2500 Serial Down - brief lab setup

Hello -

I have two 2501's in a basic lab setup, connected to each other's S1 via DCE/DTE cable. The serial interfaces' link state will not change to up. Here are the abbreviated configs:

----------------------

show run

hostname TopRouter

interface Serial1 ip address 172.16.0.2 255.255.255.0 clockrate 56000 ! router rip network 172.16.0.0 network 172.18.0.0

show cont serial 1

HD unit 1, idb = 0x263BC8, driver structure at 0x26B6F0 buffer size 1524 HD unit 1, V.35 DCE cable, clockrate 56000 cpb = 0xE2, eda = 0x3140, cda = 0x3000

show int ip brief

Ethernet0 172.18.0.2 YES NVRAM up up

Serial0 unassigned YES NVRAM administratively down down

Serial1 172.16.0.2 YES NVRAM up down

**************************
show run

hostname BottomRouter ! interface Serial1 ip address 172.16.0.1 255.255.255.0 ! router rip network 172.16.0.0 network 172.18.0.0 !

show cont serial 1

HD unit 1, idb = 0x263BC8, driver structure at 0x26B6F0 buffer size 1524 HD unit 1, V.35 DTE cable cpb = 0xE2, eda = 0x3140, cda = 0x3000

show ip int brief

Ethernet0 172.18.0.1 YES NVRAM up up

Serial0 unassigned YES NVRAM administratively down down

Serial1 172.16.0.1 YES NVRAM up down

-------------------------------

If I issue a shutdown on s1, and then follow up with a no shutdown, the interface will change its link state to up, but only for a few seconds.

The same issue occurs if I change the configurations to use Serial 0 on both routers.

Any idea what is going on here?

Thanks

-tom

Reply to
tom
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apply a "no keep-alive" to the serial interfaces

BernieM

Reply to
BernieM

Well, that gave me up up line protocol, but no connectivity.

Oddly, one of the routers can see the other via CDP, whereas the other can't.

How should I follow-up?

Thanks

Reply to
tom

This could possibly be an issue with the cable or the connector.

Try the following and the answers to the experiments will guide you towards the source of the problem or at least rule out some potential sources of the problem thus narrowing down the list of suspects.

  1. Make sure that the cables are firmly and properly inserted into the connectors. The try your ping test again.

  1. Turn on "debip ip icmp" on both ends and ping each router from the other one. Do you see debug output on one but not the other?

  2. Move to the other serial interface on each router. Does the problem persist?

  1. Turn the cable around thus reversing the DTE/DCE. Don't forget to apply the clock rate command to the new DCE interface. Did the problem also move around or did it stay the same?

  2. If you have another cable, try using that. Does the problem go away?

Cisco da Gama

formatting link

Reply to
ciscodagama

I appreciate your suggestions, though with the exception of debip(sic) ip icmp, I have tried them all . . .

I can tell that the CDP frames are not reaching the router that doesn't show any CDP neighbors . . .

Thanks

-tom

Reply to
tom

Oops, I meant "debug ip icmp".

So, what were the results from the experiments? The answers should have helped you isolate the problem to the point where you know that it is either a cable fault, a problem with a particular serial interface or a problem with a particular router?

Cisco da Gama

formatting link

Reply to
ciscodagama

I haven't taken it up in a couple of days, but will be shortly. I have tried multiple cables, with the same results. Reversing DCE/DTE has the same results. I have not ruled out a bad interface, but I am not sure how to go about troubleshooting a hardware problem like that - what debug command would I use? I'll look at debug ip icmp and post.

Thanks

Reply to
tom

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