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New Member

Newbie stack/vlan question

Hi,

We've bought 9x 3750s to setup for a new office. We will be stacking them but I've also been asked to setup VLANs (see attachment). So I wanted to know:-

a) Is this a good idea on a stacked system and,

b) will it be difficult to implement.

I'd be grateful for any comments - I am new to this! Am more than happy to provide more info if needed.

-H

7 REPLIES

Re: Newbie stack/vlan question

a) Althought they are 9 physical switches, they are 1 logical switch from a config point of view.

b) No

The VLAN setup you have - indicates that each switch is a single point of failure for a specific vlan number/ip subnet. Perhaps not the best way to go about it in my opinion.

Perhaps you might consider 3 switches in a stack group, that are connected via redundant fibre trunk links.

Then assign specific ports into the relevant VLAN's.

HTH>

New Member

Re: Newbie stack/vlan question

Thanks for coming back. I wanted to clairfy a couple of things.

Given that the 9 switches are 1 logical switch from a config point of view is it possible to set each one up with VLANs as described?

Do you think there will be a performance benefit of having mulitple VLANs - or do you think just 1 voice and 1 data VLAN will suffice?

Is the benefit of the "3 switches in a stack group" configuration you propose to tolerate a switch failure?

Appreciate you help with this.

-H

Re: Newbie stack/vlan question

Given that the 9 switches are 1 logical switch from a config point of view is it possible to set each one up with VLANs as described? Yes - you would create the vlans on the master switch. The assign the relevant interfaces into the speicifc VLAN you want.

Do you think there will be a performance benefit of having mulitple VLANs - or do you think just 1 voice and 1 data VLAN will suffice? - for eas of troubleshooting - data vlan and voice vlan. If that is all you have keep it simple. if you have to segregate inter-vlan traffic, then do so.

Is the benefit of the "3 switches in a stack group" configuration you propose to tolerate a switch failure? Yes - only if you want a vlan/ip subnet per switch. If you decide with only 2 vlans, stack all 9.

However if you want to add a 10th switch, you cannot - 9 is the max limit in a stack group.

Another option could be 1 stack of 5 switches, and the other stack of 4 switches. So you could add 4 switches to stack 1 and 5 switches to stack 2.

I always try to plan for the future.....people allways need more ports!!!!

HTH>

New Member

Re: Newbie stack/vlan question

I've just found out the will be using phones and PCs on the port. Hence I will need 2 VLANs on each port and the 2 stack option is not viable.

We've also just found out that the switches supplied are not PoE - again needed for the phones. Nice!

Anyway thanks for your help - much appreciated!

-H

Re: Newbie stack/vlan question

Why is the 2 stack option not viable?

In one of my offices, I have 22 switches, in various stack configurations - mainly 3 switch stacks. All switches have VoIP phones connected, with a PC connected to the phones?

All stacks are in seperate racks, with seperate power and UPS.

If you bundle all switches into 1 stack and all in 1 rack, all connected to the same power - where is your resiliance? Your stack is a single point of failure?

What are you using for Layer 3 routing? A seperate router or the 3750 MLS? Are you connecting the layer 3 into the stack? Is your stack going to provide Core<>Dsitribution<>Access layers all in one go?

Think failover, think redundancy.

New Member

Re: Newbie stack/vlan question

I've obviously misunderstood! I thought you were suggesting 1 VLAN per stack - my apologies.

I will be using the MLS and will be providing all three layers - do you see a problem with this?

Re: Newbie stack/vlan question

OK here's the thing with 1 stack.

You have layer 2/3 functions all in one stack - nice for standardisation, one stop shop for troubleshooting. If the master fails, then the next in-line will take over - lovely.

If the whole stack fails - you have lost everything no connectivity to anything - bad idea.

If you are going to core-dis-access all in the stack - you need to split it (in my opinion) you don't want all your eggs in one basket - you need to plan for the worst and hope for the best.

If you have critical servers etc - they need a redundant topology. I would:-

1) Have 2 stacks

2) Configure Trunking between the stacks.

3) Configure VTP - easy for vlan creation blah blah

4) Configure layer 3 interfaces in both stacks for management and inter-vlan routing if needed

5) Either configure HSRP or VRRP between the 2 stacks, if the primary layer 3 interface fails, the secondary takes over.

6) With the above - with any mission critical servers, they should have dual NIC's - then cable 1 into each stack.

7) Distribute the VoIP phones and PC's between the stacks - say a 50/50 if possible

For a belts a braces thinking if the site is really important - you would have two internet links and two firewalls, each on their

own stack.

So if 1 stack complety fails (un-likely) at least 50% of the site can still carry on working!

Like I said - plan for the worst and hope for the best! just my opinion

HTH>

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