How to use SPNs when you configure Web applications that are hosted on Internet Information Services

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SUMMARY

This article describes service principal names (SPNs). This article also describes how to use SPNs when you configure Web applications that are hosted on Microsoft Internet Information Services (IIS). This article also describes the Negotiate process in Windows Integrated authentication. The Negotiate security header lets clients select between Kerberos authentication and NTLM authentication.

Additionally, this article describes common scenarios that require an SPN to enable Kerberos authentication. The last section describes situations in which Kerberos authentication may fail. The last section also provides troubleshooting steps.

INTRODUCTION

Important The topics that are discussed in this article apply to Internet Information Services (IIS) 6.0. The topics also apply to IIS 7.0 and 7.5 if Kernel-Mode Authentication is disabled by setting the configuration setting useKernelMode to false.
This step-by-step article describes how to use service principal names (SPNs) when you configure Web applications that are hosted on IIS.IIS passes the Negotiate security header when Windows Integrated authentication is used to authenticate client requests. The Negotiate security header lets clients select between Kerberos authentication and NTLM authentication. The Negotiate process selects Kerberos authentication unless one of the following conditions is true:
  • One of the systems that is involved in the authentication cannot use Kerberos authentication.
  • The calling application does not provide enough information to use Kerberos authentication.
To enable the Negotiate process to select the Kerberos protocol for network authentication, the client application must provide an SPN, a user principal name (UPN), or a NetBIOS account name as the target name. If the client application does not provide a target name, the Negotiate process cannot use the Kerberos protocol. If the Negotiate process cannot use the Kerberos protocol, the Negotiate process selects the NTLM protocol.

MORE INFORMATION

Concepts

Definition of an SPN

An SPN is the name by which a client uniquely identifies an instance of a service. If you install multiple instances of a service on computers throughout a forest, each service instance must have its own SPN. A particular service instance can have multiple SPNs if there are multiple names that clients might use for authentication. For example, an SPN always includes the name of the host computer on which the service instance is running. Therefore, a service instance might register an SPN for each name or alias of its host.

The HTTP service class

The HTTP service class differs from the HTTP protocol. Both the HTTP protocol and the HTTPS protocol use the HTTP service class. The service class is the string that identifies the general class of service. Well-known service class names include "www" for a Web service and "ldap" for a directory service. Generally, the service class name can be any string that is unique to the service class. Be aware that the SPN syntax uses a forward slash character (/) to separate elements. Therefore, the forward slash character (/) cannot appear in a service class name.

The HOST service and the HTTP service class

The HOST service represents the host computer. The Kerberos protocol uses the HOST SPN to access the host computer. The Kerberos protocol uses the long-term key on the host computer to create a service ticket.

The HTTP service class is one of the built-in services that act as an alias to the HOST SPN. The HOST SPN is mapped to the host computer account. Therefore, when you use the default HTTP service class, the Kerberos protocol uses the computer account as the service account to request a service ticket.

Common scenarios

This section describes scenarios that may require an SPN. Additionally, this section demonstrates how to determine which SPN to set for each scenario. The following terms are used in these scenarios:
Collapse this tableExpand this table
IIS6server1The host name of the computer that is running IIS
mydomainThe domain to which the IIS6server1 computer is joined
appPool1The user account in the mydomain domain that is used for the application pool identity
appPool2The user account in the mydomain domain that is used for the second application pool identity
www.test.comThe first host header for a Web site
www.test2.comThe second host header for a Web site
www.test3.comThe third host header for a Web site
www.myIIScluster.comThe fully qualified domain name of a cluster of computers that are running IIS
www.myEXCHcluster.comThe fully qualified domain name of a cluster of computers that are running Microsoft Exchange on IIS

The Setspn.exe tool

The Setspn.exe tool enables you to read, modify and delete the SPN directory property for an Active Directory service account. SPNs are used to locate a target principal name for running a service. The SetSpn.exe tool also enables you to view the current SPNs, reset the account's default SPNs, and add or delete supplemental SPNs.

To obtain the Setspn.exe tool for Microsoft Windows Server 2003, click the following article number to view the article in the Microsoft Knowledge Base:
970536 Setspn.exe support tool update for Windows Server 2003

Scenario 1: Access an IIS application when the application pool identity has been modified

When an IIS application runs under a domain user account instead of under the default network service account, you must set the SPN for the HTTP service under the domain account. In this scenario, you access the IIS application by using either the NetBIOS name of the server that is running IIS or the FQDN of the server that is running IIS.

To access the IIS application by using the NetBIOS name, use the following command, where NETBIOS_NAME_OF_IIS_SERVER is the NetBIOS name of the server that is running IIS:
Setspn –S HTTP/NETBIOS_NAME_OF_IIS_SERVER domain\username
For example, the command may resemble the following command:
Setspn –S HTTP/iis6server1 mydomain\appPool1
To access the IIS application by using the FQDN, use the following command, where FQDN_OF_IIS_SERVER is the FQDN of the server that is running IIS:
Setspn –S HTTP/FQDN_OF_IIS_SERVER domain\username
For example, the command may resemble the following command:
Setspn –S HTTP/iis6server1.mydomain.com mydomain\appPool1

Scenario 2: Access a Web application by using a host header

When you access a Web application by using a host header, you must set an SPN for the HTTP service.

When you run the Web application under a default account such as the network service account, the local service account, or the local system account, you can use the following command:
Setspn –A HTTP/HOST_HEADER NETBIOS_NAME_OF_IIS_SERVER
In this command, HOST_HEADER is the host header that you type in a browser window to access the application, and NETBIOS_NAME_OF_IIS_SERVER is the NetBIOS name of the server that is running IIS.

For example, the command for the application may resemble the following command:
Setspn –A HTTP/www.test.com iis6server1
If you run the application under a domain account, you can use the following command:
Setspn –A HTTP/HOSTHEADER_OR_DNS_ALIAS domain\username
In this command, HOSTHEADER_OR_DNS_ALIAS is the host header or DNS alias that you use to access the Web application.

For example, the command for the application may resemble one of the following commands:
  • Setspn –A HTTP/www.test.com mydomain\appPool1
  • Setspn –A HTTP/www.test3.com mydomain\appPool2

Scenario 3: Access an IIS application in a clustered or load-balanced environment

When you run IIS in a clustered environment or in a load-balanced environment, you access applications by using the cluster name instead of by using a node name. This scenario includes network load balancing. In cluster technology, a node refers to one computer that is a member of the cluster. To use Kerberos as the authentication protocol in this scenario, the application pool identity on each IIS node must be configured to use the same domain user account. To configure each IIS node to use the same domain user account, use the following command:
Setspn –A HTTP/CLUSTER_NAME domain\username
For example, the command may resemble one of the following commands:
  • Setspn –A HTTP/www.myIISCluster.com mydomain\appPool1
  • Setspn –A HTTP/www.myEXCHCluster.com mydomain\appPool2

Scenario 4: Use SQL Server to access an application

The SPNs on the back-end server may have to be verified if the IIS Web application requires access to a back-end computer that is running SQL Server. The Web application may not work correctly if the required SPNs are configured incorrectly.

If the back-end computer that is running SQL Server is running under the local system account, the MSSQLSvc/FQDN_OF_SQL_SERVER:port port number must be available for the computer name. Use the following command to determine the SPNs for the computer that is running SQL Server:
Setspn –L SQL_SERVER_COMPUTER_NAME
Use the following command to set the SPN for the name of the computer that is running SQL Server:
Setspn –A MSSQLSvc/FQDN_OF_SQLSERVER:port SQLSERVER_COMPUTER_NAME
If the back-end computer that is running SQL Server is running under a domain account, the MSSQLSvc/FQDN_OF_SQL_SERVER:port port number must be available for the domain account. Use the following command to determine the SPNs for the domain account:
Setspn –L domain\username
Use one of the following commands to set the SPN for the name of the computer that is running SQL Server:
  • Setspn –A MSSQLSvc/FQDN_OF_SQLSERVER:portFQDN_OF_SQLSERVER
  • Setspn –A MSSQLSvc/FQDN_OF_SQLSERVER:portdomain\username

The SPN helper script

You can use the following sample script to find the SPNs for an IIS application. You can also use this script to find duplicate SPNs. To use this script, follow these steps:
  1. Click Start, click Run, type Notepad, and then click OK.
  2. In the Notepad file, paste the following script:
    Dim argSPN, argUser, argComputer, spnToSearch, objCategory, strFilter, searchCategory, domainInput
    
    Function Help()
    Dim strMessage
    strMessage = strMessage & "Usage:" & chr(13)
    strMessage = strMessage & "For accurate results run this script from the IIS server or a member server in the same domain as IIS server." & chr(13)
    strMessage = strMessage & "Check the article's failure scenarios and make sure no duplicate SPNs exist." & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:spn /spn:HTTP/www.test.com /user:mydomain\apppool1" & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:spn /spn:HTTP/www.test.com /computer:iis6server1" & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:user /user:mydomain\apppool1" & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:computer /computer:iis6server1" & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:duplicatespn /spn:HTTP/www.test.com" & chr(13)
    strMessage = strMessage & "cscript spnHelper.vbs /f:requiredspn" & chr(13)
    	MsgBox strMessage,,"SPN Helper"
    	WScript.Quit
    End Function
    
    Function setArguments()
    	argSPN = lcase(WScript.Arguments.Named("spn"))
    	argUser =  lcase(WScript.Arguments.Named("user"))
    	argComputer = lcase(WScript.Arguments.Named("computer"))
    	searchCategory = lcase(WScript.Arguments.Named("f"))
    	if instr(argUser,"\")>0 then
    		domainInput = ",DC=" & split(argUser,"\")(0)
    		argUser = split(argUser,"\")(1)
    	end if
    End Function
    
    Function resetValues()
    	spnToSearch = ""
    	objCategory = ""
    	strFilter = ""
    End Function
    
    Function getGCPath()
    	Dim tempGCPath, objGC, tempGC, tempStr
    	Set objGC = GetObject("GC:")
    	for each tempGC in objGC
    		tempGCPath = tempGC.ADsPath
    	next
    	if tempGCPath <> "" then
    		getGCPath = tempGCPath
    	else
    		WScript.Echo "Unable to find active directory"
    		WScript.Quit
    	end if
    	For tempCounter=0 to UBound(split(lcase(split(getGCPath,"//")(1)),"."))
    		If tempCounter = UBound(split(lcase(split(getGCPath,"//")(1)),".")) Then tempSeperator="" else tempSeperator = ","
    		tempStr = tempStr & "DC=" & split(lcase(split(getGCPath,"//")(1)),".")(tempCounter) & tempSeperator
    	Next
    	getGCPath = tempGCPath & "/" & tempStr
    End Function
    
    Function getSPNClass()
    	Dim tempSPNClass
    	If trim(argSPN)="" Then getSPNClass = "*": Exit Function
    	If instr(argSPN,"/")=0 Then getSPNClass = "*": Exit Function
    	If instr(split(argSPN,"/")(0),"*")>0 Then getSPNClass = "*": Exit Function
    	getSPNClass = split(argSPN,"/")(0)
    End Function
    
    Function isSPNInputValid(spnIN)
    	isSPNInputValid = ""
    	If instr(spnIN,"/")=0 Then Exit Function
    	If instr(spnIN,"*")>0 Then Exit Function
    	isSPNInputValid = spnIN
    End Function
    
    Function Main()
    	Dim paramSPN
    	paramSPN = ""
    	call  resetValues()
    	call setArguments()
    	Select Case searchCategory
    		Case "spn"
    			if (argUser = "" and argComputer = "") or (argUser <> "" and argComputer <> "") then WScript.Echo "You must use /spn along with /computer or /user": WScript.Quit
    			if argSPN = "" then argSPN = "*"
    			spnToSearch = "(servicePrincipalName=" & argSPN & ")"
    			if argUser <> "" then objCategory = "(objectCategory=person)(sAMAccountName=" & argUser & ")"
    			if argComputer <> "" then 
    				objCategory = "(objectCategory=computer)(cn=" & argComputer & ")"
    			End If
    			strFilter = "(&" & spnToSearch & objCategory & ")"
    		Case "duplicatespn"
    			If isSPNInputValid(argSPN)="" Then WScript.Echo "Invalid SPN input. Please verify and try again.": WScript.Quit
    			spnToSearch = "(servicePrincipalName=" & argSPN & ")"
    			strFilter = spnToSearch
    			paramSPN = argSPN
    		Case "requiredspn"
    			call showRequiredSPNs("IIS")
    			WScript.Quit
    		Case "computer"
    			objCategory = "(&(objectCategory=computer)(cn=" & argComputer & "))"
    			strFilter = objCategory
    		Case "user"
    			objCategory = "(&(objectCategory=person)(sAMAccountName=" & argUser & "))"
    			strFilter = objCategory
    		Case else
    			call Help()
    			WScript.Quit
    	End Select
    	call getSPNs(paramSPN)
    End Function
    
    Function getPingResult(hostName,errorMessage)
    'On Error Resume Next
    getPingResult = ""
    	If instr(hostName,".")=0 Then
    		Dim tempGCPath, objGC, tempGC
    		Set objGC = GetObject("GC:")
    		for each tempGC in objGC
    			tempGCPath = tempGC.ADsPath
    		next
    		if tempGCPath <> "" then
    			gcPath = tempGCPath
    		else
    			WScript.Echo "Unable to find active directory"
    			WScript.Quit
    		end if
    		Set adConn = CreateObject("ADODB.Connection")
    		Set adCmd = CReateObject("ADODB.Command")
    		adConn.Provider = "ADsDSOObject"
    		adConn.Open "ADs Provider"
    		Set adCmd.ActiveConnection = adConn
    		adQuery = "<" + gcPath + ">;" & "(&(objectCategory=computer)(cn=" & hostName & "))" & ";dnsHostName;subtree"
    		'WScript.Echo adQuery
    		'WScript.Quit
    		adCmd.CommandText = adQuery
    		Set adRecordSet = adCmd.Execute
    		if adRecordSet.RecordCount>0 Then 
    			If IsNull(adRecordSet.Fields("dnsHostName"))=0 Then 
    				getPingResult = adRecordSet.Fields("dnsHostName") 
    				hostName = getPingResult 
    			Else 
    				getPingResult = hostName
    			End If
    		else 
    			errorMessage = "Could not find " & hostname & " in the active directory"
    		end if
    
    		Exit Function
    	End If
    	getPingResult = hostName
    Exit Function
    'If Err Then getPingResult = hostName
    End Function
    
    Function getSPNs(spn)
    	Dim spnClass, duplicateSPNArray
    	spnClass = getSPNClass()
    	duplicateSPNArray = ""
    	gcPath = getGCPath()
    	Set adConn = CreateObject("ADODB.Connection")
    	Set adCmd = CreateObject("ADODB.Command")
    	adConn.Provider = "ADsDSOObject"
    	adConn.Open "ADs Provider"
    	Set adCmd.ActiveConnection = adConn
    	adQuery = "<" + gcPath + domainInput + ">;" & strFilter & ";distinguishedName,objectCategory,dnsHostName,servicePrincipalName,sAMAccountName;subtree"
    	'WScript.Echo adQuery
    	'WScript.Quit
    	adCmd.CommandText = adQuery
    	Set adRecordSet = adCmd.Execute
    	if adRecordSet.EOF and adRecordSet.Bof Then
    		WScript.echo "No " & searchCategory & " found with the given criteria."
    	else
    		If adRecordSet.RecordCount>10 Then
    			If msgbox(adRecordSet.RecordCount & " Records are returned with the given criteria. Printing all of them might take a long time" & chr(13) & " Do you want to print all of them?",vbYesNo,"Kerberos")=vbNo Then Exit Function
    		End If
    		Do While not adRecordset.Eof
    			If Err Then Exit Do
    			WScript.echo "Class: " & split(split(adRecordSet.Fields("objectCategory"),",")(0),"=")(1)
    			WScript.Echo adRecordSet.Fields("distinguishedName")
    			if UCase(adRecordSet.Fields("objectCategory")) = "COMPUTER" Then
    				WScript.echo "Computer Name" & adRecordSet.Fields("dnsHostName")
    			else
    				WScript.echo "User Name: " & adRecordSet.Fields("samAccountName")
    			end if
    			if instr(searchCategory,"spn")>0 Then
    				spnCollection = adRecordSet.Fields("servicePrincipalName")
    				for each individualSPN in spnCollection
    					if spnClass="*" Then
    					WScript.Echo Chr(9) + individualSPN
    					else
    						Select Case searchCategory
    							Case "spn"
    								if Lcase(split(individualSPN,"/")(0)) = lcase(spnClass) Then
    									WScript.Echo Chr(9) + individualSPN
    								end if
    							Case "duplicatespn"
    								if Lcase(individualSPN) = lcase(spn) Then
    									duplicateSPNArray = duplicateSPNArray & Lcase(individualSPN) & " for " & split(split(adRecordSet.Fields("objectCategory"),",")(0),"=")(1) & ":" & adRecordSet.Fields("samAccountName") & Chr(29)
    								end if
    							Case "requiredspn"
    						End Select
    					End if
    				next
    			end if
    			WScript.Echo
    			adRecordSet.MoveNext
    		Loop
    		If searchCategory = "duplicatespn" Then
    			If UBound(Split(duplicateSPNArray,Chr(29)))>1 Then
    				WScript.Echo "Duplicate SPNs found"
    				For tempDuplicateCount=0 to UBound(Split(duplicateSPNArray,Chr(29)))-1
    					WScript.Echo Split(duplicateSPNArray,Chr(29))(tempDuplicateCount)
    				Next
    			End If
    		End If
    		WScript.Echo ""
    		If adRecordset.RecordCount>1 Then WScript.Echo "Found " & adRecordset.RecordCount & " accounts" Else WScript.Echo "Found " & adRecordset.RecordCount & " account"
    	end if
    	adRecordset.Close
    	adConn.Close
    	If Err Then MsgBox Err.Message
    End Function
    
    Function getCategoryCount(myFilterValue, myFilterCategory)
    'This function accepts 2 parameters. First paramenter is the filter value and second param is filter category.
    'If you want to pass in your own filter string with various categories, you can pass "" as the second param.
    	gcPath = getGCPath()
    	searchCategory = myFilterCategory
    	Select Case lcase(searchCategory)
    		Case "spn"
    			tempFilter = "(servicePrincipalName=" & myFilterValue & ")"
    		Case "user"
    			tempFilter = "(&(objectCategory=person)(sAMAccountName=" & myFilterValue & "))"
    		Case "computer"
    			tempFilter = "(&(objectCategory=computer)(cn=" & myFilterValue & "))"
    		Case else
    			tempFilter = myFilterValue
    	End Select
    	Dim tempCategoryCount
    	tempCategoryCount = 0
    	Set adConn = CreateObject("ADODB.Connection")
    	Set adCmd = CReateObject("ADODB.Command")
    	adConn.Provider = "ADsDSOObject"
    	adConn.Open "ADs Provider"
    	Set adCmd.ActiveConnection = adConn
    	adQuery = "<" + gcPath + domainInput + ">;" & tempFilter & ";objectCategory,dnsHostName,servicePrincipalName,sAMAccountName;subtree"
    	'WScript.Echo adQuery
    	'WScript.Quit
    	adCmd.CommandText = adQuery
    	Set adRecordSet = adCmd.Execute
    	if adRecordSet.EOF and adRecordSet.Bof Then
    	else
    		Do While not adRecordset.Eof
    			If Err Then Exit Do
    			if searchCategory = "spn" Then
    				spnCollection = adRecordSet.Fields("servicePrincipalName")
    				for each individualSPN in spnCollection
    					If lcase(individualSPN) = lcase(myFilterValue) Then
    						tempCategoryCount  = tempCategoryCount  + 1
    					End If
    				next
    			else
    				tempCategoryCount = tempCategoryCount + 1
    			end if   
    			adRecordSet.MoveNext
    		Loop
    	end if
    	getCategoryCount = tempCategoryCount
    	adRecordset.Close
    	adConn.Close
    End Function
    
    Function showRequiredSPNs(Product)
    	Select Case Product
    		Case "IIS"
    			If MsgBox("Is IIS running in a Cluster or NLB",vbYesNo)=vbYes Then 'Running in Cluster or NLB is true
    				strClusterName = InputBox("Enter the Cluster Name")
    				If strClusterName = "" Then WScript.Quit
    				If getPingResult(strClusterName,errorMessage)="" Then
    					If MsgBox(errorMessage & ". Do you want to continue?",vbYesNo)<>vbYes Then WScript.Quit
    				End If
    				strDomainAccount = InputBox("Enter the Domain Account that the application pool is running under")
    				If strDomainAccount = "" Then WScript.Quit
    				strRequiredSPN = "HTTP/" & strClusterName
    				If instr(strDomainAccount,"\") > 0 then
    					If getCategoryCount(split(strDomainAccount,"\")(1), "user")=0 Then
    						WScript.Echo "Domain account " & strDomainAccount & " does not exist"
    						WScript.Quit
    					End If
    				Else
    					If getCategoryCount(strDomainAccount, "user")=0 Then
    						WScript.Echo "Domain account " & strDomainAccount & " does not exist"
    						WScript.Quit
    					End If
    				End If
    				If getCategoryCount(strRequiredSPN, "spn")>0 Then
    					WScript.Echo "SPN " & " is already set. Use search option for finding the account that it is set for"
    					WScript.Quit
    				End If
    				WScript.Echo "You need to set the SPN " & strRequiredSPN & " for domain account " & strDomainAccount
    			Else
    				If MsgBox("Is IIS application pool running under domain account",vbYesNo)=vbYes Then 
    					strHostName = InputBox("Enter the hostname or host header or FQDN that you use to access the application")
    					If strHostName = "" Then WScript.Quit
    					If getPingResult(strHostName,errorMessage)="" Then
    						If MsgBox(errorMessage & ". Do you want to continue?",vbYesNo)<>vbYes Then WScript.Quit
    					End If
    					strDomainAccount = InputBox("Enter the Domain Account that the application pool is running under")
    					If strDomainAccount = "" Then WScript.Quit
    					If instr(strDomainAccount,"\") > 0 then
    						If getCategoryCount(split(strDomainAccount,"\")(1), "user")=0 Then
    							WScript.Echo "Domain account " & strDomainAccount & " does not exist"
    							WScript.Quit
    						End If
    					Else
    						If getCategoryCount(strDomainAccount, "user")=0 Then
    							WScript.Echo "Domain account " & strDomainAccount & " does not exist"
    							WScript.Quit
    						End If
    					End If
    					strRequiredSPN = "HTTP/" & strHostName
    					If getCategoryCount(strRequiredSPN, "spn")>0 Then
    						WScript.Echo "SPN " & strSPNRequired & " is already set. Use search option for finding the account that it is set for"
    						WScript.Quit
    					Else
    						WScript.Echo "You need to set SPN " & strRequiredSPN & " for domain account " & strDomainAccount
    						WScript.Quit
    					End If
    				Else
    					strHostName = InputBox("Enter the host header or FQDN that you use to access the application")
    					If strHostName = "" Then WScript.Quit
    					If getPingResult(strHostName,errorMessage)="" Then
    						If MsgBox(errorMessage & ". Do you want to continue?",vbYesNo)<>vbYes Then WScript.Quit
    					End If
    					If MsgBox("Are you accessing the application with netbios name or FQDN or CNAME alias of IIS server?",vbYesNo)=vbYes Then
    						strRequiredSPN = "host/" & strHostName
    						If getCategoryCount(strRequiredSPN, "spn")>0 Then
    							WScript.Echo "Required SPN " & strRequiredSPN & " is already set. Use search option for finding the account that it is set for"
    							WScript.Quit
    						Else
    							WScript.Echo "You need to set SPN " & strRequiredSPN & " for IIS server's netbios name"
    							WScript.Quit
    						End If
    					End If
    					strHostHeader = InputBox("Enter the host header that you use to access the application")
    					If strHostHeader = "" Then WScript.Quit
    					strRequiredSPN = "http/" & strHostHeader
    					If getCategoryCount(strSPNRequired, "spn")>0 Then
    						WScript.Echo "A required SPN " & strSPNRequired & " is already set. Use search option to find the account the SPN is set to. If the required SPN is found under a different account, remove and add it to the IIS server's machine account."
    						WScript.Quit
    					Else
    						WScript.Echo "You need to set SPN " & strRequiredSPN & " for IIS server's netbios name"
    						WScript.Quit
    					End If
    				End If
    				
    			End If
    		Case Else
    			call Help()
    	End Select
    End Function
    
    call Main()
    '
    
  3. Save the file as Spnhelper.vbs.
  4. At a command prompt, run the Spnhelper.vbs file by using the appropriate command-line option.

    Note To view the command-line options for the Spnhelper.vbs file, type Spnhelper.vbs/help at a command prompt, and then press ENTER.

Additional considerations

Kerberos authentication may fail when the required SPNs are set for the computer accounts or for the domain accounts. If Kerberos authentication fails unexpectedly, do the following:
  • Verify that no duplicate SPNs exist in the global catalog for an SPN.

    For example, if the HTTP/www.test.com SPN is set for the myDomain\appPool1 account and for the myDomain\appPool2 account, a duplicate SPN exists even though the SPNs are set for different accounts. Additionally, if the HTTP/iis6server1.mydomain.com SPN is set for the myDomain\appPool1 account, and the HTTP/iis6server1.mydomain.com SPN is also associated with the computer account for the server, you also have a duplicate SPN. You can have one HOST SPN and one HTTP SPN. The explicit HTTP SPN will override the implicit one that is covered under the HOST entry. However, if the URL that the user types is associated with more than one user account or with more than one computer account, you have a duplicate SPN.
  • Verify that the SPNs have replicated to other domain controllers.

    Replication issues between the domain controllers can prevent the SPNs from replicating to the other domain controllers. When the SPNs do not replicate to the other domain controllers, the application may not work from some client computers. For example, if the HTTP/www.test.com SPN is set for the myDomain\appPool1 account on a domain controller, the HTTP/www.test.com SPN may not be found for the myDomain\appPool1 account on a second domain controller if the SPN has not been replicated to the second domain controller.

    Note By default, replication takes 15 minutes.
  • Verify that the Web server is configured to support Kerberos authentication. To do this, verify that the setting for the NTAuthenticationProviders key in the IIS metabase has not been changed to NTLM. The default setting is Negotiate,NTLM.
  • Verify that the server or service that is delegating the credentials is trusted for delegation.
  • Verify that the account that the service is running under is trusted for delegation.
  • In Active Directory, verify that the Account is sensitive and cannot be delegated check box is cleared for users who access the application.
  • If you are accessing the application directly from the server, verify that the Loopback Security Check check box is cleared. For more information about how to verify that the loopback check is disabled, click the following article number to view the article in the Microsoft Knowledge Base:
    896861 You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or IIS 6
  • Verify that the client is a Kerberos-enabled client. Also, verify that the Enable Windows Integrated Authentication setting is enabled in Internet Explorer. To do this, click Internet Options on the Tools menu, click the Advanced tab, and then make sure that the Enable Windows Integrated Authentication check box is selected.
  • Verify that all computers that are part of the Kerberos process have consistent name resolution and are connected by Kerberos trust. For example, verify that the computers that are involved in the Kerberos process are in the same forest or are part of a cross-forest Kerberos trust.
  • Verify that the token size does not exceed the value that is set for the MaxTokenSize property. Also, verify that the request size does not exceed the value that is set for the MaxFieldLength property. These values may be exceeded if users who are part of the Kerberos process are members of many groups.
    920862 Error message when an Outlook Web Access user tries to access a mailbox in Exchange Server 2003: “HTTP 400 Bad Request (Request header too long)”
  • Verify that the required security policies are enabled when you configure domain accounts for application pools. To do this, verify that the domain account is a member of the following local security policies on the computer that is running IIS:
    • Adjust memory quotas for a process
    • Logon as a service
    • Replace a process level token
  • Verify that Kerberos authentication is working correctly over UDP. By default, Kerberos authentication uses UDP. However, the loss of UDP packets can cause Kerberos authentication to fail. When this issue occurs, you can force Kerberos authentication to use TCP. For more information about how to force Kerberos authentication to use TCP, click the following article number to view the article in the Microsoft Knowledge Base:
    244474 How to force Kerberos to use TCP instead of UDP in Windows Server 2003, in Windows XP, and in Windows 2000
  • Verify that the time stamp on the authenticator does not differ by more than five minutes from the time stamp of the server. For more information about how to resolve timestamp differences, click the following article number to view the article in the Microsoft Knowledge Base:
    232386 Cannot log on if time and date are not synchronized
  • Verify that TCP/UDP port 88 is not blocked by a firewall or a router. By default, Kerberos authentication uses TCP/UDP port 88.
  • Verify that the domain mode environment is at least a Microsoft Windows 2000 native mode environment. For more information about how to determine the domain mode, visit the following Microsoft Web site:
    http://technet2.microsoft.com/windowsserver/en/library/11b2d3d3-980c-4b64-9ed3-51778f1fe5771033.mspx?mfr=true
  • On the client, verify that the URL for the Web application is added to the local intranet sites. For more information about how to add a URL to the local intranet, click the following article number to view the article in the Microsoft Knowledge Base:
    303650 Intranet site is identified as an Internet site when you use an FQDN or an IP address
  • Verify that each gigabit ethernet device is using the latest driver version. For more information about issues that can occur when the drivers for gigabit Ethernet devices are outdated, click the following article number to view the article in the Microsoft Knowledge Base:
    326152 Cannot connect to domain controller and cannot apply Group Policy with Gigabit Ethernet devices

REFERENCES

For more information about how to use Kerberos authentication with load-balanced Web sites, visit the following Microsoft Web site:
http://technet.microsoft.com/en-us/library/cc757299.aspx
For more information about problems that can occur when you use Kerberos authentication with proxy servers, click the following article number to view the article in the Microsoft Knowledge Base:
321728 Internet Explorer does not support Kerberos authentication with proxy servers
For more information about how to configure IIS to support both the Kerberos protocol and the NTLM protocol for network authentication, click the following article number to view the article in the Microsoft Knowledge Base:
215383 How to configure IIS to support both the Kerberos protocol and the NTLM protocol for network authentication
For more information about how to configure a Windows SharePoint Services virtual server to use Kerberos authentication and how to switch from Kerberos authentication back to NTLM authentication, click the following article number to view the article in the Microsoft Knowledge Base:
832769 How to configure a Windows SharePoint Services virtual server to use Kerberos authentication and how to switch from Kerberos authentication back to NTLM authentication
For more information about problems that can occur when you use Kerberos authentication protocol to connect to a Web server that uses a non-standard port on Windows XP or Windows Server 2003, click the following article number to view the article in the Microsoft Knowledge Base:
908209 Internet Explorer 6 cannot use the Kerberos authentication protocol to connect to a Web server that uses a non-standard port on Windows XP or Windows Server 2003

Properties

Article ID: 929650 - Last Review: May 12, 2010 - Revision: 5.0
APPLIES TO
  • Microsoft Internet Information Services 7.5
  • Microsoft Internet Information Services 7.0
  • Microsoft Internet Information Services 6.0
Keywords: 
kbinfo kbhowto KB929650

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