Re: [Lsr] Regarding OSPF extension for inter-area topology retrieval

[Peter Psenak <[e-mail]>]

Hi Aijun,

you are trying to reconstruct the topology of the remote area based on 
the fact that two routers are connected to the same subnet. It does not 
work because:

1. connections between routers can be unnumbered
2. routers can be connected via LAN, in which case only DR announces the 
prefix.

In summary, what you propose does not work.

thanks,
Peter



On 23/07/18 09:49 , Aijun Wang wrote:
> (Sorry for my previous mail sent wrongly to the IDR mail list, please
> reply on this thread within the LSR wg)
>
> Hi, Peter:
>
> I am Aijun Wang from China Telecom, the author of draft about “OSPF
> extension for inter-area topology retrieval”
> <https://datatracker.ietf.org/doc/draft-wang-lsr-ospf-inter-area-topology-ext/>,
> which is presented by Mr.Jie Dong during the IETF102 meeting.
>
> Thanks for your comments on the presentation material
> <https://datatracker.ietf.org/meeting/102/materials/slides-102-lsr-ospf-inter-area-topology-retrieval-00>.
>
> Below are my explanation that regarding to the question about “how it
> retrievals the inter-area topology based on the extension information”:
>
> Let’s see the graph that illustrates in Fig.1 at section 3
> <https://tools.ietf.org/html/draft-wang-lsr-ospf-inter-area-topology-ext-00#section-3>
> of the draft(I copy it also below for your conveniences ):
>
> Assuming we want to rebuild the connection between router S1 and router
> S2 that locates in area 1:
>
> 1)Normally, router S1 will advertise prefix N1 within its router LSA
>
> 2)When this router LSA reaches the ABR router R1, it will convert it
> into summary LSA, add the “Source Router Information”, which is router
> id of S1 in this example, as proposed in this draft.
>
> 3)R1 then floods this extension summary LSA to R0, which is running
> BGP-LS protocol with IP SDN Controller. The controller then knows the
> prefixes of N1 is from S1.
>
> 4)Router S2 will do the similar process, and the controller will also
> knows the prefixes N1 is also from S2
>
> 5)Then it can reconstruct the connection between S1 and S2, which prefix
> is N1. The topology within Area 1 can then be recovered accordingly.
>
> Does the above explanation can answer your question. if so, I can add it
> into the context of this draft in updated version.
>
> Best Regards.
>
> Aijun Wang
>
> Network R&D and Operation Support Department
>
> China Telecom Corporation Limited Beijing Research Institute,Beijing, China.
>