Do multiple router interfaces affect the amount of IP addresses?

Somebody told me that if a router has four interfaces (let's say four RJ-45 Jacks,) then it will have four IP addresses. Is that true? Can you please elaborate on the IP addresses of routers?

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Routers usually have a variety of interfaces, including Fast Ethernet (RJ-45.) Some vendors, such as Cisco, give you the ability to add different types of interfaces depending on your needs. That way, you don't need to change your router to cover new needs.

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Almost all interfaces on a router are configurable with an IP address. Some interfaces, such as the Fast Ethernet you mentioned, can be configured with one or two IP addresses. This way, you can have one physical interface configured to support two logical networks.

For example, the Fast Ethernet interface can have IP addresses 192.168.0.1 and 192.168.1.1 assigned to it. This means both networks (192.168.0.0/24 & 192.168.1.0/24) can 'see' the router.

 

This was first published in July 2008

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