Subject: [Idr] Regarding OSPF extension for inter-area topology retrieval

From: "Aijun Wang" <[email-masked]>
Date: Mon, 23 Jul 2018 15:16:46 +0800

Hi, Peter:

I am Aijun Wang from China Telecom, the author of draft about
<https://datatracker.ietf.org/doc/draft-wang-lsr-ospf-inter-area-topology-ex
t/> "OSPF extension for inter-area topology retrieval", 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-inte
r-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.