Re: [irs-discuss] IRS comments

Edward Crabbe <edc@google.com> Fri, 31 August 2012 01:16 UTC

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From: Edward Crabbe <edc@google.com>
Date: Thu, 30 Aug 2012 18:16:11 -0700
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To: "Dutta, Pranjal K (Pranjal)" <pranjal.dutta@alcatel-lucent.com>
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Cc: "irs-discuss@ietf.org" <irs-discuss@ietf.org>, "UTTARO, JAMES" <ju1738@att.com>, "Shah, Himanshu" <hshah@ciena.com>, Alia Atlas <akatlas@gmail.com>
Subject: Re: [irs-discuss] IRS comments
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Yep;  not having to run an IGP on the box, which is great for those people
not wanting / needing core internet protocols on their devices.  The
standard set of 'SDN' talking appoints applies here in terms of development
speed, performance improvements resulting from use of modern commodity
compute, friendliness of development environment, potential for decreased
bug count* etc etc.

It's a specialized use case, but it exists.

However, my fundamental point is that with IRS as defined currently (ie PBR
with extensible match fields on on RIB recursion + additional monitoring
and data collection hooks) you can do hypothetically do away with IGPs.
 Indeed, assuming that the encaps is applied at some other device (since
IRS as currently described doesn't account for encap/decap application or
negotiation functionality)  you can effectively replace a significant
number of protocols (including stateful PCE) should you want to.   :P

<can of worms>

*The benefits in terms of decreased bug counts above is really varies with
how complex we make IRS of course.

On Thu, Aug 30, 2012 at 6:01 PM, Dutta, Pranjal K (Pranjal) <
pranjal.dutta@alcatel-lucent.com> wrote:

> **
>
> Yep, the context of our original discussion was never PCE as we understand
> its CSPF or some form like that. Our concern was – is there a strong use**
> **
>
> case for non-constrained SPF?  ****
>
> ** **
>  ------------------------------
>
> *From:* Edward Crabbe [mailto:edc@google.com]
> *Sent:* Thursday, August 30, 2012 5:34 PM
>
> *To:* **Dutta, Pranjal K** (Pranjal)
> *Cc:* Alia Atlas; UTTARO, JAMES; **Shah, Himanshu**; **
> irs-discuss@ietf.org**
> *Subject:* Re: [irs-discuss] IRS comments
> ****
>
>  ** **
>
> Nope, not specifically, but it strongly implies that there is some form of
> SPF running given the use of constraints in the draft.   ****
>
> On Thu, Aug 30, 2012 at 4:16 PM, **Dutta, Pranjal K** (Pranjal) <
> pranjal.dutta@alcatel-lucent.com> wrote:****
>
> That doesn’t talk about centralized SPF, does it ?****
>
>  ****
>  ------------------------------
>
> *From:* Edward Crabbe [mailto:edc@google.com]
> *Sent:* Thursday, August 30, 2012 4:12 PM****
>
>
> *To:* **Dutta, Pranjal K** (Pranjal)
> *Cc:* Alia Atlas; UTTARO, JAMES; **Shah, Himanshu**; irs-discuss@ietf.org
> *Subject:* Re: [irs-discuss] IRS comments****
>
>  ****
>
> http://tools.ietf.org/html/draft-ietf-pce-stateful-pce-01****
>
> On Thu, Aug 30, 2012 at 4:09 PM, **Dutta, Pranjal K** (Pranjal) <
> pranjal.dutta@alcatel-lucent.com> wrote:****
>
> ‘operational model’ = IETF draft that describes the use case.****
>
> ‘large’ = 40K LSAs, 500 IGP nodes.****
>
>  ****
>  ------------------------------
>
> *From:* Edward Crabbe [mailto:edc@google.com]
> *Sent:* Thursday, August 30, 2012 2:44 PM****
>
>
> *To:* **Dutta, Pranjal K** (Pranjal)****
>
> *Cc:* Alia Atlas; UTTARO, JAMES; **Shah, Himanshu**; irs-discuss@ietf.org*
> ***
>
>
> *Subject:* Re: [irs-discuss] IRS comments****
>
>  ****
>
> please define 'operational model' ( and 'large' :) .  ****
>
> On Thu, Aug 30, 2012 at 1:40 PM, **Dutta, Pranjal K** (Pranjal) <
> pranjal.dutta@alcatel-lucent.com> wrote:****
>
> Hi,****
>
>          I believe that’s 10% of what overall work that router does today
> w.r.t routing. I would like to see an operational model how such
> centralized SPF can ****
>
> provide end-to-end convergence of large number of flows efficiently. ****
>
>  ****
>
> Thanks,****
>
> Pranjal****
>
>  ****
>  ------------------------------
>
> *From:* Edward Crabbe [mailto:edc@google.com]
> *Sent:* Thursday, August 30, 2012 11:59 AM
> *To:* Alia Atlas
> *Cc:* **Dutta, Pranjal K** (Pranjal); UTTARO, JAMES; **Shah, Himanshu**;
> irs-discuss@ietf.org****
>
>
> *Subject:* Re: [irs-discuss] IRS comments****
>
>  ****
>
> Alia;****
>
>  ****
>
> If there is ****
>
>  ****
>
> a) a mechanism for installing routes, pbr or otherwise, which recurse to
> directly connected nexthops****
>
> b) a mechanism for gathering topological information****
>
>  ****
>
> then you've inherently enabled centralized spf. ****
>
>  ****
>
> On Thu, Aug 16, 2012 at 9:34 AM, Alia Atlas <akatlas@gmail.com> wrote:****
>
> I haven't seen a good description of what is intended or desired by
> moving the SPF functionality to a centralized location.  Clearly such
> centralization can have a very bad impact on convergence - which is a
> strong motivator for simultaneously computing fast-reroute
> alternatives (with guaranteed coverage ala MRT) and installing both.
>
> I don't see IRS as having a way of "turning off" the SPF computation
> in the IGP; a different lobotomized IGP protocol/process would be
> needed.
>
> Alia****
>
>
> On Thu, Aug 16, 2012 at 12:14 PM, **Dutta, Pranjal K** (Pranjal)
> <pranjal.dutta@alcatel-lucent.com> wrote:
> > "LSDB (I saw an email which talks about reducing IGP to link
> >> distribution protocol and running SPF in centralized network
> >> controller)"
> >
> > I have seen discussions in the past on this and in fact I didn't get
> precisely what is meant. If anybody in the list could brief very
> > precisely that would help a lot.
> >
> > Here is my understanding - the routers would do LSA/LSP flooding for
> OSPF/ISIS as it is done today. So routers would build neighboring
> relationship/adjacencies to participate in flooding and each router builds
> its LSDB.
> >
> > Then the IRS "application" would track LSDB changes and pull up the
> "diffs" from each router (thru "controller") whenever there is a change.
> The application would compute SPF on behalf of each router (LSDB). The
> result of the compute would be pushed by application to each Router (thru
> controller) and inject entries into RIB.
> >
> > Is that correct? How different this going to be from PCE?
> >
> > If this is correct then perhaps we would like to ask what are the
> scalability numbers in LSDB we are talking about?
> >
> > The "application" would be running in a high performance server and so
> SPF compute there is not an issue and perhaps it is good way to synchronize
> FIB update (to a certain extent) to avoid u-loops etc.
> >
> > But when we are managing all routers in the purview of the application,
> the computing power in each router is not uniform. To be realistic, I have
> some concerns on how much "real-timeness" we could achieve between
> application and controllers on such proposals, esp. when scaling numbers
> are high. This leads to higher time lag on inconsistency between
> application SPF compute and FIB update. It's almost like the classic "slow
> peering" issues with TCP like protocols - the high performance peer is
> slowed down by low performance peer.
> >
> > Static route interface is good thing because it is a state that persists
> longer.
> >
> > IGPs may be deployed in very dynamic environments where tight coupling
> is desirable between SPF compute and FIB update. In scaled environments the
> issue is less about SPF compute time and is more about synchronizing the
> FIB.
> >
> > Running on-demand CSPF by IRS application may be fine because of
> persistency of RSVP-TE tunnels in dynamic environments.
> >
> > I apologize if I misunderstood the intent.
> >
> > Thanks,
> > Pranjal****
>
> ---snip---****
>
> _______________________________________________
> irs-discuss mailing list
> irs-discuss@ietf.org
> https://www.ietf.org/mailman/listinfo/irs-discuss****
>
>  ****
>
>  ****
>
>  ****
>
> ** **
>