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Port 3431 (ndl-als)

IANA assigns port 3431 to ndl-als: Active License Server Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ndl-als TCP Active License Server Port Quentin Brown -
ndl-als UDP Active License Server Port Quentin Brown -

Registry dates for this port: registered 2002-03.

Check what is listening on port 3431

Linux: is anything listening on TCP 3431?
sudo ss -tlnp 'sport = :3431'
Linux: UDP 3431
sudo ss -ulnp 'sport = :3431'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3431
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3431 '
Windows (Command Prompt)
netstat -ano | findstr :3431
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3431 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3431
From Windows
Test-NetConnection HOST -Port 3431
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3431

Block port 3431 in the firewall

ufw
sudo ufw deny 3431/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3431 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3431 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3431' -Direction Inbound -Protocol TCP -LocalPort 3431 -Action Block
ufw
sudo ufw deny 3431/udp
iptables
sudo iptables -A INPUT -p udp --dport 3431 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3431 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3431' -Direction Inbound -Protocol UDP -LocalPort 3431 -Action Block

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3429gcsp3430ssdispatch3432osdcp3433opnet-smp

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.