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Port 3646 (xss-srv-port)

IANA assigns port 3646 to xss-srv-port: XSS Server Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
xss-srv-port TCP XSS Server Port Joe Purcell -
xss-srv-port UDP XSS Server Port Joe Purcell -

Registry dates for this port: registered 2003-01.

Check what is listening on port 3646

Linux: is anything listening on TCP 3646?
sudo ss -tlnp 'sport = :3646'
Linux: UDP 3646
sudo ss -ulnp 'sport = :3646'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3646
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3646 '
Windows (Command Prompt)
netstat -ano | findstr :3646
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3646 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3646
From Windows
Test-NetConnection HOST -Port 3646
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3646

Block port 3646 in the firewall

ufw
sudo ufw deny 3646/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3646 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3646 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3646' -Direction Inbound -Protocol TCP -LocalPort 3646 -Action Block
ufw
sudo ufw deny 3646/udp
iptables
sudo iptables -A INPUT -p udp --dport 3646 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3646 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3646' -Direction Inbound -Protocol UDP -LocalPort 3646 -Action Block

Related ports

3644ssowatch3645cyc3647splitlock-gw3648fjcp

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