Uplinks on Switch Stack, Design question

[neteng2323]

I need advice on where to place uplinks on switch stack, and which switch should be secondary master.  For example, I have a stack of 5 switches (1-5 racked vertically) my first switch is set as the master, second switch is set to take over for the master.  Does it matter where I place the uplinks?  My plan is to have 3 stacks like this in a closet, and 2 uplinks back to a distribution switch on each stack.  I would give the Master the first uplink, and maybe the 3rd switch the second uplink.... Should I make a different switch the secondary other than the second switch?

EDIT:  The Switch stack model:  2960-X

[Joseph W. Doherty]

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Posting

What switch model series are you asking about?

On the 3750 series, Cisco recommends stack master not host uplinks, but personally I think it makes little difference.

[neteng2323]

Sorry, I should have specified that... They are 2960-Xs.

[Masoud Pourshabanian]

Hello,

All members of stacks send controls messages to the stack masters and stack master sends control messages such as STP out; however, traffic will be sent out by all members.

If the other side is only one switch, it does not matter where to put uplink, but if you are using  technologies such VSS or VPC which several switches can be acted as a single switch, master should be connected to master since master members pass control messages to master.

If the switches on other sides are also stack, then master should be connected to master to avoid control messages pass over stack cable.

You can connect them randomly and it works because control traffic is not comparable to data traffic. If you are very concern about the best performance, then connecting master to master is suggested.

Hope it helps,

Masoud

[neteng2323]

I'm not sure I'm following, I will have 2 uplinks per stack that connect back to  a Nexus distro switch in a VPC configuration. 

[Masoud Pourshabanian]

I am sorry. I misunderstood your question. If you have five stack members, you should have 10 uplinks to VPC.

I hope I understood your question this time.

Masoud

[neteng2323]

The otherside of the uplinks will be a VPC configuration on the Nexus distribution switch.  The stacks of 2960s will have a port channel between the 2 uplinks.  5 uplinks would mean I would need 15 sfp's on the Nexus?  Thats gonna be expensive.

[Masoud Pourshabanian]

How did you calculate 15? If you have 5 stack switches, each switch should be connected to VPC by two uplinks. If you have 2 VPC members, you need 10 uplinks totally. 

Masoud

[neteng2323]

Ok, gotcha.. I misunderstood this time.  I thought you were saying each switch in the stack is getting an uplink.  I will have 2 uplinks per stack, for a total of 6 physical connections (3 VPCs) back to the Nexus.

[Masoud Pourshabanian]

If you use stack member instead of stack, it will be more clear. 2 uplinks per stack means to me that if you have 5 stack members you only have 2 uplinks for all 5.

If you have 5 switches are stack together, you will have 2 uplinks for eack stack member and 10 total uplinks for stack(or per stack).

Are we on the same page :)?

Masoud

[neteng2323]

Yes, 2 uplinks for all 5.  So, anything more than that is just for redundancy correct?  The stack ring speed is only 20G... What are the other benefits of having 1 link per stack member?

[Masoud Pourshabanian]

Since ether channel is used to connect stack members to VPC, having more uplinks, gives you more bandwidth. In my opinion,2 uplinks, for 5 switch is not enough. Full mesh is suggest, but if achieving full mesh is difficult, use at least 4 links to create cross topology. One of the links from active switch. Give more stack priority to other switches which have uplink to VPC.

Connect master switch to VPC master.

Hope it helps,

Masoud