Choice of Stack Master

[paul driver]

Hello
Curious - I am aware on previous stackable switch platforms it was a Cisco suggestion to select the stack master in a stack of more than 3 switches not have any upliinks, I have from this continued it as a best practice to do this whenever i am faced with installing a new stack, However it has recently occurred to me if this recommendation is still a valid one, So after a brief check on the recent LAN design guide it isn't a surprise I cannot see any reference to this anymore, so i am assuming this recommendation isn't valid anymore but what do you guys think?

Please share your thoughts.

[Reza Sharifi]

Hi Paul,

Cisco suggestion to select the stack master in a stack of more than 3 switches not have any upliinks,

Let me see if I understand the question correctly. So, if I have a 4 switches in a stack, the master switch should not have any uplinks but if I have up to 3 switches, it is OK for master to have uplinks? If yes, I did not know there is such a recommendation :-)

Reza

[paul driver]

Hello Reza
In a 3 switch stack the middle switch would be the master -no uplinks.

When there are multiple Cisco Catalyst 2960-X or 3750-X Series Switches configured in a stack, one of the

switches controls the operation of the stack and is called the stack master. When three or more switches are

configured as a stack, configure the stack master switch functionality on a switch that does not have uplinks

configured

CampusWiredLANDesignGuide

[Reza Sharifi]

Hi Paul,

Thanks for clarifying this. I am not sure what benefit not using an uplink from the stack master will provide. On the other hand, I have always used one of the uplinks from the master switch (regardless of the number of switches in a stack) and have never seen on issue. So, I think you will be ok uplinking the master switch as well as other members when you have more than 3 switches in an stack.

HTH

[paul driver]

Cheers Reza

yes i am aware masters indeed have uplinks and tbh I too haven’t seen a indifference with connectivity of such - utilisation etc apart from the resiliency of the stack master failing and not having any uplinks to to fail over also however as I’ve been aware of this recommendation for some time and as I said it was just curious post to see if any other do indeed implement the “best” practice on newer stack switches  or this recommendation still was valid - cheers anyway 

[Martin L]

what about c3850 ?  is this still true "select the stack master in a stack of more than 3 switches not have any upliinks " 

[Leo Laohoo · Accepted solution]

The "best practice" is actually DO NOT put (any) uplink on the stack master. Logic behind this is because it is the stack master, if the stack master crashes, the secondary will take over. Since the uplink not on the stack master, the LAN link will continue to work even if the stack master crashes.

[paul driver]

Hello leo

so I take it from this you would say its still a valid recommendation even though it seems it’s only stated on the lan guide from previous EOL models but saying that the master resiliency with no uplinks can be still valid on any 3+ physical stack topology regards of its model 

[Leo Laohoo]

EoL or not, I still say it is a good idea. So say, you have a stack of 3 and 1 uplink.
I'd leave the uplink on the 3rd member.
If there are 2 uplinks, 2nd and 3rd member.

[paul driver]

Hello leo

so do i- as I stated in the OP I still implement it this way whenever I can- I wanted to put it out to others to see if it’s still seems a good idea as the current lan design guide doesn’t mention it but obviously you agree with me so I’m good with that!

cheers

[Reza Sharifi]

Paul / Leo,

I still don't see any benefit in not having any uplink from the master. I use the same scenario Leo used. So, let's say you have 3 switches in a stack with 2 uplinks, switch-1 is the master and uplinks are on the 2nd and 3rd switch. If switch-1 crash and fail physically, the 2nd switch will take over as master (this is assuming switch-2 has higher priority than switch-3) and continue forwarding traffic. So far all good. Now, let's say switch-1 IOS crash and hang, in this case it does not matter what switch has uplinks, the whole stack will go out of business. 

So, now let's use the same exact scenario except this time the uplinks are from switch-1 and 2. Again, if switch-1 crash and fail physically, switch-2 will become the master, traffic will be forwarded using the uplink from switch-2. And again if the IOS crash and hang, it does not matter what switch has uplinks, the whole stack will be out of business.  So, maybe I am missing something but I don't see a difference. 

Now, I think what can be helpful is having uplinks from switches with higher amount of user ports and higher density.  So, say you have a stack of 3 switches and one is a 24 port and the other 2 are 48 ports and you are connecting more devices to the 48 port switches. In this case, I would put the uplinks on the 48 ports switches, because you don't want your end device to connect to say the first 48 port switch, traverse the stacking cable to get to the 24 port switch and exit the stack.

And finally if all 3 switches are 48 ports or 24 ports than it doesn't matter which 2 have uplinks.

For simplicity and ease of management, using the same scenario, I personally do this if all switches have the same user density.

sw-1 priority 14 master/uplink

sw-2 priority 12 member/uplink

sw-3 priority 10 member/no uplink

Thanks,

Reza

[Leo Laohoo]

There is no hard-and-fast rule to this. 

Some people like the "look" of the uplink to be on the stack master.  

Either scenario works.  

However, if I only have a single uplink, it will not go on the stack master.  

[paul driver]

Hello Reza
I am not saying you don't need uplinks on a master switch however it is preferred not to have it as i understand.

So whatbout the below scenario

sw-1 priority 10 member/primary uplink

sw-2 priority 14 master/no uplink

sw-3 priority 12 member/uplink

If sw1 fails master is retained and path rerouted via sw3
If sw2 fails master failsover to sw3 but no path reroute

[Reza Sharifi]

Hi Paul,

So whatbout the below scenario

sw-1 priority 10 member/primary uplink

sw-2 priority 14 master/no uplink

sw-3 priority 12 member/uplink

I think this set up will also work just fine.

Thanks,

Reza