Wired Intelligent Edge (Campus Switching and Routing)

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Regular Contributor I

Stacking question, 2930M switches

We are running 2930M switches in most of our wiring closets. Some of these are in a three-switch stacking configuration. We have DACs connecting the switches as follows:

Sw. 1 stackport 2 connects to Sw. 2 stackport 1

Sw. 2 stackport 2 connects to Sw. 3 stackport 1

Sw. 3 stackport 2 connects to Sw. 1 stackport 1

What we're seeing is that, on some switch stacks, the connection from Sw. 3 to Sw. 1 shows the LEDs flashing green and the CLI command 'show stacking stack-ports' indicates that these two ports are down. So instead of a ring topology, it's a chain topology. Also, the 'show logging' command output lists these two ports (stackport 1, Sw.1 and stackport 2, Sw. 3) constantly being inserted and removed. 

We're not seeing this on all our stacks - some are fine with solid green LED status on the stack ports, 'up' status in the 'show stacking stack-ports' command output and not flapping indicated in the log output.

Any idea what might be causing such a condition? First thought is a cable not seated securely, but I'm reluctant to just pull it and re-connect it during working hours - not sure of the effect that would have on connectivity for users, etc.

 

 

MVP Expert

Re: Stacking question, 2930M switches

Hi! what Switch is actually owning the Commander role?

Regular Contributor I

Re: Stacking question, 2930M switches

Sw. 1 is commander, Sw. 2 is standby, Sw. 3 is member.

MVP Expert

Re: Stacking question, 2930M switches

HI! Given that your issue is between SW1 and SW3 and SW3 has the Member role...if you are going to reseat DAC Cable between SW3 and SW1 you will cause the stack to split in two unequal (in size) fragments...the larger one will contain Commander (SW1) and Standby (SW2)...the smaller one will contain the Member (SW3)...this one will become inactive...so connected user will suffer disconnections (that should be the expected behaviour). That's a reasonable approach if the purpose is to firmly reseat involved DAC Cable to exclude it's just a physical issue.
Occasional Contributor I

Re: Stacking question, 2930M switches

Can i ask when stacking 2930M swtiche using the DACS and the 2 port stacking module - should the cables "cross" 

 

IE Switch 1 - Port 1 connects to Switch 2 Port 2

 

Or should they be Switch 1 port 1 connects to Switch 2 port 1

 

Many thanks

MVP Expert

Re: Stacking question, 2930M switches

On Aruba 2930M - first thing first - you don't for a Backplane Stack by using "normal" DAC Cables but, instead, you must use special Stacking Cables (they look similar to DAC but they haven't the typical expected SFP+ form factor).

 

So...on a two Members Backplane Stack you can use both Stacking Ports concurrently (each Stacking Module has 2 Stacking Ports) and you can do it by linking any-to-any:

 

SW1 Stack Module Port 1 <--> Port 1 Stack Module SW2

SW1 Stack Module Port 2 <--> Port 2 Stack Module SW2

 

or:

 

SW1 Stack Module Port 1 <--> Port 2 Stack Module SW2

SW1 Stack Module Port 2 <--> Port 1 Stack Module SW2

 

in any case you're forming a Ring Topology.

 

It's clear that if you have Three Aruba 2930M you will be forced to a Chain Topology where:

 

SW1 Stack Module Port 1 <--> Port 2 Stack Module SW2

SW2 Stack Module Port 1 <--> Port 2 Stack Module SW3

SW3 Stack Module Port 1 <--> Port 2 Stack Module SW1 (which closes the loop into SW1)

 

or:

 

SW1 Stack Module Port 1 <--> Port 1 Stack Module SW2

SW2 Stack Module Port 2 <--> Port 2 Stack Module SW3

SW3 Stack Module Port 1 <--> Port 2 Stack Module SW1 (which closes the loop into SW1)

 

 

Occasional Contributor I

Re: Stacking question, 2930M switches

Fantastic - thats as i expected as how i have set them up.

 

Many thanks for your assistance

Frequent Contributor II

Re: Stacking question, 2930M switches

Do the ports have to match, or can you do:

 

SW 1 port 1 --> SW 2 port 2

SW 2 port 1 --> SW 3 port 2

SW 3 port 1 --> SW 1 port 2?

 

So "crossing over" every time you connect? (Btw is the logic same for VSF on 2930F)?

MVP Expert

Re: Stacking question, 2930M switches

Aruba 2929 Backplane Stacking cabling: it can be any-to-any.

 

So on a Three Member Stack you can have:

 

SW 1 port 1 --> SW 2 port 2

SW 2 port 1 --> SW 3 port 2

SW 3 port 1 --> SW 1 port 2

 

SW 1 port 1 --> SW 2 port 1

SW 2 port 2 --> SW 3 port 2

SW 3 port 1 --> SW 1 port 2

 

SW 1 port 2 --> SW 2 port 2

SW 2 port 1 --> SW 3 port 1

SW 3 port 2 --> SW 1 port 1

 

On a Two Member Stack:

 

SW 1 port 1 --> SW 2 port 1

SW 1 port 2 --> SW 2 port 2

 

SW 1 port 1 --> SW 2 port 2

SW 1 port 2 --> SW 2 port 1

 

It's more a matter of having good stacking cabling on the backplane than respecting a particular connection pattern.