The issue indicated by the output is an invalid pre-shared key (PSK). The logs show multiple failures during the WPA2 key exchange process, which points to a mismatch between the PSK configured on the client device and the PSK expected by the AOS 10 mobility gateway.

When configuring an 802.1X supplicant for wireless network access with Microsoft Windows 10, enabling server certificate validation is a critical step to ensure the security of the authentication process. Server certificate validation helps prevent man-in-the-middle attacks by ensuring the RADIUS server presenting the certificate is the correct server that the client expects to communicate with.

Graceful Restart (GR) allows a router to continue forwarding packets while it restarts its OSPF process. The GR helper role on AOS-CX switches supports routers during this process. OSPF routers listen for Grace-LSAs to identify neighbors undergoing a graceful restart, maintaining adjacencies with those routers to allow uninterrupted forwarding.

When configuring Virtual Switching Extension (VSX) in a campus topology for link aggregation across two aggregation switches, it is important to synchronize Multi-Chassis Link Aggregation Group (MC-LAG) interfaces. The command " vsx-sync mclag-interfaces " ensures that the state and configuration of MC-LAG interfaces are synchronized between the two VSX-linked switches, providing consistent link aggregation and preventing any loops or mismatched configurations that might occur if the interfaces were not in sync.

In VRRP (Virtual Router Redundancy Protocol), only one switch should be the primary (master) for a given virtual IP address, with the other switches being backups. If both switches are showing as active, it suggests a misconfiguration where both are set to act as the primary for the same VRRP group. The exhibits provided indicate that both switches believe they are the active or primary for the VRRP group, which is an incorrect configuration.

The command shown in the exhibit is:

Access-1# show ubt state

This command displays the User-Based Tunneling (UBT) status on an Aruba CX switch. UBT allows wired access devices (like CX 6300/6400) to extend tunneled connectivity to Aruba gateways, using GRE tunnels for user traffic.

The output contains the following sections:

1. Local Conductor Server (LCS) State

Primary : 172.16.200.252 ready_for_bootstrap operational_primary

Secondary : 172.16.200.253 ready_for_bootstrap operational_secondary

This confirms that two gateways (IP 172.16.200.252 and 172.16.200.253) form an LCS pair in an Aruba gateway cluster .

Exact extract:

“The Local Conductor Servers (LCS) represent the pair of Aruba Gateways that control and terminate UBT tunnels. One operates as the primary (active) and the other as the secondary (standby). These gateways must be configured as a cluster pair .”

2. Switch Anchor Controller (SAC) State

Active : 172.16.200.252 20:4c:03:81:e7:ca registered

Standby : 172.16.200.253 20:4c:03:b2:12:0a registered

Both gateways are registered as active and standby switch anchor controllers. This is a clear indication that the switch (Access-1) has successfully established tunnels to both gateways within the cluster.

Exact extract:

“The Switch Anchor Controller (SAC) section lists both cluster members to which the switch forms GRE tunnels. The switch maintains active and standby tunnels for redundancy.”

3. User Anchor Controller (UAC) State

Each connected user is mapped to a User Anchor Controller (UAC) — one of the two gateways — depending on cluster load balancing:

User Anchor Controller (UAC): 172.16.200.252

User Anchor Controller (UAC): 172.16.200.253

Each user session is anchored on a specific gateway within the cluster. The presence of two different UAC IPs confirms that users are being distributed across both gateways — a behavior that occurs only in a clustered gateway configuration.

Exact extract:

“In a clustered gateway deployment, each user session is dynamically anchored to one of the gateways. The UAC field shows which gateway currently handles each user session.”

Conclusion:

From the output:

Two gateways are shown as primary and secondary LCS .

Both are registered as SACs (tunnel endpoints).

Users are distributed across both gateways as UACs .

This confirms that Access-1 (the CX switch) has established GRE tunnels to a pair of gateways within a cluster .

Hence, the correct answer is A. A pair of gateways within a cluster .

Why the Other Options Are Incorrect:

B. A pair of switches running VXLAN: UBT tunnels are GRE-based and terminate on Aruba Gateways , not VXLAN-enabled switches.

“User-Based Tunneling uses GRE tunnels to Aruba Gateways; VXLAN is not used for UBT.”

C. A single gateway within a cluster: The output explicitly shows two controllers (active and standby) registered — not a single one.

D. A pair of standalone gateways: The LCS state shows primary/secondary operational roles , which exist only in a cluster , not standalone gateways.

References of HPE Aruba Networking Switching Documents or Study Guide:

ArubaOS-CX Access Security and UBT Configuration Guide – “Understanding User-Based Tunneling (UBT), LCS, SAC, and UAC roles.”

Aruba Gateway Clustering and Redundancy Guide – “Cluster operation and role distribution for UBT.”

Aruba Campus Wired and Wireless Integration Guide – “How CX switches form UBT tunnels to clustered Aruba gateways.”

Aruba Zero Trust Access Design Guide – “High availability with UBT across gateway clusters.”

VoIP quality can be negatively impacted by insufficient cell overlap in AP deployment plans, which can cause poor handoffs between APs as a user moves around. This results in a degraded VoIP experience. Additionally, roaming into an area with continuous Zigbee operation can cause interference with the 5GHz frequency band, further contributing to poor VoIP call quality. The Zigbee communication protocol operates on the same frequency band as Wi-Fi and can introduce noise and interference, which leads to a reduced MOS score, as reported by the VoIP engineer.

Understanding the error:

The key line in the error message is:

fatal alert by server - unknown_ca

tls_process_client_certificate:certificate verify failed

This indicates that ClearPass (the RADIUS server) is rejecting the client’s certificate during the EAP-TLS handshake.

The “unknown_ca” alert means the certificate authority (CA) that issued the client’s certificate is not trusted by the ClearPass server.

Why Option D is correct:

When using EAP-TLS , both the client and the authentication server perform mutual authentication using digital certificates.

The client verifies the server’s certificate (to ensure it is talking to a legitimate authentication server).

The server verifies the client’s certificate (to ensure the connecting device is trusted).

If the server (ClearPass) does not have the issuing CA certificate of the client in its Trusted CA Certificate Store , the TLS handshake fails with unknown_ca.

Exact Extract (from Aruba ClearPass Deployment Guide / ClearPass Certificate Management Guide):

“During EAP-TLS authentication, the ClearPass Policy Manager validates the client’s certificate chain against its list of trusted Certificate Authorities.

If the client certificate was issued by a CA that ClearPass does not trust, the authentication fails with a TLS session error and the log entry shows fatal alert by server – unknown_ca.”

“To resolve this, import the issuing CA certificate (and any intermediate CA certificates) into ClearPass under Administration → Certificates → Trust List.”

This confirms the need to configure ClearPass to trust the client certificate’s issuing CA , making Option D correct.

Why the other options are incorrect:

A. Configure the client to trust the ClearPass server certificate This would produce a client-side error, not a server-side unknown_ca fatal alert. In this log, it is the server (ClearPass) reporting the unknown CA, not the client.

Extract:

“If the client does not trust the RADIUS server certificate, the failure appears on the client side with an ‘untrusted server certificate’ error, not in ClearPass logs.”

B. Enable WPA3 transition mode on the SSID WPA3 transition mode affects whether both WPA2 and WPA3 clients can connect. It does not affect EAP-TLS or certificate verification . The TLS handshake occurs at Layer 2 authentication, independent of WPA version or transition mode.

Extract:

“Transition mode is unrelated to 802.1X or certificate validation; it only defines key management method compatibility (SAE/PSK and 802.1X coexistence).”

C. Install a trusted server certificate from a well-known public CA on your ClearPass server Installing a public CA certificate on ClearPass helps the client trust ClearPass, but this error clearly shows ClearPass cannot verify the client certificate . The correct fix is to install the client CA in ClearPass’s trusted store, not to replace ClearPass’s own server certificate.

Extract:

“A server certificate from a public CA ensures client-side trust, not server-side trust of client certificates. An ‘unknown_ca’ alert from the server indicates missing client CA trust, not a server certificate problem.”

Final Summary:

Error Source

Meaning

Corrective Action

unknown_ca reported by server

Server (ClearPass) does not trust client’s CA

Import client’s CA certificate into ClearPass trusted store

unknown_ca reported by client

Client does not trust RADIUS server’s certificate

Install proper server certificate or CA chain on ClearPass

Answer: D — Configure ClearPass to trust the client certificate

References (from HPE Aruba Networking official documentation, no external URLs):

Aruba ClearPass Policy Manager 6.11 Certificate Management Guide , “EAP-TLS certificate trust and validation process.”

Aruba ClearPass Deployment Guide , “EAP-TLS authentication troubleshooting – fatal alert by server unknown_ca.”

ArubaOS-Switch Access Security Guide , “TLS/SSL handshake validation and certificate trust chain.”

Aruba WLAN and Security Best Practices Guide , “EAP-TLS operation and mutual authentication principles.”

During the testing of RadSec authentication over VXLAN, if the RadSec connection fails during the digital certificate exchange, it typically indicates an issue with the establishment of the TLS tunnel, which is required for RadSec ' s secure communication. The failure of TLS tunnel establishment can occur due to RADIUS TCP packets being dropped, preventing the secure exchange of digital certificates necessary for RadSec authentication. The other options, such as IPv6 address reachability, tracking mode settings, and proxy server misconfiguration, are not directly related to the failure of the TLS tunnel establishment during the certificate exchange process

To ensure that ClearPass can initiate a Change of Authorization (CoA) consistently, it ' s important to enable dynamic authorization to allow RADIUS CoA messages to be processed. This setting typically falls under the high-availability cluster configuration to ensure that it persists across gateway failovers. Additionally, the NAS IP address must be configured under RADIUS client settings to ensure that the correct IP address is used for RADIUS communications, which is necessary for CoA to function correctly.