Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

[Andrew Qu <[e-mail]>]

Hi Shahram,

This is a question that must be answered,  but could you please hold the question for now?

I just want to have one issue clarified before moving to another.

Do we agree that _IF_ global label becomes necessary,  no-swap as primitive is necessary?

Understood that _IF_ will be next topic to follow.  

Thanks,

Andrew

-----Original Message-----
From: Shahram Davari [mailto:[e-mail]] 
Sent: Tuesday, July 28, 2015 9:40 AM
To: Andrew Qu
Cc: [e-mail]; Alexander Vainshtein; Robert Raszuk; [e-mail]
Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

Andrew

Continue operation in segment routing and in HSDN is not global label. Global label means every router knows how to forward a global label. What is the application for a global label and how does each router know how to forward it?

Regards,
Shahram


> On Jul 28, 2015, at 7:58 AM, Andrew Qu <[e-mail]> wrote:
> 
> Hi Stewart,
> 
> Agreed that SWAP must be kept because MPLS fundamentals can't be broken.
> And I agreed that _if_ there is NO such global label space idea,  
> no-swap is optimization of swap as well.
> 
> However I don't agree no-swap become an optimization in terms of 
> network Behavior when global label idea become a needed thing.
> 
> 
> When global Label introduced, then no_swap is the conceptually right 
> thing for the transition [even Local implementation can use swap to 
> achieve, again, per previous conversation, the popular wisdom, which I 
> agreed as well,  is that this is local implementation, we should not 
> get involved, so we must define no-swap as the new primitive at RFC 
> level]
> 
> 
> So the question really boils down to that do we need global label?
> 
> I believe that is the key thing here.  May be we can put swap/no-swap aside for the moment.
> 
> Thanks,
> 
> Andrew
> 
> 
> -----Original Message-----
> From: Stewart Bryant [mailto:[e-mail]]
> Sent: Tuesday, July 28, 2015 4:03 AM
> To: Andrew Qu; Alexander Vainshtein; Robert Raszuk; Shahram Davari
> Cc: [e-mail]
> Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
> 
>> Adding "NO_SWAP" for new/future generation DEVICE does NOT break 
>> backward capability.
> Andrew
> 
> Existing devices should be assumed to have non-aligned label spaces.
> (there is much empirical evidence to support this position)
> 
> So if you have a no-swap only device between two existing devices you cannot be sure that you can build an LSP.
> 
> A backwards compatible device would therefore need to support swap.
> 
> Once you support swap then no-swap become an optimization.
> 
> - Stewart
> 
> 
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