One of the advantages of a hierarchical
WAN design is that it provides a method for controlling data traffic
patterns by putting Layer 3 routing points throughout the network.
Because routers have the ability to determine paths from the source
host to destination hosts based on Layer 3 addressing, data traffic
flows up the hierarchy only as far as it needs to find the destination
host, as shown in Figure .
If Host A were to establish a
connection to Host B, the traffic from this connection would travel to
Router 1 and be forwarded back down to Host B. Notice in Figure
that this
connection does not require that any traffic be placed on the link
between Router 1 and Router 2, thus conserving the bandwidth on that
link.
In a two-layer WAN hierarchy, shown in
Figure ,
the traffic only travels up the hierarchy as far as
needed to get to the destination, thus conserving bandwidth on other
WAN links.
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