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New Member

Strange Gigastack issues

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

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: Strange Gigastack issues

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" .

21 REPLIES
Purple

Re: Strange Gigastack issues

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

Re: Strange Gigastack issues

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

New Member

Re: Strange Gigastack issues

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.

Re: Strange Gigastack issues

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'.

New Member

Re: Strange Gigastack issues

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.

Re: Strange Gigastack issues

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.

New Member

Re: Strange Gigastack issues

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

Re: Strange Gigastack issues

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

New Member

Re: Strange Gigastack issues

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.

Purple

Re: Strange Gigastack issues

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" .

New Member

Re: Strange Gigastack issues

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?

Re: Strange Gigastack issues

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!!!

New Member

Re: Strange Gigastack issues

Ok I will do.

Re: Strange Gigastack issues

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!!!

New Member

Re: Strange Gigastack issues

I went back through some logs and I found this on switch 2 when I plugged in the gbic from 2 to 3.

000032: 00:05:59: %GIGASTACK-6-LOOP_DETECTED: Gigastack GBIC in Gi0/1 is selected as Master Loop Breaker.

Link 2 of the Gigastack GBIC is disabled to break the loop.

Re: Strange Gigastack issues

If the switch detected a loop then did you have another connection to the other switch, directly or indirectly, via fastethernet interface.

New Member

Re: Strange Gigastack issues

I thought I had removed the cross over cable before that but maybe not. Is it the concensis that I put the Gbics on the vlan10 even though vlan 1 is shutdown?

Re: Strange Gigastack issues

Mitch,

You don't have to enable trunking on GBIC as someone earlier suggested. As long as, vlan 10 is the only one vlan that's in use on switch_3 then you can configure the GBIC port to be an access port on vlan 10 and ensure that's the only connection to the other switch. From your earlier post, it looks like you already have vlan 10 created. vlan 1 is the default/native vlan which is already created and you can leave it that way though the newer IOS(s) may let you remove it.

Good luck and let us know how you did.

HTH

Sundar

New Member

Re: Strange Gigastack issues

Well I will add the gbics to vlan10 tonight, I guess I just find it strange that switch 1 and switch 2 where working just fine with the gbics being trunk allowed to all vlans and then switch 3 causes this issue.

Purple

Re: Strange Gigastack issues

The question is are you actually trunking between those gbics ? Show int trunk should tell you . I think by default on the 2950's the ports are switchport mode dynamic desirable so they will trunk if you connect them togther without configuring anything . Why it won't work from 2 to 3 I'm not sure it looks ok . If the port is actually trunking then you can leave it in 1 , if it is not and is just an access port put it in vlan 10 . Check your vtp domain names on each switch if it is trunking they need to be all the same , show vtp status I believe . If switch 3 for some reason does not match the other 2 and did not bring the trunk up then connecivity would be broken because those gig uplinks are in vlan 1 , not vlan 10 . If you don't need to trunk multiple vlans down the switches I would simplify it and make all the connecting links switchports in vlan 10 .

New Member

Re: Strange Gigastack issues

Well moving the gbics to vlan 10 did the trick. Thanks folks for all your help I am sure I will be back.

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