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

Robert Raszuk <robert@raszuk.net> Fri, 24 July 2015 09:30 UTC

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Date: Fri, 24 Jul 2015 11:30:03 +0200
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From: Robert Raszuk <robert@raszuk.net>
To: Andrew Qu <andrew.qu@mediatek.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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Another way to look at this is that SWAP requires awarness of peer's labels
either by flooding, by p2p protocol like LDP or via learning to controller
and pushing it back in p2mp fashion.

NO_SWAP does not have such dependency. It can be educated about just
endpoint label mapping from controller and actual forwarding and adj
creation will be local based on the vanilla IGP SPF.

To me this is fundamental difference.

Cheers,
R.


On Fri, Jul 24, 2015 at 11:21 AM, Andrew Qu <andrew.qu@mediatek.com> wrote:

>  Agreed!   From networking point of view,  no_swap and swap is simply
> different fundamentally.  We should address that.
>
>
>
> Thanks,
>
>
>
> Andrew
>
>
>
>
>
> *From:* Lizhenbin [mailto:lizhenbin@huawei.com]
> *Sent:* Friday, July 24, 2015 10:40 AM
> *To:* mpls@ietf.org; Andrew Qu; Alexander Vainshtein; Shahram Davari;
> Robert Raszuk
> *Subject:* 答复: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
>
>
> Hi all,
>
> I think the concept is one hand, the implementation is another hand. I
> would like to clarify more about it.
>
> 1. Now all of us debates if there is NO_SWAP. I want to ask one question:
> Should there be SWAP? In fact, according to implementation, the SWAP can be
> seen as POP a label, then PUSH a label.
>
> If so, POP and PUSH is enough. Why is there SWAP.
>
> 2. For the NO_SWAP, as the introduction of H-SDN and Segment Routing, at
> least in concept, there should introduce one new label operation. Regarding
> the implementation you can use SWAP same label, or POP one label and PUSH
> the same label if you like. There is also the possible way introduced in
> the draft-fang-mpls-label-forwarding-no-swap.
>
>
>
> In addition I would like to propose the suggestion that a totally new term
> for the NO_SWAP label operation should be introduced such as CONTINUE, GO,
> DIRECTGO, etc. Why must we make it related with the existing the label
> operations?
>
>
>
>
>
> Best Regards,
>
> Zhenbin(Robin)
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>  ------------------------------
>
> *发件人**:* mpls [mpls-bounces@ietf.org] 代表 Andrew Qu [andrew.qu@mediatek.com
> ]
> *发送时间**:* 2015年7月24日 16:06
> *收件人**:* Alexander Vainshtein; Robert Raszuk; Shahram Davari
> *抄送**:* mpls@ietf.org
> *主题**:* Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
> Hi Sasha,
>
>
>
> My comments in lines…
>
>
>
>
>
>
>
> *From:* mpls [mailto:mpls-bounces@ietf.org <mpls-bounces@ietf.org>] *On
> Behalf Of *Alexander Vainshtein
> *Sent:* Friday, July 24, 2015 7:26 AM
> *To:* Robert Raszuk; Shahram Davari
> *Cc:* mpls@ietf.org
>
> *Subject:* Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
>
>
> Hi all,
>
> Please note that CONTINUE in SPRING is:
>
> 1. A DP-agnostic primitive
>
> 2. *Implemented* as SWAP instruction with MPLS DP.
>
>
>
> [Andrew]  You are contradicting with 1) and 2).
>
> With “CONTINUE” defined in SR draft,  for NEW ASIC to be designed,
>
> Why should I still use “SWAP” to achieve it? Considering that I might
>
> Have good saving in precious on-board memory for the ASIC ?
>
>
>
> You can suggest that using SWAP, however you said CONTINUE is DP-agnostic,
> then
>
> If I do it different, I am still standard compliant. RIGHT?
>
>
>
> Again,  that is exactly my point,  SWAP is NOT the same as “NO_SWAP”.
> Once you put
>
> The wording out there,  it WILL have different impact.
>
>
>
> Thanks,
>
>
>
> Andrew
>
>
>
>
>
>
>
>
>
> So claiming equivalence of CONTINUE and NO-SWAP seems to be inaccurate IMO.
>
>
>
> As for global labels (in SDN, MPLS-TP or any other technology) - this
> definitely looks to me like a very bad idea for networks comprised of
> devices that support different label ranges. From my experience these
> scenarios have been encountered in real MPLS-TP deployments  and resulted
> in eventually dropping the "simple" solution as live networks have been
> extended with new NEs supporting a more narrow label space than the
> original ones.
>
>
>
> Adding a new forwarding primitive to MPLS architecture (yet another
> argument on this thread) immediately raises the question:
>
>
>
> Is support of the new primitive mandatory?
>
>
>
> If it is not (and this is clearly the case for NO-SWAP), then why should
> we bother? Occam's rasor cuts this off IMHO.
>
>
>
> My personal bottom line: this is a strictly NO GO proposal.
>
>
>
> My 2c.
>
>
>
> Thumb typed on my LG,
> Sasha
>
> ------ Original message ------
> *From: *Robert Raszuk
> *Date: *24/07/2015 00:22
> *To: *Shahram Davari;
> *Cc: *mpls@ietf.org;
> *Subject:*Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much
> does it really save?
>
>
>
> 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.
>
>
>
>
>
>
>
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