What is Port 9100?
by Colin Cohen | Published on October 18, 2024
Port 9100 is dedicated to raw network printing. It allows a device to send a printer-ready file over a TCP/IP network to a printer that’s listening on the port, which then prints the file.
To understand port 9100, you need to understand network printing.
In today’s world, printers are devices that exist in a TCP/IP network in the same way that computers do. To print a document to a network printer, you can use various ports, protocols and systems. Network printers often listen on port 9100 for raw print jobs, especially in Windows environments and when using the Common Unix Printing System (CUPS).
When a network printer uses port 9100, a client sends a printer-ready file (raw printer data) to it over an unencrypted and unauthenticated TCP connection, and the printer then prints the file.
Technical Aspects
When using Windows or CUPS, the default network printing port is typically port 9100. This is because it allows a client to send a printer-ready file to a network printer over TCP/IP quickly and reliably. However, when using port 9100, there is no authentication of the connection and there is no encryption of the printer data.
Printing documents to a network printer over port 9100 exists in the Session, Presentation and Application layers of the Open Systems Interconnection (OSI) model.
Protocol Association
When you send print jobs to network printers over port 9100, you do so using TCP as a transport protocol. This is because TCP, unlike User Datagram Protocol (UDP), supports the type of reliable, error-free connections that are necessary for printing documents.
What is Port 9100 Used for?
Printers use port 9100 for raw network printing. They listen on the port for print jobs from clients on a network.
Primary Functions
The primary purpose of port 9100 is to facilitate network printing. It allows clients to send printer-ready files (raw printer data) to a network printer in a fast and reliable way. But it doesn’t use authentication or encryption.
Industry Use Cases
In Windows environments, and in environments where CUPS is run, port 9100 is typically the default port for network printing. It allows clients to quickly and effectively send printer-ready files to network printers. Printers listen on the port for print jobs sent by clients over a network and print them when the jobs are received.
How to Ensure Port 9100 is Secure
As there are many serious exploitation risks associated with port 9100, it is important to secure the port on your devices. Toward this end, you should know how to close the port in your firewalls.
Exploitation Risks
Using port 9100 for raw network printing can come with serious risks, as there is no support for authentication or encryption. This can lead to the following exploitations:
Privilege escalations
Information disclosure
Denial-of-service (DoS) attacks
Remote code executions (RCEs)
Because of this, it is important to properly secure port 9100.
Best Practices for Security
If you are using port 9100 for network printing, you should block connections to it from external IP addresses. This may require you to set up a virtual private network (VPN) to allow remote users to print to your network printers.
You can also consider using Internet Printing Protocol (IPP) instead of raw network printing, as it supports both authentication and encryption.
Disabling and Closing Port 9100
To block port 9100 in Windows, do the following:
Open the Firewall Control Panel by running firewall.cpl in a command prompt.
Select Advanced Settings and click Inbound Rules.
Click New Rule under Action.
Select TCP and Specific local ports, and enter 9100.
Under Action, select Block the connection and click Next.
Under Profile, select Domain and Private and click Next.
Under Name, enter a name for the rule and click Finish.
Repeat steps 2 through 7 for Outbound Rules.
Monitoring and Troubleshooting Port 9100
If your organization uses port 9100 for network printing, you need to know how to detect traffic on the port. You also need to know how to resolve conflicts relating to the port.
Detecting Port 9100 Activity
To determine whether port 9100 is open on a printer, run the following command from a command prompt or terminal:
netstat-aonResolving Port 9100 Conflicts
Only one service can listen to port 9100 at a time. If you want your network printer to listen for print jobs on port 9100 and discover through the netstat command that another service is listening on this port, you will need to disable this other service before the printer can start listening.
Frequently Asked Questions
The following FAQs answer questions typically asked relating to port 9100. They provide a basic understanding of the port and its uses.
What is Port 9100 Used For?
You use port 9100 for raw network printing. It lets a client send a printer-ready file to a network printer over a TCP connection in a fast and reliable manner.
How to Enable 9100 Port?
How you enable port 9100 on your printer and in your firewall is dependent on the systems that you are using. Follow the instructions for your particular printer and firewall.
What Protocol is 9100?
When you are using raw network printing over port 9100, you use TCP. This is because TCP, unlike UDP, allows for the type of reliable connections that are required to properly print documents.
Conclusion
Network printers often use port 9100 to listen for print jobs from clients. The port allows clients to send printer-ready documents to the printer over TCP/IP using raw printing, which can be a fast and reliable way of network printing. But as there are serious exploitations related to the port, you need to know how to properly secure it.