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

Stewart Bryant <stbryant@cisco.com> Tue, 28 July 2015 11:03 UTC

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Date: Tue, 28 Jul 2015 12:03:22 +0100
From: Stewart Bryant <stbryant@cisco.com>
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To: Andrew Qu <andrew.qu@mediatek.com>, Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>, Robert Raszuk <robert@raszuk.net>, 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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> 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