What is Port 111?

by Colin Cohen | Published on November 15, 2024

Port 111 is dedicated to the Remote Procedure Call (RPC) portmapper service, which allows RPC clients to discover what ports RPC services are available.

To understand the purpose of port 111, you need to understand RPC and its portmapper service.

RPC is a protocol that lets a client request services from a server across a network. The RPC portmapper service allows RPC services on UNIX-like systems to register at which ports their services are available so that RPC clients can call them.

RPC clients contact the RPC portmapper service over port 111.

Understanding Port 111

Port 111 facilitates the RPC protocol by allowing RPC clients to find RPC services and their port numbers so that they can access them. It does this by using the RPC portmapper service over the port.

Purpose

RPC is a standard network protocol in modern operating systems. After RPC services on UNIX-like systems register their port numbers to the portmapper service, clients over port 111 can contact it so that they know how to call these services.

How Port 111 is Used in Network Communication

The RPC protocol is an important tool in network communication. It allows one device to run a procedure on another device in the network as if it were running it itself. Port 111 provides the glue to this by letting devices know where to make RPC calls.

Technical Specifications

Port 111 allows RPC clients to learn at which ports RPC services have been mapped through the portmapper service. Clients can then make RPC calls to the appropriate service.

Details of Port 111 Protocol

After RPC services register their port numbers with the portmapper service, RPC clients can contact the portmapper service over port 111 to determine which ports they need to make particular RPC calls to. 

They can communicate with the portmapper service either through User Datagram Protocol (UDP) or Transport Control Protocol (TCP). They use UDP when queries are small and transmission reliability is not a pressing concern, and they use TCP otherwise.

Key Technical Aspects Relevant to Users and Administrators

Administrators must start the portmapper service (rpcbind) on the server and enable it at boot. They also have to ensure that port 111 is open on the device (and accessible through the firewall) and that all services have been properly configured on it.

Uses of Port 111

Port 111 is used for many network applications in UNIX-like systems. The port lets clients learn how to connect with specific services available within these applications.

Explanation of Common Applications

Network applications often rely on RPC, so that one device can run a procedure on another across the network. In UNIX-like operating systems such as Linux, clients learn which RPC services are available at which ports through the portmapper service over port 111.

Examples of Applications that Utilize Port 111

Two applications that utilize the RPC portmapper service through port 111 are the Network File System (NFS) and the Network Information System (NIS). NFS lets devices share files over a network, while NIS is a directory service that enables devices to distribute configuration data.

Security Concerns

Exposing port 111 on your devices can result in serious exploits, so it’s important to secure the port properly on your devices.

Overview of Security Risks Associated with Port 111

If you don’t properly secure port 111 on your devices, you can expose them to serious vulnerabilities. These vulnerabilities can lead to the release of sensitive information and to network disruptions.

Common Vulnerabilities and Threats

Common vulnerabilities associated with port 111 include information disclosure and denial-of-service (DoS) attacks. Information disclosure can further lead to the exploitation of RPC services.

Recommendations for Securing Port 111

You should only allow access to port 111 on your devices from those within trusted networks. You should also keep your system software up to date and regularly monitor traffic on the port.

Configuring Port 111

To use the RPC portmapper service, you need to configure it on your devices and manage its settings. You also need to be able to troubleshoot issues with it.

Basic Setup and Configuration Steps

To set up and configure the RPC portmapper over port 111 on a device running a UNIX-like operating system, do the following: 

1. Install and start the rpcbind service, and enable it to run on boot.

2. Verify that the service is running over port 111 by running the rpcinfo -r command.

3. Check that your firewall is allowing access to the port for both TCP and UDP while only allowing access from trusted networks.

 After configuration, you should periodically manage port settings, monitor port traffic, and keep your system software updated.

Best Practices for Managing Port 111 Settings

You can manage settings for the RPC portmapper over port 111 through the rpcinfo -r command. It will also tell you what RPC services are running as well as the current port mappings.

Troubleshooting Port 111

To troubleshoot issues with the RPC portmapper over port 111, do the following:

1. Check if the rpcbind service is running over the port on the device.

2. Check your configuration through the rpcinfo -r command.

3. Check both your firewall configuration and any system logs related to the rpcbind service.

4. Update your system software and restart the rpcbind service.

FAQs About Port 111

The following FAQs answer questions typically asked about port 111 and provide a basic understanding of the port and its uses.

What is Port 111 Used for in Linux?

Port 111 is used in Linux for the RPC portmapper. This allows RPC clients to learn at what ports they can find RPC services.

How Do I Check If Port 111 Is Open?

You can check if port 111 is open on a device by using the netstat -aon command in a command prompt or a terminal. It will also show you if the rpcbind service is listening on the port.

Can Port 111 Pose a Security Risk?

Port 111 can pose security risks to your network if you do not properly secure it on your devices. You should follow the guidelines within the Recommendations for Securing Port 111 section.

Is Port 111 Necessary for All Applications?

Having port 111 open is only necessary for running the RPC portmapper in UNIX-like systems such as Linux. If you do not need to run this service, you probably do not need port 111 open on your devices.

How Do I Close Port 111 on My System?

How you close port 111 on your system depends on your operating system. In Windows, you can do this through the Firewall Control Panel, and in Linux, you can do this through the iptables command.

Conclusion

You use port 111 for the RPC portmapper service. This service lets RPC clients learn at what ports various RPC services are available so that they can make RPC calls to them. Those using the service need to know how to configure and troubleshoot it and how to properly secure the port on their devices.