2950 to 3500XL Connectivity problem

[jonnyknowsbest]

Hi

We have a cross over cable going from port 8 on our 2950 to port 23 on our 3500XL, but we have a problem with the two devices "seeing" each other.
Unless we specify on BOTH ports to use Half Duplex and 10mbps, then they will not communitate.

Any ideas what might be causing this?

 

[vipergg]

Not really if you set both ports to auto speed and auto duplex on both sides it should negotiate 100 full duplex if the cable is ok . Maybe if you post the interface config from both sides we can see something . Both sides must be either auto on both sides or hardcoded to speed and duplex .

 

[jneiberger]

jonnyknowsbest:

Were you hard-setting your speed and duplex settings to 100/Full? Have you tried setting both sides to Auto?

Auto would be the recommended setting in this situation. If you manually set both sides to 100/Full, Nway autonegotiation is completely disabled on the 2950 but the 3500XL will leave Nway turned on. When the 3500XL doesn't detect an autonegotiating link partner on the other side it will assume that it's connected to a hub and will fall back to half-duplex.

Have you tried setting both sides to 100 Mbps but leaving them at half duplex? If that fails then you probably have a cable problem.

 

[jonnyknowsbest]

What happens is unless both sides are hard coded to be half duplex running at 10mbps, we keep getting:

Interface FastEthernet0/8 is up
Interface FastEthernet0/8 is down
Interface FastEthernet0/8 is up
Interface FastEthernet0/8 is down

(rinse and repeat)

If we set both sides to autonegotiate, they never complete the autonegotiation and we loose connectivity, which is pain since the routers are physically 150 miles away from where i am

 

[jonnyknowsbest]

Sorry, they are not routers they are SWITCHES.

My small brain is overheating

 

[jneiberger]

What software release is running on these switches? This sounds like either a bad cable or an IOS bug.

Have you tried a known good cable?

 

[jonnyknowsbest]

We had a comms engineer in who swapped the crossover cable. One switch is running 12.0 (Cisco 2950) and the 3500XL is running 12.1 i think.

Hopefully next week i can get to the site and do basic physical checks, and more in depth troubleshooting. Will post my results back