The five nines (99.999% availability of a service) is the holy grail of many Chief Information Officers (CIO). To reach this goal, the average monthly downtime should be less than 25 seconds, which is extremely hard to achieve even in a fully redundant architecture. The scheduled router outages (upgrades, hardware maintenance), while being necessary, can also impact the safety margin you have. In this IP Corner article, Ivan Pepelnjak describes how you can reduce the network downtime caused by scheduled router outages if your network uses OSPF (Open Shortest Path First) routing protocol.