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Port 3998 (dnx)

IANA assigns port 3998 to dnx: Distributed Nagios Executor Service.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dnx TCP Distributed Nagios Executor Service John Calcote -
dnx UDP Distributed Nagios Executor Service John Calcote -

Registry dates for this port: registered 2007-11-06.

Check what is listening on port 3998

Linux: is anything listening on TCP 3998?
sudo ss -tlnp 'sport = :3998'
Linux: UDP 3998
sudo ss -ulnp 'sport = :3998'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3998
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3998 '
Windows (Command Prompt)
netstat -ano | findstr :3998
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3998 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3998
From Windows
Test-NetConnection HOST -Port 3998
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3998

Block port 3998 in the firewall

ufw
sudo ufw deny 3998/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3998 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3998 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3998' -Direction Inbound -Protocol TCP -LocalPort 3998 -Action Block
ufw
sudo ufw deny 3998/udp
iptables
sudo iptables -A INPUT -p udp --dport 3998 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3998 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3998' -Direction Inbound -Protocol UDP -LocalPort 3998 -Action Block

Related ports

3996abcsoftware3997agentsease-db3999nvcnet4000terabase

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