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Port 3651 (xrpc-registry)

IANA assigns port 3651 to xrpc-registry: XRPC Registry.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
xrpc-registry TCP XRPC Registry Slava Monich -
xrpc-registry UDP XRPC Registry Slava Monich -

Registry dates for this port: registered 2003-01.

Check what is listening on port 3651

Linux: is anything listening on TCP 3651?
sudo ss -tlnp 'sport = :3651'
Linux: UDP 3651
sudo ss -ulnp 'sport = :3651'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3651
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3651 '
Windows (Command Prompt)
netstat -ano | findstr :3651
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3651 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3651
From Windows
Test-NetConnection HOST -Port 3651
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3651

Block port 3651 in the firewall

ufw
sudo ufw deny 3651/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3651 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3651 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3651' -Direction Inbound -Protocol TCP -LocalPort 3651 -Action Block
ufw
sudo ufw deny 3651/udp
iptables
sudo iptables -A INPUT -p udp --dport 3651 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3651 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3651' -Direction Inbound -Protocol UDP -LocalPort 3651 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.