What is a gateway?

A gatewayis a "gateway" that connects one network to another.

According to different classification standards, there are many types of gateways, the TCP/IP protocol gateway is the most commonly used, here we talk about the "gateway" refers to the TCP/IP protocol gateway;

In essence, it is the IP address of a network to other networks

In essence, it is the IP address of a network to other networks

In essence, it is the IP address of a network to other networks.

In the absence of a router, TCP/IP communication between the two networks is not possible, even if the two networks are connected to the same switch (or hub), the TCP/IP protocol will be based on the subnet mask (255.255.255.0) to determine that The hosts in the two networks are in different networks. To communicate between these two networks, they must pass through a gateway. If a host in network A realizes that the destination host of a packet is not in the local network, it forwards the packet to its own gateway, which in turn forwards it to network B's gateway, which in turn forwards it to one of network B's hosts (as shown in the attached figure). The process of forwarding packets from Network B to Network A is similar.

So, only by setting the IP address of the gateway, the TCP/IP protocol can enable different networks to communicate with each other.