Date: Wed, 14 Mar 2001 09:15:49 -0800 From: Lars Eggert <larse@ISI.EDU> To: David Malone <dwmalone@maths.tcd.ie> Cc: freebsd-net@freebsd.org Subject: Re: UDP datagram max size. Message-ID: <3AAFA745.AA3EC6B6@isi.edu> References: <200103141703.aa78458@salmon.maths.tcd.ie>
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[-- Attachment #1 --] David Malone wrote: > > I'm trying to figure out what #define I should use for the largest > UDP datagram. The header files don't seem to define a constant for > this. The correct size would seem to be 65535 'cos there are two > bytes in the UDP header for the size. > > IP_MAXPACKET and IPV6_MAXPACKET are available and have the right > values, but these don't really seem to be the correct thing to use > 'cos they don't take headers or the possibility Jumbo payload into > account. To support jumbograms, I don't think you'll get around dynamic memory allocation. (There is no reasonable upper bound for the buffer size.) However, RFC2675 says: The Jumbo Payload option is relevant only for IPv6 nodes that may be attached to links with a link MTU greater than 65,575 octets (that is, 65,535 + 40, where 40 octets is the size of the IPv6 header). The Jumbo Payload option need not be implemented or understood by IPv6 nodes that do not support attachment to links with MTU greater than 65,575. So it may be okay to punt on jumbograms for now, and use a 64K static buffer like the patch in the PR does. Even if you do implement support for jumbograms, I think keeping the 64K static buffer around as a "fast-path" for the common case makes sense. > I wanted to commit something for: > > http://www.FreeBSD.org/cgi/query-pr.cgi?pr=25050 > > but I'm not convinced that the patch is spot on. I could determine > the data size and malloc memory dynamically I guess. -- Lars Eggert <larse@isi.edu> Information Sciences Institute http://www.isi.edu/larse/ University of Southern California [-- Attachment #2 --] 0# *H 01 0 + 0 *H 00A#0 *H 01 0 UZA10U Western Cape10U Durbanville10 U Thawte1 0U Certificate Services1(0&U Personal Freemail RSA 1999.9.160 000824203008Z 010824203008Z0T10 UEggert1 0 U*Lars10U Lars Eggert1 0 *H larse@isi.edu00 *H 0 \p9 H;v r∩6"C?mxfJ f7I[3CF́L I - zHRVA怤2]0-bL)%X>nӅ w0u0*+e!0 00L2uMyffBNUbNJJcdZ2s0U 0 larse@isi.edu0 U 0 0 U #0`fUXF a#Ì0 *H _3 F=%nWY-HXD9UOc6ܰw f@uܶNԄR?Pr} E1֮23 mFhySwM_h|d yR= $P 00} 0 *H 01 0 UZA10U Western Cape10U Cape Town10U Thawte Consulting1(0&U Certification Services Division1$0"UThawte Personal Freemail CA1+0) *H personal-freemail@thawte.com0 990916140140Z 010915140140Z01 0 UZA10U Western Cape10U Durbanville10 U Thawte1 0U Certificate Services1(0&U Personal Freemail RSA 1999.9.1600 *H 0 iZ z]!#rLK~r$BRW{azr98e^eyvL>hpu t ,O 1ArƦ]D.Mօ>lx~@эWs0FO 7050U 0 0 U #0rIs4U vr~wƲ0 *H kY1rr`HU{gapm¥7؝(V\uoƑlfq|ko!6- -mƃRt\~ orzg,ks n Νc) ~U10001 0 UZA10U Western Cape10U Durbanville10 U Thawte1 0U Certificate Services1(0&U Personal Freemail RSA 1999.9.16#0 + 0 *H 1 *H 0 *H 1 010314171549Z0# *H 1r f{E $N0R *H 1E0C0 *H 0*H 0+0 *H @0 *H (0 *H bo븒^kHsI o 9OG ScHCEZ}-[EQ7*leQWxF|۟(̻.vmP8E߄~ŷ̰8K SLT]
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