Static path information can be manually programmed into the router and simply force the router to utilize a particular interface or next-hop IP address for forwarding packets with matching destination addresses. Static routes potentially could match a broad range of network addresses. Yet another way to obtain routing information is to use distributed applications enabled on routers that allow automatic collection and sharing of routing infor-mation. These routing applications frequently are referred to as dynamic routing protocols because they are not only automated route-gathering tools; they also work in almost real time, tracking the state of connectivity in the network to provide routing information that is as current and as valid as possible.
Contrast this behavior with static routes, which are manual route entries and require manual intervention to reprogram the network routers in case of any path changes. Obviously, dynamic routing protocols provide more convenience to the network operator than static routes in managing routing information. The price for this convenience, however, is configuration and troubleshooting complexity. Operation of dynamic routing protocols also can be resource-intensive, requiring large amounts of memory and processing resources. Hence, working with dynamic routing protocols frequently requires advanced knowledge and sophisticated expertise for handling related network design, router configuration, tuning, and troubleshooting chores.
Even though static routing is less demanding on system resources and requires a lower level of technical skill to configure and troubleshoot, the sheer effort of manually entering routes for a sizeable network makes it a less attractive option. Obviously, static routing is not a good candidate for today's large enterprise and Internet service provider (ISP) IP-based networks. Another drawback to static routing is that it is less flexible for implementation of complicated routing policies. When it comes to routing policy implementation, there is no better substitute for the intelligence and flexibility provided by dynamic routing protocols, such as BGP, OSPF, and IS-IS. The next section further discusses dynamic routing protocols.
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