Port 1434 (SQL Server Browser)

SQL Server Browser service, which tells clients the port of named instances.

Registered (user) port, 1024-49151 UDP Databases Do not expose to the internet

Port 1434 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

What port 1434 is used for

SQL Server Browser service, which tells clients the port of named instances.

Do not expose to the internet. Block at the perimeter; the SQL Slammer worm (2003) spread through UDP 1434, and it can be used for reflection.

Service nameProtoDescriptionAssigneeReference

ms-sql-m TCP Microsoft-SQL-Monitor Peter Hussey -

ms-sql-m UDP Microsoft-SQL-Monitor Peter Hussey -

Linux: UDP 1434

sudo ss -ulnp 'sport = :1434'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1434

Windows (Command Prompt)

netstat -ano | findstr :1434

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 1434

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 1434

ufw

sudo ufw deny 1434/udp

iptables

sudo iptables -A INPUT -p udp --dport 1434 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1434 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1434' -Direction Inbound -Protocol UDP -LocalPort 1434 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.