Re: [Lsr] 答复: LSR Flooding Reduction Drafts - Moving Forward

[Peter Psenak <[e-mail]>]

Aijun,

On 28/08/18 11:14 , Aijun Wang wrote:
> Hi, Robert:
>
> As stated in
> https://tools.ietf.org/html/draft-li-dynamic-flooding-05#section-6.3,
> the mentioned distributed mode is actually centrally mode. It depends on
> the area leader to advertise the algorithms.

above is not correct. draft-li-dynamic-flooding supports both 
centralized and distributed modes of operation. All routers in the area 
though MUST agree on which mode they operate in and if they operate in 
distributed mode, which algorithm is used to compute the flooding topology.


>
> The ideal distributed mode is depending only the action/calculation from
> each individual node as done in current SPF calculation. No leader
> election process within whole area scope.

please see above.

>
> Can we focus on finding one common algorithms that can deducing the
> optimized flooding topology based on the initial synchronized LSDB for
> further LSA flooding reduction?

one algorithm may not fit all environments and all users. Having at 
least one standardized algorithm is definitely a goal, but I see  no 
reason to limit ourselves to single one in long run. The framework in
draft-li-dynamic-flooding does give us all the flexibility. And the 
leader election is quite simple mechanism to achieve consistency and 
maintain the flexibility of the solution.

thanks,
Peter


>
> Best Regards.
>
> Aijun Wang
>
> Network R&D and Operation Support Department
>
> China Telecom Corporation Limited Beijing Research Institute,Beijing, China.
>
> *发件人:*Robert Raszuk [mailto:[e-mail]]
> *发送时间:*2018年8月28日0:57
> *收件人:*Huaimo Chen
> *抄送:*[e-mail]; Acee Lindem (acee); [e-mail]; Jeff Tantsura;
> Tony Przygienda; Peter Psenak
> *主题:*Re: [Lsr] LSR Flooding Reduction Drafts - Moving Forward
>
>> draft-cc-ospf-flooding-reduction-02 allows operators to select distributed mode, centralized one or static one smoothly.
>
> Aside from static approach can you summarize in purely technical points
> advantages your draft proposes over draft-li-dynamic-flooding-05?
>
> Many thx,
>
> R.
>
> On Mon, Aug 27, 2018 at 6:41 PM, Huaimo Chen <[e-mail]
> <mailto:[e-mail]>> wrote:
>
> Hi Robert,
>
>>Leader election happens automatically and procedures for that are to be vastly similar to today's DR or DIS election. So with this in mind one may observe that both OSPF and ISIS are pretty centralized on multiaccess networks today :)
>
> Today’s DR or DIS election is local to a special interface/network such
> as a broadcast interface. Leader election in a network is global. Every
> node in the network depends on it (its flooding topology). These two
> seems different.
>
>>Btw I don't think there is any problem here .... The text added to -05 version allows very seamless choice of centralized vs distributed topology computation by signalling either zero or non zero value in the added to version -05 area leader sub-tlv.
>
>>
>
>>In other words I don't see any problem or room for debate .. adopting and implementing -05 allows use of centralized or distributed optimal flooding computation at the operator's discretion.
>
> draft-cc-ospf-flooding-reduction-02 allows operators to select
> distributed mode, centralized one or static one smoothly.
>
> Best Regards,
>
> Huaimo
>
> *From:*Robert Raszuk [mailto:[e-mail] <mailto:[e-mail]>]
> *Sent:* Monday, August 27, 2018 11:31 AM
> *To:* Huaimo Chen <[e-mail] <mailto:[e-mail]>>
> *Cc:* [e-mail] <mailto:[e-mail]>; [e-mail]
> <mailto:[e-mail]>; Jeff Tantsura <[e-mail]
> <mailto:[e-mail]>>; Acee Lindem (acee)
> <acee=[e-mail] <mailto:[e-mail]>>;
> Peter Psenak <[e-mail] <mailto:[e-mail]>>; Tony
> Przygienda <[e-mail] <mailto:[e-mail]>>
> *Subject:* Re: [Lsr] LSR Flooding Reduction Drafts - Moving Forward
>
> Hi Huaimo,
>
>> Introducing centralized feature into IGP will break IGP's distributed nature
>
> That clearly proves that word "centralized" has been significantly
> overloaded here.  To many indeed "centralized" means a controller (like
> OpenFlow or SDN) and that such device added to a network is to push
> information - typically 1RU linux blade -  here optimized flooding
> graph. But this never was the plan with this proposal from its start ie.
> -00 version.
>
> Centralized means that optimized flooding graph comes from single
> redundant node.
>
> Leader election happens automatically and procedures for that are to be
> vastly similar to today's DR or DIS election. So with this in mind one
> may observe that both OSPF and ISIS are pretty centralized on
> multiaccess networks today :)
>
> To your point of multi-vendor networks true - and that is precisely why
> upgrade network wide to a release containing consistent algorithm from
> more then a single vendor (and even for single vendor) is practically a
> very time consuming and difficult process.
>
> Btw I don't think there is any problem here ... The text added to -05
> version allows very seamless choice of centralized vs distributed
> topology computation by signalling either zero or non zero value in the
> added to version -05 area leader sub-tlv.
>
> In other words I don't see any problem or room for debate .. adopting
> and implementing -05 allows use of centralized or distributed optimal
> flooding computation at the operator's discretion.
>
> Thx,
>
> R.
>
> On Mon, Aug 27, 2018 at 5:10 PM, Huaimo Chen <huaimo.chen@huawei..com
> <mailto:[e-mail]>> wrote:
>
>     >> I think distributed is more practical too.
>     >I would appreciate more detailed insights as to why you (and others) feel this way.  It is not at all obvious to me.
>     IGP is distributed in nature. The distributed computation of
>     flooding topology like distributed SPF will keep IGP still
>     distributed in nature. Introducing centralized feature into IGP will
>     break IGP's distributed nature, which may cause some issues/problems.
>
>     >> For computing routes, we have been using distributed SPF on every node for many years.
>     >True, but that algorithm is (and was) very well known and a fixed algorithm that would clearly solve the problem at the time. If we were in a similar situation, where we were ready to set an algorithm in >concrete, I might well agree, but it’s quite clear that we are NOT at that point yet.  We will need to experiment and modify algorithms, and as discussed, that’s easier with a centralized approach.
>     After flooding reduction is deployed in an operational (ISP)
>     network, will we be allowed to do experiments on their network?
>     After an algorithm is determined/selected, will it be changed to
>     another algorithm in a short time?
>
>     >> In fact, we may not need to run the exact algorithm on every node. As long as the algorithms running on different nodes generate the same result, that would work.
>     >Insuring a globally consistent result without running the exact same algorithm on the exact same data will be quite a trick.  Debugging distributed problems at scale is already a hard problem.  Having >different algorithms in different locations would add another order of magnitude in difficulty.  No thank you.
>     In some existing networks, some nodes run IGPs from one vendor, some
>     other nodes run IGPs from another vendor, and so on. Some may use
>     normal SPF, some others may use incremental SPF. It seems that we
>     have had these cases for many years.
>     >Tony
>
>     Best Regards,
>     Huaimo
>
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