What is an interface identifier

Question

I have a laptop that is connected to my organization's network using one or more network adapters. I am trying to write a tool that will continuously monitor the connectivity status and connection quality of each network. However my networking knowledge to limited and the terminology confuses me.

Specifically finding all the network adapters. Someone suggested that I use the command ifconfig and it gave me what are called "interface identifiers".

ex:

['lo0', 'gif0', 'stf0', 'en0', 'en1', 'en2', 'bridge0', 'p2p0']

I'm not quite sure how this helps me solve my problem because I don't know what interface identifiers are and I am not sure how to leverage this information. My assumption is that they represent a computer or a router in the network.

If someone could clear this up or explain it to me in layman's terms that would be really helpful.

Answer 1

First of all, you need to understand that there may be physical network cards(OR/AND logical network adapters) present in the computer to identify connection/manage connection.

Next, you have an incorrect notion about interface identifier. What you talked about(eth,virbr,lo) are interfaces. In IPv4 addressing scheme, we don't have interface ID. We have interface ID's in IPv6 addresses.

As mentioned in The Payoff of IPv6’s Very Large Address Size

In IPv4, IP addresses have no relationship to the addresses used for underlying data link layer network technologies. A host that connects to a TCP/IP network using an Ethernet network interface card (NIC) has an Ethernet MAC address and an IP address, but the two numbers are distinct and unrelated in any way.

With the overhaul of addressing in IPv6, an opportunity presented itself to create a better way of mapping IP unicast addresses and physical network addresses. Implementing this superior mapping technique was one of the reasons why IPv6 addresses were made so large. With 128 total bits, even with a full 48 bits reserved for network prefix and 16 bits for site subnet, we are still left with 64 bits to use for the interface identifier, which is analogous to the host ID under IPv4.

Having so many bits at our disposal gives us great flexibility. Instead of using arbitrary “made-up” identifiers for hosts, we can base the interface ID on the underlying data link layer hardware address, as long as that address is no greater than 64 bits in length. Since virtually all devices use layer two addresses of 64 bits or fewer, there is no problem in using those addresses for the interface identifier in IP addresses. This provides an immediate benefit: it makes networks easier to administer, since we don't have to record two arbitrary numbers for each host. The IP address can be derived from the MAC address and the network identifier. It also means we can in the future tell the IP address from the MAC address and vice-versa.

Visit this link for more clear understanding about interface ID.

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Now,returning to clear your confusion,

all of the connections(interfaces) such as Ethernet-0,Ethernet-1,WiFi-1,etc. have their own interface identifier.You can think of them as a kind of special identification number which identifies the kind of interfaces available at that moment!

When you type ifconfig in Linux, it displays the status of the currently active interfaces.

Now,coming on the example part, let's say you have two Ethernet connections on your system, say, eth0 and eth1(these are interface names) ---so ifconfig will print these two as a result of it's output!

So,to identify these two separate interfaces,there must be an interface identifier.The interface identifier(generally 64-bit) is either automatically generated from the interface's MAC address using the modified EUI-64 format, obtained from a DHCPv6 server, automatically established randomly, or assigned manually.

Also,the interfaces which you have mentioned are some of the most-commonly used interfaces :-

'lo0', 'gif0', 'stf0', 'en0', 'en1', 'en2', 'bridge0', 'p2p0'

1. lo0---local network connection(0 for 1st connection of lan)
2. en0---ethernet connection(0,1,2 for 1st,2nd and 3rd connection on Ethernet)
3. bridge0---a bridged connection to this machine
4. p2p0---a peer-to-peer connection

don't know about gif,stf.Please note that there are logical connections/virtual connections,instead of limitation of physical connections(using NIC cards) too!

Answer 2

I discovered that there are man entries for gif and stf -- on OSX, at least. These are generic tunnel interface, and IPv6 to IPv4 tunnel interface ("Six To Four"), respectively.