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Port 21846 (netspeak-is)

IANA assigns port 21846 to netspeak-is: NetSpeak Corp. Directory Services.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
netspeak-is TCP NetSpeak Corp. Directory Services Toby Hosterman -
netspeak-is UDP NetSpeak Corp. Directory Services Toby Hosterman -

Check what is listening on port 21846

Linux: is anything listening on TCP 21846?
sudo ss -tlnp 'sport = :21846'
Linux: UDP 21846
sudo ss -ulnp 'sport = :21846'
Linux / macOS: which process owns the port
sudo lsof -nP -i :21846
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':21846 '
Windows (Command Prompt)
netstat -ano | findstr :21846
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 21846 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 21846
From Windows
Test-NetConnection HOST -Port 21846
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 21846

Block port 21846 in the firewall

ufw
sudo ufw deny 21846/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 21846 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 21846 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 21846' -Direction Inbound -Protocol TCP -LocalPort 21846 -Action Block
ufw
sudo ufw deny 21846/udp
iptables
sudo iptables -A INPUT -p udp --dport 21846 -j DROP
nftables
sudo nft add rule inet filter input udp dport 21846 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 21846' -Direction Inbound -Protocol UDP -LocalPort 21846 -Action Block

Related ports

21801sal21845webphone21847netspeak-cs21848netspeak-acd

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