance) interfereing with each other. If you have RIP and pretty much anything else configured, the router will pick the protocol with the lower AD.

In the real world, when you are all done, you would do a NO ROUTER RIP command but in the lab it doesn't matter.

 

[rc240sx]

I have experienced in the past that ethernet interfaces aren't up until connected to a hub or switch. 90% of problems occur at the physical layer so check that. Also do a show interfaces command to check if they are indeed all up. Also give them time to update the routing table. How long did you wait for each ping? Do a show CDP neighbors to see if you can see the directly connected routers. Make sure the pins in the serial cables arent bent. You dont know how many times people bend them. I concur completly with FATT. The easiest way would be erase start, reload, and start the system configuration dialog. If that doesn't help, then I am almost certain its a physical layer problem.

PS 2501 routers are weird, sometimes things just dont work with them even though everything is 100% correct.

 

[rc240sx]

Im sure you learned this in class but let me say this anyway. Troubleshooting starts at the Physical layer then moves one level up at a time. For example, Physical-cables, interfaces, transceivers DataLink-encapsulation , clockrate Network- IP addressing , subnetmask, Routed and Routing protocol.......

No offense but I dont know your instructors competance as an instructor. When I graduated from semester 2 I had troubleshooting down to a T.

 

[Fatt]

... The easiest way would be erase start, reload, and start the system configuration dialog....

Actually, I want to clear up that misunderstanding before it gets started. I don't believe in using the dialog. I firmly believe tha the best way to run a cisco router is to write the entire configuration yourself.

 

[fitzhue]

well yea as i said before, i've isolated the problem to the line protocol on the serial ports. it has to do with router B -> router C. I made sure that its a DCE connection. when i do a show interfaces command, it shows that the line protocol is down on serial 0 for router B and serial 1 for router C. i just don't know how to get those back up. someone told me it might be an encapsulation irregularity. i don't know any commands that might fix that.

 

[rc240sx]

I dont think thats the problem because erasing startup will change the encapsulation to HDLC when you reload. But you can try this , go go global config, int s 0 or s1, ecapsulation HDLC.

 

[Fatt]

Yeah.

 

[fitzhue]

is there any way to check what encapsulation the router is using? someone said that the router was using x.25 and he just disabled it and it worked.

 

[rc240sx]

I take it you didn't do a erase start command. You can check the encapsulation by typing show int.

 

[fitzhue]

i've probably done the erase start command 10 times within my process of trying to config this router. i configured it at least 10 times after erase the the startup config and starting from scratch, but i still had the same problem.