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How network works - MAC-address and IP-address relationship.

MAC-address and IP-address relationship - MAC-addresses are used on local Ethernet networks. IP-addresses are more abstract and can be used on top of multiple types of networks.

Where does IP-addresses come in? - Local networks like an Ethernet network sends all traffic to all computers that sits on the same network bus. Global networks like the Internet will not send all traffic to all of the connected computers. IP-communication (that is used on the Internet) have a much more sophisticated way to deal with sending and routing the data communication that we will not cover here. If you want to learn more about how the Internet communication works there is plenty of information on the Internet. However IP-communication is very useful on local networks as well but we have to separate the physical part of the network from the logical part.

The communication difference between the physical and the logical part of the networks goes within a grey area in software.

To the physical (hardware) domain belongs cables and network cards. Ones the data signals have been detected on the network card the low level software on the card and in the operating system takes on the task to process this data. That processing is divided in different levels.

There are standard models for this leveling of software. One such model is called the OSI model and have 7 levels. When studying the IP-communication you will find that it doesn't comply fully with the OSI model but in general it works the same way. The OSI model will not be explained here. You will find plenty of information on the Internet about the OSI model.

On an Ethernet network you do not have to use IP-communication to communicate. Before the Internet become popular and dominating other protocols like NOVELL IPX was common on local networks. Many companies already have working local networks when Internet and IP-communication become popular. However there is no problem running several different protocols at the same time on an Ethernet network as long as all "physical" (low level) communication uses the fundamental Ethernet rules using Ethernet frames with source and destination MAC-addresses. Today the majority of Ethernet networks only runs the IP-protocol.

Network packets are like Russian dolls. An IP-packet resides within an Ethernet-packet. A TCP-packet resides within an IP-packet. A HTTP-packet resides within a TCP-packet.

Ethernet network packet holding an IP packet

The data part of an Ethernet packet can hold up to 1500 bytes. MAC-addresses (48bits) are 6 bytes wide each and the Number Of Bytes field is 2 byte wide. That gives the maximum size of an Ethernet frame to be 1514 bytes.

When introducing the IP-protocol on Ethernet the Number Of Bytes field is used to mark that the Ethernet frame holds an IP-packet by the number of 0x0800. By using a number that is greater than the maximum length an Ethernet frame can hold indicates that the Ethernet frame holds another protocol frame in the data part. The Ethernet standard says that if the Number Of Bytes field is greater than 0x0600 the Ethernet frame holds another protocol.

How will LANeye benefit from this?

LANeye detects devices by their MAC-address. As shown in the picture, IP-addresses in that perspective have no meaning to LANeye. This gives that LANeye will detect all devices on the network regardless of the device uses IP-protocol or any other protocol. This is because all devices that communicate on an Ethernet network have to use Ethernet frames. LANeye works on Ethernet level and not on protocol level.

However, LANeye make use of information on protocol level. LANeye will recognize IP-protocol packets and can extract information from IP-protocol packets like IP-addresses, Communication port number and higher level of protocols.

Learn about how computers become part of a network in the next sections.

Read more on this topic

3.   HOW NETWORK WORKS - MAC-address and IP-address relationship

The difference between MAC-addresses and IP-addresses and how they are used on a local network.


4.   HOW NETWORK WORKS - How computers become part of a network

How computers announces their network presence by broadcasts.

External Links


Wikipedia about MAC-address


Wikipedia about IP-address

OSI Model

Wikipedia about the OSI Model

TCP/IP Model

Wikipedia about TCP/IP Model

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