DISTANCEVECTORROUTINGPROTOCOLSDr.RockyK.C.Chang15November2010
DISTANCE VECTOR ROUTING PROTOCOLS Dr. Rocky K. C. Chang 15 November 2010 1
Theroutingproblem Problem:How can a router/host determine the pathto a destination? Any routing protocol must allow routers to make acorporate, consistent,and correct local forwardingdecisions regarding any destinationin a globalrouting fabric. Sources and destinations are generally not directlyconnected. Routers are generally not directly connected
The routing problem 2 Problem: How can a router/host determine the path to a destination? Any routing protocol must allow routers to make a corporate, consistent, and correct local forwarding decisions regarding any destination in a global routing fabric. Sources and destinations are generally not directly connected. Routers are generally not directly connected
Designissues3 Scalability:scale to the number of networks Routing table sizeRouting messagesTimeto converge Free of permanent/transient routing loops Optimal paths: hop count, type-of-service, qualityof-service, etc. Security Host mobility and perhaps router mobility
Design issues 3 Scalability: scale to the number of networks Routing table size Routing messages Time to converge Free of permanent/transient routing loops Optimal paths: hop count, type-of-service, qualityof-service, etc. Security Host mobility and perhaps router mobility
DesignchoicesCentralized vs decentralized口A central processorcomputesthe routes. Source-based vs hop-by-hop E.g., source routing and destination-based routing With or without the global topological info.E.g.,OSPFvsRIP Dynamic (or state-dependent) vs static routing IP routing vs ATM routingSinale-path vs multiple path7
Design choices 4 Centralized vs decentralized A central processor computes the routes. Source-based vs hop-by-hop E.g., source routing and destination-based routing With or without the global topological info. E.g., OSPF vs RIP Dynamic (or state-dependent) vs static routing IP routing vs ATM routing Single-path vs multiple path
Two main routing approachesDistance vector (DV) and link state (LS)口 Both are implemented as distributed protocols. Both are hop-by-hop routing protocols.DV routers do not have the complete topological infobut LS routers do (partially). Both are dynamic routing protocols. Both could maintain multiple paths. Each DV router tells its neighbor routers what it haslearnt.EachLS routertellsall routersthe states ofits directly connected links
Two main routing approaches 5 Distance vector (DV) and link state (LS) Both are implemented as distributed protocols. Both are hop-by-hop routing protocols. DV routers do not have the complete topological info but LS routers do (partially). Both are dynamic routing protocols. Both could maintain multiple paths. Each DV router tells its neighbor routers what it has learnt. Each LS router tells all routers the states of its directly connected links