Distance Vector Routing

• From time-to-time, each node sends distance vector estimate
• Each node then updates: $D_x(y)$ ← $\mathrm{min}v(c{x,v}+D_v(y))$
• Estimate converges $d_x(y)$

Algorithm:

1. Wait for change in cost/msg
2. Recompute from DV from neighbor
3. If any destination changed, notify neighbors

However, good news travels fast (notify neighbors, instant min)

But, bad news travels slow (if a neighbor relies on you to give min, if yours goes up dramatically, it will take lots of iterations to correct)

Routing Protocols

Inter-AS: BGP (path vector based)

Intra-AS: OSPF (Dijkstra’s based)

Could also be hierarchical