Re: [Pce] Virtual Network Topology (VNT) changes and IP layer routing loops

[JP Vasseur <[e-mail]>]

Hi Greg,

Thanks for your note. I just wanted to add that this is no different  
from IGP Link weight tuning and off-line algorithms/heuristics  
computing link costs already take such constraint into account. One  
can expect an PCE implementation for VNT computation to also take  
such constraint into account.

Cheers,

JP.

On Jun 5, 2006, at 12:17 PM, Greg Bernstein wrote:

> Hi folks, in drafts draft-ietf-ccamp-gmpls-mln-reqs-00.txt and  
> draft-ietf-pce-inter-layer-frwk-00.txt the concepts of multi-layer  
> and multi-region networking are defined and discussed.
> An important case is when the IP layer rests directly upon a  
> "virtual network topology" layer that we will desire to change via  
> GMPLS signaling. Changes to the IP layer VNT can produce "transient  
> IP layer routing loops" also known as "micro loops" which can last  
> 100's of mili seconds or more.  Hence any time we change a  
> connection between IP layer routers via GMPLS we can cause  
> significant outages compared to the recovery times that we set out  
> to achieve with GMPLS fast reroute and other mechanisms such as SDH  
> APS (rings and linear).
>
> At the Routing working group, Alex's draft draft-ietf-rtgwg- 
> microloop-analysis-01.txt provides some analysis and a method to  
> reduce the impact (duration too) of the transient loops.  More  
> recently the drafts:
> (1) draft-bryant-shand-lf-applicability-01.txt
> (2) draft-bryant-shand-lf-conv-frmwk-02.txt
> (3) draft-francois-ordered-fib-01.txt
> Address this problem more generally including in (3) a method that  
> guarantee loop free convergence.
>
> The problem is that these have generated very little interest at  
> the RTG WG and may not move forward.  This area is not within PCE  
> or CCAMPs charter but can have an impact on the adoption of GMPLS  
> in multi-layer/region networking. If you're interested please take  
> a look and comment to the RTG WG.  Note I wasn't involved with  
> writing these, but came across them when considering the effects of  
> GMPLS changes on the IP layer VNT.
>
> Thanks
>
> Greg B.
>
> -- 
> ===================================================
> Dr Greg Bernstein, Grotto Networking [phone]
>
>
>
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