Distance vector Poison reverse If Z routes through Y to get to X 60 Z tells Y its(zs)distance to X is infinite(so Y wont route toⅩaZ) Eliminates some possible timeouts with split horizon 50 Will this completely solve count to infinity problem? algorithm terminates X Z DI X Z DI X Z D x Z DxZ X(4 X|(60∞X(60∞X60(51x60 vIa X X Y x Y X X X50 x(5061x65061x C(X,Y time change 9/28/2006 Lecture 10: Intra-Domain routing 16
9/28/2006 Lecture 10: Intra-Domain Routing 16 Distance Vector: Poison Reverse If Z routes through Y to get to X : • Z tells Y its (Z’s) distance to X is infinite (so Y won’t route to X via Z) • Eliminates some possible timeouts with split horizon • Will this completely solve count to infinity problem? X Z 4 1 50 Y 60 algorithm terminates
Poison reverse failures Table for a Table for B Table for D Table for F Dst Cst Hop Dst Cst Hop Dst Cst Hop DstCstHop 7 F C 8 A C 9 B C Table for a Table for F Forced Dst Cst Hop Forced Update Update Dst Cst Hop C C Table for A Better Dst Cst Hop,Route B C 13D Table for B Forced Update dst Cst Hop Iterations dont converge C14A Count to infinity Table for d Forced Solution Update Dst Cst Hop C Make "infinity smaller 15 Table for a What is upper bound on Dst Cst Hop Forced maximum path length? Update 19D Lecture 10: Intra-Domain routing 17
9/28/2006 Lecture 10: Intra-Domain Routing 17 Poison Reverse Failures • Iterations don’t converge • “Count to infinity” • Solution • Make “infinity” smaller • What is upper bound on maximum path length? Table for A Dst Cst Hop C 7 F Table for B Dst Cst Hop C 8 A Table for F Dst Cst Hop C 1 C Table for F Dst Cst Hop C – Table for A Dst Cst Hop C – Forced Update Table for B Dst Cst Hop C 14 A Forced Update F C 6 1 1 1 B D A 4 Table for D Dst Cst Hop C 9 B Forced Update Table for A Dst Cst Hop C 13 D Better Route Table for D Dst Cst Hop C 15 B Table for A Dst Cst Hop C 19 D Forced Update • • • Forced Update