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Port 3631 (cs-services)

IANA assigns port 3631 to cs-services: C&S Web Services Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cs-services TCP C&S Web Services Port Computer Software Gm -
cs-services UDP C&S Web Services Port Computer Software Gm -

Registry dates for this port: registered 2002-10.

Check what is listening on port 3631

Linux: is anything listening on TCP 3631?
sudo ss -tlnp 'sport = :3631'
Linux: UDP 3631
sudo ss -ulnp 'sport = :3631'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3631
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3631 '
Windows (Command Prompt)
netstat -ano | findstr :3631
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3631 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3631
From Windows
Test-NetConnection HOST -Port 3631
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3631

Block port 3631 in the firewall

ufw
sudo ufw deny 3631/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3631 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3631 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3631' -Direction Inbound -Protocol TCP -LocalPort 3631 -Action Block
ufw
sudo ufw deny 3631/udp
iptables
sudo iptables -A INPUT -p udp --dport 3631 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3631 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3631' -Direction Inbound -Protocol UDP -LocalPort 3631 -Action Block

Related ports

3629escvpnet3630cs-remote-db3632distcc3633wacp

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