61200263L1-1.2A ATLAS Router User Manual 2-1
Chapter 2 Technology OverviewIP ROUTING
Internet Protocol (IP) routing is performed at layer 3 of the Open System Intercon-
nection (OSI) model. (Refer to the Frame Relay User Manual for a description of the
OSI model.) The routing process determines the optimal path for data packets to
travel and then moves the data packets along that path. Routers exchange infor-
mation about paths or routes that reach additional LAN segments. This exchange
of routing information allows a router to build a detailed knowledge of the net-
work topology. Criteria for selecting the best path can include such items as dis-
tance, number of hops (servers or routers), and cost of the transportation media.
ATLAS supports Routing Information Protocol (RIP), a protocol based on hops.
Each route has a set number of hops (routers or servers) that it must travel
through to reach a final destination. If a new route to a host address that has a
fewer number of hops is learned, it becomes the preferred route. When a new
route is learned, the router increments the hop count by one and immediately
broadcasts the new route over the other interfaces. To prevent routing loops, RIP
defines a hop count of 16 as an infinite or unreachable route.