ELSA Cable manual

56Technical basics

Host 'Smith'

External host

Marketing	Example
	Inc.'s router
	Superordinate
	network:
	Example Inc.

	External router as a
Development	connection to other net-
	works

As an example, think of a company with one large network, in which the different divisions are incorporated as small subnets. The address of the network for the marketing division is made up hierarchically from the address of the company and that of the department.

Whenever a host external to the company network sends a packet to a host in the Example Inc., this is what happens:

aThe sender gives the packet the destination address “host 'Smith' – Marketing – Example Inc.”.

bAll an external router that establishes the connections to other networks has to know is how to reach Example Inc. As soon as it receives a packet with the address for Example Inc., it passes the packet on to the router responsible for Example Inc.

cThe router at Example Inc. receives the packet and extracts from the address the information that it is directed at Example Inc. Since it is itself part of Example Inc., it takes a closer look at the address to find the name of the division. It then passes the packet on to the router in the marketing division.

dThe router in the marketing division receives the packet and extracts from the address the information that it is directed at the marketing division of Example Inc. Since it is itself part of this division, it takes a closer look at the address to find the name of the host. It then passes the packet on to the host of the employee Sam 'Smith'.

Now we shall take a look at the example using proper IP addresses instead of symbolic names. The network of Example Inc. has the numerical space '192.168.100.0' to '192.168.100.255' at its disposal, with the '0' for the network address and the '255' for the sender address.

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