Hello Everyone!
Today, we will continue to briefly discuss about IPv4 addressing.

Figure a. 6 subnets are connected by 3 routers.
A subnet's IP definition isn't limited to Ethernet segments connecting several hosts to a router interface. Listed in above figure a., which depicts 3 routers linked to each other via point-to-point links.
Each router has three interfaces: one for each point-to-point link and one for the broadcast link, which connects the router to two hosts directly. What subnets are there in this area? The subnets 223.1.1.0/24, 223.1.2.0/24, and 223.1.3.0/24 are comparable to those in the below Figure b.

Figure b: Subnets and interface addresses
However, there are 3 extra subnets in this illustration: one for the interfaces connecting routers R1 and R2, another for the interfaces connecting routers R2 and R3, and a third for the interfaces connecting routers R3 and R1. One could use following formula to define the subnets in a typical interconnected system of routers and hosts:
Disassociate each interface from its host or router to create islands of separated networks, with interfaces terminating the isolated networks' end points, to identify the subnets. Every one of these separate networks is referred to as a subnet.
We get 6 islands or subnets if we apply this approach to the interconnected system in Figure a.
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