Wireless Roaming using 3750Gs with OSPF Routing to the Access Layer.

[joshrathke]

We are currently redesigning a network for a small-"ish" college campus and have landed on routing to the access layer using OSPF on Catalyst 3750G switches. We use Ubiquiti Unifi Access Points and plan on keeping it that way for financial reasons. So the plan is to use OSPF to route between buildings, and have subnets local to each building along with corresponding DHCP pools.

Currently we span 3 SSIDs throughout the campus by trunking VLANs....pretty much everywhere. We have reached a point where an entirely layer 2 setup just doesn't make sense and adds more security vulnerabilities and troubleshooting black holes than we care to keep catering to.

My question is what is the best method for getting clients to roam from one building to the next without being stranded on a subnet that they don't have access to anymore? I don't care about a seamless handoff. Primarily, is there a way to nudge a client to ask for a new DHCP lease anytime they roam?

My current plan is to decrease the DHCP lease time to a minute. I know there is an overhead cost involved, but it wouldn't be enough for me to really care too much about. Are there any ways to make this process more seamless using a setting in IOS that anyone knows about?

Thanks,

[Reza Sharifi]

The new OSPF design should work fine.  In the old design you have 3 SSIDs that span across all 3 buildings and each SSID is in one IP segment.  In the new design the buildings are separated by layer-3 links (OSPF). So, you would need 3 SSIDs per building and each SSID will be in its own vlan/subnet with DHCP scopes per building. So, say you are in building 1, when you leave building 1 to go to building 2, you will release the IP that belongs to building 1 and will get a new IP when you get to building 2.

HTH

[joshrathke]

Thanks! That's the idea...but to clarify are you referring to each building having unique SSIDs per building, or 3 SSIDs that are the same all around the campus?

[Reza Sharifi]

I think you can deploy the same 3 SSIDs across all building.  This would make it simpler for the users to member which SSID they need to connect to when they go from one building to another.

I use the same SSID in buildings that are 30 miles apart. After you login once in each building, the next time you go there, there is no more login needed as the device remembers the username and password and you get connected.

HTH