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

Robert Raszuk <robert@raszuk.net> Thu, 23 July 2015 21:22 UTC

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Date: Thu, 23 Jul 2015 23:22:19 +0200
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From: Robert Raszuk <robert@raszuk.net>
To: Shahram Davari <davari@broadcom.com>
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Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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The point is that new control plane is already defined. In fact we already
have two :)

As I mentioned in my first mail to the list the concept of NO_SWAP/CONTINUE
is common to both H-SDN and SEGMENT ROUTING architectures.

Ref: https://goo.gl/3oxRbl

Thx,
R.


On Thu, Jul 23, 2015 at 11:16 PM, Shahram Davari <davari@broadcom.com>
wrote:

>  Robert,
>
>
>
> So instead of calling it no-swap probably you should call it global label
> or so, and then define new control plane for it. But seems the data-pane
> behavior does not change and existing hardware can support this global
> label.  So maybe you just need new control plane.
>
>
>
> Thx
> Shahram
>
>
>
> *From:* rraszuk@gmail.com [mailto:rraszuk@gmail.com] *On Behalf Of *Robert
> Raszuk
> *Sent:* Thursday, July 23, 2015 2:12 PM
> *To:* Shahram Davari
> *Cc:* Eric C Rosen; stbryant@cisco.com; mpls@ietf.org
>
> *Subject:* Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
>
>
> Hi Shahram,
>
>
>
> Labels which are non of a local significance can be distributed by
> flooding protocols extensions (ISIS, OSPF) or by direct p2p sessions (BGP
> 3107, sessions from the controller, XMPP etc ...)
>
>
>
> The important part is that the actual forwarding is computed recursively
> or set at the controller.
>
>
>
> AFAIK I have not seen any proposal where LDP would play any role in such
> distribution.
>
>
>
> Regards,
>
> R.
>
>
>
>
>
>
>
>
>
>
>
> On Thu, Jul 23, 2015 at 11:07 PM, Shahram Davari <davari@broadcom.com>
> wrote:
>
> Hi Robert,
>
>
>
> How are these labels distributed? Via LDP or via SDN controller?
>
>
>
> Thanks
>
> Shahram
>
>
>
> *From:* rraszuk@gmail.com [mailto:rraszuk@gmail.com] *On Behalf Of *Robert
> Raszuk
> *Sent:* Thursday, July 23, 2015 12:58 PM
> *To:* Eric C Rosen
> *Cc:* Shahram Davari; stbryant@cisco.com; mpls@ietf.org
> *Subject:* Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
>
>
> ​Hi Eric,​
>
>
>
>  ​​
>
> If you notice that the incoming label needs to be 'replaced' by an
> outgoing label of the same value, you could just make the rewrite string
> shorter, so it won't overwrite the top label on the stack.  This seems to
> be what the draft suggests, but it could be done as an optimization for the
> particular case where the incoming and outgoing labels have the same value.
>
>
>
> ​This is precisely ​the crux where your statement fails.
>
>
>
> You use term "incoming label" and "outgoing lable" ... well in the new
> architectures there is no such things.
>
>
>
> It is a "global label" or "path label" with adjacency information.
>
>
>
> So to support legacy hardware new control plane has to make up from single
> label now two (identical) labels to pass it to data plane. Now also data
> plane must be smart to check that and program its state per your
> suggestion.
>
>
>
> Why would we do that other then due to worry about legacy chipsets feared
> to be non compliant to new RFC ?
>
>
>
> Many thx,
>
> R.
>
>
>
>
>