HTTPfy

Port 221 (fln-spx)

IANA assigns port 221 to fln-spx: Berkeley rlogind with SPX auth.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
fln-spx TCP Berkeley rlogind with SPX auth - -
fln-spx UDP Berkeley rlogind with SPX auth - -

Check what is listening on port 221

Linux: is anything listening on TCP 221?
sudo ss -tlnp 'sport = :221'
Linux: UDP 221
sudo ss -ulnp 'sport = :221'
Linux / macOS: which process owns the port
sudo lsof -nP -i :221
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':221 '
Windows (Command Prompt)
netstat -ano | findstr :221
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 221 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 221
From Windows
Test-NetConnection HOST -Port 221
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 221

Block port 221 in the firewall

ufw
sudo ufw deny 221/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 221 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 221 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 221' -Direction Inbound -Protocol TCP -LocalPort 221 -Action Block
ufw
sudo ufw deny 221/udp
iptables
sudo iptables -A INPUT -p udp --dport 221 -j DROP
nftables
sudo nft add rule inet filter input udp dport 221 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 221' -Direction Inbound -Protocol UDP -LocalPort 221 -Action Block

Related ports

219uarps220imap3222rsh-spx223cdc

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