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What method is used by ospf protocol to prevent looping of flooded packets for link state advertisements? The packet header does not contain any timestamp. How do the routers recognize that it is the same advertisement that they sent before?

Update ospf is an intranetwork routing protocol

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migrated from May 6 '10 at 5:18

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Whenever an LSA is about to be sent out, the router checks against a list of unacknowledged announcements sent to a given adjacent router. If it's on the list, it doesn't need to be sent. If it's not on the list, a copy is placed on the list for that adjacency and it is then sent.

All LSAs use sequence numbers and the latest LSA is kept. If an older LSA is received, it's (essentially) ignored.

There's also an Age field in all LSAs that is incremented as the LSA is re-transmitted across the network.

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