OSPF and IS-IS: Choosing an IGP for Large-Scale Networks

Afterword: The Future of Link State Protocols

OSPF and IS-IS are both almost 20 years old, and are based on a mathematical algorithm that is almost 50 years old; in Internet years, this is nearly prehistoric. They were designed in the days when processors were slow, memory was expensive, and each router added significant latency to the network. As a result both protocols have features and characteristics that no longer matter, meant to solve problems that no longer exist. The 32-bit alignment of all OSPF data units for orderly processing and the original 6-bit IS-IS metric for faster processing are just two examples. Although the operational experience gained from the original link state protocol used in the ARPANET led to some key design differences ...