Network Tools in Linux

Motivation

We have learned the basics of how a network works. Now lets look at more tools that help you debug and troubleshoot network issues.

DNS Lookup

When you go to a website you do not need to remember the IP address. You use a name for that. e.g. you go to www.google.com. In order to find the associated IP address you need to lookup that name. The tools for that are: host nslookup or dig. For simple lookups I prefer host, while the other tools will give you more detailed information of how the lookup worked.

 host www.google.com
www.google.com has address 172.217.16.196
www.google.com has IPv6 address 2a00:1450:4001:817::2004

Sometimes you want to define aliases for certain hosts. Especially in your private network at home you will not want to run your own DNS system. A simple file that relates IP addresses to names will be sufficient to make your life easiser. This is the /etc/hosts file where you can add names to your IP addresses. E.g. your hosts file could look like this:

$ cat /etc/hosts
127.0.0.1	localhost
::1     localhost ip6-localhost ip6-loopback

192.168.19.27 laptop1 acer
192.168.19.101 handy lg200
192.168.19.1 netgear

In this example we have defined 3 names in the 192.168.19.0/24 network. You can add alias names after the first name. It is also good to have the name of your own computer defined. Also the loopback interface should be named localhost. In the above example we also name the IPv6 address (::1) to be localhost.