Port 990 (FTPS (implicit, control))

FTP over implicit TLS control channel (989 is the data channel).

Well-known (system) port, 0-1023 TCP File transfer and storage Expose only to trusted sources

What port 990 is used for

FTP over implicit TLS control channel (989 is the data channel).

Expose only to trusted sources. Encrypted, but needs a passive port range open as well; SFTP is simpler to firewall.

Service nameProtoDescriptionAssigneeReference

ftps TCP ftp protocol, control, over TLS/SSL Christopher Allen -

ftps UDP ftp protocol, control, over TLS/SSL Christopher Allen -

Linux: is anything listening on TCP 990?

sudo ss -tlnp 'sport = :990'

Linux / macOS: which process owns the port

sudo lsof -nP -i :990

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':990 '

Windows (Command Prompt)

netstat -ano | findstr :990

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 990 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 990

From Windows

Test-NetConnection HOST -Port 990

Replace 203.0.113.10 with the address or network you trust. With ufw, make sure the default incoming policy is deny.

ufw (one trusted source)

sudo ufw allow from 203.0.113.10 to any port 990 proto tcp

iptables

sudo iptables -A INPUT -p tcp --dport 990 -s 203.0.113.10 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 990 -j DROP

nftables

sudo nft add rule inet filter input ip saddr 203.0.113.10 tcp dport 990 accept
sudo nft add rule inet filter input tcp dport 990 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'TCP 990 trusted' -Direction Inbound -Protocol TCP -LocalPort 990 -RemoteAddress 203.0.113.10 -Action Allow

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.