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That's pretty much my question.

What is an interface address? What is it used for? How is it different from a normal IP address in a network?

I can't seem to find a good explanation/definition on the internet.

This is the best I got : CISCO: what is the interface address?

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3 Answers 3

An Interface address is an interface (network) address, is just a network address that belongs to an interface. Though almost all belong to an interface if they're being used. The term you've used brings up an important point.

Almost all network addresses e.g. IP addresses, belong to a network interface. (if they're used at all). Any device with an IP Address, has an IP Address on an interface.

A network interface is the electronics of the part where the network cable connects to - the controller there. Or where the wireless device connects to. NIC stands for network interface controller or network interface (controller) card. WNIC is wireless network interface controller or wireless network interface (controller) card.

IP Addresses belong to network interfaces, not to the computer itself. You don't ping a computer, you ping a computer's network interface.

Even if you ping , is known as the loopback interface. So even that is known as an interface.

A computer could have a NIC with many ethernet sockets, many network interfaces and each one with a different IP Address, see the IP Address belongs to an interface. And electronically, if you ping a computer, you're actually pinging in particular, a or the network interface on the computer.

There aren't many examples of IP Addresses that do not belong to an interface. An IP Address you haven't assigned to an interface (so it isn't assigned to a device, because IPs aren't exactly assigned to devices, only to interfaces of devices). The network address I suppose does not and even cannot belong to any interface(though I may be wrong on that). And the broadcast address e.g. designed to be sent to all interfaces, no interface would have that address.

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A network interface is … the part where the network cable connects to. Or where the serial cable connects to. Or a virtual connection point, such as an end of a VPN tunnel or a virtual network connection between two virtual machines on the same physical machine. Or, as you implied, a pseudo-interface for loopback. –  Scott Dec 20 '12 at 1:52
Also, I believe multicast (class D) IP addresses are not assigned to interfaces. –  Scott Dec 20 '12 at 1:54

Depending on the context, “interface address” might be used to refer to a MAC address.  An exhaustive discussion of MAC addresses could fill a book, but, in short,

  • MAC addresses operate at a lower level of the protocol stack (see also this) than IP addresses,
  • MAC addresses are used only for communicating between network interfaces in the same LAN segment, and
  • MAC addresses are (typically) (semi-)permanently assigned (often, if you can change the MAC address at all, it has to be done by physically manipulating the network interface hardware), in contrast to IP addresses, which can be mercurial.
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I think in the context of where I saw the term, an IP address sounds like what they might have been referring to. But it doesn't hurt to know alternate usages :) –  ffledgling Dec 20 '12 at 13:18
Cable Modems(for whatever reason) seem from what i've heard, to have IP and MAC addresses(maybe just for managing I don't know why else they'd need it). I suppose DSL modems do too. And it's the case, at least for NAT routers or NAT modem routers, that some have the option to clone the MAC of the PC, i.e. changing their MAC -with software-. This certainly wasn't an uncommon thing, and maybe is still not uncommon. It may even be common. for ref here's a good article on it techtips.salon.com/clone-computer-mac-address-router-2471.html –  barlop Dec 20 '12 at 14:46
I suppose perhaps semi-permanent means it stays after the NIC is reset/restarted or taken out and put back in / loses power. As far as things being stored in hardware, I suppose everything is ultimately stored in hardware! –  barlop Dec 20 '12 at 14:49

In the case you linked, what is called interface address is the gateway address (the address of the router of the subnet you are connected).

I don't think Interface address can be used with this meaning as I think an interface address is the group of parameters you need to supply to an interface for it to work like:

iface eth0 inet static

You can see an example in Juniper routers technical documentation

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I'm a little confused. Will the interface address be eth0 or the IP-Address eth0 that might be assigned? –  ffledgling Dec 20 '12 at 13:20
eth0 is the name of the interface. Interface Address is not a well defined name. As said by Scott in his answer, it can be considered as being the MAC address or as Juniper considers in its routers manuals, it can be the whole interface group of parameters you define using address {...} keyword (different than the address keyword above in an IF definition). Many people refer to the IP address as the interface address and so on. That depends on context and uses. The address keyword above in an interface definition refers to the IP assigned to eth0 but it is not the interface address. –  laurent Dec 20 '12 at 16:03

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