# Duplicate IPv6 Prefix Check Overview

You can configure AAA service to detect duplicates of IPv6 Neighbor Discovery router advertisement prefixes and DHCPv6 delegated prefixes. If a non-unique IPv6 prefix is detected by AAA, the subscriber session corresponding to the duplicate prefix is terminated.

In some network environments where the same customer logs in from multiple locations, terminating sessions with duplicate IPv6 prefixes might result in breaking subscriber setup. The duplicate IPv6 prefix-check capability is disabled by default.

If a duplicate prefix is detected by AAA before a subscriber is granted access, the subscriber is denied access. However in some cases, when two subscribers having the same IPv6 prefix log in simultaneously, the duplicate might be detected only after access is granted to both subscribers. AAA terminates the duplicate subscriber session immediately upon detecting the duplicate IPv6 prefix.

| Note: AAA cannot detect duplicates of overlapping IPv6 prefixes.

#### Related Documentation

- Configuring Duplicate IPv6 Prefix Check
- Configuring Standard RADIUS IPv6 Attributes for IPv6 Neighbor Discovery Router Advertisements and DHCPv6 Prefix Delegation