Search results
CSE 123 – Lecture 12: Link-state Routing 24 Getting consistent routing information to all nodes E.g., all nodes having the same link-state database
a) Consider a positively weighted graph G. Applying the Bellman-Ford (used by distance-vector protocols) or Dijk-stra (used by link-state protocols) algorithm on G would lead to the same forwarding state. Solution: False. In general, both solve the shortest-path problem.
Most widely used intra-domain routing protocols Run by almost all ISPs and many large organizations Basic link state algorithm plus many features: Authentication of routing messages Extra hierarchy: Partition into routing areas » “Border”router pretends to be directly connected to all routers in an area (answers for them)
Table lookup for forwarding (why faster than IP lookup?) How to choose best path? How to scale to millions of users? How to adapt to failures or changes? Today’s lecture! Next time... So you have all of these LSPs. Now what?
Link State Approach: Share the Map! • Dijkstra’s algorithm takes a weighted graph as input – ... and computes shortest paths on that graph • Link State routing protocols instruct routers to collectively build a map of the whole network – each router shares its local information
Link State Approach to Routing •Shortest paths in graph: classic theory problem •Classic centralized single-source shortest paths algorithm: Dijkstra’s Algorithm –requires map of entire network •Link State (LS) Routing: –push network map to every router –each router learns link state database –each router runs Dijkstra’s locally
In link-state routing, each node:! • floods the network with the state (up, down) of its links! • uses Dijkstra’s Shortest Path First (SPF) algorithm to compute a
