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Port 73 (netrjs-3)

IANA assigns port 73 to netrjs-3: Remote Job Service.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
netrjs-3 TCP Remote Job Service - -
netrjs-3 UDP Remote Job Service - -

Check what is listening on port 73

Linux: is anything listening on TCP 73?
sudo ss -tlnp 'sport = :73'
Linux: UDP 73
sudo ss -ulnp 'sport = :73'
Linux / macOS: which process owns the port
sudo lsof -nP -i :73
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':73 '
Windows (Command Prompt)
netstat -ano | findstr :73
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 73 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 73
From Windows
Test-NetConnection HOST -Port 73
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 73

Block port 73 in the firewall

ufw
sudo ufw deny 73/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 73 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 73 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 73' -Direction Inbound -Protocol TCP -LocalPort 73 -Action Block
ufw
sudo ufw deny 73/udp
iptables
sudo iptables -A INPUT -p udp --dport 73 -j DROP
nftables
sudo nft add rule inet filter input udp dport 73 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 73' -Direction Inbound -Protocol UDP -LocalPort 73 -Action Block

Related ports

71netrjs-172netrjs-274netrjs-475any private dial out service

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