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Port 539 (apertus-ldp)

IANA assigns port 539 to apertus-ldp: Apertus Technologies Load Determination.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
apertus-ldp TCP Apertus Technologies Load Determination - -
apertus-ldp UDP Apertus Technologies Load Determination - -

Check what is listening on port 539

Linux: is anything listening on TCP 539?
sudo ss -tlnp 'sport = :539'
Linux: UDP 539
sudo ss -ulnp 'sport = :539'
Linux / macOS: which process owns the port
sudo lsof -nP -i :539
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':539 '
Windows (Command Prompt)
netstat -ano | findstr :539
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 539 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 539
From Windows
Test-NetConnection HOST -Port 539
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 539

Block port 539 in the firewall

ufw
sudo ufw deny 539/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 539 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 539 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 539' -Direction Inbound -Protocol TCP -LocalPort 539 -Action Block
ufw
sudo ufw deny 539/udp
iptables
sudo iptables -A INPUT -p udp --dport 539 -j DROP
nftables
sudo nft add rule inet filter input udp dport 539 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 539' -Direction Inbound -Protocol UDP -LocalPort 539 -Action Block

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