Solved: Uplink problem between two 2950T switchers

h2odata_ab · ‎02-21-2008

Hi there,

I decided to setup two 2950T's that we weren't using at the the office to try some VLAN scenarios I had been pondering.

I started by updating IOS in both switches and did a "write erase" to clear all configuration. I deleted vlan.dat as well. Then I proceeded by doing basic configuration like setting manegement IPs and passwords.

I connected Gi0/1 on the one switch to Gi0/2 on the other but got no link. I tried a brand new cable, still no link. Tried some other ports but no link there either. No matter what cables or ports I used I couldn't get the LEDs to light up. "show interfaces" confirmed that nothing was happening.

As an experiment I tried connection an HP switch to both of the C2950s. They lit up on every port I tried with no changes to configuration. I did a "write erase" on both switches again and tried linking them with no configuration done whatsoever but still no go. I also tried uplinking them to our production switch (C2950) but no go there either.

What can be the cause of this odd behaviour? They uplink fine to the HP switch but just not to a Cisco swith.

Thanks for your help,

Dan

glen.grant · ‎02-21-2008

You were probably using a straight thru cable which will not light up the port on the 2950 because 2950's do not support the mdix function . Probably the HP does support mdix so when you plugged that in you got a light . On older cisco switches you need a crossover because they do not support mdix, whereas newer models do support it so you can use a stright or crossover in those if the port is set correctly as auto .

View solution in original post

lamav · ‎02-21-2008

Im assuming you are using a copper cable...

Make sure the copper cable is a crossover cable

make sure that the speed and duplex settings match. Since its a gigabi tport, it should autonegotiate to 1000/Full.

make sure both ports are administratively "up"

If youre configuring the ports as trunks, make sure the dot1q/isl encapsulation is configured on both sides.

I may help if you post the configs on both switches...

Check out the stuff I mention and let us know what happens...

HTH

Please rate my post if it helps.

Victor

glen.grant · ‎02-21-2008

You were probably using a straight thru cable which will not light up the port on the 2950 because 2950's do not support the mdix function . Probably the HP does support mdix so when you plugged that in you got a light . On older cisco switches you need a crossover because they do not support mdix, whereas newer models do support it so you can use a stright or crossover in those if the port is set correctly as auto .

h2odata_ab · ‎02-21-2008

Thanks for your help. The crossover cable did the trick. I thought about trying that yesterday but dismissed it as I could never imagine a switch like this not supporting mdix. I appreciate the quick help.