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Address Resolution Through Direct Mapping
(Page 3 of 3)
Inflexibility of Direct Mapping
Now lets consider the next
version 6? IPv6 supports massive 128-bit
addresses. Furthermore, regular (unicast) addresses are even defined
using a method that creates them from data link layer addresses using
a special mapping. This would in theory allow IPv6 to use direct mapping
for address resolution.
However, the decision was made to
have IPv6 use dynamic resolution just as IPv4 does. One reason might
be historical, since IPv4 uses dynamic resolution. However, the bigger
reason is probably due to a disadvantage of direct mapping: its inflexibility.
resolution is a more generalized solution,
because it allows data link layer and network layer addresses to be
independent, and its disadvantages can be mostly neutralized through
careful implementation, as we will see.
In fact, evidence for this can be
seen in the fact that dynamic resolution of IP is in fact defined on
ARCNet, the example we just used. We could do direct mapping there,
but it restricts us to a certain pattern of IP addressing that reduces
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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