Re: Is Fragmentation at IP layer even needed ?

Mark Andrews <marka@isc.org> Mon, 08 February 2016 19:54 UTC

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To: David Borman <dab@weston.borman.com>
From: Mark Andrews <marka@isc.org>
References: <CAOJ6w=G4ysJGsNC_F-N5+-P9-OmUYDx1f14mew7GNAEaUmDfYg@mail.gmail.com> <20160208155214.91667.qmail@ary.lan> <CAOJ6w=H3F5Tyez0=hJYnq+wscBsCN0ROxwA4RppjfXzV5nwBJw@mail.gmail.com> <2F942F4E-F890-49A1-91C8-F304B9FBA2D3@weston.borman.com> <CAHw9_iKw5chdJqy4QTqAKXa5q3pMgSQFdbZfi-7TKOs325+1wA@mail.gmail.com> <AA50FF2F-8E00-4D63-944F-75C3D5A82F48@weston.borman.com>
Subject: Re: Is Fragmentation at IP layer even needed ?
In-reply-to: Your message of "Mon, 08 Feb 2016 12:56:57 -0600." <AA50FF2F-8E00-4D63-944F-75C3D5A82F48@weston.borman.com>
Date: Tue, 09 Feb 2016 06:54:41 +1100
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In message <AA50FF2F-8E00-4D63-944F-75C3D5A82F48@weston.borman.com>, David Borm
an writes:
>
> > On Feb 8, 2016, at 12:23 PM, Warren Kumari <warren@kumari.net> wrote:
> ...
> > On Mon, Feb 8, 2016 at 9:05 AM David Borman <dab@weston.borman.com>
> wrote:
> ...
> > So if you are writing an application that needs >1500 octets, use an
> IPv6 implementation that supports >1500 octet fragmentation and
> reassembly.
> >
> > ... but as an application writer (or, basically anyone else), I have no
> control over the "IPv6 implementation". Even if I'm in an environment
> where I do control the OS / model of all devices, and I know they support
> >1500 octet, it seems like a bad idea to *rely* on that. Sometime I'm
> going to want to change OS / add some other device, be able to interact
> with some other system. This sounds like vendor lock at its worst…
>
> If you wind up in a scenario where you get locked to a particular OS
> vendor because it’s the only one that supports IPv6 fragmentation >1500
> octets, then that is probably the least of your worries.  I’d be much
> more worried about IPv6 fragmentation in light of Ron Bonica’s comment
> that intermediary nodes drop packets with extension headers, which is bad
> news even for fragmented packets in the 1280-1500 range.
>
> 			-David

Just about every OS supports > 1500 byte fragmentation reassembly.  4K, 8K and
greater reassembly buffers commonly exist.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka@isc.org