On Wed, Nov 21, 2018, 8:47 AM Templin (US), Fred L < [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]] On Behalf Of Ron > Bonica > > Sent: Wednesday, November 21, 2018 6:32 AM > > To: int-area <[email protected]>; [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 > > > > _______________________________________________ > > Int-area mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/int-area > > _______________________________________________ > Int-area mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/int-area >
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