Zhenqiang,

please see inline

Cheers,
Jeff


4. I want to know the path for a specific IP Flex-Algorithm is calculated 
distributedly by each nodes paticipating this Flex-Algorithm or calculated 
centralized by an controller? I wonder we can guarantee the loop free  path 
with IP Flex-Algorithm especially when the path is calculated distributedly?

The valid topology must consist of a set of connected routers sharing a common 
Calc-Type, then loop-free calculation is done accordingly


Best Regards,
Zhenqiang Li
[email protected]

From: Jeff Tantsura
Date: 2020-12-04 09:18
To: Tony Li; Robert Raszuk
CC: lsr; Acee Lindem \(acee\)
Subject: Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms 
(Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
Anything else than IGP metric based SPT is considered TE. Looking holistically 
- topology virtualization (or similar) could have been a better name.

Cheers,
Jeff
On Dec 3, 2020, 4:25 PM -0800, Robert Raszuk <[email protected]>, wrote:
        Hi Tony,

The moment I hit "Send" I knew that this response may be coming as it really 
depends what is one's definition of TE.

If indeed IGP TE is anything more then SPF - then sure we can call it a TE 
feature.

However, while a very useful and really cool proposal, my point is to make sure 
this is not oversold - that's all.

Best,
R.


> On Fri, Dec 4, 2020 at 1:13 AM Tony Li <[email protected]> wrote:
> >
> > Hi Robert,
> >
> >
> > > However I really do not think that what Flexible Algorithm offers can be 
> > > compared or even called as Traffic Engineering (MPLS or SR).
> > >
> > > Sure Flex Algo can accomplish in a very elegant way with little cost 
> > > multi topology routing but this is not full TE. It can also direct 
> > > traffic based on static or dynamic network preferences (link colors, rtt 
> > > drops etc ... ),  but again it is not taking into account load of the 
> > > entire network and IMHO has no way of accomplish TE level traffic 
> > > distribution.
> > >
> > > Just to make sure the message here is proper.
> >
> >
> > It’s absolutely true that FlexAlgo (IP or SR) has limitations. There’s no 
> > bandwidth reservation. There’s no dynamic load balancing. No, it’s not a 
> > drop in replacement for RSVP. No, it does not supplant SR-TE and a good 
> > controller. Etc., etc., etc….
> >
> > However I don’t feel that it’s fair to say that FlexAlgo can’t be called 
> > Traffic Engineering.  After all TE is a very broad topic. Everything that 
> > we’ve done that’s more sophisticated than simple SPF falls in the area of 
> > Traffic Engineering.  Link coloring and SRLG alone clearly fall into that 
> > bucket.
> >
> > I’ll grant you that it may not have the right TE features for your 
> > application, but that doesn’t mean that it’s not sufficient for some.  
> > Please don’t mislead people by saying that it’s not Traffic Engineering.
> >
> > Regards,
> > Tony
> >
> >
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