- Keep directory and authentication services on internal networks.
- Require signing or TLS and disable anonymous queries.
- Monitor authentication failures for spraying and brute force.
Port 221: Berkeley rlogind with SPX auth
Port 221 is assigned by IANA to fln-spx (Berkeley rlogind with SPX auth).
221
How fln-spx works
Directory & authenticationThe client proves who it is on port 221 and gets an answer (or a ticket) it can use with other services.
- Transport
- TCP · UDP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
- Directory & authentication
Is port 221 dangerous?
We have no specific security note for port 221. Its risk depends on the program actually listening on it. General advice for directory & authentication services:
IANA registry entries for port 221
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| fln-spx | 221 | TCP, UDP | Berkeley rlogind with SPX auth | - | - |
// source: IANA service name and port number registry
Which program uses port 221, and is it reachable?
Linux
sudo ss -ltnup 'sport = :221' # process listening on 221
sudo lsof -nP -i :221macOS
sudo lsof -nP -i :221
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 221 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 221 netstat -ano | findstr :221
From another machine
nmap -p 221 -sV <host> sudo nmap -sU -p 221 <host> nc -zv <host> 221
Block it in the firewall
sudo ufw deny 221/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 221" -Direction Inbound -LocalPort 221 -Protocol TCP -Action Block # Windows
What is port 221 used for?
Port 221 is assigned by IANA to fln-spx (Berkeley rlogind with SPX auth).
Is port 221 TCP or UDP?
Port 221 is registered for TCP and UDP.
Is it safe to open port 221?
It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Keep directory and authentication services on internal networks.
How do I check if port 221 is open?
On Linux run "ss -ltnup 'sport = :221'", on macOS "lsof -nP -i :221", and on Windows "netstat -ano | findstr :221" to see the local process. From another machine, "nmap -p 221 <host>" shows whether it is reachable.
Other directory & authentication ports
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp