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

[Peter Psenak <[e-mail]>]

Hi Aijun,

On 24/07/18 05:37 , Aijun Wang wrote:
> _Hi, Peter:_
>
> For point-to-point interface, as described in  OSPFv2(RFC2328 12.4.1.1.  Describing point-to-point interfaces)  <https://tools.ietf.org/html/rfc2328#page-130>, the router LSA will include two links description for each interface, within which the “type 3 link”(stub network) will describe the subnet mask of the point-to-point interface.
>
> For broadcast/NBMA interface, the DR will be elected and it will
> generate the network LSA which will include also the subnet mask of the
> connected interface.
>
> For unnumbered and virtual link, if you consider we should include them
> also for all possible scenarios even if we seldom use them in large
> network, we can consider expand the summary LSA to cover it, as done by
> this draft.

there is no way to address unnumbered p2p case your way, because there 
is no Summary LSA generated to other area in such case.

Anyway, reconstructing a topology of a remote area based on the prefix 
announcements that come from it is a broken concept. I have given you 
several examples where your proposal does not work.

thanks,
Peter

>
> For Anycast prefixes situation that you described(although we seldom
> plan our network in such way), the PCE controller will not deduce the
> wrong information from the reported information------Different router
> advertise the same prefix, why can’t they be connected in logically?
>
> On summary, the ABR can know and report the originator of the connected
> interface’s prefixes, and also the connected information for the
> unnumbered/virtual link from the traditional router LSA/network LSA
> message, thus can transfer them to the router that run BGP-LS, then to
> the PCE controller to retrieval the topology.
>
> _To Rob: _
>
> BGP-LS is one prominent method to get the underlay network topology and
> has more flexibility to control the topology export as described in RFC
> 7752 <https://tools.ietf.org/html/rfc7752#section-1>.
>
> Solution 1) that you proposed is possible, but we will not run two
> different methods to get the topology.
>
> Solution 2) is also one possible deployment, but it eliminates the
> advantage of the BGP-LS, in which it needs several interaction points
> with the underlay network. and such deployment is not belong to
> redundancy category as information got from different areaes are different.
>
> Solution 3)--Streaming telemetry technology should be used mainly for
> the monitor of network devices, it requires the PCE controller to
> contact with every router in the network, is also not the optimal
> solution when compared with BGP-LS.
>
> We can update the current draft to include all possible scenarios that
> we are not aiming at beginning for integrity consideration. The proposed
> extension does not add to complexity of IGP. What we discussed here is
> the complexity of IGP protocol itself.
>
> Best Regards.
>
> Aijun Wang
>
> Network R&D and Operation Support Department
>
> China Telecom Corporation Limited Beijing Research Institute,Beijing, China.
>
> *发件人:*Rob Shakir [mailto:[e-mail]]
> *发送时间:*2018年7月24日7:04
> *收件人:*Peter Psenak
> *抄送:*Dongjie (Jimmy); [e-mail]; Ketan Talaulikar (ketant);
> Aijun Wang; [e-mail]; Acee Lindem (acee)
> *主题:*Re: [Lsr] 答复: 答复: Regarding OSPF extension for inter-area
> topology retrieval
>
> +1 to Peter. We should not define fragile solutions within the IETF.
>
> There are also a multitude of other solutions here already:
>
> 1) IGP adjacency with one router in each area (at a minimum - probably
> two for a robust system) over a tunnel. Deployed in many networks for
> years.
> 2) BGP-LS to one router (ditto robustness comment) in each area.
> 3) streaming telemetry of the LSDB contents via gNMI.
>
> All these solutions exist in shipping implementations - please let’s not
> add to the system complexity of the IGP here.
>
> r.
>
> On Mon, Jul 23, 2018 at 12:30 Peter Psenak
> <ppsenak=[e-mail] <mailto:[e-mail]>>
> wrote:
>
>     Hi Aijun,
>
>     On 23/07/18 13:07 , Aijun Wang wrote:
>     > Hi, Peter:
>     >
>     > For routers that connected by LAN, the router will establish adjacent
>     > neighbor with DR, but not only DR advertises the connected prefixes.
>
>     only the Network LSA includes the network mask, other routers would
>     include the interface address only.
>
>
>     > DR and
>     > DRother will all advertise type 1 and type 2 LSA with each other, then the
>     > process and proposal described in this draft will still work.
>     > We seldom use the ip unnumbered features in our network, can we ignore it
>     > then? Or other persons has some idea on such situation?
>
>     the fact that you do not use unnumbered is not really relevant. IETF
>     defines solutions that MUST work for all possible scenarios, not only
>     for a specific one.
>
>     > Anycast prefixes are often /32 long, this can be easily filtered by SDN
>     > controller because the link prefixes between two routers will be no larger
>     > than /32 for IPv4 network.
>
>     protocol allows to advertise the same prefix with an arbitrary mask from
>     multiple routers without these routers being directly connected. Your
>     proposal is based on the assumptions that are incorrect.
>
>     thanks,
>     Peter
>
>     >
>     > Best Regards.
>     >
>     > Aijun Wang
>     > Network R&D and Operation Support Department
>     > China Telecom Corporation Limited Beijing Research Institute,Beijing, China.
>     >
>     > -----邮件原件-----
>     >发件人: Peter Psenak [mailto:ppsenak
>     <mailto:ppsenak>=[e-mail]
>     <mailto:[e-mail]>]
>     >发送时间: 2018年7月23日18:20
>     >收件人: Aijun Wang; 'Peter Psenak'; [e-mail]
>     <mailto:[e-mail]>
>     >抄送: [e-mail] <mailto:[e-mail]>; 'Ketan Talaulikar
>     (ketant)'; 'Acee Lindem (acee)';
>     > 'Dongjie (Jimmy)'
>     >主题: Re: [Lsr] 答复: Regarding OSPF extension for inter-area topology
>     > retrieval
>     >
>     > Hi Aijun,
>     >
>     > On 23/07/18 11:16 , Aijun Wang wrote:
>     >> Hi, Peter:
>     >>
>     >> Actually, I consider mainly the point-to-point connection and the
>     >> numbered interface, which are normal in our network.
>     >> For the two situations that you mentioned, I will investigation the
>     >> possible solutions and feedback you later.
>     >>
>     >> For the point-to-point and numbered interface, do you have other
>     >> questions then?
>     >
>     > the fact that two routers announce the same subnet, does not mean they are
>     > connected together by p2p link. Anycast prefix is an example.
>     >
>     > The idea you are proposing simply does not work.
>     >
>     > thanks,
>     > Peter
>     >
>     >
>     >>
>     >> Best Regards.
>     >>
>     >> Aijun Wang
>     >> Network R&D and Operation Support Department China Telecom Corporation
>     >> Limited Beijing Research Institute,Beijing, China.
>     >>
>     >> -----邮件原件-----
>     >>发件人: Peter Psenak [mailto:ppsenak
>     <mailto:ppsenak>=[e-mail]
>     <mailto:[e-mail]>]
>     >>发送时间: 2018年7月23日16:15
>     >>收件人: Aijun Wang; [e-mail] <mailto:[e-mail]>
>     >>抄送: [e-mail] <mailto:[e-mail]>; 'Ketan Talaulikar
>     (ketant)'; 'Acee Lindem (acee)';
>     >> 'Dongjie (Jimmy)'
>     >>主题: Re: [Lsr] Regarding OSPF extension for inter-area topology
>     >> retrieval
>     >>
>     >> 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-topo
>     >>> l ogy-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-osp
>     >> f-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-
>     >>> e xt-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.
>     >>>
>     >>
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