The Hidden Authentication Protocol
In a large corporate environment running Windows Active Directory, you do not actually log into every single server or file share individually. When you log into your laptop in the morning, a central Domain Controller verifies your password and hands your computer a hidden digital passport. This passport is called a Kerberos Ticket.
Whenever you try to access a restricted network folder or a secure intranet website, Windows silently flashes this Kerberos Ticket to the server. If the ticket is valid, you are granted instant access without ever seeing a password prompt. This seamless experience is called Single Sign-On (SSO).
However, these tickets expire (usually after 10 hours). If a ticket expires, or if your IT department recently changed your network permissions but your computer is still holding onto an old ticket, you will suddenly be denied access to files you normally use every day. To diagnose these authentication failures and force Windows to request new passports, you must use the klist (Kerberos List) command.
Step 1: Open the Command Prompt
You can run this command as a standard user, because you are only querying the tickets assigned to your specific user account.
- Press the Windows Key, type
cmd. - Press Enter.
Step 2: Viewing Active Kerberos Tickets
To see every single digital passport your computer is currently holding, simply run the command with no additional flags.
klist
The terminal will output a list of your cached tickets. You will usually see a primary “Ticket Granting Ticket” (TGT), which is your master passport, followed by several specific service tickets (e.g., a ticket specifically for accessing the FILE-SERVER-01).
For each ticket, the output will clearly display the StartTime and the EndTime. If you are being denied access to a server, checking the EndTime instantly tells you if your ticket has simply expired.
Step 3: Purging the Ticket Cache
If an IT administrator just granted you access to a highly restricted HR folder, you will not be able to open it immediately. Your computer is still attempting to use the old Kerberos ticket it acquired three hours ago, which does not contain the new HR permissions.
Normally, you would have to completely log out of Windows and log back in to force the system to fetch new tickets. Instead, you can use the purge flag to instantly destroy all your old tickets without logging out.
klist purge
The terminal will delete every cached ticket in memory. The very next time you click on the restricted HR folder, Windows will realize it has no ticket, silently contact the Domain Controller in the background, fetch a brand new ticket containing your updated permissions, and instantly grant you access.
Step 4: Querying Specific Servers
If you are a system administrator troubleshooting a highly specific connection issue, you can ask the Domain Controller for a Kerberos ticket for a specific server to see if the authentication protocol is actually working.
Use the get flag, followed by the Service Principal Name (SPN) of the target server.
klist get host/FILE-SERVER-01.corp.example.com
If Kerberos is functioning correctly, the command will successfully fetch the ticket and cache it. If the server is misconfigured in Active Directory, the command will instantly throw a specific Kerberos error code, proving the problem is with the domain configuration, not the user’s password.