Port 1742 (3Com-nsd)

IANA assigns port 1742 to 3Com-nsd.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

3Com-nsd TCP 3Com-nsd Nitza Steinberg -

3Com-nsd UDP 3Com-nsd Nitza Steinberg -

Linux: is anything listening on TCP 1742?

sudo ss -tlnp 'sport = :1742'

Linux: UDP 1742

sudo ss -ulnp 'sport = :1742'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1742

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1742 '

Windows (Command Prompt)

netstat -ano | findstr :1742

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1742 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 1742

From Windows

Test-NetConnection HOST -Port 1742

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

nc -vzu -w 5 HOST 1742

ufw

sudo ufw deny 1742/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1742 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1742 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1742' -Direction Inbound -Protocol TCP -LocalPort 1742 -Action Block

ufw

sudo ufw deny 1742/udp

iptables

sudo iptables -A INPUT -p udp --dport 1742 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1742 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1742' -Direction Inbound -Protocol UDP -LocalPort 1742 -Action Block

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.