PortAtlas.
Well-known port (0–1023) Standard/Low risk

Port 221 FLN-SPX

Quick answer

Port 221 is the IANA-assigned fln-spx port for Berkeley rlogind with SPX auth (TCP / UDP).

Check and block Is it safe? Troubleshooting FAQ
TransportTCP / UDP
RiskStandard/Low
Typical useRemote access

What is port 221 used for?

Port 221 is assigned to fln-spx and uses TCP / UDP. The IANA registry describes the service as “Berkeley rlogind with SPX auth”. It sits in the well-known range, which operating systems reserve for core network services, so software expects it at this number by default.

Ports are the transport-layer address a service listens on. A client that wants to reach fln-spx connects to port 221. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.

Use the commands below to confirm whether port 221 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.

Browse all Remote access ports

Source: IANA Service Name and Transport Protocol Port Number Registry.

Check and block port 221

Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.

Check on Linux

sudo ss -tlpn 'sport = :221' sudo ss -ulpn 'sport = :221'

Check on Windows

Get-NetTCPConnection -LocalPort 221 -State Listen -ErrorAction SilentlyContinue Get-NetUDPEndpoint -LocalPort 221 -ErrorAction SilentlyContinue

Block with UFW

sudo ufw deny 221/tcp sudo ufw deny 221/udp

Block with iptables

sudo iptables -A INPUT -p tcp --dport 221 -j DROP sudo iptables -A INPUT -p udp --dport 221 -j DROP

These commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.

Is port 221 safe to expose?

Standard/Low

This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.

Where port 221 is usually used

Most traffic on port 221 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.

Demo

Test the listener

A TCP probe shows whether the remote-access service is reachable; the protocol client may still reject the session later.

nc -vz 127.0.0.1 221

Common problems with port 221

Connection refused or timed out

Refused usually means the host is reachable but nothing is listening on port 221. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.

Port already in use

Find the process holding the port with sudo ss -tlpn 'sport = :221' or sudo lsof -i :221. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.

Firewall rule did not survive a reboot

UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.

The port is blocked but still reachable

A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.

Port 221 at a glance

Port number221
Service namefln-spx
Transport protocolTCP / UDP
CategoryRemote access
RangeWell-known port (0–1023)
Risk levelStandard/Low
Registered assigneeNot listed
Registry descriptionBerkeley rlogind with SPX auth
SourceIANA Service Name and Transport Protocol Port Number Registry

Frequently asked questions

What is port 221 used for?

Port 221 (FLN-SPX) uses TCP / UDP. Berkeley rlogind with SPX auth.

How do I check if port 221 is open?

On Linux run `sudo ss -tlpn 'sport = :221'` and `sudo ss -ulpn 'sport = :221'`. On Windows run `Get-NetTCPConnection -LocalPort 221 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 221 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 221; empty output usually means nothing is bound to it.

How do I block port 221?

With UFW run `sudo ufw deny 221/tcp` and `sudo ufw deny 221/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 221 -j DROP` and `sudo iptables -A INPUT -p udp --dport 221 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.

Is port 221 safe to expose?

This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Nevertheless, keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.

See all Remote access ports

Primary data: IANA Service Name and Transport Protocol Port Number Registry.

Last reviewed 2026-10-30 · Methodology · About · Privacy