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// IoT & industrial (ICS)

Port 2221: EtherNet/IP over TLS

Port 2221 is assigned by IANA to ethernet-ip-s (EtherNet/IP over TLS).

2221

How ethernet-ip-s works

IoT & industrial (ICS)
controllerPLCethernet-ip-sno authentication controllerPLCethernet-ip-sno authentication

A controller sends commands to an industrial device on port 2221, which acts on the physical process. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
IoT & industrial (ICS)
01 Security

Is port 2221 dangerous?

We have no specific security note for port 2221. Its risk depends on the program actually listening on it. General advice for iot & industrial (ics) services:

  • Industrial and IoT protocols often have no authentication: never expose them to the Internet.
  • Segment OT networks from IT and use protocol-aware firewalls.
  • Monitor with an ICS-aware intrusion detection system.
02 Registry

IANA registry entries for port 2221

ServicePortTransportDescriptionReferenceUpdated
ethernet-ip-s 2221 TCP, UDP EtherNet/IP over TLS - 2015-05-28

// source: IANA service name and port number registry

03 Check it

Which program uses port 2221, and is it reachable?

Linux

sudo ss -ltnup 'sport = :2221'      # process listening on 2221
sudo lsof -nP -i :2221

macOS

sudo lsof -nP -i :2221

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 2221 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 2221
netstat -ano | findstr :2221

From another machine

nmap -p 2221 -sV <host>
sudo nmap -sU -p 2221 <host>
nc -zv <host> 2221

Block it in the firewall

sudo ufw deny 2221/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 2221" -Direction Inbound -LocalPort 2221 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 2221 used for?

Port 2221 is assigned by IANA to ethernet-ip-s (EtherNet/IP over TLS).

Is port 2221 TCP or UDP?

Port 2221 is registered for TCP and UDP.

Is it safe to open port 2221?

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. Industrial and IoT protocols often have no authentication: never expose them to the Internet.

How do I check if port 2221 is open?

On Linux run "ss -ltnup 'sport = :2221'", on macOS "lsof -nP -i :2221", and on Windows "netstat -ano | findstr :2221" to see the local process. From another machine, "nmap -p 2221 <host>" shows whether it is reachable.

05 Related
:1883 MQTT tcp · udp · high risk :8883 MQTT over TLS tcp · udp · moderate risk :502 Modbus TCP tcp · udp · critical risk :102 Siemens S7 (ISO-TSAP) tcp · udp · critical risk :47808 BACnet udp · tcp · critical risk :20000 DNP3 tcp · udp · sctp · critical risk :44818 EtherNet/IP tcp · udp · critical risk :802 Modbus Application Protocol Secure tcp · udp

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