Wednesday, June 20, 2012

How to Add a Linked Server

Adding a Linked server can be done by either using the GUI interface or the sp_addlinkedserver command.
Adding a linked Server using the GUI
There are two ways to add another SQL Server as a linked server.  Using the first method, you need to specify the actual server name as the “linked server name”.  What this means is that everytime you want to reference the linked server in code, you will use the remote server’s name.  This may not be beneficial because if the linked server’s name changes, then you will have to also change all the code that references the linked server.  I like to avoid this method even though it is easier to initially setup.  The rest of the steps will guide you through setting up a linked server with a custom name:
To add a linked server using SSMS (SQL Server Management Studio), open the server you want to create a link from in object explorer.
  1. In SSMS, Expand Server Objects -> Linked Servers -> (Right click on the Linked Server Folder and select “New Linked Server”)
  2. Add New Linked Server
    Add New Linked Server
  3. The “New Linked Server” Dialog appears.  (see below).
  4. Linked Server Settings
    Linked Server Settings
  5. For “Server Type” make sure “Other Data Source” is selected.  (The SQL Server option will force you to specify the literal SQL Server Name)
  6. Type in a friendly name that describes your linked server (without spaces). I use AccountingServer.
  7. Provider – Select “Microsoft OLE DB Provider for SQL Server”
  8. Product Name – type: SQLSERVER (with no spaces)
  9. Datasource – type the actual server name, and instance name using this convention: SERVERNAME\INSTANCENAME
  10. ProviderString – Blank
  11. Catalog – Optional (If entered use the default database you will be using)
  12. Prior to exiting, continue to the next section (defining security)
Define the Linked Server Security
Linked server security can be defined a few different ways. The different security methods are outlined below.  The first three options are the most common:
Option NameDescription
Be made using the login’s current security contextMost Secure. Uses integrated authentication, specifically Kerberos delegation to pass the credentials of the current login executing the request to the linked server. The remote server must also have the login defined. This requires establishing Kerberos Constrained Delegation in Active Directory, unless the linked server is another instance on the same Server.  If instance is on the same server and the logins have the appropriate permissions, I recommend this one.
Be made using this security contextLess Secure. Uses SQL Server Authentication to log in to the linked server. The credentials are used every time a call is made.
Local server login to remote server login mappingsYou can specify multiple SQL Server logins to use based upon the context of the user that is making the call.  So if you have George executing a select statement, you can have him execute as a different user’s login when linking to the linked server.  This will allow you to not need to define “George” on the linked server.
Not be madeIf a mapping is not defined, and/or the local login does not have a mapping, do not connect to the linked server.
Be made without using a security contextConnect to the server without any credentials.  I do not see a use for this unless you have security defined as public.
  1. Within the same Dialog on the left menu under “Select a Page”, select Security
  2. Enter the security option of your choice.
  3. Linked Server Security Settings
    Linked Server Security Settings
  4. Click OK, and the new linked server is created

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