Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile

Ron Bonica <rbonica@juniper.net> Wed, 25 July 2018 22:39 UTC

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From: Ron Bonica <rbonica@juniper.net>
To: "int-area@ietf.org" <int-area@ietf.org>
Thread-Topic: WG Adoption Call: IP Fragmentation Considered Fragile
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Archived-At: <https://mailarchive.ietf.org/arch/msg/int-area/HgmQIjV3LlbljS8_anQn1kL6jko>
Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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> 
> Message: 4
> Date: Tue, 24 Jul 2018 16:46:16 -0700
> From: Tom Herbert <tom@herbertland.com>
> To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
> Cc: Wassim Haddad <wassim.haddad@ericsson.com>om>,
> 	"internet-area@ietf.org" <int-area@ietf.org>rg>,
> 	"intarea-chairs@ietf.org" <intarea-chairs@ietf.org>
> Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered
> 	Fragile
> Message-ID:
> 	<CALx6S354kjyNaMYDo-XgsuiijapONC4GH+ozH8AXw-
> tQr0Ci=A@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> 
> On Tue, Jul 24, 2018 at 3:54 PM, Templin (US), Fred L
> <Fred.L.Templin@boeing.com> wrote:
> > I have an observation that I would like to see addressed in the
> > document. Some applications (e.g., 'iperf3' and others) actually
> > leverage IP fragmentation to achieve higher data rates than are possible
> using smaller (but unfragmented) whole packets.
> >
> > Try it - by default, iperf3 sets an 8KB UDP packet size and allows
> > packets to fragment across paths that support only smaller MTUs. I
> > have seen iperf3 exercise IP reassembly at line rates on high-speed links,
> i.e., it shows that reassembly at high rates is feasible.
> >
> > We know from RFC4963 that there are dangers for reassembly at high
> > rates, but there are applications such as iperf3 that ignore the
> > "SHOULD NOT" and leverage IP fragmentation anyway. So, should the
> "SHOULD NOT" have an asterisk?
> >
Fred, Tom,

The draft doesn't intend to forbid fragmentation in all cases. It is perfectly appropriate some scenarios.

I will add clarifying text in the next version.

                                       Ron



> Fred,
> 
> My reading of the draft is that IP fragmentation is fragile on the open
> Internet and should be avoided for applications that run over the Internet.
> That doesn't mean that fragmentation should be avoided in all use cases. In
> particular, if fragmentation is used in a closed network with low loss and has
> appropriate security measures in place, then it can be beneficial. I suspect
> that describes the network that your're running iperf in. If this interpretation
> of the draft's intent is correct, maybe there could be some words to clarify
> that.
> 
> Tom
> 
> > Thanks - Fred
> >
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