# Considerations for Using the LLID

The following considerations apply when you configure the router for subscriber preauthentication:

- Only PPP subscribers authenticating through RADIUS can use the AAA LLID feature on the router. PPP subscribers tunneled through domain maps cannot take advantage of this feature.
- The Calling-Station-Id [31] attribute is typically sent in RADIUS Access-Request messages, not in Access-Accept messages as is the case for this feature. As a result, your RADIUS server might require special configuration procedures to enable the Calling-Station-Id attribute to be returned in Access-Accept messages. See the documentation that came with your RADIUS server for information.
- The router ignores any RADIUS attributes other than the Calling-Station-Id that are returned in the preauthentication Access-Accept message.
- If a preauthentication request fails due to misconfiguration of the preauthentication server, timeout of the preauthentication server, or rejection of the preauthentication request by the preauthentication server, the authentication process continues normally and the preauthentication request is ignored.
- The router preserves the LLID value for established subscribers after a stateful SRP switchover.
- The radius rollover-on-reject enable command has no effect for a RADIUS preauthentication server. That is, you cannot use the radius rollover-on-reject enable command to configure the router to roll over to the next RADIUS preauthentication server when the router receives an Access-Reject message for the user it is authenticating. For information, see Configuring RADIUS AAA Servers.