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Technical basics
ELSA MicroLink Cable
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MAC address
Specific LAN addresses hardwired into the interfaces by their manufacturers are used to
manage the transfer in the LAN. Since the LAN addresses are used for communication
via the MAC protocol, they are called MAC addresses. They can be thought of as the
fingerprint of the interface hardware. MAC addresses can look like this, for example: 00-
80-C7-6D-A4-6E.
MAC addresses are independent of IP addresses. An IP host whose interface works
through a LAN has an IP and a MAC address. Whereas the structure of IP addresses with
its similarity to postal addresses is supposed to simplify routing in enormous IP networks,
the fingerprint-like MAC addresses are designed to make the connection to a LAN as
easy as possible.
Transfer in LAN is also packet-oriented. Every MAC packet contains the MAC addresses
of the source and of the recipient. Although every packet is received by all computers, it
is processed only by the target computer. There is an additional MAC broadcast address
that is processed by all computers in the LAN.
IP in the LAN
Every LAN packet contains an entry with the type of the network protocol. An IP packet
can be transferred through a LAN by packing it in a LAN packet and adding the 'IP'
protocol type to it. Because of the IP entry, the LAN interface at the receiving host
recognizes that the LAN packet contains an IP packet, extracts it and processes it as an
ordinary IP packet. In this way, IP packets and packets of other network protocols like
IPX can be transferred simultaneously through the same LAN without conflicts (this is
why a LAN is called multiprotocol-capable).
To an IP host, a LAN behaves as if it were an independent network with a router. The
hosts gives the packets to the LAN which handles the further distribution of the data
packets. This is why only IP addresses from the numerical space of the specific network
should be used for the internal communication of the hosts in a LAN through the IP
protocol.
To a router in the LAN, a host in its own LAN seems to be located behind another router.
So the task for the router is very simple: all it has to know for operating in the IP network
are the IP addresses
of the directly connected hosts and
of the available networks and subnets,
IP host
in the LAN
LAN with router function:
distributes the LAN packets
IP host
in the LAN
IP host
in the
LAN