Network Design & stack question

[loiccruchade]

Hello everyone,

I have a little question about an architectural design for the network i'm managing.

Actually, we use two stack of 3*3750-X (using 2*10Gbits/s interconnection) as core, and 4*2960-X as access.

All those switch are in the same room.

So today i'm wondering one thing about this design.

Why not using a stack of 6*3750-X instead of two, since we get everything to do it ?

Since I was not present when the architecture design was developped and installed, i'm not certain my idea is a good one.

Thanks for your help !

[Leo Laohoo]

Why not using a stack of 6*3750-X instead of two

Co$t.

[loiccruchade]

Well since we allready have the switchs, the stacks modules and the cable, there is no cost for me to proceed.

I'm just wondering why the network was designed this way (2 stack).

[Joseph W. Doherty · Accepted solution]

A couple of possible reasons, some don't believe in running stacks with a large number of stack members.  Or, having two independent stacks might improve reliability as you're running two IOS images rather than one (i.e. avoiding a single IOS image being a single point of failure).

If you're doing L2 between the stacks and the access switches, normally I would run a single stack with MEC.

[loiccruchade]

Thanks Joseph.

Well then i see no reasons to not stack those switchs.

[Joseph W. Doherty]

Oh, for a 3750X stack, there is another consideration.  The 3750X supports PowerStack, but that's limited to 4 stack members (that interconnect their PowerStack cables).  If you're using the PowerStack feature, that might also be a reason why six units are running in two stacks.

I recall (?) you can have multiple PowerStack in the same data stack, but if so, I have no experience with such.

[loiccruchade]

Outch,  then i'll have to take a look then.

Thanks again, i'll let you know when i'll have more informations to provide.

[Joseph W. Doherty]

Ok, if you're using PowerStack, something that's not well documented with the 3750X, there's an amperage limit to what the PowerStack cables will support.  E.g. you cannot load one 3750X with a pair of 1500W PSs, and power an adjacent  3750X PoE ports w/o it having some on-board power on that switch.

Assuming you can have two PowerStacks in the same data stack, you could probably interconnect powered cables, just as they interconnect now.  Whether that would be the optimal choice is a different question.

[loiccruchade]

So i've just took a look at our physical configration.

We use 6 *3750-X, divided in 2 stack, using StackWyse and Powerstack.

I'm actually reading this article, talking about what you just said on using both Stackwyse and Powerstack :

https://supportforums.cisco.com/document/12575126/how-form-catalyst-3850-data-stack-and-power-stack

I have some research to do, but i think we can do it.

Thanks again for your help Joseph.