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Port 4031 (suucp)

IANA assigns port 4031 to suucp: UUCP over SSL.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
suucp TCP UUCP over SSL Harald Welte -
suucp UDP UUCP over SSL Harald Welte -

Check what is listening on port 4031

Linux: is anything listening on TCP 4031?
sudo ss -tlnp 'sport = :4031'
Linux: UDP 4031
sudo ss -ulnp 'sport = :4031'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4031
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4031 '
Windows (Command Prompt)
netstat -ano | findstr :4031
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4031 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4031
From Windows
Test-NetConnection HOST -Port 4031
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4031

Block port 4031 in the firewall

ufw
sudo ufw deny 4031/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4031 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4031 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4031' -Direction Inbound -Protocol TCP -LocalPort 4031 -Action Block
ufw
sudo ufw deny 4031/udp
iptables
sudo iptables -A INPUT -p udp --dport 4031 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4031 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4031' -Direction Inbound -Protocol UDP -LocalPort 4031 -Action Block

Related ports

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