
Configuring IP, ARP, RARP, RIP, and OSPF 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. CIDR reduces the size of the routing tables used to store
advertised IP routes.
OSPF supports classless routing within a domain.
Autonomous Systems
LANs and WANs interconnected by IP routers form a group of networks called an
internetwork. For administrative purposes, an internetwork is divided into
autonomous systems. An autonomous system (AS) is simply a collection of
routers (called gateways in IP terminology) and hosts run by a single technical
administrator that has a single, clearly defined routing policy. Each autonomous
system has its own unique AS number assigned by the appropriate Internet
Registry entity. Figure 1-3
depicts a sample internetwork segmented into three
autonomous systems.
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