Any time two neighbors are first forming an adjacency and are going thru the INIT 2-WAY ExStart Exchange Loading Full process; LSA's must be explicitly acknowledged.
Most of the time explicit acknowledgements are used between neighbors on a segment. When the OSPF flooding interval is occurring and a device on a segment receives a bunch of LSA's it may decide to group all the LSA's together and send an implicit LSA acknowledgement thru a single LSA Ack instead of sending an explicit acknowledgement for each LSA. And the third is it must send an explicit any time it decides not to forward an LSA either because of an error or better SPF known locally. This is from RFC 2328 which is the OSPFv2 RFC. Look it up and see if you can find any more information if you are interested. If you are looking for more detail then that you are going to have to go to the writer of the RFC ;). I am not sure of any more detail than above. Regards, Tyson Scott - CCIE #13513 R&S, Security, and SP Managing Partner / Sr. Instructor - IPexpert, Inc. Mailto: <mailto:[email protected]> [email protected] Telephone: +1.810.326.1444, ext. 208 Live Assistance, Please visit: <http://www.ipexpert.com/chat> 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 <http://www.ipexpert.com/communities> www.ipexpert.com/communities and our public website at <http://www.ipexpert.com/> www.ipexpert.com From: Joshua Yost [mailto:[email protected]] Sent: Thursday, June 03, 2010 2:23 PM To: Tyson Scott Cc: ccie_rs Subject: Re: [OSL | CCIE_RS] OSPF Acknowledgements "Decides not to forward the LSA" When could this happen? I am thinking that this means like in a DR/BDR situation where the only routers sending to ALLSPFROUters are the DR and BDR, so the neighbors need to ackknowledge specifically as they are not flooding? Does that seem right? On Thu, Jun 3, 2010 at 12:06 PM, Tyson Scott <[email protected]> wrote: 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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