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

[Christian Hopps]

[JD]  Both discuss centralized and distributed
[HC] Both drafts talk about both now. It is not reasonable to say one is a 
derivative of another.

I think calling the OSPF draft a derivative of the other was probably 
counter-productive here, and if we consider the earlier publications, it is 
technically wrong. As originally presented each draft seemed to focus on one 
type of solution. It's important that people are given credit for work they 
have done and ideas they have had.

That said, it's also important to consider the quality of the work, and when 
the distributed OSPF solution was first presented there were some obvious 
problems with the algorithm that were raised in the room during the meeting by 
people after having just seen the work for the first time.

Now I'm assuming John arrived at his conclusion of one being a derivative of 
the other based on reading the drafts as they stand now. So while the 
conclusion may have been historically incorrect, it also may be indicative of 
which document is of higher quality and better suited for use by the WG going 
forward.

Thanks,
Chris.

Huaimo Chen <huaimo.c...@huawei.com> writes:

Hi John,

    See my comments inline below.

Best Regards,
Huaimo
From: Huaimo Chen <huaimo.c...@huawei.com<mailto:huaimo.c...@huawei.com>>
Sent: Tuesday, September 4, 2018 9:50 AM
To: John E Drake <jdr...@juniper.net<mailto:jdr...@juniper.net>>; Robert Raszuk 
<rob...@raszuk.net<mailto:rob...@raszuk.net>>
Cc: tony...@tony.li<mailto:tony...@tony.li>; Acee Lindem (acee) 
<acee=40cisco....@dmarc.ietf.org<mailto:acee=40cisco....@dmarc.ietf.org>>; lsr@ietf.org<mailto:lsr@ietf.org>; Jeff 
Tantsura <jefftant.i...@gmail.com<mailto:jefftant.i...@gmail.com>>; Tony Przygienda 
<tonysi...@gmail.com<mailto:tonysi...@gmail.com>>; Peter Psenak <ppse...@cisco.com<mailto:ppse...@cisco.com>>
Subject: RE: [Lsr] LSR Flooding Reduction Drafts - Moving Forward

Hi John,

I have reviewed both of the flood reduction drafts and the draft referenced below, 
draft-cc-ospf-flooding-reduction-02, seems to me to be a derivative document inferior in 
>quality to the draft, draft-li-dynamic-flooding-05, from which it is derived.  For 
example, the referenced draft fails to include a description of the message used to 
deliver the >flooding topology when using centralized mode, it neglects to include 
any analysis of error conditions, and it neglects to include any description of the 
interactions with down->level nodes.

It seems that your word “derivative” is not correct. Our draft originally 
focuses on distributed solution, Tony’s on centralized one. It is not 
reasonable to say that a distributed solution is a derivative from a 
centralized one.

[JD]  Both discuss centralized and distributed
[HC] Both drafts talk about both now. It is not reasonable to say one is a 
derivative of another.

Regarding to missing message for centralized mode in our draft as you 
mentioned, it is for new ones to be added. We will fill this gap.

[JD] Please see:   
https://tools.ietf.org/html/draft-li-dynamic-flooding-05#section-5

Regarding to missing analysis of error conditions, we will consider and add it.

[JD] Please see:   
https://tools.ietf.org/html/draft-li-dynamic-flooding-05#section-4.6
[HC] For this, our draft talks about it. We will add more in details.

Regarding to interactions with down-level nodes, can you give more details?

[JD]  Please see:   
https://tools.ietf.org/html/draft-li-dynamic-flooding-05#section-4, 
https://tools.ietf.org/html/draft-li-dynamic-flooding-05#section-4.1
[HC] For this, our draft talks about it.

Yours Irrespectively,

John

From: Lsr <lsr-boun...@ietf.org<mailto:lsr-boun...@ietf.org>> On Behalf Of 
Huaimo Chen
Sent: Thursday, August 30, 2018 11:01 AM
To: Robert Raszuk <rob...@raszuk.net<mailto:rob...@raszuk.net>>
Cc: tony...@tony.li<mailto:tony...@tony.li>; Acee Lindem (acee) 
<acee=40cisco....@dmarc.ietf.org<mailto:acee=40cisco....@dmarc.ietf.org>>; lsr@ietf.org<mailto:lsr@ietf.org>; Jeff 
Tantsura <jefftant.i...@gmail.com<mailto:jefftant.i...@gmail.com>>; Tony Przygienda 
<tonysi...@gmail.com<mailto:tonysi...@gmail.com>>; Peter Psenak <ppse...@cisco.com<mailto:ppse...@cisco.com>>
Subject: Re: [Lsr] LSR Flooding Reduction Drafts - Moving Forward

Hi Robert,

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 ?

Initially, our draft focused on distributed solution for flooding reduction, 
and Tony’s on centralized way. This should be one advantage. Distributed 
solution is more practical.
In addition, we proposed the followings during the progress of our draft:

1)    A method to allow flooding topology to be lean and to allow multiple 
failures in an area;

2)    A procedure for establishing a new adjacency between a (new) node and  an 
existing node supporting flooding reduction;

3)    A way in which one touch (or command) to enable flooding reduction in a 
whole area within a short time;

4)    A way in which one touch (or command) to rollback flooding reduction to 
normal flooding in a whole area smoothly;

5)    A TLV for distributing the priority of a node to become a leader;

6)    Three algorithms for building a flooding topology.
Distributed solution for flooding reduction is stable after we resolve the 
issues raised by other experts during the last few IETFs.
BTW, as a service provider, which mode/solution (distributed or centralized) 
will you select to use in an operational network?

Best Regards,
Huaimo

Many thx,
R.

On Mon, Aug 27, 2018 at 6:41 PM, Huaimo Chen 
<huaimo.c...@huawei.com<mailto:huaimo.c...@huawei.com>> 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:rob...@raszuk.net<mailto:rob...@raszuk.net>]
Sent: Monday, August 27, 2018 11:31 AM
To: Huaimo Chen <huaimo.c...@huawei.com<mailto:huaimo.c...@huawei.com>>
Cc: tony...@tony.li<mailto:tony...@tony.li>; lsr@ietf.org<mailto:lsr@ietf.org>; Jeff Tantsura 
<jefftant.i...@gmail.com<mailto:jefftant.i...@gmail.com>>; Acee Lindem (acee) 
<acee=40cisco....@dmarc.ietf.org<mailto:40cisco....@dmarc.ietf.org>>; Peter Psenak 
<ppse...@cisco.com<mailto:ppse...@cisco.com>>; Tony Przygienda <tonysi...@gmail.com<mailto:tonysi...@gmail.com>>
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.c...@huawei.com<mailto:huaimo.c...@huawei.com>> 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
_______________________________________________
Lsr mailing list
Lsr@ietf.org<mailto:Lsr@ietf.org>
https://www.ietf.org/mailman/listinfo/lsr<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ietf.org_mailman_listinfo_lsr&d=DwMGaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=CRB2tJiQePk0cT-h5LGhEWH-s_xXXup3HzvBSMRj5VE&m=dQNetSHGAsFGcKk3dMxdWF6zY3NJc1cUOiTIkr-KOMA&s=aj_vuMJsmKUm-qly2FE2m_7WtK2ra7w4ftfPz37zXB8&e=>


_______________________________________________
Lsr mailing list
Lsr@ietf.org
https://www.ietf.org/mailman/listinfo/lsr

_______________________________________________
Lsr mailing list
Lsr@ietf.org
https://www.ietf.org/mailman/listinfo/lsr