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Technical basics
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ELSA LANCOM Business 6000
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122
EN
for example. In case of the point-to-multipoint connection to the LAN, it has
to distinguish two cases, however.
A packet with an address outside the LAN is passed on to a router in the
LAN that takes care of the further processing of the packet.
A packet with an address within the LAN has to be sent immediately to
the target host, since the router in the network does not know the
addresses of all the different hosts.
Data transfer within the LAN
Let's use an example to explain this. Imagine the hosts of the subnet in the
marketing division are linked via a LAN. The hosts have IP addresses from the
numerical space '137.226.4.1' to '137.226.4.254' (the addresses '137.226.4.0'
and '137.226.4.255' are reserved), the network address is '137.226.4.0' and
the netmask is '255.255.255.0'. A router connected to the LAN provides
access to the wide world of the Internet. Its LAN interface has the IP address
'137.226.4.1' and the MAC address '00-80-C7-6D-A4-6E'.
Imagine wanting to send an IP packet from host 'Smith' (with IP address
'137.226.4.10' and MAC address '00-10-5A-31-20-DF') to host 'Miller' (with IP
address '137.226.4.20' and MAC address '00-10-5A-31-20-EB'). Using the
network address and the netmask, host 'Smith' recognizes that host 'Miller'
is located in the own network. It therefore has to send the packet through the
LAN, directly to host 'Miller'. Unfortunately the LAN interface cannot say:
“Send the IP packet to IP address 137.226.4.20”, because the LAN interface
only understands MAC addresses.
This is why every host has to manage a table that translates IP addresses to
MAC addresses. But how do the entries end up in the table? They could be
entered manually, but that would not satisfy the objective of making the
connecting of a new computer to the LAN as easy as possible.
ARP
Therefore the LAN has a special mechanism that automates this process: the
A
dress-
R
esolution-
P
rotokoll, ARP. The table itself is called the ARP table.
Whenever a host does not find an entry in the table for a particular IP address
(in our example '137.226.4.20'), it sends an ARP request packet to all hosts in
the LAN (with the LAN broadcast address as a target address).
Содержание LANCOM Business 6000
Страница 1: ...ELSA LANCOM TM Business 6000...
Страница 4: ...ELSA LANCOM Business 6000 EN...
Страница 10: ...Introduction ELSA LANCOM Business 6000 10 EN...
Страница 52: ...Connection via 2 Mbit interface ELSA LANCOM Business 6000 52 EN...
Страница 110: ...Operating modes and functions ELSA LANCOM Business 6000 110 EN...
Страница 162: ...Technical data ELSA LANCOM Business 6000 162 EN...
Страница 166: ...Appendix ELSA LANCOM Business 6000 166 EN...
Страница 174: ...Index ELSA LANCOM Business 6000 174 EN...