Second in both vector and link state protocols

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Unformatted text preview: ertisements ensure that over time the nodes all have all the information necessary to compute correct routes. Second, in both vector and link-state protocols, periodic advertisements are the fundamental mechanism used to overcome the effects of link and node failures (as well as packet losses). 3. Integrating advertisements: In this step, a node processes all the advertisements it has recently heard and uses that information to produce its version of the routing table. Because the network topology can change and because new information can become available, these three steps must run continuously, discovering the current set of neighbors, disseminating advertisements to neighbors, and adjusting the routing tables. This continual operation implies that the state maintained by the network switches is soft: that is, it refreshes periodically as updates arrive, and adapts to changes that are represented in these updates. This soft state means that the path used to reach some destination could change at any time, potentially causing a stream of packets from a source to destination to arrive reordered; on the positive side, however, the ability to refresh the route means that the system can adapt by “routing around” link and node failures. We will study how the routing protocol adapts to failures in the next lecture. A variety of routing protocols have been developed in the literature and several different ones are used in practice. Broadly speaking, protocols fall into one of two categories depending on what they send in the advertisements and how they integrate advertisements to compute the routing table. Protocols in the first category are called vector protocols because each node, n, advertises to its neighbors a vector, with one component per destination, of information that tells the neighbors about n’s route to the corresponding CHAPTER 18. NETWORK ROUTING - I 6 WITHOUT ANY FAILURES destination. For example, in the simplest form of a vector protocol, n advertises its cost to reach each destination as a vector of destination:cost tuples. In the integration step, each recipient of the advertisement can use the advertised cost from each neighbor, together with some other information (the...
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This document was uploaded on 02/26/2014 for the course CS 6.02 at MIT.

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