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Topics from the Microsoft SQL Server Protocols team - Netlibs, TDS, SQL Browser, etc...
Unable to connect to a SQL Server named instance on a cluster

We have been seeing several occurrences where users failed to connect to SQL Server named instance on cluster. The error messages are usually as follow:

 

For SNAC:

C:\>osql -E -S cluster\inst

[SQL Native Client]SQL Network Interfaces: Error Locating Server/Instance Specified [xFFFFFFFF].

[SQL Native Client]Login timeout expired

For MDAC:

C:\>osql -E -S cluster\inst

[DBNETLIB]Specified SQL server not found.

[DBNETLIB]ConnectionOpen (Connect()).

 

In all occurrences, customers already tried some basic steps for solving similar issues, such as, enabling TCP protocol, enabling remote connection, put SQL Server named instance into firewall exception list, etc. After we tracked down to the issues, we found that it's a combination of the specifics of Windows Cluster and the way we discover SQL Server named instance. When connecting to SQL Server named instances, our client components rely on SQL Browser to discover the server and its parameters. The discovery process is:

 

The client sends a UDP packet to SQL Browser on the target machine. When the named instance is on a windows cluster, the packet is sent to the cluster IP (or more specifically, the IP address corresponding to the virtual SQL Server). However, SQL Browser is not cluster-aware and listens on IP ANY. When SQL Browser receives the UDP request packet, it sends a response UDP packet back the client. The destination IP address is the client's IP address, however, the source IP address is changed. It's now the IP address for the NIC card on the physical machine, rather than the virtual SQL Server IP address. The source IP address of the response UDP packet is determined by Windows OS, based on the routing table. Because both virtual SQL Server IP address and the IP address attached to physical NIC are usually on the same subnet (thus belong to same route), physical IP address is selected preferably. Depends on the security settings on the client and server machines, this response UDP packet may be dropped because the peer IP address is changed. We have been seeing that the response packet is dropped by Firewall and/or IPSec.

 

Windows Firewall does not drop the packet. However, a third-party firewall may drop the packet. In addition, IPSec may also drop the packet if IPSec policy is enabled on the client and it can not establish a trust connection between the client and server. (Important update: If your client is a Vista machine, you will see this issue. A workaround is to specify tcp port or pipe name in your connection string directly.)

 

We decided not to fix this minor issue because it is determined by the nature of UDP protocol. A UDP socket can response to multiple senders and the socket layer never knows which one it is actually replying to. We may consider letting SQL Browser listen on individual IPs but the cost will be high. A workaround is to specify TCP port number in the connection string in which case we bypass the discovery process.

 

Please refer to the following links for additional information. The articles talk about issue for SQL Server 2000, but it also applies to SQL Server 2005 as the fundamentals did not change.

http://support.microsoft.com/?kbid=888228

http://support.microsoft.com/default.aspx?scid=kb;[LN];318432

 

*********Important update 2: regarding SQL Server 2008. ***************

We had a fix for this issue in SQL Server 2008. Unfortunately, the fix is still partial. We identify another issue which invalidate the fix on X64 machine. Other than that, the issue is fixed if the server is SQL Server 2008 on Vista/Windows Server 2008 on X86/IA64. We don't have to do anything on the client side for these scenario. Note: the issue still applies to all version of SQL Server 2005.

 

Update3: (Mar/2009)

If you upgrade your OS to Vista SP2 or Windows Server 2008 SP2, and your SQL Server 2008 is SP1, the partial issue on X64 is fixed. Meanwhile, we identified another related issue which affect the ability to enumrate SQL instances on Vista/Windows 2008 on network . The fix is also in SQL Server 2008 SP1.

 

 

 

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

Posted: Monday, February 27, 2006 6:26 AM by SQL Protocols

Comments

trac said:

You said that this issue won't fix; so what do we do now (after search knowledge base for enabling TCP/IP port and some more)
# May 4, 2006 12:23 AM

SQL Protocols said:

As I mentioned in the blog: "A workaround is to specify TCP port number in the connection string in which case we bypass the discovery process. "

Also, you can change your Firewall/IPSec settings so that this response UDP packet won't be filtered. E.g, put your client application under exception list of your firewall.

Thanks.
Xinwei
# May 4, 2006 1:31 PM

Len Binns said:

Would installing SQL2005 as a default instance (instead of a named instance) help avoid the problem?  Since you can only have one named instance per virtual server (in a clustered environment), what is the advantage of a named instance over a default instance anyway?
# May 31, 2006 4:56 PM

Xinwei said:

If it's default instance, client can connect the server using default port number (1433). So, it's not an issue unless you change the server TCP port.

For the other question, Yes. One named instance per virtual server. But, you can install multiple virtual servers on one physical machine, in which case, you would need named instances so that we can distinguish those instances on the physical machine.
# June 1, 2006 12:44 AM

Erik Van Reeth said:

We do have the same phenomenon.

When running osql on the cluster node, randomly the connection fails or succeeds.

When doing this workaround to specify the port, than it works.

Is this bug in SQL Browser still not fixed in the upcoming SQL2005 SP2 ?

# December 6, 2006 8:08 AM

Microsoft » Blog Archives » SQL Protocols : Unable to connect to a SQL Server named instance on a said:

PingBack from http://chaespot.com/mssql/2007/02/24/sql-protocols-unable-to-connect-to-a-sql-server-named-instance-on-a/

# February 24, 2007 5:25 PM

lukek said:

would this scenario also apply to multiple instances on a host, each bound to two VLANs on two NICS?

# March 7, 2007 5:53 AM

Xinwei Hong said:

Your scenario is different. Say you have IP1 on VLAN1 and IP2 on VLAN2. SQL Instance 1 listens on IP1, SQL Instance 2 listens on IP2. SQL Browser listens on IP ALL. You can only make a SQL connection to INST1 from VLAN1 and to INST2 from VLAN2. In this case, UDP packets input/output from the same IP address on the server, so no such issue. If you try to connect to INST1 from VLAN2 or INST2 from VLAN1, you will fail. But that's because of routing, not because of Firewall issue I described.

Please let me know if your scenario is different than what I just assumed.

# March 7, 2007 12:25 PM

lukek said:

thanks for the feedback - our setup is slightly more complicated : SQL 2005 - two instances listening on both vlans, and one sql 2000 instance.

We were getting intermittent prelogin failures to the SQL 2005 instances, but usage is currently light so its hard to get accurate pictures.

I changed the bindings on the SQL 2005 instances so that they listen on only one VLAN and we still get the issue. I'm planning to simplify further as the second VLAN was only required for internet access for service pack 1.. so I'll take that out of the equation, and hopefully that will cure the problem - otherwise I'll have to start looking at removing the sql2000 instance.

# March 9, 2007 6:49 AM

Xinwei Hong said:

The issue I mentioned in the blog only happens when you connect one IP but the return packet changed the server IP to another one. With two VLANs, networks are seperated by lower layer(link layer). IPs usually won't be messed up. Unless your client also attachs to both VLANs, you should not see the issue I mentioned. Also, if you do have this issue, you won't be able to connect your server at all (without the workaround). Since you see intermittent pre-login error, I believe your issue is different.

What's the exact error message?

# March 9, 2007 12:29 PM

lukek said:

removing the multiple vlans has cured the problem, thanks.

exact error message was: The SQLBrowser service was unable to process a client request.

# April 26, 2007 9:46 AM

SQL Protocols said:

Users often see this error message when connection to a SQL Server and don't know where to start to solve

# May 13, 2007 6:35 PM

Mike said:

So is this a bug that will be corrected in a Service pack at some point? I am hoping it is not as I have the same issue in an active active cluster each with a named instance.

Thanks,

Mike

# September 18, 2007 1:18 PM

Xinwei Hong said:

You can consider this as a bug for us, but its origin is the nature of UDP. We hope to fix this in coming releases. For now, you can either use the workaround I mentioned, or define an exception between your server and client on your client Vista machine. Thanks.

# September 18, 2007 1:43 PM

Rob P said:

I'm trying to register a database engine (named instance of a cluster) in SQL Server Management Studio and I can't connect.  I also can't connect if I drop down to osql.  I've added exceptions to my firewall for ports and programs but still no luck.  If I try to register or connect to the default instance of the cluster I can connect fine.  It's only the named instance which I'm having problems with.  It also only happens on one PC.  I hate to refresh the PC if there's a workaround.  Any ideas?

# October 3, 2007 9:04 AM

Xinwei Hong said:

Can you check my following blog about Connection Alias: http://blogs.msdn.com/sql_protocols/archive/2007/01/07/connection-alias.aspx

Make sure you don't have an outdated entry there on the machine you have problem. Thanks.

# October 3, 2007 1:18 PM

Mark Sowul said:

Ran into the same issue on a multihomed SQL box.  I connect using IP 1, SQL Browser response comes back on IP 2 and sure enough, the client firewall blocks it (this is on Vista).

# February 25, 2008 12:25 PM

SQL Protocols said:

Hi, Mark

We have a fix for this in SQL Server 2008(will be released mid this year). If your server is  SQL Server 2008 and the OS is Vista/Win2008, you will not see this issue anymore.

# February 25, 2008 12:50 PM

Mark Sowul said:

If this has been a problem since SQL 2000, how come it's taken so long to get it fixed?

# February 25, 2008 8:52 PM

Scott Monte said:

I'm trying to connect to a clustered server (SQL 2000) with two named instances on two nodes in the cluster, and i have tried setting up sql alias entries for each, using both named pipes:

\\192.168.104.51\pipe\$$\CACLMSDBINST1\MSSQL$LMSINST1\sql\query

and tcp

192.168.104.51,1461

Both of which i got from the server configuration. The IP address is the sql cluster ip address, not either named instance ip, which i believe is correct.. The other variable here is i am trying to connect through a VPN. Where should i start looking next as far as firewall rules on the other side of the vpn, etc?

# March 25, 2008 9:48 PM

Jeff Bennett said:

Does anyone see these type of login failures showing up on stand-alone servers with multiple instances of SQL 2005 and 2000 installed?  The OS is win2000 sp2

# May 23, 2008 11:32 AM

SQL Protocols said:

On a Windows Cluster it is possible to install a SQL Server Cluster, which will be a separate entity

# June 16, 2008 11:02 PM

dbrooks7 said:

We have intermittent issues with connecting to named instances of Analysis Services on a cluster.  So, does the initial situation described by Xinwei apply in this case?  It seems that the situation described either always works or never works.

# July 28, 2008 4:34 PM

SQL Protocols said:

dbrooks7,

This blog does not applies your case. The discovery of Analysis Service is totally different. SQL Browser will load a dll which takes care of AS discovery.

Thanks. Xinwei

# July 30, 2008 1:14 AM

Tone Poem said:

Top things I always forget when logging into SQL Server:   1. SSL Self-Signed Cert Does Not Work

# August 28, 2008 6:56 PM

Joseph Swann said:

Have they come out with a Fix to this yet? I've prefer named instances over Default but i've run into this problem as well and opened ports, enabled remote connections, pinged, shared drives, folders... everything short of glueing the two servers together. It simply acts as if it doesn't want to connect to the named instance

Have they come out with a Patch yet, or and upgrade/ fix?

# September 4, 2008 5:34 PM

Xinwei Hong said:

We had a fix in SQL Server 2008 for this issue. However, we found another issue and this issue makes the fixs does not work for x64 machine (server machine). So, if your server is SQL Server 2008 on Vista/Win2k8 on X86/IA64, you should have no problem connecting to your server even if you have firewall enabled on your client Vista/W2k8 machine. Thanks.

# September 8, 2008 1:41 PM

David said:

I have also been stalled by Error:26 issue.

The followings are my current installed applicaions and related info:

1. OS: Vista Home Premium with SP1

2. SQL Server 2005 SP1 and SQWL Server Management Studio Express edition.

3. Web Developer 2008 Express.

Symptom:

When I tried to create a connection to SQL Server by clciking the mdf in Database Explorer of VWD, it displayed the Error 26. However, I can attach the mdfs in Management studio and access the file at all.

Thank you in advance for any idea.

# September 25, 2008 12:29 AM

John Teutsch said:

I am trying to connect from Server 2008x64 to Clustered SQL 2008x64 on Server 2008x64, (named instance) and I continually get the error 26. Have checked all the issues you list. When will the fix for Server 2008 x64 - Clustered SQL 2008 be available?

Thanks,

# October 26, 2008 2:58 PM

John Teutsch said:

Nevermind. Firewall was "on", albeit showed up as red in control panel because wasn't configd with all of the recommened settings.

# October 26, 2008 5:51 PM

Lakshmi said:

I have been able to connect to Sql Express using the Data connection Wizard.But when I connect using code I have an error that says that remote connection is not possible error 40.In spite of doing all possible changes to the settings of SQL Config manager and firewall. Please help me fix this problem.Thanking you in advance.

# November 10, 2008 1:05 AM

SQL Protocols said:

What's the connection string in your code?

Do you run your code and Data connection Wizard under different account? Can you make sure the account under which you run your code has permission to at least open a fileshare to the target machine(if not local)?

Thanks,

Xinwei

# November 12, 2008 1:44 PM

Miles said:

we installed 2 virtual server on a cluster, each with 1 named instance but no DEFAULT instance. we set the port for both instances to 1433, do we still have to specify "server=ip,1433" in the connect string?

# November 26, 2008 10:41 PM

Florian's weblog said:

If you have a clustered SQL Server 2000 or SQL Server 2005 you might have the following error message:

# December 4, 2008 10:07 AM

Pieter Kops said:

We had similar issues.

The servers on the LAN side worked fine. The one in the DMZ could not connect to the SQL server. We could ping it and browse.

The reason it didn't work in our network was this.

The SQL browser listened on IP adres 10.0.0.44 (the IP address of the virtual node) and replied using the IP address of the physical node.

Our Firewall blocked the packet because it was no reply to a request and therfore had no business getting into the DMZ.

After creating a policy in the Firewall allowing the ip address to access the DMZ it all worked fine.

# December 23, 2008 7:35 AM

Ben Miller said:

There have been a couple of issues that keep pestering the SQL Server community for those that use Vista

# February 13, 2009 1:08 PM

Spike Robinson said:

We are about to move a very large number of databases from SQL2000 and SQL2005, on to a SQL2005 Cluster. As I am reading this article, named instance resolution on SQL2005 Clusters is going to break with Vista, and also break with any app or device that enforces strict UDP i.e. checks that the IP address of the reply matches the IP address of the original destination. This is an important test to apply because it screens off a lot of serious UDP attacks, including attacks that target SQL Server specifically.

Xinwei, you are saying the problem originates in the UDP protocol but is it not the case that this could be fixed in the SQL Browser Service? Other services can listen on specific IPs and ports, is it that expensive to have the *option* to configure SQL Browser the same way?

I also have another suggestion that you can implement which is much less expensive and makes the Browser service compliant with correct UDP checks. Have the Browser Service inspect the UDP packet header and check the destination address. If the destination address is an available direct attached interface and routable to the sender, have the Browser Service send the response packet with an origin address of this interface, via the interface. That will then pass strict UDP checking and contribute to everyone's security.

As a bonus you could also have the Browser (optionally) discard packets that had a (forged) origin on a local interface or a (forged) destination that is not a local interface.

We really need this fixed on 2005, not just 2008. To be honest we are avoiding Vista as it's a nightmare. But we still need our SQL2005 Cluster to work properly. Microsoft should make sure that all its supported products comply with security best practices. Sending UDP replies, with a different origin than they were originally sent to, does not comply.

I hope you will be able to do something. Thanks very much to Xinwei and other contributors for all the excellent information here, it has helped us understand this problem.

# April 20, 2009 4:47 PM

MB said:

Please let me know in case there is any solution.

# May 22, 2009 6:05 AM

Man On The Way said:

I have 2-node SQL Server 2005 Cluster which configured as Active/Passive mode, let say A node and P node. I already install 1 CRM instance on this cluster before. Now I wanna to install a second 2-node cluster on these...

# May 29, 2009 4:09 AM

slipknot said:

Below is the error that SSIS is throwing when trying to connect to a NAMED SSAS instance on a windows CLUSTER

A connection cannot be made to redirector. Ensure that 'SQL Browser' service is running.

# June 3, 2009 2:22 PM

LC said:

The issue still isn't fixed when running Windows 2008 Ent Server w/SP2 and SQL 2008 Ent w/SP1 and CU1.  We're running sql with 2 VLANs (1 for Production and 1 for Backups) and we're still getting the infamous "The SQLBrowser service was unable to process a client request." error.  It's crippling our website and causing a lot of pain.  You mention adding the port to our connection string as a workaround which may help, but it doesn't help SQL Server Agent.  SQL Server Agent jobs (mostly T-Log backups) fail constantly with the SNAC error above.  I'm guessing it's b/c they log in via one VIP then write the backups down the 2nd VIP?    

I should note we recently upgraded the servers in-place from SQL 2005 w/SP2 and CU9 (OS stayed the same).  We never experienced this issue on SQL 2005 which is ironic b/c it seems it's been a chronic problem since the Browser's inception.  Now when it's supposed to be fixed we finally get burned.  

Please don't let this drag out like the security cache fix for SQL 2005....took multiple tries/hotfixes to finally resolve it.  

# June 22, 2009 11:04 AM

Keith said:

We ran into this as well.  We solved the problem by adding a firewall exception rule to the Vista Client box that allowed all traffic / all ports between the client PC and the Server IP Address.  We figured if the SQL Cluster got hacked we would have bigger problems than it attacking the clients.

# July 8, 2009 7:41 PM

Rx said:

Linked Server from SQL Server 2005 (on cluster) and to SQL Server (web edition) 2008 - not on cluster.

SQL 2008 has a server\dbInstanceName using SQL Server security (username & password) for a WebData database.

I am trying enterprise manager from 2005 to connect to the 2005 db - and get SQL Network Interfaces, error: 28 - server doesn't support requested protocol

Do I need to turn on a port?

Is there a sequesnce to connect?

e.g. 10.1.2.1\dbInstance  

# September 25, 2009 12:19 PM

SQL Protocols said:

Rx,

It's error 26. Did you try the steps in the blog?

http://www.bing.com/search?q=sql+protocol+error+26&form=QBLH&qs=n

Thanks.

Xinwei

# September 25, 2009 6:00 PM

Yogesh Patil said:

I have strange issue where in I am unable to connect to SQL server over local LAN. However I do not have any issue

a) if RDP to other server and try to connect from it. b) if I am on VPN then I do not have any issue.

c) if I try to connect <IPAddress>,<Port> then I am able to connect over local LAN through desktop.

Note:- IP Address of server has been changed recently and person who is in same subnet as me is able to connect to server without any issue.

Any help on it would be appreciated.

# October 26, 2009 11:08 AM

SQL Protocols said:

Hi Yogesh,

 Rather than leaving comments on this blog with questions, please post questions on the MSDN SQL Server Data Access Forum: http://social.msdn.microsoft.com/Forums/en-US/sqldataaccess/threads. When you start a thread there, please include the full, exact error message that appears when you fail to connect.

# October 26, 2009 11:18 AM

pp-roni said:

Hi i have the same issue sometime ago and i just start Sql Server Browser in services

hope it works for anotherones of you

# October 28, 2009 12:14 PM

Dee said:

Hi,

My installattion is on my Local Machine.

I reinstalled SQL Server 2005 and am unable to connect to the server.

I am using Windows authentication Mode. My computer Name is NINJA.

So I used the server name as NINJA\SQLEXPRESS.

It is giving Error 26.

TITLE: Connect to Server

# November 11, 2009 8:05 PM

Michael said:

The problem for us was the binding order on the NIC's as we had recently enabled new ones. Correct the binding order in network connections then reboot.

# November 25, 2009 8:16 AM
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