Steps to troubleshoot SQL connectivity issues

Steps to troubleshoot SQL connectivity issues

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We have been seeing and trying to resolve SQL connectivity issue all the time. I guess it would be helpful if we can put some guidance on how to resolve connectivity issues. Here comes a proposal based on my experience.


Basically, when you failed to connect to your SQL Server, the issue could be:

1) Network issue,

2) SQL Server configuration issue.

3) Firewall issue,

4) Client driver issue,

5) Application configuration issue.

6) Authentication and logon issue.


Usually, customers see connectivity issue in their applications, but it would be great if you can follow the steps below to eliminate issues one by one and post a question on SQL Server Data Access forum if needed.



Step 1: Network issue

You might be able to make local connection without a working network, but that's a special case. For remote connection, a stable network is required. The first thing to trouble shoot SQL connectivity issues is to make sure the network we rely on is workable and stable. Please run the following commands:


ping -a <your_target_machine>    (use -4 and -6 for IPv4 and IPv6 specifically)

ping -a <Your_remote_IPAddress>

nslookup (type your local and remote machine name and IP address multiple times)


Be careful to see any mismatch on the returned results. If you are not able to ping your target machine, it has high chance that either the network is broken or the target machine is not running. It's possible the target machine is behind a firewall and the firewall blocks the packets sent by ping, though. Windows firewall does not block ping (ECHO) packet by default. The correctness of DNS configuration on the network is vital to SQL connection. Wrong DNS entry could cause of all sorts of connectivity issue later. See this link for example, "Cannot Generate SSPI Context" error message, Poisoned DNS.


Step 2: SQL Server configuration issue

You need to make sure the target SQL Server is running and is listening on appropriate protocols. You can use SQL Server Configuration Manager (SCM) to enable protocols on the server machine. SQL Server supports Shared Memory, Named Pipes, and TCP protocols (and VIA which needs special hardware and is rarely used). For remote connection, NP and/or TCP protocols must be enabled. Once you enabled protocols in SCM, please make sure restart the SQL Server.


You can open errorlog file to see if the server is successfully listening on any of the protocol. The location of errorlog file is usually under:

%ProgramFile%Microsoft SQL Server/

If the target SQL instance is a named instance, you also need to make sure SQL Browser is running on the target machine. If you are not able to access the remote SQL Server, please ask your admin to make sure all these happen.


Step 3: Firewall issue

A firewall on the SQL Server machine (or anywhere between client and server) could block SQL connection request. An easy way to isolate if this is a firewall issue is to turn off firewall for a short time if you can. Long term solution is to put exception for SQL Server and SQL Browser.


For NP protocol, please make sure file sharing is in firewall exception list. Both file sharing and NP use SMB protocol underneath.

For TCP protocol, you need put the TCP port on which the SQL Server listens on into exception.

For SQL Browser, please put UDP port 1434 into exception.

Meanwhile, you can put sqlservr.exe and sqlbrowser.exe into exception as well, but this is not recommended. IPSec between machines that we are not trusted could also block some packets. Note that firewall should never be an issue for local connections.



Step 4: Client driver issue

At this stage, you can test your connection using some tools. The tests need to be done on client machine for sure.


First try:

telnet <your_target_machine> <TCP_Port>

You should be able to telnet to the SQL server TCP port if TCP is enabled. Otherwise, go back to check steps 1-3. Then, use OSQL, SQLCMD, and SQL Management Studio to test sql connections. If you don't have those tools, please download SQL Express from Microsoft and you can get those tools for free.


OSQL (the one shipped with SQL Server 2000) uses MDAC.

OSQL (the one shipped with SQL Server 2005 & 2008) uses SNAC ODBC.

SQLCMD (shipped with SQL Server 2005 & 2008) uses SNAC OLEDB.

SQL Management Studio (shipped with SQL Server 2005 & 2008) uses SQLClient.


Possilbe command use be:

osql -E -SYour_target_machine\Your_instance for Windows Auth

osql -Uyour_user -SYour_target_machine\Your_instance for SQL Auth


SQLCMD also applies here. In addition, you can use “-Stcp:Your_target_machine, Tcp_port” for TCP,  “-Snp:Your_target_machine\Your_instance” for NP, and “-Slpc:Your_target_machine\Your_instance” for Shared Memory. You would know if it fails for all protocols or just some specific procotols.


At this stage, you should not see general error message such as error 26 and error 40 anymore. If you are using NP and you still see error 40 (Named Pipes Provider: Could not open a connection to SQL Server), please try the following steps:

a)       Open a file share on your server machine.

b)       Run “net view \\your_target_machine” and “net use \\your_target_machine\your_share  (You can try Map Network Drive from Windows Explorer as well)

If you get failure in b), it's very likely you have OS/Network configuration issue, which is not SQL Server specific. Please search on internet to resolve this issue first.


You can try connection using both Windows Authentication and SQL Authentication. If the tests with all tools failed, there is a good chance that steps 1-3 were not set correctly, unless the failure is logon-related then you can look at step 6.  


If you succeeds with some of the tools, but fails with other tools, it's probably a driver issue. You can post a question on our forum and give us the details.


You can also use “\windows\system32\odbcad32.exe” (which ships with Windows) to test connection by adding new DSN for various drivers, but that's for ODBC only.



Step 5: Application issue

If you succeed with steps 1-4 but still see failure in your application, it's likely a configuration issue in your application. Think about couple of possible issues here.

a) Is your application running under the same account with the account you did tests in step 4? If not, you might want to try testing in step 4 under that account or change to a workable service account for your application if possible.

b) Which SQL driver does your app use?

c) What's your connection string? Is the connection string compatible to your driver? Please check for reference.



Step 6: Authentication and logon issue

This is probably the most difficult part for sql connectivity issues. It's often related to the configuration on your network, your OS and your SQL Server database. There is no simple solution for this, and we have to solve it case by case. There are already several blogs in sql_protocols talking about some special cases and you can check them see if any of them applies to your case. Apart from that, things to keep in mind:

a) If you use SQL auth, mixed authentication must be enabled. Check this page for reference

b) Make sure your login account has access permission on the database you used during login ("Initial Catalog" in OLEDB).

c) Check the eventlog on your system see if there is more information


At last, please post question on our forum. More people could help you over there. When you post question, you can refer to this link and indicate you see failure at which step. The most important things for us to troubleshoot are a) exact error message and b) connection string.



Xinwei Hong, SQL Server Protocols
Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights

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  • Please add 4 and 6 and type the answer here:
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  • SandorVigh,

    error 10060 is:

    A connection attempt failed because the connected party did not properly respond after a period of time, or established

    connection failed because connected host has failed to respond.

    This still looks like a firewall issue if the server name is correct. Did you tried to follow my steps to troubleshoot? Is your server machine Vista/Windows Server 2008? Turning off the firewall on Vista/W2k8 is little tricky as it involves different domains.

    I would suggest you post your follow up question on our forum (mentioned at the end of the blog)



  • dmickel,

    Can you post a question on our forum and post the info in SQL Server Errorlog file?


  • Hi

    I am getting an error :

    "Message:[Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified ".

    Just to brief about my setup , It goes like this;I have a SQL server 2008 installed on Win 2008 (x64)and I also have a clinet machine installed with Win 2003(32-bit).

    Now I am trying to establish a connectivity between them by using SNAC tool (v10.0).

    Actually I am running one benchmark application script on Client machine which first tries to establish the database connectivity .

    Now I think some one can give me some clue what could be the reason for the error.I also have created Aliases on both server as well as Client machine (Was not very sure where they required to be created).

    I have been strugling all alone for quite a time now.Hope someone can help me to reach at the solution.

    Thanks & Regards,


  • Hi

    I am getting an error :

    "[DBNETLIB][ConnectionOpen (Connect()).]SQL Server does not exist or access denied"

    While accessing SQL Server 7.0 from a MS Access 2007 application. My client m/c OS: Windows XP Service Pack 2. The same access application is working on other desktop (XP SP2) in the same network. I have performed the following steps, but no hope.

    #1: I found sqloledb.rll file was missing, i placed the above resource file in appropriate location. No luck.

    #2: Tried repairing MDAC from INF folder, no luck.

    Any suggestion? Thank you in advance.

  • I am getting this error sometime only when connecting to my sql server 2000 from my client machine using isql

    OLE DB provider "SQLNCLI" for linked server "oa-citrix02" returned message "Login timeout expired".

    OLE DB provider "SQLNCLI" for linked server "oa-citrix02" returned message "An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections.".


    Server: Msg 50000, Level 16, State 1, Line 15

    Named Pipes Provider: Could not open a connection to SQL Server [5].

    OrangeNamed Pipes Provider: Could not open a connection to SQL Server [5].

  • Hello,

    I seem to be in deep trouble over a linked server setup. I have 2 servers running SQL server 2005 standard x64 SP3. I am trying to create a linked server from one to another.

    I createa link server and map a login called testuser2 (sql login) on both servers, and has sysadmin permissions. However, after running sp_addlinkedserver and sp_addlinkedsrvlogin, if I attempt running a query or run "Test Connection" the query times out or gives an error " login failed for NT AUTHORITY\ANYONYMOUS LOGON..with the client name.

    If I check in the server logs (to which I was trying to query ), it gives me an error  

    Error: 18456, Severity: 14, State: 11.

    I tried pinging and doing an nslookup from client machine and it succeeds. These are servers on same domain and in the same location. I have also ensured that both servers have named pipes enabled on them..

    I also sometimes get error 7399. Linked server authentication failed, even through I can connect remootely through the same login 'testuser2' on either server.

    Any help would be appreciated.



  • Akhil,

    Can you check this blog see if it can solve your problem?



  • Hi,

    We have some erratic performance with our .net app which uses connection pooling and has a VERY high throughput to our SQL Server 2005 database.

    We were wondering when is it appropriate to configure an additional port for SQL Server to listen on.

    There are NO error messages in the SQL Server log nor in the client logs indicating a particular problem, but netstat reports a high number of TCP failed connections.

    TCP Statistics for IPv4

     Active Opens                        = 690858

     Passive Opens                       = 140956

     Failed Connection Attempts          = 650737  

     Reset Connections                   = 6829

     Current Connections                 = 24

     Segments Received                   = 2971348717

     Segments Sent                       = 1947969915

     Segments Retransmitted              = 5448550

    Note our SQL Server version string is:

    Microsoft SQL Server 2005 - 9.00.4035.00 (X64)   Nov 24 2008 16:17:31   Copyright (c) 1988-2005 Microsoft Corporation  Enterprise Edition (64-bit) on Windows NT 5.2 (Build 3790: Service Pack 2)

    The server is a cluster using ipv4 and listening on 1433.

    Thank you,


  • Sometimes the port is not 1433

    Look in the registry using regedit.exe at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\SQLEXPRESS\MSSQLServer\SuperSocketNetLib\Tcp.

    One of the nameValue pairs has name TcpPort and a value, which is the port that the SQL Server is listening on (mine was set to 1030).

  • Hai,

    We have 2008 Server & SQL 2008.

    Networking load balancing also has been installed.

    for 6 ips and virtual ip is

    Nat policy has been created in sonicall to route the static ip to local ip.

    Now i am trying to conect the odbc it say server does not exist.

    What must be the issue

    please help me.

    Thanks & REgards

    S. Balakrishnan

  • Hai

    We have 2008 Server & SQL 2008

    Networking Load Balance has been configured

    the virual ip is

    Nat policy has been created throguh sonicwall to this ip from the public ip (static Ip).

    Now i am strying to connect the odbc. it says server does not exist

    Please help me to trouble shoot


    S. Balakrishnan

  • Thank You so much Keik. You helped determine the last port I had to unblock. I am running SQL 2008 on WS 2008. For anyone else having this issue for me I did this.

    On my Windows Server 2008 I did the following:

    1.Added an exception for the SQL Browser exe file.

    2.Added an exception for the UDP Port 1434.

    3.Found out what the listening port was by following Keik's advice which is

       "Look in the registry using regedit.exe at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\SQLEXPRESS\MSSQLServer\SuperSocketNetLib\Tcp.

    One of the nameValue pairs has name TcpPort and a value, which is the port that the SQL Server is listening on (mine was set to 1030)."

    Mine was 51070 then added the exception to that tcp in the windows firewall.

    Then boom all access finally granted. Thank you Keik for suggesting that as it finally became unblocked and now works like a champ. I have spent litterally 2 days getting this to work and I had figured that it was a simple firewall issue but was lost on where to find the information. God Bless you Sir!

  • I installed sql server 2005 (dev)

    I have a java program which takes connection from database connection string is :


    when i ru this iit works fine. I modified the code now it takes connection and with out closing it tries to take another connection second time it throws an exception msg saying:: "An I/O error occurred while receiving the TDS prelogin response."  

    I thought its because of maximum no of connection but maximum no of conn is  set to 0(ulimited).

    please help mee  

  • What version of the driver you are using?

  • Hi Ashu,

    SQL Server uses port TCP/1434 for Dedicated Administrator Connections (see

    One of the restrictions with Dedicated Administrator Connections is:

    "To guarantee that there are resources available for the connection, only one DAC is allowed per instance of SQL Server. If a DAC connection is already active, any new request to connect through the DAC is denied with error 17810."

    That is why only the first connetion succeeds.


    --David Olix [SQL Server]

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