Fred,
I am happy to add a section about LTP. However, I agree with Tom that we should
not be talking about iPERF because:
- It is a test utility
- I can’t find a stable reference
Also, given that NFSv2 was obsoleted by RFC 3010 in 2000. I don’t think that it
is relevant any longer.
Ron
From: Tom Herbert <[email protected]>
Sent: Tuesday, November 27, 2018 11:34 AM
To: Templin (US), Fred L <[email protected]>
Cc: Ron Bonica <[email protected]>; int-area <[email protected]>;
[email protected]
Subject: Re: [Int-area] draft-ietf-intarea-frag-fragile-03
On Wed, Nov 21, 2018, 8:47 AM Templin (US), Fred L
<[email protected]<mailto:[email protected]>> wrote:
Hi Ron,
There needs to be a new subsection in Section 6 on UDP applications that
rely on IP fragmentation for greater performance. Here is proposed text:
"Some UDP applications rely on IP fragmentation to achieve acceptable levels
of performance. These applications use UDP datagram sizes that are larger than
the path MTU so that more data can be conveyed between the application and
the kernel in a single system call.
Historically, NFS version 2 [RFC1094] set a UDP datagram size of 8KB which is
greater than the path MTU of most paths, resulting in IP fragmentation.
Currently, the Licklider Transmission Protocol [RFC5326] which is in current
use on the International Space Station (ISS) uses UDP datagram sizes larger
than the path MTU to achieve acceptable levels of performance even though
this too invokes IP fragmentation. Also, the commonly-used iperf3 [IPERF3]
performance testing utility by default sets an 8KB UDP datagram size even
though IP fragmentation is invoked since the performance of smaller UDP
datagrams is much lower.
Hi Fred,
I agree that NFS and ISS protocol are worth mentioning, but iperf shouldn't be
mentioned since it is just a test program.
While it is natural to suggest that such applications should adjust their
application layer framing to better match the path MTU, such does
not always result in greater performance. For example, although the
"sendmmsg()" system call was designed to present the kernel with
multiple UDP datagrams in a single call, not all applications benefit
from its use."
The hardest part is pmtu discovery, signaling discovered pmtu to the UDP
application, and then the application needs to know how to make smaller packets
to fit into mtu. The last step is especially problematic since it's application
specific logic. The natural recourse applications have is to just assume
minimal MTU, but as you point out that can be poor performance compared to
using fragmentation
Tom
Thanks - Fred
> -----Original Message-----
> From: Int-area
> [mailto:[email protected]<mailto:[email protected]>] On
> Behalf Of Ron Bonica
> Sent: Wednesday, November 21, 2018 6:32 AM
> To: int-area <[email protected]<mailto:[email protected]>>;
> [email protected]<mailto:[email protected]>
> Subject: [Int-area] draft-ietf-intarea-frag-fragile-03
>
> Chairs,
>
> I have posted a new version of draft-ietf-intarea-frag-fragile, working in
> comments from Tom and Brian.
>
> If you see fit, please initiate a working group last call.
>
> Ron
>
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