Set the Maximum UDP Packet Size

Reflection supports both TCP and UDP protocols for communicating with the KDC. By default, Reflection attempts to communicate using UDP. However, if the packet size exceeds the value specified for the Maximum UDP packet size, Reflection switches to TCP (which may require more time to initiate a connection).

If you are having problems authenticating to a Windows KDC and you belong to a large number of groups, or if Use Windows logon credentials is selected, decreasing the value for Maximum UDP packet size may help. Alternatively, try increasing the setting for the Maximum UDP packet size.

To change the maximum UDP packet size

Start Kerberos Manager.
From the Configuration menu, choose Configure Realms.
From the Configuration tab, select a realm from the Realm list, and then click Properties.
On the KDC tab, specify a value for Maximum UDP packet size. To use only TCP communications, set this value to 0.