After the adjacency as been formed between two routers, a master-slave-relationship between two routers is formed too, where the master begins to send Database Description (DBDs).

My question is: What do Database Descriptions contain? the whole LSDB?

I also read this:

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The router recognizes that the DBD contains more current link-state-entries due to the squence-number, right? If it contains more current link-state-entries, the router transitionsto the Loading State, in which the router asks with LSR (Link State Requests) for more information. But why does the router need to send LSRs? What Information would he want to have? Isn't everything in the DBD which got send to him?


1 Answer 1


Isn't everything in the DBD which got send to him?

No, the DBD's only contain a summary of the LSA. To get all the LSA information, the router requests the full LSA from the neighbor.

It may seem strange that only a summary is sent, when just a few more bytes would contain it all. Remember that OSPF was developed at a time when bandwidth and processing power were precious commodities, so the developers tried every way to save both.

  • But doesn't asking for further information (LSR) and re-sending (there's a header too for the LSU) consume more bandwidth (not at once, yes, but considering all those LSRs and LSUs), wouldn't the network converge even faster? And do you know what information is requested for instance? Just that I know what the DBD doesn't include.
    – watchme
    Jun 6, 2018 at 18:48

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