HTTPfy

Port 491 (go-login)

IANA assigns port 491 to go-login.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
go-login TCP go-login Troy Morrison -
go-login UDP go-login Troy Morrison -

Check what is listening on port 491

Linux: is anything listening on TCP 491?
sudo ss -tlnp 'sport = :491'
Linux: UDP 491
sudo ss -ulnp 'sport = :491'
Linux / macOS: which process owns the port
sudo lsof -nP -i :491
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':491 '
Windows (Command Prompt)
netstat -ano | findstr :491
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 491 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 491
From Windows
Test-NetConnection HOST -Port 491
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 491

Block port 491 in the firewall

ufw
sudo ufw deny 491/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 491 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 491 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 491' -Direction Inbound -Protocol TCP -LocalPort 491 -Action Block
ufw
sudo ufw deny 491/udp
iptables
sudo iptables -A INPUT -p udp --dport 491 -j DROP
nftables
sudo nft add rule inet filter input udp dport 491 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 491' -Direction Inbound -Protocol UDP -LocalPort 491 -Action Block

Related ports

489nest-protocol490micom-pfs492ticf-1493ticf-2

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