Security Troubleshooting and Validation
Core concepts
Troubleshoot systematically along the AAA path. For 802.1X failures, verify: supplicant config (EAP method, certs), authenticator config (RADIUS server, shared secret, NAS attributes), and ClearPass service match (conditions, method, role mapping). Use ClearPass Access Tracker to see the request, matched service, and enforcement result. Use controller/switch show commands to confirm role assignment and ACL application.
Validation
Validation means proving the control works: test authentication with valid and invalid credentials, confirm the correct role and VLAN, verify ACLs permit/deny as intended, and check that CoA changes take effect. For wireless, validate certificate trust on the supplicant to prevent evil-twin acceptance. For wired, confirm DHCP snooping bindings and DAI behavior. Packet captures (RADIUS, EAPOL) confirm the exchange.
Common failure patterns
Shared-secret mismatch → RADIUS rejects; wrong NAS-Port-Type or Calling-Station-Id → service mismatch; missing client cert → EAP-TLS failure; expired server cert → supplicant rejects; wrong enforcement profile → correct auth but wrong role. Distinguish authentication failure (rejected credentials) from authorization failure (authenticated but wrong access).
Traps to watch
A successful authentication with wrong access is an authorization/enforcement problem, not an authentication problem. Do not blame the supplicant when the Access Tracker shows a service mismatch. Remember that a role may be correct but the ACL direction wrong.
Rule of thumb
Follow the packet: EAPOL → RADIUS request → service match → enforcement → role → ACL. The first place the chain breaks is the root cause.