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Port 903 (ideafarm-panic)

IANA assigns port 903 to ideafarm-panic: self documenting Telnet Panic Door.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ideafarm-panic TCP self documenting Telnet Panic Door Wo o Ideafarm -
ideafarm-panic UDP self documenting Panic Door: send 0x00 for info Wo o Ideafarm -

Check what is listening on port 903

Linux: is anything listening on TCP 903?
sudo ss -tlnp 'sport = :903'
Linux: UDP 903
sudo ss -ulnp 'sport = :903'
Linux / macOS: which process owns the port
sudo lsof -nP -i :903
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':903 '
Windows (Command Prompt)
netstat -ano | findstr :903
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 903 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 903
From Windows
Test-NetConnection HOST -Port 903
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 903

Block port 903 in the firewall

ufw
sudo ufw deny 903/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 903 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 903 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 903' -Direction Inbound -Protocol TCP -LocalPort 903 -Action Block
ufw
sudo ufw deny 903/udp
iptables
sudo iptables -A INPUT -p udp --dport 903 -j DROP
nftables
sudo nft add rule inet filter input udp dport 903 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 903' -Direction Inbound -Protocol UDP -LocalPort 903 -Action Block

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