Setting up a multi-floor wifi guest access

Question

i just graduated from a CS bachelor so while i'm familiar with networking, i never deployed an actual "business" network before, and i was just asked to provide wifi guess access to a 16-floors building. The most important perks i have to deliver are a captive portal and the ability to roam in the whole building. Each floor has ~23 rooms, so on the worst case scenario i expect 1500 concurrent users. The internet connection is not my business, they will provide it and give me access to it.

About the configuration:

• Each floor will have 4 Access Points. I'm thinking of using Dlink 6600AP. (~ 70 APs in total)
• There will be one switch every 3 floors which the APs will use to connect to the ground floor. I'm thinking of using MikroTik CRS226-24G-2S+RM
• On the ground floor there will be:
  • a switch that will be connected to the other switches distributed on the other floors via optic fiber
  • An Access Gateway Controller combined to an appliance which will provide the captive portal funcionality/syslog/radius server. I'm thinking of using a MikroTik routerboard RB1100ahx2 configured as hotspot. The routerboard should be the DHCP server.
  • 2 Dlink DWS-3160 (Wireless Controller) to manage the APs

I'd like to keep everything on the same subnet (a /16).

Now some questions:

1. Will the routerboard handle 1500 concurrent users? One person i spoke to strongly suggested to use 3 RB1100ahx2 instead of just 1, everyone of them setup as an Hotspot. Wouldn't that mean that i should segment the network into 3 subnets?Doesn't that give problems when roaming (both because of different subnets and because connecting to a different hotspot, even if configured in the same manner)?
2. If i use 3 routerboards, can i do it without splitting up into 3 subnets?If yes, how?
3. In case i use a single subnet, is setting up the same SSID and Authentication enough to enable roaming?

Thanks everyone!

Answer 1

My comments are turning into an answer, so here's some thoughts:

1. DLink is a terrible idea, I can't say enough bad things about their equipment.

   MikroTik can probably handle this, but they're off in the DIY land more than Professional (supportable, maintainable, etc). If I were doing this on a shoestring budget I'd be looking for some used ProCurve MSM422 APs (208.11n, <$50 typically), a MSM730 Mobility Controller for seamless roaming, and 3500yl-24G switches (if you're looking for 24 port switches, which sounds reasonable), about $8,000 total with what I could get right now. Everyone has their favorite vendor, ProCurve is mine. I've heard great things about Aruba and Cisco (we used to have Cisco WiFi, only switched because of price).

2. Using one subnet should work fine with good equipment. Just setup a /21 and call it good. If those are going to be different users in a somewhat short amount of time, make sure the DHCP lease is about 1/3 of the turnover time (ie, if there are different people ever day then 1/3 of that is an 8 hour lease). You don't want your DHCP range to get exhausted.

3. There are different kinds of roaming. If you have the same SSID and Auth then clients can connect from AP to AP automatically. This is roaming at it's most basic. Any TCP sessions will be cut during the roam. So if they're Skyping or have a Remote Desktop session open, it will be disconnected (many services automatically reconnect, so this might not be obvious to the user).

   If you want seamless roaming then you need some kind of AP mobility. SOHO APs don't support mobility (at least none that I've seen). Business-grade APs usually do, though I've seen some that claim to be business-grade that don't, generally super cheap models.

   Of the APs that support mobility, some have the functionality built-in and do distributed mobility, others need a mobility controller. In general the distributed mobility will have lower limits as to how many APs can participate in a service network (usually a few dozen). Using separate mobility controllers generally scales into the hundreds of APs.

   Also, business-grade APs will have important features, like band-steering, foreign network suppression, auto-channeling, auto-power backoff/scaling, DHCP Filtering, multiple SSID, vLAN support, etc (just the security and performance features I could think of off the top of my head).

I can't stress enough: Hire a professional consultant who's setup wireless networks before. You're already heading down the road of unsupportable and unlikely to work well. This stuff ain't easy.