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

Eric C Rosen <erosen@juniper.net> Fri, 24 July 2015 15:53 UTC

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To: 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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Subject: Re: [mpls] =?utf-8?b?562U5aSNOiBkcmFmdC1mYW5nLW1wbHMtbGFiZWwtZm9yd2Fy?= =?utf-8?q?ding-no-swap_-_how_much_does_it_really_save=3F?=
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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.

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.