Troubleshooting Kerberos Errors
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This white paper can help you troubleshoot Kerberos authentication problems that might occur in a Microsoft® Windows Server™ 2003 operating system environment. It outlines some simple troubleshooting basics and explains the causes of common Kerberos errors. It also summarizes common tools used to troubleshoot problems with Kerberos authentication.
To troubleshoot Kerberos authentication, you need to understand how Kerberos authentication interacts with its supporting technologies (such as Active Directory® directory service and time servers) as well as how the Kerberos authentication process works. With that understanding, you can use specific diagnostic tools to find answers to specific questions, and to identify and resolve problems.
This white paper does not provide detailed information about Kerberos authentication or its supporting technologies, but does provide references to that information.
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Introduction
The Kerberos V5 protocol assumes that transactions between clients and servers take place on an open network, in which packets transmitted along the network can be monitored and modified at will. The assumed environment, in other words, is very much like today’s Internet, where an attacker can easily pose as either a client or a server, and can readily eavesdrop on or tamper with communications between legitimate clients and servers.
Microsoft’s implementation of the Kerberos V5 protocol is the default authentication package for Windows Server 2003. The Kerberos V5 protocol became the default authentication package with Windows 2000. Windows Server 2003 still supports NTLM for non-Kerberos clients such as the Windows NT® Server 4.0 operating system.
Infrastructure Requirements
Problems with Kerberos authentication often involve technologies on which the Kerberos SSP depends, or stem from easy-to-correct oversights in the configuration of Kerberos settings. This section reviews these dependencies and summarizes how they relate to troubleshooting Kerberos authentication.
Active Directory Domain
Kerberos authentication is not supported in earlier operating systems such as Windows NT. For more information about the Active Directory® directory service, see “Active Directory Collection” on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=25389.
TCP/IP Network Connectivity
For Kerberos authentication to occur, there must be TCP/IP network connectivity between the client and the domain controller(s), and the client and the target server. Issues that can affect network connectivity include:
| • | Firewalls. If you use a firewall, be sure that the Kerberos ticket-granting service ports (TCP port 88, UDP port 88) are enabled on the network. TCP and UDP Ports Required for Correct Operation of the Kerberos Protocol
For more information about ports domain controllers use, see “A List of the Windows Server Domain Controller Default Ports” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=22894. For more information about TCP/IP, see “TCP/IP Technical Reference” on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=25392. | |||||||||||||||
| • | Cached credentials. A user who can log on with cached credentials might not be aware of a connectivity issue. |
Domain Name System
The client uses the fully qualified domain name (FQDN) to access the domain controller. In order for the client to obtain the FQDN, DNS must be functioning. For best results, do not use host files with DNS. For more information about DNS, see “Deploying DNS” in the Microsoft Windows Server 2003 Deployment Kit at http://go.microsoft.com/fwlink/?LinkId=23041.
Time Service
For Kerberos authentication to function properly, it is vital that the time on all of the computers on a network be synchronized — that is, that all of the domains and forests in a network are using the same time source. An Active Directory domain controller will act as an authoritative source of time for its domain, which guarantees that an entire domain will have the same time. For more information, see “Windows Time Service Technical Reference” on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=25393.
Operating System
Kerberos authentication relies on client functionality that is built in to Windows 2000, Windows Server 2003, and the Microsoft Windows® XP operating system. If a client, domain controller, or target server is running an earlier operating system, it cannot use Kerberos authentication natively.
Troubleshooting Strategies
As with most technologies, the better you understand how Kerberos authentication should work and how to confirm whether it is being used, the better you can isolate a problem and determine a solution.
Kerberos Authentication Basics
Kerberos authentication provides a mechanism for mutual authentication between a client and a server on an open network, and in which packets transmitted along the network can be monitored and modified at will. In order to provide secure authentication, Kerberos authentication uses symmetric keys, encrypted objects, and Kerberos services.
Keys
Kerberos authentication relies on different types of keys:
| • | User, service, and system keys. Long-term symmetric keys generated from passwords. |
| • | Public keys. Long-term asymmetric keys used with smart cards. |
| • | Session keys. Short-term symmetric keys created by domain controllers. |
Tickets
The main component in Kerberos authentication is the ticket. Essentially, the goal of Kerberos messages is to request and deliver tickets. There are two types of tickets used in Kerberos authentication, ticket-granting tickets (TGTs) and session tickets:
| • | TGT. The KDC responds to a client’s authentication service request by returning a session ticket for itself. This special session ticket is called a ticket-granting ticket (TGT). A TGT enables the authentication service to safely transport the requestor’s credentials to the ticket-granting service. |
| • | Session ticket. A session ticket allows the ticket-granting service (TGS) to safely transport the requestor’s credentials to the target server or service. |
Key Distribution Center
To solve the problem of key distribution, the Kerberos protocol, similar to its namesake in Greek mythology, uses three “heads” — a client, a server, and a trusted third party that mediates between the other two.
The trusted intermediary in the protocol is the Key Distribution Center (KDC).The KDC is a service that runs on a physically secure server. The KDC maintains a database with account information for all security principals in its realm (the Kerberos equivalent of a Windows Server 2003 domain). Along with other information about each security principal, the KDC stores a cryptographic key known only to the security principal and the KDC. This key is used in exchanges between the security principal and the KDC.
As in other implementations of the Kerberos protocol, Microsoft implements the KDC as a single process that provides two services:
| • | Authentication service (AS). The AS issues TGTs good for admission to the ticket-granting service in its domain. Before network clients can get tickets for services, each client must get an initial TGT from the AS in the user’s account domain. |
| • | Ticket-granting service (TGS). The TGS issues tickets good for admission to other services in the TGS’s domain or to the ticket-granting service of a trusted domain. When a client wants access to a service, it must contact the ticket-granting service in the service’s account domain, present a TGT, and ask for a ticket. If the client does not have a TGT valid for admission to that TGS, it must get one through a referral process that begins at the TGS in the user account’s domain and ends at the TGS in the service account’s domain. |
Windows Server 2003 implements the KDC as a domain service. It uses the domain’s Active Directory as its account database and gets some information about users from the global catalog.
Kerberos Exchange and Message Summary
Authentication service exchange
Kerberos authentication service request (KRB_AS_REQ)
The client contacts the KDC’s authentication service for a short-lived ticket (a message containing the client’s identity and — for Windows clients — SIDs) called a ticket-granting ticket (TGT). This happens at logon.
Kerberos authentication service response (KRB_AS_REP)
The AS constructs the TGT and creates a session key the client can use to encrypt communication with the ticket-granting service.
The TGT has a limited lifetime, which is 10 hours by default. At the point that the client has received the TGT, the client has not been granted access to any resources, even to resources on the local computer.
Ticket-granting service exchange
Kerberos ticket-granting service request (KRB_TGS_REQ)
The client wants access to local and network resources. To gain access, the client sends a request to the TGS for a ticket for the local computer or some network server or service. This ticket is referred to as the session ticket. To get the ticket, the client presents the TGT, an authenticator, and the Service Principal Name (SPN) of the target server.
Kerberos ticket-granting service response (KRB_TGS_REP)
The TGS examines the TGT and the authenticator. If these are acceptable, the TGS creates a service ticket. The client’s identity is taken from the TGT and copied to the session ticket. Then the ticket is sent to the client.
Important
The TGS cannot determine if the user will be able to get access to the target server. It simply returns a valid ticket. Authentication does not imply authorization.
Client/server exchange
Kerberos application server request (KRB_AP_REQ)
After the client has the session ticket, the client sends the ticket and a new authenticator to the target server, requesting access. The server will decrypt the ticket, validate the authenticator, and for Windows services, create an access token for the user based on the SIDs in the ticket.
Kerberos application server response (KRB_AP_REP)
Optionally, the client might request mutual authentication — that is, that the target server verify its own identity. If mutual authentication is requested, the target server will take the client computer’s timestamp from the authenticator, encrypt it with the session key the TGS provided for client-target server messages, and send it to the client.
For more detailed information about how Kerberos authentication works, see:
| • | “Windows 2000 Kerberos Authentication White Paper” on the Microsoft website at http://go.microsoft.com/fwlink/?LinkId=23128. |
| • | Windows Server 2003 Technical Reference on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=21711. |
Isolating the Problem
Knowing where a problem exists and whether that problem might indicate a problem with Kerberos authentication is crucial to success.
Any issue related to authentication such as console logon, network logon, access to network resources, or remote access might possibly indicate some sort of Kerberos error because Kerberos is the default authentication protocol.
How do you determine that a problem is occurring with Kerberos authentication? If the system event log shows errors from any services that provide authentication such as Kerberos, KDC, LsaSrv, or Netlogon, there might be Kerberos errors associated, as well. Also failure audits in the security event log might show that the Kerberos protocol was being used when a logon failure occurred.
Where to start
1. | Use Kerberos Tray or Kerberos List to confirm that you have a session ticket for the server you are attempting to connect to. If you have a session ticket for the server and you are still getting an error message, consider these two possibilities:
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2. | If you do not have a session ticket, then use Kerberos Tray or Kerberos List to confirm that you have a TGT.
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3. | If you are auditing successful logons, then you can check the security event log on the client to see if the system is using NTLM instead of Kerberos authentication. Use of NTLM can occur because:
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4. | If Kerberos authentication is failing, the system event log or captured data in a network trace should contain the Kerberos error code that was returned by the KDC or the Kerberos SSP. You can also debug to get more information. |
Common Issues
The following sections detail the most common problems encountered by users in Kerberos authentication environments, explain the possible causes of those problems, and suggest how to resolve those problems.
Time Synchronization (Clock Skew)
One type of attack that Kerberos authentication was designed to prevent is known as a “replay” attack. In a replay attack, a malicious user captures the network traffic and replays it to fool the authenticating server into accepting the attacker as a legitimate user who is providing credentials. Kerberos authentication prevents a replay attack with two mechanisms:
| • | The Kerberos client on the local computer encrypts a timestamp inside the authenticator and then sends it to the KDC. If the KDC verifies that the time it decrypts from the authenticator is within a specified amount of the local time on the KDC (the default is 5 minutes), the system can assume that the credentials presented are genuine. |
| • | All tickets issued by the KDC have an expiration time. Thus, if a ticket is compromised, it cannot be used outside of a specified time range — usually short enough to make the risk of a replay attack minimal. |
Because of these mechanisms, Kerberos authentication relies on the date and time that are set on the KDC and the client. If there is too great a time difference between the KDC and a client requesting tickets, the KDC cannot determine whether the request is legitimate or a replay. Moreover, if the time difference is so great that the client is far into the future, the client might attempt to compensate for the clock skew, but will receive tickets that have already expired and are useless. If the client requests new tickets, that will not solve the problem because the KDC uses its own clock as a reference instead of the time on the client computer.
Therefore, it is vital that the time on all of the computers on a network be synchronized in order for Kerberos authentication to function properly. This means that all of the domains and forest in a network must use the same time source. An Active Directory domain controller will act as an authoritative time server for its domain, which guarantees that an entire domain will have the same time. However, multiple domains might not have their times synchronized. It is recommended that you use either an external time source or a single time source within the network to synchronize all computers.
Problem
The difference between client timestamp in the authenticator or KRB_AS_REQ and the server is greater than the Maximum tolerance for computer clock synchronization setting in the domain policy.
Confirmation
Clock skew can be easily diagnosed by reviewing data in Event Viewer. For more information, see:
| • | 0x25: KRB_AP_ERR_SKEW: Clock Skew too great later in this white paper. |
| • | Clock Skew network trace in Appendix A. |
Resolution
For information about how to use an external time source to synchronize all the computers in a domain, see “How to Configure an Authoritative Time Server in Windows 2000” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23042.
UDP Fragmentation
By default, Kerberos authentication uses User Datagram Protocol (UDP) to transmit its data.
Problem
UDP provides no guarantee that a packet sent along the network will reach its destination intact. Thus, in environments with a high amount of network congestion it is common for packets to get lost or fragmented on the way to their destination.
Confirmation
You can diagnose UDP fragmentation by reviewing Network Monitor captured data. For more information, see the UDP Fragmentation network trace in Appendix A.
Resolution
Because the only way to decrease the likelihood of UDP fragmentation occurring is to reduce network traffic — a usually impractical solution — it is almost always better to configure the Kerberos authentication service to use TCP instead of UDP. TCP provides a guarantee that a packet that is sent will reach its destination intact and can therefore be used in any network environment. In order to force Kerberos authentication to use TCP, see “How to Force Kerberos to Use TCP Instead of UDP” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23043.
Group Membership Overloads PAC
In order to provide the proper authorization information to a user after the user logs on with Kerberos authentication, the KDC will transmit Privilege Attribute Certificate (PAC) data in the TGT. The PAC contains various types of authorization data including groups that the user is a member of, rights the user has, and what policies apply to the user. When the client receives a ticket, the information contained in the PAC is used to generate the user’s access token.
Problem
In order to optimize performance, the buffer size for the PAC is pre-allocated. The pre-allocated buffer size is usually adequate to hold all the required authorization data. However, if a user has a very high group membership — from over 70 to over 120, depending on what groups — the size of the PAC might exceed the pre-allocated buffer size. In such a case, the system will generate a memory allocation error, PAC creation will fail, and the Kerberos ticket-granting service will either fail to generate a valid ticket or will generate a ticket with an empty PAC. This sort of error usually manifests itself in the form of a memory allocation error, which gets reported as 0x3C - KRB_ERR_GENERIC: Generic error. This also can result in the failure of clients to apply Group Policy settings.
Confirmation
The Kerberos Token Size tool, described in the Diagnostic Tools section of this white paper, is specifically designed to check for this problem.
Resolution
You can solve this problem in two ways:
| • | Reduce the number of groups that the user is a member of. Because nested groups are expanded out within the PAC, the actual number of groups that the user is a member of might be greater than you suspect. |
| • | Alternatively, install a hotfix that will enable you to set the maximum size of a Kerberos token via the registry. See “New Resolution for Problems That Occur When Users Belong to Many Groups” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23044. |
Need an SPN Set
Service Principal Names (SPNs) are unique identifiers for services running on servers. Each service that will use Kerberos authentication needs to have an SPN set for it so that clients can identify the service on the network. It is registered in Active Directory under a user account as an attribute called Service-Principal-Name. The SPN is assigned to the account under which the service the SPN identifies is running. Any service can look up the SPN for another service. When a service wants to authenticate to another service, it uses that service’s SPN to differentiate it from other services running on that computer.
SPNs are crucial to constrained delegation. When you set up a computer for delegation, one of the steps of the process is to list the services on other computers that the computer is allowed to delegate to. This list forms a type of ACL. The services running on the other computers are identified by the SPNs that are issued to those services.
In general, SPNs should be set when you create an account, because setting an SPN on an account is virtually the security equivalent of creating that account. Special accounts that were created for services are useless until an SPN is set on those accounts for whatever service will be running under them.
Problem
If an SPN is not set for a service, then clients will have no way of locating that service. Thus, common results of not setting an SPN are KDC_ERR_C_PRINCIPAL_UNKNOWN or KDC_ERR_S_PRINCIPAL_UNKNOWN errors. These two errors usually indicate that an SPN has not been set correctly. Furthermore, there are many other errors for which the cause might be a missing or incorrectly set SPN. Kerberos authentication is not possible without properly set SPNs.
Resolution
Because multiple services can run simultaneously under the same account, setting an SPN requires four pieces of information that will make the SPN unique:
| • | The service class. This allows you to differentiate between multiple services running under the same account. |
| • | The account under which the service is running. |
| • | The computer on which the service is running, including any aliases that point to that computer. |
| • | The port on which the service is running. |
These four pieces of information uniquely identify any service running on a network and can be used to mutually authenticate to any service.
An SPN itself consists of ServiceClass/Host:Port, where:
| • | ServiceClass is the service class of the SPN. |
| • | Host is the name of the computer to which the SPN belongs. |
| • | Port is the port on which the service that the SPN is registered to run. |
For more information about how to set SPNs using setspn.exe, see Setspn in the Diagnostic Tools section later in this white paper.
Kerberos Logons Failing in a Mixed Windows and UNIX Environment with Windows NT 4.0 Computers
In an environment where there exists a trust between a Kerberos realm and an Active Directory domain, authentication data can come from one of two sources, either a UNIX KDC or the Active Directory domain controller. If the authentication data is coming from a UNIX KDC, then Windows users have account mappings set up for them to map their UNIX user account to a Windows user account. Normally, the password on the Windows account does not matter, because all authentications are done by the UNIX KDC.
Problem
The Windows NT 4.0 operating system does not support Kerberos authentication. Therefore, if there are Windows NT computers on the network running services, any authentications involving these computers will occur using NTLM and these authentications will be conducted by the domain controller. In this scenario, the password on the domain controller must match the password stored on the UNIX KDC. The passwords must match because the fallback to NTLM occurs transparently. If the passwords do not match, the domain controller will return an Access denied error because the user has provided a password that does not match the one stored on their Active Directory account.
Resolution
Reset the password on the account that the user’s UNIX principal is mapped to in order to match the password stored on the UNIX KDC.
NTLM Fallback
You might find that the security log recorded an event in which logon occurred using NTLM when it should have occurred using Kerberos authentication.
Problem
There are two situations in which this might happen:
| • | The first situation is where the system attempts authentication using the Kerberos protocol but it fails. As a result, the system attempts to authenticate using NTLM. Windows Server 2003, Windows XP, and Windows 2000 use an algorithm called Negotiate (SPNEGO) to negotiate which authentication protocol is used. Although the Kerberos protocol is the default, if the default fails, Negotiate will try NTLM. |
| • | The second situation is one in which a call to Negotiate returns NTLM as the only protocol available. |
Confirmation
The first situation will result in a failed Kerberos authentication that you can investigate by examining errors in the event log or data packets captured by Network Monitor. Both investigation methods are discussed later in this document.
The second situation is much more difficult to diagnose. There are two common causes of the second situation — when Internet Explorer is being used and the Kerberos protocol is not being attempted:
| • | Enable Integrated Windows Authentication (requires restart) setting is not selected in Internet Explorer 6 |
| • | Internet Explorer is accessing a site in the Internet zone instead of the intranet zone. |
Resolution
Internet Explorer 6 will, by default, not attempt to use the Kerberos protocol to authenticate to any site. To change this, you must select the Enable Integrated Windows Authentication (requires restart) setting. For more information, see “Unable to Negotiate Kerberos Authentication After Upgrading to Internet Explorer 6” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23045.
The second common cause is that Internet Explorer 6 is attempting to access a site located in the Internet zone. Internet zone sites are prevented from using Integrated Windows authentication because these protocols will not typically work through Web proxies, among other reasons. If a site is located in the Internet zone, Internet Explorer 6 will not attempt to use Kerberos authentication, and will automatically try NTLM. In all versions of Internet Explorer, when accessing a website to which you want to use Kerberos authentication, you must verify that the website appears as being in the local intranet zone. An icon in the lower right-hand corner of the Internet Explorer window will indicate what zone a website is in. It will display “Internet” for the Internet zone and “Local Intranet” for the intranet zone. If the website appears as being in the Internet zone, you must manually add the site to the local intranet sites list.
To add an Internet site to the local intranet sites list
1. | Click Tools, and then click Internet Options. |
2. | Click the Security tab, then click Local Intranet, then click Sites, and then click Advanced. |
3. | In the box under Add this Web site to the zone: type the name of the website which you want to authenticate with Kerberos authentication and then click Add. |
4. | Click OK. |
After you perform the above procedure, if you find that NTLM authentication is still being used, or that Kerberos is not even being attempted in a situation where Kerberos authentication should be used, contact Product Support Services for help in diagnosing the problem.
Diagnostic Tools
Some tools — for example, Event Viewer and Network Monitor — that you use to diagnose Kerberos errors are the same you would use for other network-related or authentication issues. More specific tools — such as Kerberos List, Kerberos Tray, and Kerberos Token Size — can be used for detailed Kerberos-specific information. To get more even more detailed information, you can enable debug output. Information about troubleshooting tools is provided in this section.
Event Viewer
Event Viewer is included in Windows Server 2003, Windows XP, and Windows 2000. The system and security logs will contain Kerberos error codes and other events related to authentication. For more information about using Event Viewer, see “HOW TO: Diagnose System Problems with Event Viewer in Windows Server 2003” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23046.
System event log
The first place to look if you are experiencing a problem with Kerberos authentication is the system event log.
Any critical errors that Kerberos authentication encounters will show a Source value of Kerberos, KDC, or LsaSrv. The event itself will contain a Kerberos error code and might contain information about how to fix the problem.
If there are no errors listed in the system log or if the errors that appear are not detailed enough to pinpoint the problem, you can configure more detailed Kerberos event logging.
Windows Server 2003 and Windows 2000 can log detailed Kerberos events in the event logs. You can use the resulting information when you troubleshoot Kerberos authentication errors.
How to enable Kerberos event logging on a specific computer
1. | Start Registry Editor.
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2. | Add the following registry value: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters Registry Value: LogLevel Value Type: REG_DWORD Value Data: 0x1 |
3. | If the Parameters subkey does not exist, create it.
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4. | Quit Registry Editor, and then restart the computer. |
After you have configured the system for detailed Kerberos event logging, reproduce the problem, and then check for any Kerberos-related events in the system event log. A new set of Kerberos error messages should now appear in the system event log with event ID 4. These errors might give more specific information about the problem. However, there might be errors that are simply recording diagnostic information. You should verify that the error reported within the event pertains to the affected systems, and that it occurred in response to the specific authentication request that was performed.
Security event log
The security event log contains information that can explain whether Kerberos authentication was at fault or if perhaps some other authentication protocol was responsible. The details of a specific logon/logoff event for a user will show what authentication protocol was used.
Although Kerberos authentication is preferred, the system might revert to NTLM if errors or failures occur. This reversion can cause further problems, because the user will not have obtained any Kerberos tickets and might not be able to access Kerberos-aware services or might not have the functionality of single sign-on across the entire network.
How do you know if logging on with NTLM or Kerberos protocol?
All account logons that occur from computers running Windows Server 2003 or Windows 2000 should occur using the Kerberos protocol (or Negotiate, which could imply that Kerberos protocol was used). To catch these events you need to enable auditing of successful Account Logon events for user authentication and Logon events for computer authentication. If the security log shows that NTLM was used and there are authentication-related issues present, you will need to investigate by using some of the tools outlined in this section. The following table lists event IDs and information potentially associated with Kerberos authentication. Only relevant event information will be present in the event log. For example, only failure audits will have Kerberos error codes; smartcard logons will have certificate information.
Security Log Events That Might Contain Kerberos Error Codes
| Event ID | Account Logon Event Type | Event Information Potentially Associated with Kerberos Authentication | ||||||||||||||||||||||||||||||||
672 |
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673 |
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675 |
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676 |
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677 |
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Network Monitor
If the errors in the event logs do not help you solve the problem, or if you need more detailed information, use Network Monitor to capture a network trace for inspection of the actual Kerberos packets being sent across the network.
Note
For more information about Network Monitor, see “Network Monitor” on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=23049. For best practices and procedures associated with Network Monitor, see “Checklist: Monitoring network traffic on your local computer” on Microsoft TechNet at http://go.microsoft.com/fwlink/?linkid=23047.
The full version of Network Monitor is included with Microsoft Systems Management Server (SMS). A limited version of the tool is included with Windows 2000, Windows XP, and the Windows Server 2003 family. It is also available from Microsoft Product Support Services.
How to install Network Monitor on Windows Server 2003
1. | Open the Windows Components Wizard. |
2. | In the Windows Components Wizard, click Management and Monitoring Tools, and then click Details. |
3. | In Subcomponents of Management and Monitoring Tools, select the Network Monitor Tools check box, and then click OK. |
4. | If you are prompted for additional files, insert the installation CD for your operating system, or type a path to the location of the files on the network. |
Note
| • | To perform this procedure, you must be a member of the Administrators group on the local computer, or you must have been delegated the appropriate authority. If the computer is joined to a domain, members of the Domain Admins group might be able to perform this procedure. |
| • | To open the Windows Components Wizard, click Start, click Control Panel, click Add or Remove Programs, and then click Add/Remove Windows Components. |
| • | Certain Windows components require configuration before they can be used. If you installed one or more of these components but did not configure them, when you click Add/Remove Windows Components, a list of components that need to be configured is displayed. To start the Windows Components Wizard, click Components. |
| • | This procedure automatically installs the Network Monitor driver. |
How to install Network Monitor on Windows XP
Network Monitor is included with the Windows XP Support Tools.
1. | Insert the Windows XP CD-ROM in the drive. |
2. | Double-click My Computer, right-click the CD-ROM drive, and then click Explore. |
3. | Go to Support\Tools, and then double-click Setup.exe. |
4. | When the Windows Support Wizard starts, click Next. |
5. | Click I agree on the End User License Agreement. |
6. | Type your name and organization and then click Next. |
7. | Click either the Typical or Complete installation type, and then click Next. |
8. | Verify the installation location, and then click Install. |
How to install Network Monitor on Windows 2000
1. | Click Start, point to Settings, and then click Control Panel. |
2. | Double-click Add/Remove Programs. |
3. | Click Add/Remove Windows Components. |
4. | Click Management and Monitoring Tools, and then click Details. |
5. | Click to select the Network Monitor Tools check box, and then click OK. |
6. | Click Next. |
Important
Network monitoring on Windows XP is done with the Netcap.exe tool. This tool only allows the capture of network traffic. The capture cannot be viewed with the same tool. You must use the full version of Network Monitor on Windows 2000 or the Windows Server 2003 family to view the captured data.
How to capture network traffic with Windows XP
If you are using the version of Netcap.exe provided in the Windows XP Support Tools, use the following procedure:
1. | Click Start, click All Programs, click Accessories, and then click Command Prompt. This will open a command prompt window. |
2. | Type Netcap.exe /c:path and press ENTER, where path is the full path to the directory and file name where you want to store this network trace. |
3. | After the error has been reproduced, type Netcap.exe /remove and press ENTER. This will stop the network capture. |
The procedure for capturing network traffic with Windows 2000 and Windows Server 2003 is different than the Windows XP procedure. Use the following procedure on these operating systems:
How to capture network traffic with Windows 2000 and the Windows Server 2003 family
1. | Click Start, click Control Panel, click Performance and Maintenance, click Administrative Tools, and then double-click Network Monitor. |
2. | Click the Start button to begin capturing network traffic. |
3. | Reproduce the error. |
4. | Click the Stop button to stop capturing network traffic. |
5. | In the capture statistics information on the right-hand side, verify that no packets were lost because of the buffer overflowing. If any packets were lost, increase the buffer size in the Buffer Settings dialog box on the Capture menu and perform the capture again. |
For more information, see “To capture network frames” on Microsoft TechNet at http://go.microsoft.com/fwlink/?LinkId=23052.
How to filter Kerberos-specific network traffic
You can filter out packets from all protocols except the Kerberos protocol. To apply a filter to only show Kerberos protocol-related network traffic, perform the following steps in Network Monitor:
1. | Click Capture, and then click Display captured data. |
2. | Click the Funnel button and then double-click Protocol == ANY. |
3. | Click Disable all. |
4. | Select Kerberos from the list and click Enable. Click OK, and then click OK again. |
After you perform this procedure, the only packets that should appear are Kerberos packets.
If no packets appear after applying the filter
Three possible causes are:
| • | The Kerberos tickets have either already been issued or have been cached. You can use Kerberos List to show all the tickets currently issued on the computer. You can also use Kerberos List to purge all tickets. Kerberos List is described in further detail later in this section. |
| • | The Kerberos authentication protocol is not even being attempted. The associated logon event in the security event log should say which protocol was used to authenticate the user. If NTLM is listed, then Kerberos was not even attempted. For more information about NTLM fallback, see NTLM Fallback earlier in this white paper. If NTLM fallback is occurring at logon or when requesting a network resource, the event logs (described in the previous section) might contain useful information. |
| • | The Network Monitor buffer overflowed. On high-traffic networks, this can be easily happen if the tool is configured with the default buffer size. |
Analyzing the captured Kerberos traffic
After you have captured some Kerberos packets, the problem can be diagnosed by determining how the captured data differs from a successful authentication. In most cases, the diagnosis will involve following the packet exchange and looking for a KRB_ERROR packet somewhere in the captured data. However, in some cases, especially if everything appears normal, more in-depth analysis is required. Several examples of captured network data — demonstrating a successful logon and showing common failures — are provided in Appendix A: Network Monitor Sample Traces. The captured data is annotated to help explain each frame’s overall impact on the success or failure of the authentication attempt.
For more information, see:
| • | “How to View HTTP Data Frames Using Network Monitor” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23055. |
| • | “Frequently Asked Questions About Network Monitor” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23056. |
Klist.exe: Kerberos List
Kerberos List is a command-line tool that is used to view and delete Kerberos tickets granted to the current logon session. To use Kerberos List to view tickets, you must run the tool on a computer that is a member of a Kerberos realm.
When Kerberos List is run from a client, it shows the:
| • | Ticket-granting ticket (TGT) to a Kerberos Key Distribution Center (KDC) in Windows. |
| • | Ticket-granting ticket (TGT) to Ksserver on UNIX. |
How to install Kerberos List
Kerberos List is supported for Windows Server 2003, Windows XP, and Windows 2000.
You can download Klist.exe from “Windows Server 2003 Resource Kit Tools” on the Microsoft Download Center at http://go.microsoft.com/fwlink/?LinkID=16544.
How to use Kerberos List
Kerberos List is a command-line tool that uses the following syntax:
klist [tickets | tgt | purge] [-?]
1. | Click Start, click All Programs, click Accessories, and then click Command Prompt. This will open a command prompt window. |
2. | Type klist.exe parameter (where parameter is one of four parameters: tickets, tgt, purge, or -?) and then press ENTER. Each of these parameters is discussed in the following section. |
Kerberos List parameters
Tickets
Lists the current cached tickets of services to which you have authenticated since logging on. Tickets can be used to verify that a Kerberos ticket has been issued to the user. After an authentication request, several tickets should appear. This command will also show detailed information about the tickets obtained including the servers for which they were issued, the validity period, and ticket options.
Tickets displays the following attributes of all cached tickets:
| Option | Description |
End Time | Time when the ticket becomes invalid. After a ticket is past this time, it cannot be used to authenticate to a service. |
KerbTicket Encryption Type | Encryption type used to encrypt the Kerberos ticket. |
Renew Time | Maximum lifetime of a renewable ticket (see TicketFlags in the following table). To continue using this ticket, you must renew it before reaching the established End Time and before the expiration date established in RenewUntil. |
Server | Server and domain for the ticket. |
tgt
Lists the initial Kerberos ticket-granting ticket (TGT). Tgt displays the following attributes of the currently cached ticket:
| Option | Description |
AltTargetDomainName | Name supplied to InitializeSecurityContext that generated this ticket, typically an SPN. |
DomainName | Domain name of the service. |
EndTime | Time when the ticket becomes invalid. When a ticket is past this time, it cannot be used to authenticate to a service. |
FullServiceName | Canonical name of the account principal for the service. |
KeyExpirationTime | Expiration time from the KDC reply. |
RenewUntil | Maximum lifetime of a renewable ticket (see TicketFlags). To continue using a ticket, you must renew it. Tickets must be renewed before the expiration time set in End Time and in RenewUntil. |
ServiceName | A TGT is a ticket for the Key Distribution Center (KDC) service. The service name for a TGT is krbtgt. |
StartTime | Time when the ticket becomes valid. |
TargetDomainName | For a cross-realm ticket, this is the realm, rather than the issuing realm, in which the ticket is good. |
TargetName | Service name for which the ticket was requested. This is the name of a servicePrincipalName property on an account in the directory. |
TicketFlags | Kerberos ticket flags set on the current ticket in hexadecimal. The Kerberos Tray tool displays these flags on the Flags tab. |
Time Skew | The reported time difference between the client computer and the server computer for a ticket. |
purge
Deletes all Kerberos tickets held by the user. Purge destroys all tickets that you have cached, so use this with caution. It might stop you from being able to authenticate to resources. If this happens you must log off, and then log on again.
-?
Displays command-line help
Kerbtray.exe: Kerberos Tray
Kerberos Tray is a graphical user interface tool that displays ticket information for a computer running Microsoft’s implementation of the Kerberos version 5 authentication protocol. Kerberos Tray is supported for Windows Server 2003, Windows XP, and Windows 2000.
You can view and purge the ticket cache by using the Kerberos Tray tool icon located in the notification area of the desktop. By positioning the cursor over the icon, you can view the time left until the initial TGT expires. The icon also changes in the hour before the Local Security Authority (LSA) renews the ticket.
How to install Kerberos Tray
Kerberos Tray is included in the Windows Server 2003 Resource Kit and the Windows 2000 Resource Kit.
You can download Kerbtray.exe from “Windows Server 2003 Resource Kit Tools” on the Microsoft Download Center at http://go.microsoft.com/fwlink/?LinkID=16544.
How to use Kerberos Tray
1. | To run Kerberos Tray, double-click the Kerbtray file. The Kerbtray icon appears in the notification area. |
2. | To open the main Kerbtray window, double-click the Kerbtray icon in the notification area. Information about all tickets for the current user will be displayed. Ticket options for each ticket are displayed on the Flags tab. |
3. | To purge tickets, right-click the Kerbtray icon in the notification area, and then click Purge Tickets. |
Tokensz.exe: Kerberos Token Size
You can use Kerberos Token Size to verify whether the source of the Kerberos errors stems from a maximum token size issue. The tool will simulate an authentication request and report the size of the resulting Kerberos token. The tool will also report the maximum supported size for the token. If the size of the token exceeds this maximum supported value, then Kerberos authentication will exhibit the maximum token size behavior seen when group membership overloads PAC. This issue is described in more detail in Group Membership Overloads PAC earlier in this white paper.
Kerberos Token Size is a command-line tool that you can use to view the maximum Kerberos token size for a given account to a given service. To view maximum Kerberos token size, you must run the tool on a computer that is a member of an Active Directory domain.
When Kerberos Token Size is run from a client, it shows:
| • | The maximum Kerberos token size for the authentication package requested. |
| • | The maximum Kerberos token size required to authenticate to the service. |
How to install Kerberos Token Size
You can download Tokensz.exe from the Microsoft Download Center at http://go.microsoft.com/fwlink/?LinkId=25830.
Using Kerberos Token Size
| • | Example command: tokensz /compute_tokensize /package:negotiate / |
| • | Example output: Name: Negotiate Comment: Microsoft Package Negotiator Current PackageInfo->MaxToken: 12128 MaxTokenSize (incomplete context): 2181 |
In this example:
| • | Name shows the name of package chosen, in this case Negotiate, which is the Microsoft Package Negotiator. |
| • | Current PackageInfo shows the current MaxTokenSize value in registry when package was initialized. |
| • | MaxTokenSize is the maximum token size required to authenticate to ServerName. |
| • | Incomplete context. The tool will return (incomplete context) when it does not have the key for all the tickets. |
Note
Incomplete context versus complete context. Two situations might cause the tool to return (complete context):
| • | Using the /system switch. The tool will run the test in the system context and thus have the key needed to open the service ticket. |
| • | Using the /serveruser switch and specifying the password. The service ticket can be opened. |
Syntax and parameters
Kerberos Token Size supports two optional sets of command-line parameters, compute_tokensize or calc_groups.
| • | Compute_tokensize syntax is: tokensz /compute_tokensize [/package:PackageName] [/target_server:TargetName] [/user:UserName] [/domain:UserDomain] [/password:ClientPassword] [/serveruser:UserName] [/serverdomain:ServerDomain] [/serverpassword:ServerPassword] [/dump_groups] [/system] [/nopac][/use_delegation][/purge_tickets:[SPN | NULL]] /compute_tokensize This switch will use the SSPI APIs InitializeSecurityContext() / AcceptSecurityContext to compute the maximum token size required to authenticate using the Kerberos protocol. /package:PackageName. The default package, if none is specified, is the Kerberos package. For many applications — for example, Group Policy — the Negotiate package is used, which increases the maximum token size by about 200 bytes. To simulate the Negotiate package, use /package:negotiate. /target_server:SPN/ServerName. The proper usage of this parameter is to include an SPN — for example, host/dc.tailspintoys.com — which directs Kerberos Token Size to obtain the token size for a ticket to this specific server. If this parameter is omitted, the Kerberos package will get a service ticket to the user account running the tool, in many cases using the User-to-User extension to the Kerberos protocol. For more information about SPNs, see Need an SPN Set earlier in this white paper.
In nearly all cases, the maximum token size is determined by the first call to InitializeSecurityContext(). Thus, if you have connectivity issues to a target server you are troubleshooting, you can select another server in the same domain as a target server for this tool and be reasonably assured that accurate results will be reported. That is, if the target server is in the same domain as the user, the credentials will contain global group, domain local groups, and universal group membership. On the other hand, if you were to choose a target server in a different domain, the credentials will include the domain local groups for that domain. /user:UserName /domain:UserDomain /password:ClientPassword These switches enable you to specify client credentials. For example, if you have a user experiencing maximum token size issues, you can run this tool with that user’s credentials to get an accurate idea of the MaxTokenSize values. Alternatively, the user can run the tool. /serveruser:UserName /serverdomain:ServerDomain /serverpassword:ServerPassword These switches enable you to specify server credentials. They must match the credentials of the account specified in the [/target_server:TargetName] parameter, or you will only get information for the incomplete context. In many cases — for example, computer accounts — it is not possible to know the service password, so these switches are useful when the target is a service account. /dump_groups This switch extracts and displays all of the user’s token groups, relative to the server. The output of this switch is dependent on which server is being used. For example, domain local group membership is relative to which domain the service resides in. The choice of target domain will affect the number of groups reported and the maximum token size. /system You must have administrator rights to use this switch, which runs the test under the Local System context of the computer that the test is being run on. In these cases, you must use the [/user:UserName] [/domain:UserDomain] [/password:ClientPassword] switches, because the tool will be running under the Local System context. This switch is useful to see what groups are present in the Local System logon context. /nopac This switch uses the SEC_WINNT_AUTH_IDENTITY_ONLY flag for AcquireCredentialsHandle(), which informs the KDC not to include a PAC in the TGT or the service ticket. Because a service ticket’s size is primarily influenced by the PAC, you can use this option to determine the size of the Kerberos ticket without including the PAC. /use_delegation This switch passes the ISC_REQ_DELEGATE flag into InitializeSecurityContext(). If you are testing delegation scenarios, use this flag in conjunction with a server in the /target_server parameter that has the Trusted for Delegation option selected. When delegation is used, the system passes both a service ticket and a TGT to the remote server. This approximately doubles the required maximum token size, and is responsible for several Group Policy issues that might be encountered. /purge_tickets:[SPN | NULL] You can use this switch to purge all of the tickets for the user before starting the token size calculation. This is important if you want to judge the effects of adding groups to a user’s maximum token size. This parameter provides the same functionality as using Kerberos List to purge a user’s ticket. |
| • | Calc_groups syntax is: tokensz /calc_groups ClientName [/user:UserName] [/domain:UserDomain] [/password:ClientPassword] [/system] /calc_groups This option is only available if you are using Windows Server 2003 KDCs and running the tool on a computer running Windows Server 2003. The parameter passed to this option is a user and (optionally) a domain that this user is a member of. Kerberos Token Size will list all the groups that this user is a member of. If the user is a member of a large number of groups — generally more than 70-120 — this user might exhibit maximum token size issues. /user:UserName /domain:UserDomain /password:ClientPassword These switches enable you to specify client credentials. /system You must have administrator rights to use this switch, which runs the test under the Local System context of the computer that the test is being run on. In these cases, you must use the [/user:UserName] [/domain:UserDomain] [/password:ClientPassword] switches, because the tool will be running under the Local System context. This switch is useful to see what groups are present in the Local System / logon context. |
Examples of Kerberos Token Size in Use
Example 1: Incomplete context
To determine the maximum Kerberos token size using incomplete context:
| • | Type the following at the command line: tokensz /compute_tokensize /package:negotiate /use_delegation /target_server:host/server1 |
| • | When you press ENTER, the following output is displayed: Name: Negotiate Comment: Microsoft Package Negotiator Current PackageInfo->MaxToken: 12128 MaxTokenSize (incomplete context): 2181 |
In this example:
MaxTokenSize (incomplete context) indicates that the protocol could not perform all legs of authentication. In this case, (incomplete context) was returned because the server was specified as server 1, but the test was run under the user account. However, this is still a reasonable estimation of the maximum token size required for this user to authenticate to server 1.
Example 2: Administrator account to server host with delegation requested
To determine the maximum Kerberos token size for administrator to the host server 1:
| • | Type the following at the command line: tokensz /compute_tokensize /package:negotiate /target_server:host/server1 / |
| • | When you press ENTER, the following output is displayed: Name: Negotiate Comment: Microsoft Package Negotiator Current PackageInfo->MaxToken: 12128 Asked for delegate, but didn't get it Check if server is trusted for delegation. QueryKeyInfo: Signature algorithm = Encrypt algorithm = RSADSI RC4-HMAC KeySize = 128 Flags = 2081e Signature Algorithm = -138 Encrypt Algorithm = 23 Start:4/2/2003 5:54:19 Expiry:4/2/2003 6:54:19 Current Time: 4/2/2003 5:54:19 MaxToken (complete context) 1375 |
In this example:
| • | Asked for delegate, but didn’t get it indicates that delegation was not used. This happens if the target server is not trusted for delegation, or if the user account has the Account is sensitive and cannot be delegated option selected. |
| • | MaxToken (complete context) indicates that all authentication legs have been completed, and that this is a reliable value for maximum token size for server 1. |
Example 3: Using /calc_groups
To calculate group membership for user 1:
| • | Type the following at the command line: tokensz /calc_groups user1 |
When you press ENTER, the tool returns a list of Kerberos token contents. In this example, the following output is displayed:
Username = user1
TS Session ID: 0
User
S-1-5-21-148402017-3776891892-3157626230-1945
Groups:
00 S-1-5-21-148402017-3776891892-3157626230-513 Attributes - Mandatory Default Enabled
01 S-1-1-0 Attributes - Mandatory Default Enabled
02 S-1-5-32-545 Attributes - Mandatory Default Enabled
03 S-1-5-32-554 Attributes - Mandatory Default Enabled
04 S-1-5-2 Attributes - Mandatory Default Enabled
05 S-1-5-11 Attributes - Mandatory Default Enabled
06 S-1-5-15 Attributes - Mandatory Default Enabled
07 S-1-5-5-0-17077419 Attributes - Mandatory Default Enabled LogonId
Primary Group:
S-1-5-21-148402017-3776891892-3157626230-513
Privs
00 0x000000017 SeChangeNotifyPrivilege Attributes - Enabled Default
01 0x000000006 SeUnsolicitedInputPrivilege Attributes - Enabled Default
Auth ID 0:10494b4
Impersonation Level: Identification
TokenType Impersonation
Setspn.exe: Manipulate Service Principal Names for Accounts
The Setspn utility sets SPNs. Because SPNs are security-sensitive, you can only set SPNs for user objects if you have domain administrator privileges. Setspn.exe is included in the Windows Server 2003 Support Tools.
How to use Setspn
| • | To add an SPN, you can type the following at a command prompt: setspn –A ServiceClass/Host:Port AccountName |
| • | To delete an SPN, you can type the following at a command prompt: setspn –D ServiceClass/Host:Port AccountName |
| • | To view the SPNs that are registered for an account, you can type the following at a command prompt: setspn –L AccountName |
| • | To reset the default SPN registrations for the host names for an account, you can type the following at a command prompt: setspn –R AccountName |
The following section discusses the parameters listed above.
| • | ServiceClass. There are many different types of SPNs, and each service that is running on a computer should have the appropriate SPN service class assigned to it. If an application is written to take advantage of Kerberos authentication and delegation, it has the specific type of SPN that it needs to access predetermined. For example, when Internet Explorer 5.5 and later uses the Kerberos protocol to authenticate to a Web server, it looks for the http/ SPN, whereas a SQL Server client looks for the MSSQLSvc/ SPN. If the wrong service class is used on an SPN, then the SPN will not be located when a service searches for it. |
| • | Host. The computer to which the SPN belongs is all the names by which a computer on which the service is running can be referenced. This usually includes a NetBIOS name, the FQDN, and any aliases that might have been assigned to this computer A separate SPN will need to be set for each name by which the computer can be referenced, with the Host parameter changing respectively. |
| • | Port. The port that the service is running on. If this is a default port for that service (such as 80 for HTTP), then it can be omitted. However, it is recommended the port be included regardless of what service is running. |
| • | AccountName. The name of the domain account under which the service runs. If the service runs as Local System or Network Service, you usually do not need to set an SPN explicitly for the service because most common SPN service classes will automatically be mapped to the host/ SPN which is in turn automatically generated for each computer account. |
Debug Output
You can use debug output associated with Kerberos authentication to obtain information if other troubleshooting tools fail to produce useful information. Debug output is not meant to be used in day-to-day troubleshooting. It should only be used if there is absolutely no other means available to get information about the error. Debug output sometimes has extremely detailed error messages that might help you find the source of the problem. However, debug output also can contain messages that appear to indicate an error, but are actually normal messages that result from routine operations of the Kerberos protocol.
The directions in the following sections apply only to Windows Server 2003. In order to view the debug output on Windows 2000 Server, you must obtain instructions and a checked build of the Kerberos dynamic-link libraries (DLLs) from Microsoft Product Support Services.
How to turn on debug output
There are a number of ways to view the debug output from Kerberos. The easiest way is by logging the debug output to a file and then opening this file in Notepad.
1. | Click Start, click Run, type regedit.exe, and then press ENTER.
|
2. | Open the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters\ |
3. | Create the following entry: Value: KerbDebugLevel Type: DWORD Data: c0000043 (this value will print the most standard set of debug messages. Try it first. If you still want to see more output, set it to ffffffff). |
4. | Create the following entry in the same registry location: Value: LogToFile Type: DWORD Data: 1 |
5. | Reproduce the error |
6. | Open the file lsass.log, located in the System32 directory of your Windows folder. You can find the debug output inside this file. |
Note
After you have obtained the necessary output, delete the two registry keys that you added in order to return the system to its full performance.
You might want to view and print the debug output in real time, as the errors actually happen. To do this, you can use a debugging tool called Ntsd. Ntsd is included in both Windows 2000 and Windows Server 2003.
How to use Ntsd to view real-time debug output from Kerberos authentication
Note
Ntsd is included as a courtesy to software developers. Only system developers should use this command. For more information, see the Help file included with Ntsd.
1. | Click Start, click Run, and then type regedit.exe.
| ||||||
2. | Open the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters\ | ||||||
3. | Create the following entry: Value: KerbDebugLevel Type: DWORD Data: c0000043 (this value will print the standard set of debug message. If you still want to see more output, set it to ffffffff). | ||||||
4. | Determine the Process Identifier (PID) for the lsass.exe process from the Task Manager.
| ||||||
5. | Click Start, Run, and then type ntsd -p PID of lsass.exe. This will start the debugger and attach it to lsass. While the debugger loads, you might need to wait a few minutes before the system presents a prompt. | ||||||
6. | At the prompt, type g. The debugger will now print out any errors that Kerberos authentication encounters. | ||||||
7. | Try to authenticate using the Kerberos protocol, and then check the debug output for any error messages that might further elaborate upon the Kerberos errors seen in the event log. |
CautionThe following section about Kerberos errors lists many debug messages that are associated with Kerberos errors.
Important
After you have viewed the debug output, exit Ntsd correctly. If you do not exit Ntsd correctly, you can terminate the lsass process, which will force a system restart. To exit Ntsd, press CTRL+C. At the prompt, type qd to quit the debugger. To return the system to its full performance level, remove the KerbDebugLevel registry entry.
Kerberos Errors: Codes, Possible Causes, Resolutions
This section explains the causes and resolutions for the various Kerberos errors seen in the event logs or that Network Monitor has traced. These error codes are taken from the Kerberos RFC 1510 and draft extensions; all of the numbers and names are those that are used in the RFC. The first section explains the format of an error message and what each element means.
RFC Hex Error Value - Error Code: Description
Associated internal Windows error codes
These status codes are the internal error messages returned by Microsoft’s implementation of the Kerberos protocol. Because these error codes are proprietary, they must be converted into the standard RFC error codes in order to ensure RFC compliance. Because there are many more potential internal errors than there are RFC errors, RFC errors map to more than one internal error. This section shows which internal error codes map to a specific Kerberos error.
Corresponding debug output messages
When debug output is enabled, this is what will be printed if the corresponding Kerberos error is encountered. Debug is often more detailed than a general Kerberos error and might help to pinpoint the source of the problem.
There are two types of debug output messages:
| • | DebugLog. Will be printed if debug output is enabled. |
| • | D_DebugLog. Only printed if a checked build of the Kerberos DLL has been installed on the computer. (Checked builds can only be obtained from Microsoft Product Support Services.) |
Many of the debug output messages will only be generated in Kerberos client application development environments. An example of this would be if a Kerberos application requested an authentication service request with invalid options.
Possible Causes and Resolutions
This section explains the possible causes of the error. Not all errors mean that something is wrong; some are returned during normal operation. If the latter is the case, it is explained as such.
Resolution
This section explains how to resolve a particular error, if applicable.
0x6 - KDC_ERR_C_PRINCIPAL_UNKNOWN: Client not found in Kerberos database
Associated internal Windows error code
STATUS_NO_SUCH_USER
Corresponding debug output messages
| • | D_DebugLog(“KLIN(%x) No principal name supplied to AS request - not allowed\n”) |
| • | DebugLog(“KdcGetS4UTicketInfo normalize returned referral for S4U client\n”) |
| • | DebugLog(“Failed Authz check\n”) |
Possible Causes and Resolutions
This error can occur if the domain controller cannot find the account name in Active Directory. This can occur in three scenarios:
| • | The actual account does not exist. Resolution Verify that the name is in the Active Directory. If the principal name is not in the local Active Directory, but you know the account should exist and the user was recently added to the domain, verify that Active Directory replication is current. |
| • | A new account has been created and has not yet replicated to the KDC that the client is using for authentication. Resolution It could be that the updates have not yet reached the domain controller that is acting as the KDC for that user. For information about how to manually initiate an update, see “Initiating Replication between Active Directory Direct Replication Partners” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23063. |
| • | The user’s account has expired and the Enforce user logon restrictions Group Policy object (GPO) setting is enabled. Resolution If the user name is in Active Directory, determine whether the account has expired. Enforce user logon restrictions forces the domain controller to check the user’s account each time a TGT is presented and account expiration will cause the domain controller to refuse an otherwise valid TGT. |
0x7 - KDC_ERR_S_PRINCIPAL_UNKNOWN: Server not found in Kerberos database
Associated internal Windows error codes
| • | STATUS_NO_TRUST_SAM_ACCOUNT |
| • | STATUS_OBJECT_NAME_NOT_FOUND |
| • | STATUS_KDC_UNABLE_TO_REFER |
Corresponding debug output messages
| • | D_DebugLog(“Wrong S4UProxytarget %wZ %wZ\n”) |
| • | DebugLog(“KdcFindReferralTarget KLIN(%x) Needed exact match and got a transitively-trusted domain.\n”) |
| • | D_DebugLog(“No referral info for %wZ\n”) |
| • | D_DebugLog(“Got UPN w/ uknown trust path %x\n”) |
| • | DebugLog(“No auth info for this trust: %wZ. %ws, line %d\n”) |
Possible Causes and Resolutions
This error can occur if the domain controller cannot find the server’s name in Active Directory. This error is similar to KDC_ERR_C_PRINCIPAL_UNKNOWN except that it occurs when the server name cannot be found.
This might be because:
| • | The actual name is missing. Resolution Verify that the service is registered and has an SPN set. For more information about setting SPNs, see Need an SPN Set earlier in this white paper. |
| • | A new computer account has been created and has not yet replicated to the KDC that the client is using for authentication. Resolution It could be that the updates have not yet reached the domain controller that is acting as the KDC for that client. For information about how to manually initiate an update, see “Initiating Replication between Active Directory Direct Replication Partners” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23063. |
| • | UDP fragmentation is occurring. If the SPN is set, or if the request failed for an initial TGT (requesting a TGT does not require any SPNs to be set manually), then UDP fragmentation might be causing the failure. Resolution Capture a network trace with Network Monitor and compare it to the sample trace associated with UDP fragmentation in Appendix A. If you determine that the cause is UDP fragmentation, see UDP Fragmentation earlier in this white paper for information about how to resolve the issue. |
| • | A trust path has been incorrectly configured. If the SPN is set correctly and this error is not related to UDP fragmentation, then there might be an error while doing the referral. This can occur if the trust path leading to the server has been incorrectly configured. Resolution Verify that there is a valid trust path to the server’s domain and that this path can be followed. You can do this by attempting to logon as a user in the server’s domain in the client domain. If the logon is successful and occurs using the Kerberos protocol (this can be verified in the security log), then the trust path is set up correctly. |
0x8 - KDC_ERR_PRINCIPAL_NOT_UNIQUE: Multiple principal entries in database
Associated internal Windows error codes
| • | STATUS_OBJECT_NAME_COLLISION |
| • | KDCEVENT_NAME_NOT_UNIQUE |
Corresponding debug output messages
| • | None |
Possible Cause and Resolution
| • | This error occurs if duplicate principal names exist. Unique principal names are crucial for ensuring mutual authentication. Thus, duplicate principal names are strictly forbidden, even across multiple realms. Without unique principal names, the client has no way of ensuring that the server it is communicating with is the correct one. Resolution You must remove the duplicate principal name in order for Kerberos authentication to function. To find the duplicate SPN, you can use the LDP tool, or you can use the Ldifde utility. The two methods are described below. How to use the LDP tool
For more information about using ldp.exe to search Active Directory, see “Using Ldp.exe to Find Data in the Active Directory” in the Microsoft Knowledge Base at http://go.microsoft.com/fwlink/?LinkId=23064. How to use Ldifde To use the Ldifde utility to extract the accounts for the domain, or from the suspected container or OU: |
1. | From the domain controller, open a command prompt, and then:
| ||||
2. | Open the text file in Notepad, and then search for the SPN that is reported in the security event log. | ||||
3. | Note the accounts under which the SPN is located. Use Setspn to rename or delete the duplicates. For more information about setting SPNs, see Need an SPN Set earlier in this white paper. |
0xA - KDC_ERR_CANNOT_POSTDATE: Ticket not eligible for postdating
Associated internal Windows error codes
| • | None |
Corresponding debug output messages
| • | DebugLog(“Asked for postdate but start time not present\n”) |
Possible Causes and Resolutions
| • | This error can occur if a client requests postdating of a Kerberos ticket. Postdating is the act of requesting that a ticket’s start time be set into the future. Resolution Windows KDCs do not support postdating and clients should never request the postdating of a ticket. |
| • | There is a time difference between the client and the KDC. Resolution Verify whether there is a time difference between the client and the KDC. For information about this error and about how to resolve time differences, see Time Synchronization (Clock Skew) earlier in this white paper. |
0xB - KDC_ERR_NEVER_VALID: Requested start time is later than end time
Associated internal Windows error codes
| • | None |
Corresponding debug output messages
| • | DebugLog(“Client asked for endtime before starttime\n”) |
Possible Cause and Resolution
| • | There is a time difference between the KDC and the client. |
Resolution
For Kerberos authentication to work, you must synchronize clocks on the client and on the server. For more information about this error and how to resolve it, see Time Synchronization (Clock Skew) earlier in this white paper.
0xC - KDC_ERR_POLICY: KDC policy rejects request
Associated internal Windows error codes
| • | STATUS_ACCOUNT_RESTRICTION |
| • | STATUS_AUTHENTICATION_FIREWALL_FAILED |
| • | STATUS_CROSSREALM_DELEGATION_FAILURE |
| • | STATUS_PASSWORD_RESTRICTION |
| • | STATUS_DOMAIN_TRUST_INCONSISTENT |
Corresponding debug output messages
| • | D_DebugLog(“KLIN(%x) Additional ticket client realm is wrong: %s instead of %s\n”) |
| • | DebugLog(“Trying to renew a non-renewable ticket or against policy\n”) |
| • | DebugLog(“AuthzInitializeContextFromSid() failed in KerbPerformTgsAccessCheck%x\n”) |
| • | DebugLog(“CrossOrg authz AC failed %x\n”) |
| • | DebugLog(“AuthzAccessCheck() failed in KerbPerformTgsAccessCheck%x\n”) |
| • | DebugLog(“Trying to do S4UProxy to another realm %wZ\n”) |
| • | DebugLog(Failed to change password for user %wZ: 0x%x\n”) |
| • | DebugLog(“Missing PAC verifier in S4U Tickets\n”) |
| • | DebugLog(“S4U Pac verifier missing @ sign\n”) |
| • | DebugLog(“KdcBuildTicketTimesAndFlags asked for allow postdate but not allowed: “) |
| • | DebugLog(“Trying to validate a valid ticket\n”) |
Possible Causes and Resolutions
| • | KDC_ERR_POLICY is usually the result of logon restrictions in place on a user’s account. This error is usually accompanied by an error packet which might contain additional information that can be viewed with a Network Monitor capture. Resolution Use Active Directory Users and Computers to verify whether restrictions in place on this account might prevent this user from logging on. To use Active Directory Users and Computers:
|