Is modem a network interface?

Question

According to this article a "A network interface is the point of interconnection between a computer and a private or public network. A network interface is generally a network interface card (NIC), but does not have to have a physical form."

I have a few basic questions based on this

1. As per the above definition, is a modem a Network interface?

2. I read that a Network interface can have multiple ip addresses. Does that mean that the modem at my home has multiple ip addresses?(I have a regular modem that connects me to the internet)

3. Is a router same as the modem?

Answer 1

1. A modem is not a network interface. A modem has 2 network interfaces. The interface is where the cables plug into the modem. So you have a cable coming from the cable company connecting to it. That connection is one interface and the ethernet connection going from your computer or router to it is the other. Now, Im not talking about the physical jacks themselves, they are the physical connection to the network interface - the electronics behind the jacks.

2. A network interface can be assigned any number of IP addresses. This can range from 0, to 1, to 2, to 100, to infinity (well maybe not that high). But I do not believe there is a limit, other than what the hardware is capable of. Does your modem have more than one address? Most likely not. Unless you have a special setup from your ISP, your modem is only given one address.

3. A router is not the same as a modem. In short, a router is a device that forwards data packets to parts of a computer network. A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. In short, the modem is what sends and receives the signals to and from the ISP, and the router is supplying the information being sent. So as you can see, they have completely different purposes.

Answer 2

1>As per the above definition, is a modem a Network interface?

According to the above general definition it would fit the description and you could argue yes it's a network interface in that it interfaces between two network types as that is what the definition of an interface is. But in computing when we talk about a "Network Interface" we really mean a NIC which is a device in the computer that connects to (usually) ab ethernet network.

2> I read that a Network interface can have multiple ip addresses. Does that mean that the modem at my home has multiple ip addresses?(I have a regular modem that connects me to the internet)

If you mean by "regular modem?" - one that uses USB or serial, the IP addressing is against the virtual PPP adaptor. Yes you could have in theory multiple addresses against that. But it's hard to tell what you mean by this question exactly. You'd have to describe your setup in more detail as there are several devices that are now classed as modems that are not quite the same as your old school modem any more.

3>Is a router same as the modem?

No, a router routes IP packets from one LAN to another modify the packets as they pass. Modems are devices that convert digital data and allow it to travel over analog style phone lines.

Having said that, you now have devices called modem/router as they can combine both functionality. There are several ADSL style modem/routers out there.

Answer 3

1>As per the above definition, is a modem a Network interface?

Modem is not a network interface. A (wan) port on that modem is.

2> I read that a Network interface can have multiple ip addresses. Does that mean that the modem at my home has multiple ip addresses?(I have a regular modem that connects me to the internet)

No. Your home modem has 1 public IP address and 1 private IP address, but these addresses were assigned to different network interface.

3>Is a router same as the modem?

No. Your home modem has a modem and a router (and probably a switch) inside, but it's not true for general case.

Answer 4

1>As per the above definition, is a modem a Network interface?

No. Like @Keltari says, It connects to a network interface on your computer. It also has a network interface to connect to your ISP's network, the telephone network, or otherwise upstream.

2> I read that a Network interface can have multiple ip addresses. Does that mean that the modem at my home has multiple ip addresses?(I have a regular modem that connects me to the internet)

Typically modems act as bridges, meaning they take what is coming out of the ISP's side and send it to whatever is connected to your side, and vice versa. Bridges don't have IP addresses - not in the way you are thinking.

The one exception is that the modem may be running an internal webserver where you can look up diagnostic info on your side. This is a separate thing from the internet service provided via this modem.

3>Is a router same as the modem?

Typically modems act as bridges, meaning they take what is coming out of the ISP's side and send it to whatever is connected to your side, and vice versa. If you need routing for the machines in your home network, a separate router needs to be provided.

Why would you need routing? So that multiple machines in your home can use the ISP's network connection as a gateway to the rest of the Internet, and vice versa.

Some ISP's give you a device that has both of these functions built in (some DSL "modems" are a combination of "modem" and router) - but they are separate functions. Usually on these you can disable the routing and tell the device to operate in "bridge mode" if you want to use your own router.