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

Loa Andersson <loa@pi.nu> Sat, 25 July 2015 08:00 UTC

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Date: Sat, 25 Jul 2015 10:00:16 +0200
From: Loa Andersson <loa@pi.nu>
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To: Eric C Rosen <erosen@juniper.net>, Lizhenbin <lizhenbin@huawei.com>, "mpls@ietf.org" <mpls@ietf.org>, Andrew Qu <andrew.qu@mediatek.com>, Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>, Shahram Davari <davari@broadcom.com>, Robert Raszuk <robert@raszuk.net>
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Folks,

On 2015-07-24 17:53, Eric C Rosen wrote:
> On 7/24/2015 4:40 AM, Lizhenbin wrote:
>> In fact, according to implementation, the SWAP can be seen as POP a
>> label, then PUSH a label.
>
> Certainly the architecture could have been written this way.  But it
> wasn't ;-)  It was written in such a way as to emphasize the difference
> between operations that change the size of the label stack and
> operations that do not.

In addition the intention of a pop (in most cases) is to make the next
label in the stack available to take decisions on, a swap does not do
this.

/Loa
>
> These concepts do not necessarily show up at all in the forwarding
> logic.  All the forwarding plane has to know is what the rewrite string
> is, where to put it, and how to adjust any TTL and/or checksum fields
> that might be in it.
>
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