HTTPfy

Port 21848 (netspeak-acd)

IANA assigns port 21848 to netspeak-acd: NetSpeak Corp. Automatic Call Distribution.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
netspeak-acd TCP NetSpeak Corp. Automatic Call Distribution Toby Hosterman -
netspeak-acd UDP NetSpeak Corp. Automatic Call Distribution Toby Hosterman -

Check what is listening on port 21848

Linux: is anything listening on TCP 21848?
sudo ss -tlnp 'sport = :21848'
Linux: UDP 21848
sudo ss -ulnp 'sport = :21848'
Linux / macOS: which process owns the port
sudo lsof -nP -i :21848
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':21848 '
Windows (Command Prompt)
netstat -ano | findstr :21848
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 21848 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 21848
From Windows
Test-NetConnection HOST -Port 21848
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 21848

Block port 21848 in the firewall

ufw
sudo ufw deny 21848/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 21848 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 21848 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 21848' -Direction Inbound -Protocol TCP -LocalPort 21848 -Action Block
ufw
sudo ufw deny 21848/udp
iptables
sudo iptables -A INPUT -p udp --dport 21848 -j DROP
nftables
sudo nft add rule inet filter input udp dport 21848 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 21848' -Direction Inbound -Protocol UDP -LocalPort 21848 -Action Block

Related ports

21846netspeak-is21847netspeak-cs21849netspeak-cps22000snapenetio

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