Port 1903 (linkname)

IANA assigns port 1903 to linkname: Local Link Name Resolution.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

linkname TCP Local Link Name Resolution Dan Harrington -

linkname UDP Local Link Name Resolution Dan Harrington -

Linux: is anything listening on TCP 1903?

sudo ss -tlnp 'sport = :1903'

Linux: UDP 1903

sudo ss -ulnp 'sport = :1903'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1903

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1903 '

Windows (Command Prompt)

netstat -ano | findstr :1903

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1903 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 1903

From Windows

Test-NetConnection HOST -Port 1903

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

nc -vzu -w 5 HOST 1903

ufw

sudo ufw deny 1903/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1903 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1903 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1903' -Direction Inbound -Protocol TCP -LocalPort 1903 -Action Block

ufw

sudo ufw deny 1903/udp

iptables

sudo iptables -A INPUT -p udp --dport 1903 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1903 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1903' -Direction Inbound -Protocol UDP -LocalPort 1903 -Action Block

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