I understand OSPF uses five different packet types. These are:

  • Hello
  • DB descriptor
  • Link state request
  • Link state update
  • Link state acknowledgement

However, I'm confused which of these can are used to exchange LSA information.

Can someone please explain it to me or point me to some reading?



  • "unclear" close-voters: can we help him improve the Q with some Qs in comments? Apr 28, 2015 at 11:22

2 Answers 2


In the OSPF 'Ex Start' state, the master begins the Database Description (DBD) packets exchange. Following this, through the 'Loading' state, Link State Requests (LSR) and Link State Updates (LSU) are exchanged to get more information on the routes in the DBD. The DBD contains abbreviated list of the sending routers Link State Database (LSDB) and is used by the receiving router to check against its own LSDB. Receiving routers can request more information about any entry in the DBD by sending a LSR, for example for new entries or entries with a higher sequence number. The LSU's are used to reply to LSR's. Link State Ack's are used to confirm receipt of LSUs. - Source: From my own CCNA study, thanks for the revision practice! (Maybe try Cisco Learning Network for more formal explanations.)


I think RFC 1583 is good reading material, and it seems to answer your question (section A.3, emphasis mine):

All OSPF packet types (other than the OSPF Hello packets) deal with lists of link state advertisements. For example, Link State Update packets implement the flooding of advertisements throughout the OSPF routing domain. Because of this, OSPF protocol packets cannot be parsed unless the format of link state advertisements is also understood. The format of Link state advertisements is described in Section A.4.

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