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I have installed the software on my clients system where sql server was already installed. I have installed another named instance.

I am able to login to the SQL server from another computers, when I check the settings if found that.

  1. TCP IP of my named instance is Disabled
  2. SQL Browser is running
  3. There is no UDP port open for sql browser i.e 1434
  4. SQLSever.exe is not added as exception in Firewall
  5. Firewall settings are off in the Quickheal antivirus
  6. I am using connection string as "computername\instancename" to connect

I wish to know how the are other computers able to connect when Port 1434 is off

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    You mentioned TCP/IP is disabled. Perhaps Named Pipes is enabled. – Dan Guzman Nov 29 '18 at 10:59
  • Have you tried rebooting it? In case of pending changes. – George.Palacios Nov 29 '18 at 11:17
  • yes Named pipes are enabled, but as per my knowledge to connect to an named instance sql browser is required, and UDP port should be enabled, am i correct? – Aashish Agarwal Nov 29 '18 at 11:21
  • @AashishAgarwal, yes, generally the SQL Brower service needs to be running and UDP 1434 available to connect to a named instance when the instance name specified. This allows the actual TCP port or named pipe name the instance is listening on to be determined. You mentioned that SQL Server isn't listed as a firewall exception. What about the SQL Server Browser service (sqlbrowser.exe)? – Dan Guzman Nov 29 '18 at 12:08
  • @AashishAgarwal, also, remote clients can connect to a named instance without needing SQL Browser if the instance is listening on the default TCP port or named pipe but the instance name would need to be omitted, or an explict port or pipe name specified to connect. – Dan Guzman Nov 29 '18 at 12:10
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UDP 1434 is only for the discovery of database and port. If you still have named pipes enabled and provide the correct name or IP Adress of the host where your database is running and it runs on default port 1433 you will be able to connect. With right username + password.

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  • There is also an 'SQLExpess' instance, whose Dynamic port for IPALL is 0 and TCP Port is 1433, these are also the settings for my named instance, the sqlexpress instance is also running – Aashish Agarwal Nov 29 '18 at 11:14
  • It's UDP 1434, not 1443. – Dan Guzman Nov 29 '18 at 12:11
  • @AashishAgarwal They can't both be running on port 1433 at the same time, unless you have multiple network adapters and running on completely different IPs. – Aaron Bertrand♦ Nov 29 '18 at 13:57
  • Hi @AashishAgarwal By default, when SQL Server Express is installed it gerates a random port to listen on. In addition, SQL Server Express only listens for connection on localhost. So most likely you will connect to your MSSQLSERVER Service – Frank P. Nov 29 '18 at 14:00
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    No port is required when connecting over Named Pipes. The Instance name is embedded in the pipe name, and all the Named Pipes for a server are accessible over the standard ports for NetBIOS over TCP/IP. – David Browne - Microsoft Nov 29 '18 at 14:17

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