By default, a switch enables end devices, including computers, servers, smartphones, and printers, to communicate with any other device within the local network. However, the routing capabilities of a switch are limited unless it is a Layer 3 switch, which constrains internetwork communication.
Additionally, end devices lack routing capabilities, and as with switches, they require Layer 3 devices to transmit data outside the local network. These Layer 3 devices are known as default gateways and are crucial in network communications to correctly route data traffic to its intended destination.
A default gateway is an essential networking component that serves as a routing device used to forward network traffic from a device in one network to another network. In simple terms, it's the network's exit point that connects different networks, allowing devices on one network to communicate with devices on another network.
Using a default gateway in networking ensures that all outgoing traffic from a device on a local network is correctly routed to its destination network. Without a default gateway, devices on a local network could not communicate with devices on other networks, including the internet.
Therefore, when a device on a network sends data to a destination that's not on the same local network, the data is sent to the default gateway, which then forwards the data to the destination network. The default gateway is usually a router or a firewall device configured with the necessary routing information to forward the data to the ultimate destination.
As you can see in the image above, both computers, PC1 and PC2, are part of the same 192.168.1.0/24 network. This allows them to communicate with each other only with the help of the switch (SW1) through which they connect to the local network.
However, if either of these computers needs to send data to the web server on the internet, they must know the appropriate route to reach the destination network. Since PC1 and PC2 lack routing capabilities like SW1, the only alternative is to use a default gateway.
In our case, router R1 is part of the same network as the computers that need a default gateway and offers that service to them. Because R1 can route data, it can forward traffic to the web server. As a result, the computers first send their data to the default gateway, which then forwards it to the web server