enable address_binding roaming
Purpose
This command is used to enable the IMPB roaming.
Format
enable address_binding roaming
Description
This command is used to enable the IMPB roaming. By default, roaming state is enabled.
Station Move: A client is marked as Station Move when a client packet’s L2 source VID+MAC match one IMPB entry, and the receive port is different with the IMPB entry. A client is distinguished by VID+MAC. If MAC is same, but VID is not same as IMPB entries, it’s not Station Move.
Roaming: When the client was authenticated on the specific port under DHCP (include IPv4 and IPv6)/ND snooping function, Switch will allow this authenticated client to change to another port if it detects a new DHCP/ND process to cause Station Move. This kind of behavior we define it as roaming.
IMPB roaming behavior:
1. For static entry: Switch will not allow changing learning port no matter roaming is enabled or disabled, and packets from other ports will be dropped.
2. For dynamic entry: Whether the roaming state is enabled or disabled, if Switch detects a new DHCP/ND process to generate a Station Move from the IMPB disable port to an IMPB enabled port, the entries with same VID+MAC on the original port will be deleted, and a new entry will be added via the DHCP/ND process on the new port.
3. For active dynamic entry: If the roaming state is disabled, Switch will not allow the entry changing learning port until it’s aged out, and the traffic from this client via the new port will be dropped.
4. For active dynamic entry: If the roaming state is enabled, and Switch detects a new DHCP/ND process with same VID+MAC address from the IMPB enabled port, Switch will delete the entries with same VID+MAC on the original port, and add a new entry via the DHCP/ND process on the new port.
5. For inactive dynamic entry (When the port link down, all entries learned on this port will change status from active to inactive.): Whether the roaming state is enabled or disabled, if Switch detects a new ND/DHCP process with same VID+MAC address from the IMPB enabled port, Switch will delete the inactive entries with same VID+MAC on the original port and add a new entry via the DHCP/ND process on the new port.
6. For inactive dynamic entry: If roaming state is enabled, and Switch detect IP/ARP packets with same VID+MAC +IP from the IMPB enabled port, the inactive entries with same VID+MAC on the original port will be deleted and an active entry with the VID+MAC+IP will be added on the new port.
7. For inactive dynamic entry: If roaming state is enabled, and Switch detects IP/ARP packets with same VID+MAC, but different IP from the IMPB enabled port. Switch will drop packets on the new port and do nothing.
*Note 1:
If the roaming is enabled, and a new DHCP/ND procedure belong to same VID+MAC is detected from another port, all of the original DHCP, DHCPv6 and ND entries will be deleted, and then create the new roaming entry. In other word, IPv4 DHCP roaming may lead the IPv6 entry deleted.

Правильно ли я понимаю, что теперь возможна миграция связки ип+мак с порта на порт, причем данная "фича" включена по дефолту?

заодно спрошу как работает download address_binding snoop_entry_fromTFTP ?

This command is used to download the DHCPv4 snooping binding entries from TFTP server. You can recover the DHCPv4 snooping database when reboot the device.
Constraints when downloading DHCP snooping bind entries:
 If IMPB is disabled, the download binding entries can not be performed
 If DHCP snooping is disabled, the download binding entries can not be performed
 The binding entry will be discarded if the data integrity check failed.
 The binding entry will be discarded if the entry does not match IMPB configuration (sucah as port, VLAN… configuration).
 The binding entry will be discarded if the entry is conflict with current binding table.
 The binding entry will be discarded if the entry is already existed.
 The binding entry will be disacrded if the hardware resource is not available.
 The left time of the binding entry will be recorded when uploaded and restore while the entry is downloaded.
 The lease time of the entry will not be modified and the live time will be continued to count while the entry is provisioned.