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Port 223 (cdc)

IANA assigns port 223 to cdc: Certificate Distribution Center.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cdc TCP Certificate Distribution Center Kannan Alagappan -
cdc UDP Certificate Distribution Center Kannan Alagappan -

Check what is listening on port 223

Linux: is anything listening on TCP 223?
sudo ss -tlnp 'sport = :223'
Linux: UDP 223
sudo ss -ulnp 'sport = :223'
Linux / macOS: which process owns the port
sudo lsof -nP -i :223
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':223 '
Windows (Command Prompt)
netstat -ano | findstr :223
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 223 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 223
From Windows
Test-NetConnection HOST -Port 223
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 223

Block port 223 in the firewall

ufw
sudo ufw deny 223/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 223 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 223 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 223' -Direction Inbound -Protocol TCP -LocalPort 223 -Action Block
ufw
sudo ufw deny 223/udp
iptables
sudo iptables -A INPUT -p udp --dport 223 -j DROP
nftables
sudo nft add rule inet filter input udp dport 223 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 223' -Direction Inbound -Protocol UDP -LocalPort 223 -Action Block

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221fln-spx222rsh-spx224masqdialer242direct

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