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Re: [Lsr] Question about OSPF (transit area routing loop)

Sergey SHpenkov <sergey.v.shpenkov@gmail.com> Thu, 27 February 2020 17:46 UTC

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From: Sergey SHpenkov <sergey.v.shpenkov@gmail.com>
Date: Thu, 27 Feb 2020 20:44:36 +0300
Message-ID: <CAD4HJpqQQ8PHui1UFFxa7UQyqqaoKfKkmTmifuEc0rkOLHb2Bw@mail.gmail.com>
To: "Acee Lindem (acee)" <acee@cisco.com>
Cc: "lsr@ietf.org" <lsr@ietf.org>
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Subject: Re: [Lsr] Question about OSPF (transit area routing loop)
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Hi Acee,

Yes, I was able to reproduce the loop

Thanks,
Sergey

чт, 27 февр. 2020 г. в 19:54, Acee Lindem (acee) <acee@cisco.com>:

> 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 <lsr-bounces@ietf.org> on behalf of Sergey SHpenkov <
> sergey.v.shpenkov@gmail.com>
> *Date: *Wednesday, February 26, 2020 at 2:22 AM
> *To: *"lsr@ietf.org" <lsr@ietf.org>
> *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) <acee@cisco.com>:
>
> Hi Sergey,
>
> I don’t see why RT_1 wouldn’t go through ABR_1 to get to the ASBR.
>
> Thanks,
>
> Acee
>
>
>
> *From: *Lsr <lsr-bounces@ietf.org> on behalf of Sergey SHpenkov <
> sergey.v.shpenkov@gmail.com>
> *Date: *Tuesday, February 25, 2020 at 2:38 PM
> *To: *"lsr@ietf..org <lsr@ietf.org>" <lsr@ietf.org>
> *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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