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How OSPF Survives Without Full Updates


The router that creates each LSA also has the responsibility to reflood the LSA every 30 minutes (the default), even if no changes occur. Distance vector protocols send full updates over a short time interval, listing all routes (except those omitted due to loop-avoidance tools such as split horizon). OSPF does not send all routes every 30 minutes. Instead, each LSA has a separate timer, based on when the LSA was created. So, there is no single moment when OSPF sends a lot of messages to reflood all LSAs. Instead, each LSA is reflooded by the router that created the LSA, every 30 minutes.







References

Odom, Wendell (2008) CCNA ICND2 Official Exam Certification Guide, Second Edition. Indianapolis: Cisco Press.