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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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4 Answers 4

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An Interface address is an interface (network) address, a network interface address, it's 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 127.0.0.1 which 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. 255.255.255.255 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 - Слава Україні
    Commented Dec 20, 2012 at 1:52
  • Also, I believe multicast (class D) IP addresses are not assigned to interfaces.
    – Scott - Слава Україні
    Commented Dec 20, 2012 at 1:54
  • interface address.. would be the network address at that network interface.
    – barlop
    Commented Feb 19, 2015 at 10:22
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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
    Commented Dec 20, 2012 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
    Commented Dec 20, 2012 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
    Commented Dec 20, 2012 at 14:49
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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
    address 192.168.1.180
    netmask 255.255.255.0
    broadcast 192.168.1.255
    network 192.168.1.0
    gateway 192.168.1.1

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
    Commented Dec 20, 2012 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
    Commented Dec 20, 2012 at 16:03
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Short answer

What is an interface address?

Network interfaces have two addresses:

A layer 2 address - The MAC address (Also called Hardware , physical or burned-in address).

A layer 3 address - The IP address (version 4 or 6).

What is it used for?

Both addresses are used in order to communicate between network devices.

MAC address - to uniquely identify every node (e.g., workstations and printers) on a network.

IP Address - used in order to communicate with a device on a network, or between different networks.


How is it different from a normal IP address in a network?

By ‘normal’ IP address you probably mean the gateway (router) external IP - this is what you will see if you’ll search “what is my IP address” in Google.
If you didn’t mean the router - so the normal IP addresses are probably the network interface IPs.

Some more information:

A MAC address is a six-byte identifying number which is permanently embedded in the firmware of the adapter. It is readable by the network and the OS of the device on which the adapter is installed. Every adapter has a unique MAC address.
Because MAC addresses never change, they are very useful on preventing unwanted network access by hackers and intruders. Read more about MAC filtering.

The IP address of network interface is in most cases a dynamic, private IP address which was given to the network interface by the DHCP (server or router).

If device A and device B are on the same network, and the MAC address of device B is known by device A - they can communicate directly based on the MAC address.

If the two devices are on different networks, they will have to go through a router and the communication is done one level up in the TCP/IP model and will be based on the IP addresses.

The mapping between the IP and MAC address is done by the ARP protocol.

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