🧠 SSMS Connectivity Fails Without Port, Here’s Why

IT & Systems
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:brain: SSMS Connectivity Fails Without Port, Here’s Why

Troubleshooting a subtle but frustrating SQL Server connectivity issue
:hammer_and_wrench::light_bulb::puzzle_piece::fire:

Recently, I was asked to help troubleshoot a SQL Server Management Studio (SSMS) connection issue that had gone unresolved for over two weeks. The issue turned out to be simple, but only if you knew exactly what to check.

:white_check_mark: The Problem

Two nearly identical Windows Server 2019 machines were attempting to connect to the same remote SQL Server instance using SSMS. One connected without issue using the hostname only. The other required manually specifying the port number to connect.

:brain: The Assumption

At first glance, this might look like a SQL Server configuration problem or maybe even an issue with named instances. But that wasn’t it. The issue came down to SQL Server Browser resolution (What is UDP?).

SSMS can use the SQL Server Browser service to automatically resolve the correct TCP port for a named instance. That resolution depends on UDP port 1434 being reachable from the client machine.

:magnifying_glass_tilted_left: The Clue

  • Server A could connect using only the hostname
  • Server B could not, unless the port was specified

That suggested Server A could talk to the SQL Server Browser, while Server B could not.

:test_tube: How We Confirmed It

We used portqry.exe to test UDP port 1434 from both servers:

portqry -n <SQL_SERVER_IP> -p udp -e 1434
  • Server A showed a response from SQL Browser
  • Server B timed out , confirming the port was blocked

We also confirmed that the SQL Server Browser service was actively running on the destination SQL Server.

:white_check_mark: The Fix

We opened UDP 1434 in the firewall for Server B. Once that was done, SSMS connected without needing to specify the port, just like Server A.

:brain: Why This Matters

SQL Server’s dynamic port resolution via SQL Server Browser is often overlooked, especially when it works on one machine but fails on another. If you ever run into an SSMS connection issue where you must hardcode the port, check UDP 1434 before diving into more complex diagnostics.

:link: Tools Used

:warning: Disclaimer: This example is anonymized and based on internal troubleshooting in a secure environment. Server names, networks, and IPs have been redacted.

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