That is a great question. Doyle is the man so I am going to hope this is helpful.
Explicit acknowledgements are required anytime the router decides not to forward the LSA as part of the flooding procedure. The article that I found that states this is RFC 5449 on OSPFv3 but I think the same principle applies It is found in Section 5.4.2 Paragraph 3 sub-paragraph 2. Regards, Tyson Scott - CCIE #13513 R&S, Security, and SP Managing Partner / Sr. Instructor - IPexpert, Inc. Mailto: [email protected] Telephone: +1.810.326.1444, ext. 208 Live Assistance, Please visit: www.ipexpert.com/chat eFax: +1.810.454.0130 IPexpert is a premier provider of Self-Study Workbooks, Video on Demand, Audio Tools, Online Hardware Rental and Classroom Training for the Cisco CCIE (R&S, Voice, Security & Service Provider) certification(s) with training locations throughout the United States, Europe, South Asia and Australia. Be sure to visit our online communities at www.ipexpert.com/communities and our public website at www.ipexpert.com <http://www.ipexpert.com/> From: [email protected] [mailto:[email protected]] On Behalf Of Joshua Yost Sent: Thursday, June 03, 2010 11:31 AM To: ccie_rs Subject: [OSL | CCIE_RS] OSPF Acknowledgements When/How are implicit acknowledgements of LSAs done as opposed to Explicit Acknowledgements? Per Doyle, implicit is we just send a copy of the LSA back to the originating neighbor in an update. Explicit would be direct or delayed Link State Acknowledgement. It is explained when direct vs delayed is used, but not explained when implict vs explicit is used.
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