WiSM redundancy, mobility groups and RF groups

[Dominic Stalder (old profile)]

Hi there

we would like to implement the following:

- Support for about 2000 LAP's

- 1 x Catalyst 6509

- 1 x Sup 720

- 7 x WiSM's

What I'm interesting is are the following points:

1. I thought that we would build the switch completly redudant, so we have to wlan switches (switch A and B) with 7 WiSM's eatch. So I can garanty a N+N redundancy --> each LAP's has a primary controller on switch A and it's secondary controller on switch B. The LAP's can be splitted on the two switches, but for your understanding there is a 1:1 redundancy. What do you think of this design, is the too much or is this appropriate?

2. As I know you can build up a mobility group of a maximum of 24 controllers or 12 WiSM's. I would put only these controllers in a mobility group, where Layer 2 roaming can occure.

3. But what is about the RF groups - there is a maximum of 1000 LAP's, so I can put only 3 WiSM's in one group. But this would not work form me, then I would have 2 WiSM's on switch A and only 1 WiSM on switch B in a RF group (not a 1:1 redundancy). First is it possible to put WiSM-A and WiSM-B into different RF groups, I think so because they are logically splitted, aren't they?

And what RF group design would be best (just as a reference)? I thought that it would make sense to form a RF group for each of the seven pairs (1 WiSM on switch A and 1 WiSM on switch B) for redundancy? What do you think of that approach?

4. So I would have 1 mobility group and 7 RF groups. Or do you recommend to form the mobility groups like the RF groups? But what happens with Layer 2 roaming in that case?

I'm sorry for the long and messy text, but I hope you can see my design questions?

Thanks a lot in advance.

Dominic

[gamccall]

Is it possible to logically divide your 2000 APs into smaller inventory sets based on different sites, campuses, etc? Or is everything on the same site with the real possibility of roaming between all 2000 APs without losing the wireless connection?

My impulse would be to go to more chassis with fewer WiSMs in them, and then one more for N+1 redundancy. For example, if it's possible to divide your wireless into 3 campuses of ~700 APs each, then you could support each campus with a 3-WiSM chassis, and then a fourth chassis as backup for all of them. This would actually save you 2 WiSMs and would keep you from running up against some of the scalability issues.

[Dominic Stalder (old profile)]

Hi gamccall

we can divide the campus into smaller RF locations because there are a lot of different buildings, which aren't "connected" over wireless. There are about 30 small buildings, would you put them into one RF group, even if they can't hear each other - because we can not create 30 RF groups?

With N+1 redundancy, don't we have the problem if 2 Cat6503 chassis go down?

[Scott Fella · Accepted solution]

One WiSM has two wlc's built in, so with 7 WiSM's, you can have 14 RF Groups and 14 Mobility Groups, since you have two chassis. You can even have more if you add another chassis. What you have to look at is how many per RF Group, since one wlc can support 150 ap's. You will have to try to break down or combine builldings to a wlc or else you might need more WiSM's. Get as many ap's on one wlc as you can. One wlc can belowng to one RF group and one mobility group. So maybe you can break it down to sections of your campus.

With N+1, you will have an issue if both chassis fail. Since you would be splitting up primary and seconday on each chassis. Never seen two chassis fail.

[rduke]

It sounds like you already have some good replies. Personally I like N+1 redundancy, but that is a designers choice. One thing I should point out is that the 6500 can only support 5 WiSM cards each. In this case a 4 WiSM x 3 chassis option would give your more spare capacity with only 12 total cards. The lower WiSM cost (12 vs 14) would help offset the cost of the extra chassis. You could also support 2400 APs with 8 WiSM cards even if one switch is down.

Not too long ago Cisco added the ability to set the priority of APs so your critical ones would join a controller and the less critical ones would go down if a controller failed and there were no redundancy. That is something to keep in mind when designing wireless. You may not need redundancy for all APs and that could affect your design and costs.

Randy

[Dominic Stalder (old profile)]

hi fella and randy

thanks for your replies. I already changed our design to 3 x Cat6k with 4 WiSM's per chassis each ;-) This approach sounds good for me and we will follow the N+1 redundancy strategy.

I already knew the AP priority feature, but as fella said, the possibility of 2 Cat6k down at the same time is very small.