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Unformatted text preview: o. The routers must communicate using a
routing protocol, of which there are many to choose from. The process on the router that is
running the routing protocol, communicating with its neighbor routers, is usually called a
routing daemon. As shown in Figure 9.1, the routing daemon updates the kernel's routing
table with information it receives from neighbor routers.
The use of dynamic routing does not change the way the kernel performs routing at the IP
layer, as we described in Section 9.2. We called this the routing mechanism. "The kernel still
searches its routing table in the same way, looking for host routes, network routes, and
default routes. What changes is the information placed into the routing table-instead of
coming from route commands in bootstrap files, the routes are added and deleted
dynamically by a routing daemon, as routes change over time.
As we mentioned earlier, the routing daemon adds a routing policy to the system, choosing
which routes to place into the kernel's routing table. If the daemon finds multiple routes to a
destination, the daemon chooses (somehow) which route is best, and which one to insert into
the kernel's table. If the daemon finds that a link has gone down (perhaps a router crashed or
a phone line is out of order), it can delete the affected routes or add alternate routes that
bypass the problem. file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/dynamic.htm (1 of 17) [12/09/2001 14.46.53] Chapter 10. Dynamic Routing Protocols In a system such as the Internet, many different routing protocols are currently used. The
Internet is organized into a collection of autonomous systems (ASs), each of which is
normally administered by a single entity. A corporation or university campus often defines
an autonomous system. The NSFNET backbone of the Internet forms an autonomous system,
because all the routers in the backbone are under a single administrative control.
Each autonomous system can select its own routing protocol to communicate between the
routers in that au...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12