Route Summerization

Route summarization, or route aggregation, is a method of representing a series of network numbers in a single summary address.

To implement route summarization, certain requirements are needed:

Multiple IP addresses must have the same highest-order bits

Routing decision are made based on the entire address

Routing protocols must carry the prefix (subnet mask) length

Dis-contiguous subnets are major network addresses separated by another major network address.

CIDR is a mechanism developed to alleviate exhaustion of addresses and reduce routing table sizes. With CIDR, blocks of Class C addresses are assigned to ISPs, which in turn assign subsets of address space to organizations. These blocks are then summarized in routing tables.

Planning of an IP address space requires an examination of the corporate structure. Improper addressing can result in an unscalable network design.

A scalable IP addressing scheme allows for route aggregation. Route aggregation, also known as route summarization allows for many routes to be represented with a single advertisement. This reduces routing updates and allows for greater scalability with our routing protocols.

Consider avoiding the use of the "zero subnet" to prevent problems caused by devices not compatible with this technology. In the event subnet zero is used, the "ip subnet-zero" command will correctly configure a router for this practice.

Fixed Length Subnet Masking, or FLSM, uses a constant mask everywhere in the network.

Variable Length Subnet Masking, or VLSM, uses an inconsistent mask tailoring to different sizes of networks.