The below is from the help file. To me this is a configurable parameter when Layer 3 roaming comes into play. To optimize and/or speed up roaming of Layer 3 (IP) boundaries. And not necessarily relevant to your current issue.
From the help file:
In the Roaming Configuration section, you can define the hive members to which you want other hive members to send Layer 3 roaming-related information (Included Neighbors) and those to which you do not want APs to send such information (Excluded Neighbors). Note that included and excluded neighboring hive members must have static IP addresses for this feature to work properly.
Roaming Threshold
Set the volume of traffic that the selected neighbors will accept through GRE (Generic Routing Encapsulation) tunnels to support Layer 3 roaming. This option gives hive members the ability to push tunnels to other members for better tunnel load balancing. For example, if one AP near an entrance gets overloaded with tunnels, you can lower its threshold to medium or low so that more tunnels terminate on other APs.
- This setting only takes effect when the APs function as portals and Layer 3 roaming is enabled.
From the Tunnel Threshold drop-down list, choose a level determining the amount of traffic that the selected APs will accept through GRE tunnels. To accept a relatively low number of tunnels, choose Low. To accept a relatively moderate number of tunnels, choose Medium. To accept a relatively high number of tunnels, choose High. The default setting is High.
Included Neighbors
Because basic hive communications occur within a Layer 2 broadcast domain, to span subnets, at least one hivemember in each subnet must be able to detect another member in the other subnet. If hive members in different subnets are within radio range from each other, they can discover each other automatically. If hive members in different subnets are out of radio range from each other, you can define them as neighbors to each other. A hivemember defined as a neighbor exchanges roaming cache information with all hive members outside its subnet. Wireless clients can then roam between the defined neighbor and any hive member in the other subnet.
- APs that you want to include or exclude as neighbors for Layer 3 roaming must have static IP addresses.
To add an AP in the list of included neighbors, select the AP name in the Available Neighbors column, and then click the right arrow ( > ) to move it to the Selected Neighbors column. Repeat this to add more neighbors. You can add up to 32 neighbors.
To remove an AP name from the Included Neighbors list, select the AP name in the Selected Neighbors column, and then click the left arrow ( < ) to move it back to the Available Neighbors column.
- You can select multiple APs by SHIFT-clicking to select multiple contiguous items and CTRL-clicking to select multiple noncontiguous items. You can also move all the APs from one column to the other by clicking >> and <<.
Excluded Neighbors
There might be a case where you do not want a hive member to exchange roaming cache information with other members in a different subnet. If so, add them to this list. Even if the excluded neighbor is within range of another hivemember in a different subnet, they will not exchange roaming caches.
To add an AP to the list of excluded neighbors or remove it from the list, follow the same procedure explained above for adding and removing included neighbors.
