Convergence

All of the forwarding tables indicating the same shortest path in the graph

RIP

• challenge to RIP: No convergence ⇒ existence of loop in the graph
• Distance vectors do not provide sufficient information to prevent certain types of non- convergence
  • e.g. count to infinity problem

⇒ which leads to the development of the OSPF

OSPF

• Link state routing | Dij algorithm

Count to infinity problem

Graph A

the question: How do we deal with this problem?

Solution to Count-to-infinity problem

1. Just put a hop limit to infinity (16)
2. Split horizon (don’t send roots that are learnt from a neighbor back to them)
   1. work in 2-node network
   2. Doesn’t work with larger networks
3. Split horizon with poison reverse
   1. return routes learned from neighbors to infinity
4. Disrupt timing of periodic updates
   1. Can cause longer delays in convergence