Port 1434 (SQL Server Browser): Uses and Security

What uses port 1434

Clients connecting to server\INSTANCE ask the SQL Server Browser on UDP 1434 which TCP port that named instance is using. If you give each instance a fixed port and put it in the connection string, the Browser service isn’t needed. The 2003 SQL Slammer worm spread through this port.

Should port 1434 be open to the internet?

Keep private. Never expose this port to the internet. Keep it on localhost, a private network or behind a VPN or SSH tunnel.

Check what is listening on port 1434

Linux

sudo ss -lunp 'sport = :1434'

macOS

sudo lsof -nP -iUDP:1434

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 1434
netstat -ano | findstr :1434

No output means nothing is listening. If a service should be, check that it is running and which address it binds to: 127.0.0.1 only accepts local connections, 0.0.0.0 or :: accepts them on every interface.

Allow port 1434 from trusted networks only

The examples allow 1434 only from 10.0.0.0/8; replace it with your own private network, office IP or VPN range.

Ubuntu / Debian (ufw)

sudo ufw allow from 10.0.0.0/8 to any port 1434 proto udp
# Close it again:
sudo ufw delete allow from 10.0.0.0/8 to any port 1434 proto udp

RHEL / Fedora / Rocky (firewalld)

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="10.0.0.0/8" port port="1434" protocol="udp" accept'
sudo firewall-cmd --reload

Windows (PowerShell, as administrator)

New-NetFirewallRule -DisplayName "SQL Server Browser 1434/UDP" -Direction Inbound -Protocol UDP -LocalPort 1434 -Action Allow -RemoteAddress 10.0.0.0/8

On AWS, Google Cloud and Azure, also allow the port in the security group or network firewall rules; host firewalls and cloud firewalls are separate.

Test port 1434 from another machine

macOS / Linux

nc -zvu example.com 1434   # UDP has no handshake, so "open" isn't conclusive

Related ports

Port 1433 (Microsoft SQL Server): the default port for Microsoft SQL Server.

More databases ports

1521 (Oracle Database) , 3306 (MySQL / MariaDB) , 5432 (PostgreSQL) , 6379 (Redis) , 8086 (InfluxDB) , 9042 (Cassandra / ScyllaDB) , 9200 (Elasticsearch / OpenSearch) , 9300 (Elasticsearch transport) . See all ports in the port lookup.

Sources

IANA port registry: 1434

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Frequently asked questions

What is port 1434 used for?

Port 1434 is used by the SQL Server Browser service to locate named instances. Clients connecting to server\INSTANCE ask the SQL Server Browser on UDP 1434 which TCP port that named instance is using. If you give each instance a fixed port and put it in the connection string, the Browser service isn’t needed. The 2003 SQL Slammer worm spread through this port.

Is it safe to open port 1434?

Never expose this port to the internet. Keep it on localhost, a private network or behind a VPN or SSH tunnel. Allow it only from the networks that need it, as in the firewall examples on this page.

How do I check if port 1434 is open?

On the server, list listening sockets with "sudo ss -lunp 'sport = :1434'" on Linux or "sudo lsof -nP -i :1434" on macOS. From another machine, UDP has no handshake, so a port scan can’t reliably tell whether it is open; test with a real client for the service instead.