HTTPfy

Port 588 (cal)

IANA assigns port 588 to cal: CAL.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
cal TCP CAL Myron Hattig -
cal UDP CAL Myron Hattig -

Check what is listening on port 588

Linux: is anything listening on TCP 588?
sudo ss -tlnp 'sport = :588'
Linux: UDP 588
sudo ss -ulnp 'sport = :588'
Linux / macOS: which process owns the port
sudo lsof -nP -i :588
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':588 '
Windows (Command Prompt)
netstat -ano | findstr :588
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 588 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 588
From Windows
Test-NetConnection HOST -Port 588
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 588

Block port 588 in the firewall

ufw
sudo ufw deny 588/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 588 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 588 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 588' -Direction Inbound -Protocol TCP -LocalPort 588 -Action Block
ufw
sudo ufw deny 588/udp
iptables
sudo iptables -A INPUT -p udp --dport 588 -j DROP
nftables
sudo nft add rule inet filter input udp dport 588 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 588' -Direction Inbound -Protocol UDP -LocalPort 588 -Action Block

Related ports

586password-chg587SMTP submission589eyelink590tns-cml

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