?– It provided enhanced route aggregation, also known as supernetting. As the Internet
grows, routers on the Internet require huge memory tables to store all the routing
information. Supernetting helps reduce the size of router memory tables by combining
and summarizing multiple routing information entries into one single entry. This
reduces the size of router memory tables and also allows for faster table lookup.
A CIDR network address looks like this:
192.168.54.0/23
The 192.168.54.0 is the network address itself and the /23 means that the ?¬?rst 23 bits are
the network part of the address, leaving the last 9 bits for speci?¬?c host addresses. The effect
of CIDR is to aggregate, or combine, multiple classful networks into a single larger
network. This aggregation reduces the number of entries required in the IP routing tables
and allows the provisioning a larger number of hosts within the network. Both are done
without using a network ID from the next larger classful address group.
With the CIDR approach, if you need more than 254 host addresses, you can be assigned a
/23 address instead of wasting a whole Class B address that supports 65,534 hosts.
Figure 1-37 shows an example of using CIDR. Company XYZ asks for an address block
from its ISP, not a central authority.
Pages:
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106