Information Technology Reference
In-Depth Information
Another important concept is related to supernetting (also known as prefix/route aggrega-
tion or route summarization). A supernetwork, or supernet, is created from the combination
of two or more networks with a common CIDR prefix. The new routing prefix aggregates
prefixes of the constituent networks. Any prefixes that do not lie in the same routing path are
not considered.
Consider a large company that has 100 routers in 25 districts. That means a total of
2,500 different networks and quite a large combined routing table. One way is to proceed
with this routing table, but this is inefficient in terms of memory storage of route informa-
tion and the processing overhead associated with matching routes. Another more efficient
way is to use supernets instead.
For example, consider a company has these four networks:
192.168.98.0
192.168.99.0
192.168.100.0
192.168.101.0
First, the addresses are converted to binary and aligned. The common bits are located
and redefined as the aggregated or summarized route with the remaining bits defined as the
uncommon address space. In this case, 192.168.96.0/21 depicts a supernet of the previously
mentioned four IPv4 addresses with 192.168.96.0 as the first 21 common bits. The more
networks there are to aggregate, the fewer the common bits. For example, if we had been
using only the first two networks in the preceding list, the summarized route or supernet
would have been 192.168.98.0/23.
Avoiding Topological Fragmentation
Within the Internet, supernetting can serve as a preventive strategy to avoid topological
fragmentation of the IPv4 address space. It accomplishes this by using a hierarchical alloca-
tion system that delegates control of address space segments to regional network service
providers. This also facilitates regional route aggregation.
Table 9.2 shows the OSI model. Whereas subnets are layer 3 constructs, VLANs are
layer 2 constructs that partition the network to create multiple distinct broadcast domains
so that communication between domains takes place through defined routes. VLANs help
in traffic control, provide the flexibility to adapt to changes in the network, and allow for
simplified administration.
TABLE 9.2 The OSI model—network layers
Layer (Higher Is
More Abstract)
Name
Protocols/Examples
7
Application
DHCP, FTP, HTTP, LDAP, SSH, Telnet
6
Presentation
Telnet
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