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]" <[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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