Connecting to SQLExpress Database takes long time

Question

Connecting to SQLExpress Database takes long time

Lorne Johnson 0

Upgraded .net 4.8 C# app to .net 8. The new version takes 30 seconds to connect to SQLExpress database on server (\ServerName\SQLExpress). Original version took less than 1 second to connect to same server. Management Studio and reporting tool also take less than 1 second to connect. Built a small app in .net 6 and 8 and both take 30 seconds to connect. Once the first connection completes all of the subsequent connections are less than a second. Looking for advice as to where I can look to figure out where the delay is cominmg from. I believe I have ruled out network traffic and the server. Seems .net 6/8 first connection is taking a long time to resolve but once it does it is fine.

Here are the commands I am using:

        CPLdbconnect = ("Data Source = Server\\sqlexpress; " +

        "Initial Catalog = CPL; " +

        "Persist Security Info = True; " +

        "User ID = userid; " +

        "Password = password; " +

        "TrustServerCertificate = True; " +

        "Connect Timeout = 60; ");

.net 6 - using System.Data.SqlClient.SqlConnection con = new(CPLdbconnect);

.net 8 - using Microsoft.Data.SqlClient.SqlConnection con = new(CPLdbconnect);

con.Open();

SurferOnWww 5,926 Reputation points

2025-05-20T01:33:18.32+00:00

How did you install your SQL Server Express? Are you aware that if you installed SQL Server Express with default settings, a named instance of SQLEXPRESS is used and SQL Server Browser is required for remote connection.

See the Microsoft document SQL Server Express Default and Named Instances for detail.

2 answers

Your answer

SurferOnWww 5,926 Reputation points

2025-05-20T01:33:18.32+00:00

How did you install your SQL Server Express? Are you aware that if you installed SQL Server Express with default settings, a named instance of SQLEXPRESS is used and SQL Server Browser is required for remote connection.

See the Microsoft document SQL Server Express Default and Named Instances for detail.

Answer 1

If your connection to SQL Server is fast locally (~0.3s) but takes ~5 seconds from another machine in the same LAN, and you're using IP + port (e.g. 192.168.1.10,1433), the issue may not be SQL Server itself.

In my case, I was using:

Microsoft SQL Server 2022
Microsoft.Data.SqlClient
SQL authentication (sa)
Encrypt=True and TrustServerCertificate=True

Telnet to port 1433 was instant, so network connectivity was fine. However, connection.Open() consistently took ~5 seconds.

After running Wireshark, I noticed this pattern before the TDS pre-login:

TCP handshake (instant)
Several NBNS (NetBIOS Name Service) broadcasts
ICMP “Port Unreachable” responses
Only then TDS pre-login started

The delay happened during those repeated NBNS attempts.

Root Cause

Windows was attempting NetBIOS name resolution before proceeding, even though I was connecting via IP address. Because no WINS server was present, it retried multiple times and waited for timeouts (~5 seconds total).

Fix

On the client machine, disable NetBIOS over TCP/IP:

Open Network Connections
Right-click your active adapter → Properties
Select Internet Protocol Version 4 (TCP/IPv4) → Advanced
Go to the WINS tab
Select: Disable NetBIOS over TCP/IP
Reboot (not required)

After disabling NetBIOS, the connection time dropped from ~5 seconds to <0.5 seconds.

Why This Happens

If:

Machines are in a workgroup (no domain)
No WINS server exists
NetBIOS is enabled

Windows may try legacy name resolution and wait for timeouts before continuing. This delay appears at the application level as a slow Open() call.

Tomaž Žveglič 0 Reputation points

2026-03-05T17:39:21.5+00:00

You can also resolve this issue by adding the IP address and hostname to the hosts file.

Answer 2

.net core uses tcp/ip to connect. this can be an issue when connecting to a named instance. its assumed a named instance is using a dynamic port, so it must connect to sql browser service to get the dynamic port. but you are probably not running the browser service.

to speed up connection, have SQLExpress support a fixed port, and specify in the connect string:

https://dotnet.territoriali.olinfo.it/en-us/troubleshoot/sql/database-engine/connect/static-or-dynamic-port-config

if you need dynamic ports be sure the sqlbrowser is setup correctly:

https://dotnet.territoriali.olinfo.it/en-us/sql/tools/configuration-manager/sql-server-browser-service?view=sql-server-ver16

note: you old code is probably using named pipes (netbios) to connect.

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Connecting to SQLExpress Database takes long time

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Root Cause

Fix

Why This Happens

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