Hi Sergey, Have you reproduced the loop with routers? I definitely agree that ABR_1 will prefer the path to the ASBR through area 100. I think there is some ambiguity as to the cost it uses in its ASBR-Summary LSA injected into area 200.
Thanks, Acee From: Lsr <[email protected]> on behalf of Sergey SHpenkov <[email protected]> Date: Wednesday, February 26, 2020 at 2:22 AM To: "[email protected]" <[email protected]> Subject: Re: [Lsr] Question about OSPF (transit area routing loop) Acee, Because ABR_1 creates SumLSA-4 for the ASBR not from the backbone area. The cost of SumLSA-4 for ASBR is 300. Thanks, Sergey вт, 25 февр. 2020 г. в 22:44, Acee Lindem (acee) <[email protected]<mailto:[email protected]>>: Hi Sergey, I don’t see why RT_1 wouldn’t go through ABR_1 to get to the ASBR. Thanks, Acee From: Lsr <[email protected]<mailto:[email protected]>> on behalf of Sergey SHpenkov <[email protected]<mailto:[email protected]>> Date: Tuesday, February 25, 2020 at 2:38 PM To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Subject: [Lsr] Question about OSPF (transit area routing loop) Hi, In section 16.3 of the OSPF RFC 2328 standard, it is stated that all ABR routers connected to a transit area are required to check the sumLSA contained within this area in order to possibly improve the intra-area and inter-area backbone routes for themselves. See the picture: [cid:[email protected]] The RT_1 and ABR_3 routers will use different paths to the ASBR router: ABR_3 -> RT_1 -> ABR_1 -> ASBR = cost 3 RT_1 -> ABR_3 -> ABR_2 -> ASBR = cost 21 route loop between RT_1 and ABR_3 Please explain this situation Thanks, Sergey
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