ELSA LANCOM Business 6000, Manual, Page: 124 / 174

Technical basics
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ELSA LANCOM Business 6000
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124
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Then it can finally turn to its original task: sending the IP packet to host
'Miller'. It now finds the entry “IP address 137.226.4.20 corresponding to
MAC address '00-10-5A-31-20-EB'” in the ARP table and tells his LAN
interface: “Send this IP packet to the computer with the MAC address '00-10-
5A-31-20-EB'”.
Data transfer from the LAN onto the Internet
Imagine the second task, sending an IP packet from host 'Smith' to the remote
host 'External' with IP address 151.189.12.43. Host 'Smith' compares the IP
address with his network address and realizes that host 'External' is located
outside the LAN. So host 'External' can only be reached through the router.
The MAC address of router '00-80-C7-6D-A4-6E' finds out about its IP address
by going through the ARP table (if necessary another ARP request is made).
So host 'Smith' tells its LAN interface: “Send this IP packet to the computer
with the LAN address '00-80-C7-6D-A4-6E'”. The router extracts the IP packet
from the LAN packet and finds out about the IP address of host 'External'. In
the routing table the router then looks for the network address of this host
and thus finds the interface through which to pass on the IP packet.
LAN coupling on MAC basis
You know how LANs simplify the connection of computers to a local network.
Nearly all house networks are thus LAN based. In some cases a LAN is covers
such a large area that the physical characteristics of the cable prohibit the
Host Smith
ARP-response:
'137.226.4.20' =
'00-10-5A-31-20-EB'
Host Miller