Hi, Sergey:
If so, ABR-3 should also receive this SumLSA-4 for the ASBR(with cost 300), and then prefer the path via ABR-2 to reach ASBR(with cost 20). Then there will be no loop then? Or, how many SumLAS-4 will be advertised by ABR-1? If it selects and advertises only one (3 or 300), then the loop will not be emerged. Currently, it seems it advertises this SumLAS-4 with the cost 300 to RT_1 and with the cost 3 to ABR-3? Best Regards. Aijun Wang China Telecom 发件人: [email protected] [mailto:[email protected]] 代表 Sergey SHpenkov 发送时间: 2020年2月26日 15:20 收件人: [email protected] 主题: 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]>: 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]> on behalf of Sergey SHpenkov <[email protected]> Date: Tuesday, February 25, 2020 at 2:38 PM To: "[email protected] <mailto:[email protected]> " <[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: 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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