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Port 1091 (ff-sm)

IANA assigns port 1091 to ff-sm: FF System Management.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ff-sm TCP FF System Management Fieldbus Foundation -
ff-sm UDP FF System Management Fieldbus Foundation -

Check what is listening on port 1091

Linux: is anything listening on TCP 1091?
sudo ss -tlnp 'sport = :1091'
Linux: UDP 1091
sudo ss -ulnp 'sport = :1091'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1091
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1091 '
Windows (Command Prompt)
netstat -ano | findstr :1091
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1091 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1091
From Windows
Test-NetConnection HOST -Port 1091
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1091

Block port 1091 in the firewall

ufw
sudo ufw deny 1091/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1091 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1091 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1091' -Direction Inbound -Protocol TCP -LocalPort 1091 -Action Block
ufw
sudo ufw deny 1091/udp
iptables
sudo iptables -A INPUT -p udp --dport 1091 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1091 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1091' -Direction Inbound -Protocol UDP -LocalPort 1091 -Action Block

Related ports

1089ff-annunc1090ff-fms1092obrpd1093proofd

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