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The Need For Address Resolution
(Page 3 of 3)
General Address Resolution Methods
In fact, not only do we need to have
way of making this translation, we need to be concerned with the manner
in which it is done. Since the translation occurs for each hop of every
datagram sent over an internetwork, the efficiency of the process is
extremely important. We don't want to use a resolution method that takes
a lot of network resources.
Address resolution can be accomplished
in two basic ways:
- Direct Mapping: A formula is used to map
the higher-layer address into the lower-layer address. This is the simpler
and more efficient technique but has some limitations, especially regarding
the size of the data link layer address compared to the network layer
- Dynamic Resolution: A special protocol
is used that allows a device with only an IP address to determine the
corresponding data link layer address, even if they take completely
different forms. This is normally done by interrogating one or more
other devices on a local network to determine what data link layer address
corresponds to a given IP address. This is more complex and less efficient
than direct mapping but is more flexible.
The next two topics explore these
two methods in more detail.
You should bear in mind that of necessity,
it is not possible to have a fully general address resolution method
that works automatically. Since it deals with linking data link layer
addresses to network layer addresses, the implementation must be specific
to the technologies used in each of these layers. The only method that
could really be considered generic would be the use of static, manually-updated
tables that say link this layer three address to this layer two
address. This, of course, is not automatic and brings with it
all the limitations of manual configuration.
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Version 3.0 - Version Date: September 20, 2005
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