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Strange Gigastack issues

ciscoadmin
Level 1
Level 1

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

21 Replies 21

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.

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

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?

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

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.

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 .

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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