Troubleshoot Linux Network Problems

Lab Overview:

This hands-on lab provides a Linux administrator with an understanding of how to configure IPv4 and IPv6 addressing on multiple network interfaces, configure a host to use a specified DNS server and default gateway route, and ensure that these configurations work. You will become familiar with the ifconfig command, the /etc/nsswitch.conf file, the /etc/host file, the route command, and the ping, dig, and nslookup utilities. These tools and files are commonly used to establish network configuration and troubleshoot network problems. These skills are essential for someone pursuing a career path as a Linux administrator or a penetration tester.

Understand the scenario

You are the Linux administrator for your organization. Two of your Linux virtual machines are experiencing network connectivity and name resolution issues. You need to use the Linux CLI to configure and troubleshoot your network settings.

Configure the correct IPv4 and IPv6 addressing on Ubuntu1 and Ubuntu2:

In this section, you’ll need to make sure that your systems and their interfaces are correctly configured with the right IPv4 and IPv6 network addresses. You’ll become familiar with using the interface configuration (ifconfig) utility to review the configuration of your network interfaces and then make changes to both the IPv4 and IPv6 addresses. One of your systems will have two network interfaces used, so you will have to configure both. It is common to have multiple interfaces on a single server. This allows you to segregate specific service traffic and minimize the impact on the server since a network interface has a limited capacity. Serving multiple services, such as DNS and DHCP, off the same interface could overload the interface and impact network/service performance.

Configure the default gateway and nameserver entries on Ubuntu2:

A default gateway is a node within your network that serves as the forwarding host (i.e., a router) for your IP traffic to your destination networks. It is configured, so if a route is not otherwise specified, your system will have a route to communicate (i.e., send its packets). You will become familiar with using the route command to add a static default gateway to your /etc/network/interface configuration file on your client host. Then, you will configure the Name Service Switch (NSS) configuration file so that it points to your DNS name server for performing name resolution. You will edit the .conf file using a text editor, such as vim.

Test IP connectivity and DNS name resolution:

Once you have your IPv4 and IPv6 addresses, default route, and DNS name server configured, you will use common command-line utilities to test their functionality. You will use the ping command to test the connectivity of your interfaces, using both IP version addresses. Then you will use the domain information groper (dig) utility to ensure that your client can resolve DNS names to IP addresses.

Lab Summary

In this hands-on virtual lab, you will learn how to configure, review, and troubleshoot basic network configuration on Ubuntu systems. You will configure IPv4 and IPv6 addresses, a default gateway route, and a DNS server for the systems in your environment. Once configured, you’ll then use the ping and dig utilities to ensure these configurations work properly. These skills are essential for someone pursuing a career path as a Linux administrator and are useful for penetration testers.

Other Challenges in this series

• GUIDED CHALLENGE: Design and Implement Container Applications Using the Azure Kubernetes Service (AKS)
• ADVANCED CHALLENGE: Can you Design Azure App Service API Apps?