PacketFence

PacketFence is a fully supported, trusted, Free and Open Source network access control (NAC) system. Boasting an impressive feature set including a captive-portal for registration and remediation, centralized wired and wireless management, 802.1X support, layer-2 isolation of problematic devices, integration with the Snort IDS and the Nessus vulnerability scanner; PacketFence can be used to effectively secure networks - from small to very large heterogeneous networks.
PacketFence