cancel
Turn on suggestions
Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for 
Show  only  | Search instead for 
Did you mean: 
How to use SPNs when you configure Web applications that are hosted on Internet Information Services
By
Prpillai
Published Jan 23 2019 02:36 PM 16.8K Views
Prpillai
Microsoft
‎Jan 23 2019 02:36 PM

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

‎Jan 23 2019 02:36 PM

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:
IIS6server1 The host name of the computer that is running IIS
mydomain The domain to which the IIS6server1 computer is joined
appPool1 The user account in the mydomain domain that is used for the application pool identity
appPool2 The user account in the mydomain domain that is used for the second application pool identity
www.test.com The first host header for a Web site
www.test2.com The second host header for a Web site
www.test3.com The third host header for a Web site
www.myIIScluster.com The fully qualified domain name of a cluster of computers that are running IIS
www.myEXCHcluster.com The 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:

 

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:

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/helpat 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 MaxTokenSizeproperty. 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...
  • 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

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
1 Comment
Version history
Last update:
‎Jan 23 2019 02:36 PM
Updated by: