
Configuring IP Services
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Classless Interdomain Routing
Classless interdomain routing (CIDR) is an addressing scheme that employs
supernet addresses to represent multiple IP destinations. Rather than advertise a
separate route for each destination in a supernet, a router can use a supernet
address to advertise a single route -- called an aggregate route -- that represents all
of the destinations. This reduces the size of the routing tables used to store
advertised IP routes.
BGP-4 supports classless interdomain routing. OSPF supports classless routing
within a domain.
Autonomous Systems
LANs and WANs interconnected by IP routers form a group of networks called an
internet. For administrative purposes, an internet is divided into autonomous
systems. An autonomous system (AS) is simply a collection of routers (called
gateways in IP terminology) and hosts. Figure 1-
2 depicts a sample internet
segmented into three autonomous systems.
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