Subject: [Pce] PCE Hierarchy Framework Document

From: "Daniel King" <[email-masked]>
Date: Tue, 19 May 2009 18:42:34 +0100

Hello PCE'rs, 

I recently submitted a document to the WG: 

draft-king-pce-hierarchy-fwk
http://tools.ietf.org/id/draft-king-pce-hierarchy-fwk-00.txt

The document actually replaces:

draft-king-pce-brpc-app
http://tools.ietf.org/id/draft-king-pce-brpc-app-00.txt

The document examines techniques to establish the optimum path across a
series of domains, when the sequence of domains is not known in advance. The
work builds on earlier thoughts and suggestions by Adrian and highlights how
a hierarchical PCE architecture might be used in order to derive an optimal
end-to-end path. 

As always, your feedback and suggestions are always welcome. 

Br, Dan.

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From: [email-masked]
Date: Wed, 20 May 2009 14:03:40 +0800

Hi Daniel:

   In the section 5.3, "PCE Discovery", you said "Mechanisms that rely on 
advertising 

   or querying PCE locations across domains or provider boundaries are 
undesirable.".

   I want to know why it is an "undesirable" way.

   Can you elaborate on your point of view?

Thanks
 
Yuanlin

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[email-masked] 写于 2009-05-20 01:42:34:

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From: JP Vasseur <[email-masked]>
Date: Wed, 20 May 2009 09:38:09 +0200

On May 20, 2009, at 8:03 AM, [email-masked] wrote:

>
> Hi Daniel:
>
>    In the section 5.3, "PCE Discovery", you said "Mechanisms that  
> rely on advertising
>
>    or querying PCE locations across domains or provider boundaries  
> are undesirable.".
>

For the record, we has in the WG, long discussion on whether we should  
advertise PCE across domains using for example BGP for that matter.  
There was a good consensus not to, considering the limited number of  
interconnected domains. The advantage was limited and introduces other  
issues (security) ...

Thanks.

JP.

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From: "Adrian Farrel" <[email-masked]>
Date: Wed, 20 May 2009 09:19:17 +0100

[As an individual and co-author]

>> In the section 5.3, "PCE Discovery", you said "Mechanisms
>> that rely on advertising or querying PCE locations across
>> domains or provider boundaries are undesirable.".
>>
> For the record, we has in the WG, long discussion on whether
> we should advertise PCE across domains using for example BGP
> for that matter.
> There was a good consensus not to, considering the limited
> number of interconnected domains. The advantage was limited
> and introduces other issues (security) ...

Right. I recall that discussion.

And the situation with hierarchical PCE is worse.

Consider, a child PCE in domain-A does not know where the Parent PCE is. It 
could be in *any* domain. In order to make contact with the parent PCE, the 
child must either know where the parent is (configuration as recommended in 
the I-D), or advertise itself across *all* domains. That is, for 
child-advertisement to work, every PCE in the network must broadcast an 
advertisement to every other node in every other domain in the whole 
network. This is "undesirable".

Alternatively, consider a parent PCE that wants to contact the PCEs in each 
of domain-A, B, ..., Z. It could be configured (as recommended in this I-D) 
or it must send a broadcast query message to every node in each domain. 
Since there is no domain address aggregation(CIDR being just a dream) the 
parent PCE must broadcast to every node in the entire network. This is 
"undesirable".

That is, both approaches to discovery are simply not scalable, and would 
probably be filtered out at domain boundaries anyway.

With hierarchical PCE, we are looking at a peering relationship that is 
certainly administrative and probably commercial. Such relationships involve 
a lot of configuration and negotiation. Adding the configuration of 
parent/child PCE locations is an almost trivial addition.

Cheers,
Adrian

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From: [email-masked]
Date: Wed, 20 May 2009 17:00:42 +0800

I got it. Thanks for your explanation.

Thanks

Yuanlin

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From: Greg Bernstein <[email-masked]>
Date: Wed, 20 May 2009 14:30:07 -0700

Hi Daniel, nice draft. This sounds very reasonable. As one who worked on 
G.7715, the use PCE in this context seem very natural.

Cheers

Greg

-- 
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237