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Re: [spring] Approaches to MTU efficiency in SRv6 in todays SPRING session

Greg Mirsky <gregimirsky@gmail.com> Fri, 26 July 2019 18:07 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Fri, 26 Jul 2019 14:06:44 -0400
Message-ID: <CA+RyBmU3_ciEeb3VJUQ6OiYJpdvGsmnjXoT2yne+VYKh8EbzDw@mail.gmail.com>
To: Dirk Steinberg <dirk@lapishills.com>
Cc: SPRING WG List <spring@ietf.org>
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Subject: Re: [spring] Approaches to MTU efficiency in SRv6 in todays SPRING session
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Hi Dirk, et al.,
I'd like to point to draft-mirsky-6man-unified-id-sr
<https://tools.ietf.org/html/draft-mirsky-6man-unified-id-sr-03> that
proposes the use of the SRH for identifiers of 20 and 32 bits-long.

Regards,
Greg

On Wed, Jul 24, 2019 at 12:20 PM Dirk Steinberg <dirk@lapishills.com> wrote:

> Hi All,
>
> in todays SPRING session we have heard concerns about
> MTU efficiency in certain use cases involving SRv6.
>
> It is true that using 128 bit SRv6 SIDs trades scalability
> and flexibility against MTU overhead. There will certainly
> be use cases where the additional overhead may be
> justified.
>
> For other uses cases where MTU efficiency is a major concern
> the answer within the SRv6 framework is SRv6 uSID.
>
> Another proposal to address the MTU efficiency problem today
> advertised itself as basically using the same semantics as MPLS
> encapsulated in IPv6 and also noted that SRv6 deviates from
> legacy MPLS regarding label semantics.
>
> This is exactly the point.
>
> Not being dependent on the legacy MPLS label binding semantics
> in SRv6 is a big advantage.
>
> And this advantage is carried forward in SRv6 uSID as well.
> SRv6 uSID addresses the problem of MTU efficiency while
> avoiding to fall back to MPLS label binding semantics.
>
> No separate mapping table is required to be able to forward uSID.
>
> It is also not true that uSID inflates the IGP and/or FIB tables
> more than other approaches. A uSID is advertised just like
> other SRv6 SIDs, although the prefix length will typically
> be much shorter. The fact that no extra label mapping
> table is required contributes to improved control and
> data plane efficiency and provides excellent forwarding
> ASIC efficiency, especially for low-FIB and legacy systems.
>
> Cheers
> Dirk
>
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