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Port 75 (any private dial out service)

IANA assigns port 75 to any private dial out service.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
- TCP any private dial out service Jon Postel -
- UDP any private dial out service Jon Postel -

Check what is listening on port 75

Linux: is anything listening on TCP 75?
sudo ss -tlnp 'sport = :75'
Linux: UDP 75
sudo ss -ulnp 'sport = :75'
Linux / macOS: which process owns the port
sudo lsof -nP -i :75
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':75 '
Windows (Command Prompt)
netstat -ano | findstr :75
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 75 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 75
From Windows
Test-NetConnection HOST -Port 75
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 75

Block port 75 in the firewall

ufw
sudo ufw deny 75/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 75 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 75 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 75' -Direction Inbound -Protocol TCP -LocalPort 75 -Action Block
ufw
sudo ufw deny 75/udp
iptables
sudo iptables -A INPUT -p udp --dport 75 -j DROP
nftables
sudo nft add rule inet filter input udp dport 75 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 75' -Direction Inbound -Protocol UDP -LocalPort 75 -Action Block

Related ports

73netrjs-374netrjs-476deos77any private RJE service

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