414Lecture14

414Lecture14 - Lecture 14 Network Layer Distance Vector...

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Lecture 14 Network Layer Distance Vector, NATs, IPv6 ECSE 414 – Fall 2010

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ECSE 414, Lecture 14 2 Announcements Homework Assignment #3 due Tuesday, Oct 26 2010 Michael Rabbat
ECSE 414, Lecture 13 3 Dijkstra Review 7 2 2 4 5 3 6 2 3 4 2 2 F B C E D H A G “source” 2010 Michael Rabbat

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ECSE 414, Lecture 14 4 Dijkstra’s Algorithm Summary Each node knows the entire network graph and link costs Setup a table and compute the shortest paths from one node to all other nodes in the network Example: each router computes shortest paths from itself to all other IP addresses Given shortest paths, can form the routing table used to forward packets. Key properties: Greedy algorithm Centralized (need global knowledge) 2010 Michael Rabbat
ECSE 414, Lecture 14 5 u u u 0 (u) v 2 (v) w 5 (w) x 1 (x) y z 2 5 1 w v x Initially, u only knows which nodes it is directly connected to 2010 Michael Rabbat

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ECSE 414, Lecture 14 6 u u u 0 (u) v 2 (v) w x 1 (x) y z 2 5 1 w v x message from x u 1 v 2 w 3 x 0 y 1 z message from v u 2 v 0 w 3 x 2 y z message from w u 5 v 3 w 0 x 3 y 1 z 5 Bellman-Ford Equation: D u (dest) = min n=u,v,w,x {c(u,n) + D n (dest)} 4 (x) 2 (x) 10 (w) u receives messages from each neighbor with their distance vector, stores and uses this information 2010 Michael Rabbat
ECSE 414, Lecture 14 7 u u u 0 (u) v 2 (v) w x 1 (x) y 2 (x) z 2 5 1 w v x v u 2 v 0 w 3 x 2 y z w u 5 v 3 w 0 x 3 y 1 z 5 Bellman-Ford Equation: D u (dest) = min n=u,v,w,x {c(u,n) + D n (dest)} 3 (x) 4 (x) z new msg from x u 1 v 2 w 2 x 0 y 1 z 3 u receives messages from each neighbor with their distance vector, stores and uses this information 2010 Michael Rabbat

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ECSE 414, Lecture 14 8 Distance-Vector Routing Algorithm Bellman-Ford Equation (dynamic programming) Define d x (y) := cost of least-cost path from x to y Then d x (y) = min {c(x,v) + d v (y) } where min is taken over all neighbors v of x v Decentralized: Routers only know about immediate neighbors 2010 Michael Rabbat
ECSE 414, Lecture 14 9 Bellman-Ford example u y x w v z 2 2 1 3 1 1 2 5 3 5 Clearly, d v (z) = 5, d x (z) = 3, d w (z) = 3 d u (z) = min { c(u,v) + d v (z), c(u,x) + d x (z), c(u,w) + d w (z) } = min {2 + 5, 1 + 3, 5 + 3} = 4 Node that achieves minimum is next hop in shortest path forwarding table B-F equation says: 2010 Michael Rabbat

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ECSE 414, Lecture 14 10
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture14 - Lecture 14 Network Layer Distance Vector...

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