provides a mechanism for a system functioning as a Home Agent (HA)
to communicate status information to a properly configured RADIUS
server. The status information is used by the RADIUS server to determine
the availability and readiness of the HA to accept Mobile IP (MIP)
subscriber sessions. The RADIUS server\'s awareness of the
HA status allows it to dynamically assign immediately available
HAs to subscriber sessions.
When a RADIUS server
assigns an HA to a Mobile Node (MN), it is very important that only active,
or accessible, HAs are selected for the assignment. Therefore, it
is necessary for the RADIUS server to detect the availability of
each HA before assigning it to an MN. This feature allows the RADIUS
server to gather and maintain a list of available HAs through a
detection mechanism that provides frequent updates.
With this feature,
bogus authentication messages, called probe authentication messages,
are exchanged between the RADIUS server and the HA. The HA periodically
sends Access-Request messages to the RADIUS server. The RADIUS server
distinguishes the probe authentication request from other regular
subscriber authentication messages, validates them, and sends proper response.
The probe Access-Request
contains the following attributes and expects an Access-Accept from the
User-Name = Probe-User
User-Password = 18 7F 88 02 82 1D B6 F6 70 48 B9 A1 4C 92 C3 3E
NAS-IP-Address = 188.8.131.52
Service-Type = Authenticate_Only
Event-Timestamp = 1255598429
User-Name and User-Password
are configurable in the system.
If an Access-Accept
message is sent in response to the probe authentication request,
the RADIUS server updates the status of the HA as active. If an
Access-Reject message is sent, the RADIUS server updates only the
statistics without any further action. If the RADIUS server misses receiving
a configured number of probe authentication requests, the HA, and
all of its associated IP addresses, is marked as down, or inaccessible.
When an HA is marked as down, a backup HA and its associated IP
addresses are made active and used for assignment in the place of
the inaccessible HA.