Networking at the Command Line

The command line can be used to perform various networking tasks, such as checking network connectivity, retrieving information about network interfaces, and troubleshooting network issues. In this section, we will cover some of the basic networking commands that you can use at the command line.

ping

ping is a basic tool used to check network connectivity. It sends an ICMP echo request to a specified host and waits for a response. If a response is received, it indicates that the host is reachable over the network.

The syntax for using ping is as follows:

ping [options] host 

For example, to ping the Google DNS server at IP address 8.8.8.8, you can use the following command:

ping 8.8.8.8 

You can use various options with ping to customize its behavior. For example, the -c option can be used to specify the number of ICMP echo requests to send:

ping -c 5 8.8.8.8 

ifconfig

ifconfig is a command used to retrieve information about network interfaces on a system. It can be used to view information such as IP addresses, netmasks, and hardware addresses.

The syntax for using ifconfig is as follows:

ifconfig [interface] [options] 

For example, to view information about the network interface eth0, you can use the following command:

ifconfig eth0 

You can use various options with ifconfig to customize its behavior. For example, the -a option can be used to show information about all network interfaces, even those that are currently down:

ifconfig -a 

netstat

netstat is a command used to view information about network connections and routing tables. It can be used to display information such as active network connections, listening ports, and network routing information.

The syntax for using netstat is as follows:

netstat [options] 

For example, to display a list of all active network connections, you can use the following command:

netstat -a 

You can use various options with netstat to customize its behavior. For example, the -n option can be used to display numerical addresses instead of resolving them to hostnames:

netstat -an 

traceroute

traceroute is a command used to trace the route that packets take to reach a specified host. It sends a series of packets with increasing time-to-live (TTL) values, and waits for an ICMP "time exceeded" message from each intermediate router. By doing this, it can determine the path that packets take to reach the destination host.

The syntax for using traceroute is as follows:

traceroute [options] host 

For example, to trace the route to the Google DNS server at IP address 8.8.8.8, you can use the following command:

traceroute 8.8.8.8 

You can use various options with traceroute to customize its behavior. For example, the -m option can be used to specify the maximum number of hops to try:

traceroute -m 30 8.8.8.8 

ssh

Finally, the ssh command allows you to securely connect to remote servers over the network. To use ssh, simply type ssh followed by the username and hostname of the remote server:

ssh username@remotehost 

You will be prompted for the user's password before being connected to the remote server. Once connected, you can run commands on the remote server as if you were physically present at the machine.

These are just a few examples of the many networking tools available on the command line. With these tools, you can quickly and easily diagnose and troubleshoot network issues, and manage remote servers from anywhere.