动态路由DynamicRouting-资讯管理学系.PPT

routing Which route? Depend on type of service(TOS) minimum delay or better quality(more reliable) a field specifies “min delay” or “reliable” is included in a packet How to route? Each router must have two tables One to route packets with minimum delay Another for packets that need reliablity Routing table If the routing tables are consistent, they can lead the packet to its destination Next-hop routing Hierarchical routing system Another way to reduce the size of routing table Divide the Internet into smaller sections call autonomous systems An autonomous system is a group of networks and routers under the authority of a single administration Routing inside autonomous system is refferred to as interior routing Routing between autonomous systems is referred to as exterior routing Hierarchical routing system The size of table for each interior router is nearly the number of networks inside the autonomous system Additional entry(s) is (are) required for connecting the autonomous systems 先找到正確的AS,再找到正確的Network,最後找到host(broadcast) Static routing / Dynamic routing Static routing Information entered manually Good for small internet which does not change often Dynamic routing Is updated periodically using dynamic routing protocol Whenever there is a change in the Internet (eg. shutdown of a router) Dynamic routing protocol update all the tables in the routers) Routing protocols A combination of rules and procedures That lets routers in an internet inform each other of changes Also include procedures for combining information received from other routers Internal routing : RIP, OSPF Exterior routing : BGP RIP (routing information protocol) Based on distance vector routing distance vector routing : each router periodically shares its knowledge about the entire internet with its neighbors Sharing knowledge about the entire autonomous system Sharing only with neighbors Sharing at regular intervals (eg. 30 seconds) OSPF(Open shortest path first) Use link state routing to