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Kerberos Authentication in SQLServer

  • Article

There are two authentication scheme which can be used by SQLserver when connecting to SQLserver using TCP/IP Protocol and windows authentication.

1.       NTLM

2.       Kerberos

When we use Kerberos we get ability to delegate a principal's identity and it is More efficient than NTLM - Caching mechanism and it works based on Based on encrypted tickets with client credentials

 

Let us take a small example to understand Double hop and delegation in simple way

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Refer the below image

 

clip_image001

Create a linked server from SQLServer1 to SQLserver2 (in linked server security select "be made using the logins current security context")

Folow the below steps

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Case1

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1. Login to the server where SQLServer1 instance is running.

2. Connect to SQLServer1 instance with windows authentication using SSMO or Query analyzer,Then run a Distributed query using the linked server to SQLserver2

It will work with both NTLM and Kerberos

Case2

====

1. Login to one of your work station (It should be different server from where SQLServer1/2 instance is running).

2. Connect to SQLServer1 instance using SSMO or Query analyzer,Then run a Distributed query using the linked server to SQLserver2.

It will Not work with NTLM.

It will work only with Kerberos.

To find which authentication scheme we are using run the below query

select net_transport,auth_scheme from sys.dm_exec_connections where session_id=@@spid

"unable to register the Service principle name." is logged in SQLerror log if the SQLServer Startup account do not have permissions to register the SPN in the active directory(SPN will registered by the SQLServer startup account every time SQLServer service is started and deleted when it is shutdown).

If we find that the Case2 did not work or Auth_scheme returned NTLM (By running select net_transport,auth_scheme from sys.dm_exec_connections where session_id=@@spid

)

Check the following check list

CLIENT ---> SQLSERVER1 ---> SQLSERVER2

User1 ---> User1(Impersonated)---> User1

Requirements

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CLIENT User Account and Startup account of SQLServer

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If the startup account/User Account is in a Windows Server 2003 functional level domain, in active directory users and computers Right-click Startup account, and then click Propertiesclick the Delegation tab. select Trust this user for delegation to any service (Kerberos only) .

 

If the startup account/User account is in a Windows Server 2000 functional level domain, in active directory users and computers Right-click Startup account, and then click , In the Account options box, confirm that Account is sensitive and cannot be delegated is not selected.

BACK END SERVER

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- SPN is registered for all the SQLServer instances.

Troubleshoot Steps

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(1) Verify from the Client Computer that ping FQDN (SQLServer) and ping -a

IP_Address (SQLServer) return the same FQDN. Also check if this is the expected

FQDN and points to the correct SPNs

Ping MySql.Domain.Com

Result 10.10.10.1

Ping -a 10.10.10.1

Result MySQl.Domain.Com

(2) Verify that SPNs are registered for the middle and back end servers

MSSQLSvc/HostComputer_FQDN:PORTNUMBER SQLServer_ServiceAccount

OR

MSSQLSvc/HostComputer_FQDN:PORTNUMBER HostComputer_ComputerAccount

AND for cluster installation (SQL Virtual Server)

MSSQLSvc/SQLVirtualServer_FQDN SQLServer_ServiceAccount

MSSQLSvc/SQLVirtualServer_FQDN:PORTNUMBER SQLServer_ServiceAccount

To add an SPN Use

setspn -A "MSSQLSvc/MySql.Domain.Com:1433" "DOMAIN\sqlsvc"

To delete an SPN use

setspn -D "MSSQLSvc/MySql.Domain.Com:1433" "DOMAIN\sqlsvc"

To List SPN for a specific account use

setspn -L "DOMAIN\sqlsvc"

setspn can be downloaded from MSN site.

- Also use SPN Query to search for duplicate spns under different accounts (This

is very common)

https://www.microsoft.com/technet/scriptcenter/solutions/spnquery.mspx

(3) SQL Server Service will automatically register its required SPN if the account

running the service has these rights in AD: Read servicePrincipalName and Write

servicePrincipalName

Read topic: How to configure the SQL Server service to create SPNs dynamically

for the SQL Server instances in KB 811889

(4) For the Client account, Verify that "Account is sensitive and cannot be

delegated is NOT selected"

Open Active Directory Users and Computers; Right-click the user account, and

then click Properties; Click the Account tab; In the Account options box, confirm

that Account is sensitive and cannot be delegated is not selected.

(5) For the Middle Server, account verify that Account is trusted for delegation or

computer is trusted for delegation is set

If middle tier service is using the computer account: Open Active Directory

Users and Computers; Right-click the computer account, and then click Properties

If the account is in a Windows 2000 functional level domain, verify that

the Account is trusted for delegation option is selected.

If the account is in a Windows Server 2003 functional level domain,

configure options on the Delegation tab.

If middle tier service is using a domain user account: Open Active Directory

Users and Computers; Right-click the service account, and then click Properties.

If the service account is in a Windows 2000 functional level domain, the

Account is trusted for delegation option on the Account tab should be selected.

If the computer account is in a Windows Server 2003 functional level

domain, configure options on the Delegation tab.

(6)For the Middle Server, verify that the account that is running SQL Server is

member of "Impersonate a client after authentication". If the client account has

not been authenticated yet (at the front line server) we need to add the "Act as

part of the operating system" policy as well.

Open the domain security policy by clicking Start, Programs, Administrative

Tools, and then Domain Security Policy; Click Local Policies, and then click User

Rights Assignment; verify that the account that is running SQL Server is member of

"Impersonate a client after authentication". If the client account has not been

authenticated yet (at the front line server) we need to add the "Act as part of the

operating system" policy as well.

Test

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- If we are using SQL2005 from a workstation you may query the sys.dm_exec_connections DMV

and look under the auth_scheme column:

select auth_scheme from sys.dm_exec_connections where session_id=@@spid

If Kerberos is being used, then it will display "KERBEROS".

Tools

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- To setup account permissions you can use "Active Directory Users and Computers"

- To manage SPNs you can use SETSPN.exe or ADSIEDIT.msc

- To manage policy use "Domain Security Policy Group Policy" or "Local Security

Policy" editors

Notes

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- Pre-Windows 2000 cannot use Kerberos natively

- TCP/IP is required for Kerberos

- Kerberos ports must be open in the Firewall (88/TCP, 88/UDP)

- DNS Must be working in the client to obtain the FQDN

- Time on computers must be synchronized

-SQLServer Service startup account should have Read servicePrincipalName and Write servicePrincipalName in AD to create SPN's Dyanamically

Common Error Messages

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- Cannot generate SSPI context

- Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server

connection.

- Logon failed for null user

- Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'

- Cannot generate SSPI Context

- Login failed for user NULL Reason not associated with a trusted SQL server

connection

References

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How to troubleshoot the "Cannot generate SSPI context" error message

< https://support.microsoft.com/kb/811889 >

How to use Kerberos authentication in SQL Server

< https://support.microsoft.com/?id=319723 >

 

1.When we are using the named pipe Protocol it will not use Kerberos authentication and can overcome any of above issues.

2.In windows 2003 and named instance of SQLserver2005 there is a problem occurs during the discovery phase of the connection. The IPSec policy on the client drops packets from the server when the source IP changes. This happens if the IPSec policy is enabled on client domain and TCP/IP sockets are used for connection.

Regards

Karthick PK

Comments

  • SSMO  . Please, could you explain what it does mean ? If SQL Server Management Objects, i think that the "official" shortcut is SMO
  • "Service principle name" . Maybe Service PrinciPal Name (SPN) Already put in my favorites ( i am sure to use it in less than 4 months ) Thanks