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Port 25604 (idtp)

IANA assigns port 25604 to idtp: Identifier Tracing Protocol.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference
idtp TCP Identifier Tracing Protocol Huang Neng-geng -

Registry dates for this port: registered 2011-08-09.

Check what is listening on port 25604

Linux: is anything listening on TCP 25604?
sudo ss -tlnp 'sport = :25604'
Linux / macOS: which process owns the port
sudo lsof -nP -i :25604
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':25604 '
Windows (Command Prompt)
netstat -ano | findstr :25604
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 25604 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 25604
From Windows
Test-NetConnection HOST -Port 25604

Block port 25604 in the firewall

ufw
sudo ufw deny 25604/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 25604 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 25604 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 25604' -Direction Inbound -Protocol TCP -LocalPort 25604 -Action Block

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