Port 591 (http-alt)

IANA assigns port 591 to http-alt: FileMaker, Inc. - HTTP Alternate (see Port 80).

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

http-alt TCP FileMaker, Inc. - HTTP Alternate (see Port 80) Clay Maeckel -

http-alt UDP FileMaker, Inc. - HTTP Alternate (see Port 80) Clay Maeckel -

Linux: is anything listening on TCP 591?

sudo ss -tlnp 'sport = :591'

Linux: UDP 591

sudo ss -ulnp 'sport = :591'

Linux / macOS: which process owns the port

sudo lsof -nP -i :591

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':591 '

Windows (Command Prompt)

netstat -ano | findstr :591

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 591 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 591

From Windows

Test-NetConnection HOST -Port 591

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 591

ufw

sudo ufw deny 591/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 591 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 591 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 591' -Direction Inbound -Protocol TCP -LocalPort 591 -Action Block

ufw

sudo ufw deny 591/udp

iptables

sudo iptables -A INPUT -p udp --dport 591 -j DROP

nftables

sudo nft add rule inet filter input udp dport 591 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 591' -Direction Inbound -Protocol UDP -LocalPort 591 -Action Block

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