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Port 4451 (ctisystemmsg)

IANA assigns port 4451 to ctisystemmsg: CTI System Msg.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ctisystemmsg TCP CTI System Msg Control Technology Inc -
ctisystemmsg UDP CTI System Msg Control Technology Inc -

Registry dates for this port: last modified 2011-10-28.

Check what is listening on port 4451

Linux: is anything listening on TCP 4451?
sudo ss -tlnp 'sport = :4451'
Linux: UDP 4451
sudo ss -ulnp 'sport = :4451'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4451
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4451 '
Windows (Command Prompt)
netstat -ano | findstr :4451
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4451 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4451
From Windows
Test-NetConnection HOST -Port 4451
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4451

Block port 4451 in the firewall

ufw
sudo ufw deny 4451/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4451 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4451 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4451' -Direction Inbound -Protocol TCP -LocalPort 4451 -Action Block
ufw
sudo ufw deny 4451/udp
iptables
sudo iptables -A INPUT -p udp --dport 4451 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4451 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4451' -Direction Inbound -Protocol UDP -LocalPort 4451 -Action Block

Related ports

4449privatewire4450camp4452ctiprogramload4453nssalertmgr

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