Re: Meta-issues: On the deprecation of the fragmentation function

[Brian Jones <[e-mail]>]

+1 - All of RJ's comments.

There has to be a solution that not only allows for but encourages IPv6
deployment, not prevents it.
--
Brian


On Tue, Jul 9, 2013 at 11:02 AM, RJ Atkinson <[e-mail]> wrote:

> All,
>
> I think everyone agrees that intermediate fragmentation
> (e.g. by routers having high-speed links in the middle of the path)
> can be problematic,and that is why IPv6 does NOT require that
> (i.e. RFC-2460 says that the "DF" bit is invisible but always
> set for IPv6).
>
> That noted, I agree very much with Fernando Gont's
> comments on 5th July 2013 that IPv6 fragmentation in
> end systems ought NOT be deprecated -- and I find his
> reasoning compelling.
>
>
> (SEPARATELY)
>
> Not all deployed links are built out of wired/wireless
> Ethernet or SONET.  The assumption that everything is either
> Ethernet or SONET (or perhaps WDM) is a bit of a "First
> World" assumption and puts lesser-developed countries/regions
> at a significant disadvantage for Internet access.
>
> Frankly it is embarrassing for IETF participants to make
> such an assumption (i.e. that all links are Ethernet,
> SONET, WDM, or better).
>
> While it is fine to optimise so that Ethernet or SONET links
> have great performance, for example by eliminating the
> requirement for backbone routers to fragment packets,
> we ought to retain the ancient  "IP OVER EVERYTHING"  mantra
> that has served the Internet (and ALL regions of the world)
> so well for so many years now.
>
> I know of a number of link technologies that simply can't
> support the existing 1280 byte minimum IPv6 MTU.  Links
> with the lower MTU overwhelmingly are relatively low speed
> wireless links (everything in the gamut from HF radio
> to SATCOM).  My concerns about this have been expressed in
> IPv6 WG meetings dating back to the early 1990s, as IETF
> meeting minutes show.  All the data available to me indicates
> that these lower-speed (and smaller MTU) links are NOT going away.
>
> For HF radio links, link transmission speed is usually
> measured in Kbps, with some deployed IPv4/HF links today
> running as low as 2.4 Kbps.  VHF and UHF line-of-sight
> links tend to be much faster than HF, but are still well
> below the slowest modern Ethernet link (i.e. 10 Mbps).
>
> The IPv6 concept of adding a special link-specific
> fragmentation/reassembly protocol layer has never been
> practical.  By definition, these links have severe bandwidth
> limitations already.  I've seen multiple instances where
> specialised routers that are connected to these LOW speed
> links insert IPv6 Fragmentation Headers and perform
> intermediate fragmentation to get IPv6 packets through
> such links.  In these special cases, there is no performance
> issue because these wireless links have such low data rates.
>
> A result of deprecating the IPv6 Fragmentation Header will be
> that such links will be running IPv4 *forever*.  This is
> the opposite of encouraging IPv6 transition -- it is preventing
> IPv6 transition.  It also probably requires the ongoing deployment
> of IPv6::IPv4 protocol translation gateways -- and also
> probably inhibits Internet deployment outside of "1st World"
> countries.
>
> Sigh.
>
>
> Deprecating IPv6 Fragmentation Header and related end-system
> support is going to harm users and inhibit transition to IPv6.
>
>
> PLEASE, PLEASE, let us NOT go there.
>
>
> Sincerely Yours,
>
> Ran Atkinson
>
>
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