Kerberos is a network authentication protocol that uses secret-key cryptography to authenticate client-server applications and securely exchange information. It is commonly used in enterprise networks to provide secure communication and access control.

Advanced Troubleshooting of Kerberos Problems with Wireshark: 5 Real-World Case Studies

Kerberos is a widely-used authentication protocol, but when issues arise, it can be challenging to pinpoint the root cause. In this article, we delve into five real-world case studies that demonstrate how to troubleshoot and resolve common Kerberos problems using Wireshark.

Kerberos is a critical authentication protocol in many enterprise environments, ensuring secure communication between clients and servers. However, when problems arise, it can be challenging to identify the exact issue. In this article, we'll explore five real-world case studies of advanced troubleshooting of Kerberos problems with Wireshark, the popular network protocol analyzer.

Case Study 1: Slow Authentication

In this case, users were experiencing slow authentication when accessing a file server. By capturing the network traffic with Wireshark, we identified an excessive number of Kerberos Error packets, indicating that the client was repeatedly attempting to authenticate. Further analysis revealed that the client's clock was significantly out of sync with the server, causing the authentication attempts to fail. By correcting the client's time settings, we resolved the issue.

Wireshark Tip: Use the display filter kerberos.msg_type == 30 to focus on Kerberos Error packets.

Case Study 2: Service Ticket Issues

A client was unable to access a particular service, despite having a valid ticket-granting ticket (TGT). Examining the Wireshark capture, we noticed that the client was requesting a service ticket for an incorrect Service Principal Name (SPN). The issue was resolved by correcting the client's configuration to use the proper SPN.

Wireshark Tip: Use the display filter kerberos.TGS_REP to focus on Ticket-Granting Server (TGS) replies.

Case Study 3: Expired Tickets

Users reported intermittent authentication failures when accessing various services. Analyzing the network traffic with Wireshark, we observed that some Kerberos tickets had expired. It turned out that the ticket lifetime settings on the clients and the server were not aligned, causing premature ticket expiration. By adjusting the ticket lifetime settings to match, the issue was resolved.

Wireshark Tip: Use the display filter kerberos.AP_REP to focus on Application Server (AS) replies containing ticket lifetimes.

Case Study 4: Encryption Type Mismatch

In this scenario, a client was unable to authenticate to a server using Kerberos. By examining the Wireshark capture, we discovered that the client and server were using different encryption types. After updating the client's configuration to support the required encryption type, the authentication issue was resolved.

Wireshark Tip: Use the display filter kerberos.encryption_type to focus on the encryption types used in Kerberos communication.

Case Study 5: Duplicate SPNs

A service was inaccessible to users, and the Wireshark capture revealed numerous Kerberos Error packets with the KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN error code. Upon further investigation, we discovered that two service accounts had the same SPN, causing a conflict. By correcting the duplicate SPN, the issue was resolved.

Wireshark Tip: Use the display filter kerberos.error_code to focus on specific Kerberos error codes.

By understanding Wireshark's powerful features and learning from these real-world case studies, you can effectively troubleshoot and resolve complex Kerberos issues. To further enhance your packet analysis skills, be sure to check out our online PCAP analyzer, PacketSafari (https://app.packetsafari.com), and our training course, WIRED for Packet Analysis (https://oripka.de/en/wired/).