What is Port 515?
by Erik Mikac | Published on May 01, 2025
In networking, ports serve as critical gateways for communication between devices and applications. Port 515 is a lesser-known, legacy player in the networking world. Network administrators use port 515 to manage network printing services.
However, that's not the whole story. Let's explore Port 515—its common uses, protocols, security implications, and troubleshooting techniques.
What is a Port?
Computer ports are logical endpoints for communication. Applications use them to send and receive data. Any application that needs network access will communicate via a port. For example, HTTPS requests typically use port 443 for secure internet communication.
Port 515 is one of many network ports available on your computer. In total, there are 65,536 network ports (ranging from 0 to 65535). Most ports are not reserved for a specific purpose—but port 515 is an exception. It’s specifically used for Line Printer Daemon (LPD) services, commonly associated with network printing.
What is LPD?
Line Printer Daemon (pronounced "demon") is a protocol that allows users to send print jobs over a network. It was one of the first of its kind, developed at Berkeley way back in the 1980s. But just because it's old doesn't mean it's not in use. So, let's walk through how LPD was used to get your Word document to a printer and into your hands.
The Client Submits a Job: This is the point when the document is all done, and the user prints the page. The print job is sent with a control file containing metadata and a data file with the data itself.
The LPD Server Receives the Request and Queues the Job: At this point, the LPD server is listening on port 515. When it sees a job, it places it on a printer's queue. This is on a first-come, first-serve basis.
LPD Server Sends the Job to the Printer: The server scans the metadata file and the data file. Then, it sends them to the printer. If the printer is busy, it tries again until it is free.
Job Completion: Once the print job is done, it is removed from the queue. Users can check its status with the lpq command or remove jobs with the lprm command.
And there you have it; that is how LPD works in a nutshell. Notice I didn't mention encryption once—and that's a big problem. Let's discuss why LPD is deprecated, and some viable alternatives.
Security Concerns with Port 515
The biggest problem with running LPD on Port 515 is that there isn't any encryption. Also, it lacks features like job prioritization, user authentication, and detailed status reporting.
In pursuit of modernization, Microsoft removed LPD print services from its default Windows 10 and Server 2012. So, if your system is modern, you can't use LPD even if you wanted to (and you shouldn't want to).
LPD has largely gone extinct. However, it's still used on legacy systems in organizations that require cross-compatibility. If you're reading this article, there is a high likelihood you're one of them. However, if you're looking for a new printing protocol, there are plenty to choose from:
If you have no choice but to remain on LPD, then let's discuss a couple of known exploits that you should beware of.
Unauthorized Access + Print Job Manipulation
This is the most concerning vulnerability. Since LPD lacks authentication, anyone can submit, delete, or manipulate print jobs. They can also initiate a DDoS attack by flooding the print queues with fake jobs.
Print Job Snooping
Since LPD transmits print jobs in plaintext, it's easy to packet sniff. An attacker with network access can see exactly what anyone is printing anywhere, anytime. This is not good if confidential information is in the job queue.
Mitigation Strategies
Anything that can be hacked can be prevented. By following common-sense network practices, you can keep your network afloat.
Restrict Access: This is the most common method of securing a network. Block Port 515 from external access and only allow trusted IPs.
Encrypt Traffic: The only way to encrypt traffic is to change protocols. Your best bet is to switch to IPPS. If that isn't possible, use a VPN or a secure network for LPD traffic.
Monitor and Limit Print Jobs: Implement rate limits to prevent job flooding. Also, continually monitor logs for unusual activity.
FAQ
What is Port 515 Used For?
Port 515 is primarily used for the Line Printer Daemon (LPD) protocol, which facilitates printing over a network. It's generally considered a legacy protocol and is rarely used in most modern networks, which have moved toward newer printing protocols like IPP (Internet Printing Protocol).
Is Port 515 Safe?
Port 515 can be vulnerable if not properly secured, as it may allow unauthorized access or exploitation by attackers.
How Do I Secure Port 515?
To secure port 515, use firewall rules to restrict access, enable authentication, and keep the associated software updated.
What Protocols Work with Port 515?
Port 515 uses the LPD protocol. If set up correctly, it may also support other printing protocols, like IPP.
How Can I Check if Port 515 is Working?
You can check if port 515 is working by using a tool like netstat or telnet to see if it is open and responsive.
What are the Common Problems with Port 515?
The biggest problems you'll find with port 515 are misconfiguration, unauthorized access, and compatibility issues with modern systems.
Final Thoughts
Port 515 and the LPD protocol were essential building blocks for network printing in the early days of computing. However, technology has advanced—and so have security threats. Unfortunately, LPD has not evolved to keep pace. Its lack of encryption, authentication, and modern features has contributed to its decline. Most contemporary environments consider LPD an impractical choice, and users have not used it since the early 2000s.
While some legacy systems still rely on LPD for compatibility, organizations should transition to more secure alternatives. There are plenty out there, too, like IPP, SMB printing, or cloud-based solutions. If LPD must be used, strict security measures should be enforced, such as firewall restrictions, VPNs, and active monitoring.
Port 515 remains a relic of early network printing, but its role in shaping modern printing protocols is undeniable. If your network uses port 515, you should know its history, risks, and options. This helps network administrators make smart choices to keep their printing systems working well and safe.
Interested in a career in network engineering? The CCNA is the perfect place to start.