Strange Gigastack issues

[ciscoadmin]

Ok I have 3 2950 48 port switches. I have been rolling my users to the new switches as they have been off the network. Today I came in and it was time to fire up the third switch in the stack. Ok I plugged the gbic into the slot powered up the switch and attached the gbic cable. This is how I have done it in the past never a problem.

All of a sudden folks on the second switch amd the test machines on the third switch lose connection to the network. I console in to switch one I can ping the internet and all my servers. I should tell you that the users are on one vlan while my servers are on another.

I disconnect the gbic as it was the last thing that changed and the users do a ipconfig /renew and bam they are back on the net. If I use a cross over cable from switch 2 to switch 3 everything works fine I have checked the configs line by line and they are all the same.

Any ideas?

Thanks

[glen.grant]

Sounds like either a spanning tree problem or your trunks aren't configured correctly.

[sundar.palaniappan]

Based on your description, it's quite possible the 3rd switch may have become the root bridge for the user_vlan and thus all traffic from the user_vlan may have been getting blackholed on the 3rd switch. As cisco switches do PVST it shouldn't have affected your server VLAN. We need more info to determine this. Do a show spanning-tree vlan (user_vlan_id) on the 2nd switch to check who is the root bridge for that VLAN. If it is the issue then configure the core switch, one that connects to your router, with the command 'spanning-tree vlan (user_vlan_id) root primary' to make it become the root.

If that doesn't help can you share the topology details and configuration with us to identify the issue quickly.

HTH

Sundar

[ciscoadmin]

Ok attached is spanning tree info and config info. I did make the first switch the root for spanning tree but still had same issue.

[sundar.palaniappan]

Can you tell us how are these switches inter-connected. Does every switch connect to the other 2 switches? Also, which ports are connecting the switches. Moreover, post the output of 'show vtp status' & 'show vlan brief'.

[ciscoadmin]

Switches are as follows. Router to switch 1 via eth cable, Switch 1 to Switch 2 via Gbic card port 1 on switch 1 to port 2 on switch 2. Then it should be gbic from switch 2 to switch 3 port1 on switch 2 to port 2 on switch 3. But that is not working so I have a cross over cable from switch 2 to switch 3. Attached is the info you asked for.

[sundar.palaniappan]

Config looks good. In your original post, you stated the connection between switch 2 & 3 is up when crossover cable is used. To connect two switches you need to use a crossover cable and I am not sure what problem you are having then.

[ciscoadmin]

When I take the cross over out and try to use the gbic switch 2 and 3 go dead.

[sundar.palaniappan]

Got it.

Are you using the Cisco proprietary cable/connector for connecting the GBIC ports. It sounds like a physical layer issue. Follow the directions at the link below to troubleshoot further.

http://www.cisco.com/en/US/products/hw/switches/ps628/products_installation_guide_chapter09186a00802acfbf.html#wp1142278

Good Luck!!

HTH

Sundar

[ciscoadmin]

Yes I am useing Cisco OEM cables and gbics. I have gone through the installation instructions. We have had our older switches connectd this way with no issues.

[glen.grant · Accepted solution]

It goes dead because it looks like the gigabit interfaces are not in vlan 10 they are in vlan 1 . Thus it would kill the switches if try to connect using the gig interfaces. Also you need to trunk all those downlinks between the switches if you have 2 different vlans on these switches . What vlans are you useing , vlan 1 and 10 ? If so then you have to trunk those downlinks between the switches , don't see any trunk configs . If these switches only need vlan 10 on them to get the gig interfaces to work put them in vlan 10 , "switchport access vlan 10" .

[ciscoadmin]

Vlan 10 is all this group of switches will run. I understand what you are saying about the gbic being on the vlan, but I ask you why does it happen when the third switch is connected. If it was a trunking issue wouldn't I have seen the issue when I gbiced the number 1 switch to the number 2 switch?

[abhishek_nandavat]

Hi,

As I said in my previous post, the trunks are not configured at all in your switches!!!

You should configure "switchport mode trunk" on all the gigabit interfaces where you have put your gigastack ports. Trunk mode is required for them to allow all the vlans to pass through.

Hope this helps...

Regards,

AbhisheK

Please rate all helpful posts!!!

[ciscoadmin]

Ok I will do.

[abhishek_nandavat]

Hi,

I think the trunk is not configured properly. Moreover, dont configure "switchport nonegotiate".

I guess the stacking cables have been connected in the proper manner.

Hope this helps...

Regards,

AbhisheK

Please rate all helpful posts!!!