By Yoobsan B 1
Configure Linux as a Router
Upon completion of this topic students will
able to:
oConfigure and use Linux as a Router
oExplains how to enable IP forwarding in
Linux.
12/30/2019
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Configuring Linux as a Router: Enabling IP Forwarding and Connecting Networks, Study notes of Computed Tomography
A step-by-step guide on how to configure linux as a router and enable ip forwarding. It explains the concept of ip networks, the need for ip forwarding, and the process of configuring linux as a router using rhel 7.2 and ubuntu 18.04 as examples. The document also covers setting ip addresses, configuring gateway ips, and testing connectivity.
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Configure Linux as a Router
Upon completion of this topic students will
able to:
o Configure and use Linux as a Router
o Explains how to enable IP forwarding in
Linux.
Introduction
o
Each computer, in the LAN network, uses a unique
software address that is known as the IP address.
o
For easier management and several technical
reasons, IP addresses are grouped into the IP
networks and the IP networks are further
categorized into the five IP classes.
o
By default, an IP address of an IP network can't
communicate with the IP address of another IP
network.
Why router?
o Router is a special device that not only provides the
IP forwarding as the main function but also supports
several other IP based features such as; packet
filtering, voice over IP, IP firewall, etc.
o Router is an expensive device.
o Configuring it is also a complex task.
o Not every network, especially the small and home
office network, can afford it.
Why configure Linux as router?
o Linux provides a zero-cost solution for the IP
forwarding.
o If you have a Linux system in your network, you can
use it for the IP forwarding.
The following image shows the IP configuration of
the PC-A (Windows 7).
The following image shows the IP configuration of
the PC-B (Ubuntu 18.04).
The following image shows my LAB with IP
configuration.
o Make a list of all gateway IPs which you assigned in your
network.
o For example, in my LAB I have two networks and the
default gateway IPs of both are; 192.168.1.1 and
o Now, configure all these gateway IP addresses in the
Linux system.
o You can use an individual network interface (LAN) for
each gateway IP or can use a single network interface for
all gateway IPs.
o Login from the root account and run the nmtui command.
o Select "Edit a connection" option and press
the Enter key.
o
Select available Ethernet (network interface)
from the left pane and the Edit option from the
right pane and hit the Enter key.
o
Select the Quit option and press Enter key.
o
Restart the network service.
o Confirm the IP configuration. To print the IP configuration of
all network interfaces, use the "ip addr" command.
o At this point, systems from different networks can access the
default gateway, but they can't access the system of another
network.
o To verify connectivity between systems and gateway, you can
use the ping command.
o
The following image shows connectivity
between PC-B and the default gateway.
o Enabling IP forwarding on Linux
o Run the following command to enable the IP forwarding.
o #echo "1" > /proc/sys/net/ip4/ip_forward
o This command enables IP forwarding in the current
session. It does not make a change in that configuration
file which Linux reads at the startup. By default, the state
of IP forwarding is disabled in the configuration file. It
means Linux will automatically disable the IP
forwarding again when you will restart the system.