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

[tony . li]

> so it's party like it's 1999, seems the peer group leader election gets 
> rediscovered ;-)  Interesting old new problems, interesting old new attack 
> vectors like https://ieeexplore.ieee.org/document/822780/ 
> 

No argument there.  There are no new problems or solutions.  Just us 
rediscovering the problems and approaches that others have used before.

That said, the solutions still need to be applied.  That is, after all, 
engineering.

Preferably in a Little Red Corvette.

Tony


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

[Tony Przygienda]

On Mon, Aug 27, 2018 at 9:41 AM Huaimo Chen  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.
>
>
>

so it's party like it's 1999, seems the peer group leader election gets
rediscovered ;-)  Interesting old new problems, interesting old new attack
vectors like https://ieeexplore.ieee.org/document/822780/

 tony

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

[Robert Raszuk]

> 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  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]
> *Sent:* Monday, August 27, 2018 11:31 AM
> *To:* Huaimo Chen 
> *Cc:* tony...@tony.li; lsr@ietf.org; Jeff Tantsura <
> jefftant.i...@gmail.com>; Acee Lindem (acee)  org>; Peter Psenak ; Tony Przygienda <
> 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 
> 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 

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

[tony . li]

Hi Huaimo,


> After flooding reduction is deployed in an operational (ISP) network, will we 
> be allowed to do experiments on their network? 


Some may well permit it.  Certainly in lab scenarios they may be very willing.  
It all depends on their motivation to achieve improvements.

It should be remembered that we are where we are today because some people were 
willing to work towards better technology and understood that there would be 
issues while we worked out issues with implementations. All protocols, 
features, and implementations have growing pains. We are where we are because 
we work through them.


> After an algorithm is determined/selected, will it be changed to another 
> algorithm in a short time? 


Possibly. Someone may have an insight that produces theoretical breakthrough 
and gives us a completely different algorithm. Or, more likely, someone 
discovers a catastrophic bug in an algorithm and moves to fix it.


> 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. 


I’m unaware of anyone trying to get EIGRP to interoperate with IS-IS at the 
protocol level.  ;-)

I’m also unaware of anyone trying to implement anything other than SPF.

And that’s what I think you’re proposing…

Tony


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

[Robert Raszuk]

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  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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