Maintain layer 3 address. Changing on layer 3 address (ex. renew dhcp-client ip address) will make disconnection time longer.
● Can use flat layer 3 network for whole wireless. Check layer 2 vendor to minimise broadcast traffic
What did the writer actually mean with this?
My MikroTik router (3011) is CAPsMan server, DHCP, etc. Do I need to do anything special to keep the IPs longer?
Also, what did he mean with second point? - As flat, meaning the same subnet?
It is meant that when you have a network of APs, it is good to configure all with same SSID and that all are members of same (V)LAN served by same DHCP server.
In that case, when client switches between APs, it’ll just do mobility on radio channel, while IP settings will remain … and whatever connections going on while doing switch between APs will just proceed as if nothing happened.
If change of AP involves address renewal (i.e. if new AP has different SSID), the interruption time will be longer. If new IP address is different than old one (i.e. different DHCP server is serving AP’s clients), then all ongoing connections will break which further prolongs interruption time (some connections might not resume automatically depending on server-side connection tracking).