Based on the information above, which of the following is causing the issue?

A systems administrator is receiving tickets from users who cannot reach the application app that should be listening on port 9443/tcp on a Linux server.

To troubleshoot the issue, the systems administrator runs netstat and receives the following output:

Based on the information above, which of the following is causing the issue?
A . The IP address 0.0.0.0 is not valid.
B . The application is listening on the loopback interface.
C . The application is listening on port 1234.
D . The application is not running.

View Answer

Answer: B

Explanation:

The server is in a "Listen" state on port 9943 using its loopback address. The "1234" is a process-id

The cause of the issue is that the application is listening on the loopback interface. The loopback interface is a virtual network interface that is used for internal communication within the system. The loopback interface has the IP address 127.0.0.1, which is also known as localhost. The netstat output shows that the application is listening on port 9443 using the IP address 127.0.0.1. This means that the application can only accept connections from the same system, not from other systems on the network. This can prevent the users from reaching the application and cause the issue. The administrator should configure the application to listen on the IP address 0.0.0.0, which means all available interfaces, or on the specific IP address of the system that is reachable from the network. This will allow the application to accept connections from other systems and resolve the issue. The cause of the issue is that the application is listening on the loopback interface. This is the correct answer to the question. The other options are incorrect because they are not supported by the outputs. The IP address 0.0.0.0 is valid and means all interfaces, the application is not listening on port 1234, and the application is running as shown by the process ID 1234.

References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 12: Managing Network Connections, page 383.