Bridge mode vs L3 roaming

[bkoch]

I recently acquired the administration of our wireless network.  We have approximately 175 access points within our main campus.  The access points are all on the same VLAN.  We are using tags to distributed the wireless clients across 5 other VLANs.  DHCP is done on the wired network.  The old administrator has L3 roaming configured.  But, from what I am reading I believe that bridge mode may be best for our situation.  Can someone tell me which is correct and why?

[cmr]

@bkoch L3 roaming is only needed, or even wanted, when one SSID has multiple IP subnets / VLANs underneath.

If all of your APs put clients in SSID 1 into VLAN 5 and the IP subnet is always the same then you want bridging. 

If some APs put clients in SSID1 into VLAN 5 and others into VLAN 7, or they have different IP subnets from the different APs, then you want L3 roaming.

L3 roaming is ONLY for this case, otherwise bridge mode will be better, especially for roaming clients. 

[AugustoLozano]

Hi @cmr 
What is the impact of changing from L3 roaming to bridge mode?
Can I make this change during the operation, or would it be better in a scheduled window?
Important to know: The SSID I want to change is not vital to my operation. Some interruption would be acceptable, as long as it is small.

Thank you in advance for your help!

[cmr]

If the SSID goes back to the same subnet and VLAN for all APs then the impact should be short.  I'd expect all clients would need to reconnect, but this should be quick.  To be safe though I'd always schedule something like this for a change window or at least a quiet time.

[CFStevens]

Hey @bkoch ,

User cmr is absolutely correct in regards to the reasoning behind why one would use L3 roaming or not. To expand on that, L3 roaming causes a bit of overhead and latency, but not nearly as much overhead and latency as if you were to not be using it in a situation where different SSIDs were mapped to different subnets. Without L3 roaming turned on, clients would be given new IP addresses whenever they roam, which will cause many disruptions on the client end (think dropped calls, packet loss, etc) in an environment where different APs are assigning IP addresses out of different pools for the same SSIDs. 

With L3 roaming, whatever AP your client initially connects to will be its designated “anchor AP”. All subsequent roams will tunnel traffic back to this anchor AP so the client device can keep it’s original IP address. This is less jarring than getting a brand-new IP, but it still introduces an additional layer of processing power and latency.

If L3 roaming isn’t needed (which it doesn’t appear to be in your case), it is highly recommended that you disable this feature.