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I have 20 3550-48 switches, I staking those

My problem is when I make a stack, upto 2 switches it works but when I add third SW the it dont ( more than three ) and I am not getting connectivity on those switches.

I am using Giga stack modules and cables.

I am providing base mac add of members to commander switch, On member switch I am providing commander base mac add.

Is some thing missing, what should I do exactly?

VIP Purple

Re: Stacking


do you have a link light on your GBICs, and if so, what color is it ? Which IOS version are you running on your 3550 ?



New Member

Re: Stacking

Could you give us the config of your cluster commander and one of the member switches you are trying to add. Just some things to check, make sure you have CDP running on the switch you want to add and that it is also enabled on the uplink interface. Do a show cdp neighbor from the switch it connects to (the one that has successfully been clustered with the commander). Also, on the commander, issue the priviledge exec command: show cluster candidates

Ensure that you see the switch you are trying to add there. If you dont but you have cdp functioning and can see the switch as a neighbor to the directly connected switch. Ensure that the appropriate vlan is enabled. In a cluster configuration, the cluster info is propagated over the same vlan. If you have vlan 1 shut down and vlan 2 no shutdown on the cluster commander, than all member switches must have the same before you can make them a member.

Hope this helps, if not please post your config.

Re: Stacking


Commander conf


no ip domain-lookup

cluster enable STACK3 0

cluster member 1 mac-address 000e.d7f8.8f80

cluster member 2 mac-address 000f.2303.8180


Here CDP is enable on all port, I can see other switch in cdp nei.

member conf.


cluster commander-address 000e.d7f8.0800 member 1 name STACK3 vlan 1

spanning-tree mode pvst

spanning-tree extend system-id


Here on all members CDP is runing, I can see nei.

This is the same conf for all members. VLan is also proper.

Bue on commander switch in 'show cluster

candidates' command I can not see members.

I am doing Daisy Chain, STP bloks the one Gigastack interface properly.

I have VTP trunk going to Core 6509 switch from members.

Finaly, I am doing stack of 3 switches (1 comm,2 mem ) -Daisy Chain.

I want trunk port from 2 member switch to core switch. But I can to ping any add out of my stack. and Can not ping from outside to stack.

Re: Stacking


the problem is your Daisy-chaining.

You need to set the trunks between the stack members to nonegotiate on both trunk sides.

Use the interface config commands:

switchport mode trunk

switchport nonegotiate

on IOS switches.

See for details.

The trunk negotiation is allowed by default on Cat3550 which caused your problem.



Re: Stacking


I should make the gigastack int as trunk. right?

These are the steps I have taken.

Making Daisy chain (cros links) to form stack.

Enabling cluster on commader.

Adding MAC of members on commander - 2 members.

Adding MAC of commander on member.

Installed GBIC SC module on first and last switch (middle is commander).

connect SC fiber connection to core switch.

I have two core 6509 switch.

One Fiber link of stack goes to First Core 6509.

Another fiber of stack goes to second Core.

Core switches have fiber trunk between them.

All fiber links are trunk ports with dot1q.

Gigastack interfaces are made trunk.

Still the problem exist, is there any issue of STP.

Re: Stacking

Well, maybe I didn't understand your problem correctly...

My advice was regarding trunks between GigaStack members. (I supposed you were using trunks between cluster members.)

But your problem seems to be in clustering.

I'd try to remove members MACs from commander config and commander MAC from members config.

Then I'd try sh cluster candidates on the commander console and check if the members MACs are detected.

If yes, add the MACs to the configs.

If not, there is something wrong - CDP, VLANs, trunks, etc.



Re: Stacking


I solved the problem, actualy I made a mistake.

I configured my core switch trunk links with dot1q and on stacks I made it ISL.

Now I made all to dot1q.

And stacks are working.

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