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10.1 | |
Routed Protocol | |
| 10.1.1 | |
Routable and routed protocols |
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A protocol is a set of rules that
determines how computers communicate with each other across networks.
Computers communicate with one another by exchanging data messages. To
accept and act on these messages, computers must have definitions of
how a message is interpreted. Examples of messages include those
establishing a connection to a remote machine, e-mail messages, and
files transferred over a network.
A protocol describes the following:
A routed protocol allows the router to
forward data between nodes on different networks.
The reason that a network mask is used
is to allow groups of sequential IP addresses to be treated as a
single unit.
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In order for a protocol to be routable, it
must provide the ability to assign a network number and a host number
to each individual device. Some protocols, such as IPX, require only a
network number because these protocols use the host's MAC address for
the host number. Other protocols, such as IP, require a complete
address consisting of a network portion and a host portion. These
protocols also require a network mask in order to differentiate the
two numbers. The network address is obtained by ANDing the address
with the network mask. 
If this grouping were not allowed, each host would have
to be mapped individually for routing. According to the Internet
Software Consortium, this would not be possible
with the 162,128,000 hosts that are currently on the Internet.
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