Thanks fyi for your answer!
It was really useful. I've got a partially roaming:
I've changed all channel and set the same lan ip address of every AP in the building and now if I go from one floor to another it reconnects automagically. It tear down the tcp connections, but at least ir reconnects automatically!
Now, I've noted that the main problem was that station (when every A had different lan IP) looked for the previous AP IP address, but it did the roaming, I don't understand why is the dhcp independent from roaming?
Below you have the messages on the STA before LAN IP change:
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Jun 7 10:11:33 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: 4-way handshake -> completed
Jun 7 10:12:23 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: completed -> authenticating
Jun 7 10:12:23 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
Jun 7 10:12:23 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: authenticating -> associating
Jun 7 10:12:23 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associating -> associated
Jun 7 10:12:26 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associated -> 4-way handshake
Jun 7 10:12:26 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
Jun 7 10:12:26 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: 4-way handshake -> completed
Jun 7 10:12:27 peque NetworkManager[770]: <info> (wlan0): roamed from BSSID D8:5D:4C:AE:40:D4 (UP-PVIII-I) to 00:25:9C:14:06:6E (UP-PVIII-I)
Jun 7 10:13:08 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: completed -> authenticating
Jun 7 10:13:08 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
Jun 7 10:13:08 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: authenticating -> associating
Jun 7 10:13:08 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associating -> associated
Jun 7 10:13:08 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associated -> 4-way handshake
Jun 7 10:13:08 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
Jun 7 10:13:08 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: 4-way handshake -> completed
Jun 7 10:13:09 peque NetworkManager[770]: <info> (wlan0): roamed from BSSID 00:25:9C:14:06:6E (UP-PVIII-I) to 00:23:69:49:09:BF (UP-PVIII-I)
Jun 7 10:13:22 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: completed -> authenticating
Jun 7 10:13:23 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
Jun 7 10:13:23 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: authenticating -> associating
Jun 7 10:13:23 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associating -> associated
Jun 7 10:13:26 peque NetworkManager[770]: <info> (wlan0): supplicant interface state: associated -> 4-way handshake
Jun 7 10:13:26 peque lldpad[1030]: vdp_ifup:wlan0 vdp data already exists !
thanks in advance!