stevens@hsi.UUCP (Richard Stevens) (09/22/88)
Is there an agreed upon max datagram size for UDP packets ??
I couldn't find one in RFC 768. In looking at the systems
I have access to, I see the original 4.3 BSD had a 9,000-byte
limit on transmit which was then reduced to 2,048 with the
4.3 network updates from Berkeley a few months back. The PC
RT under AIX has a 512-byte limit, while the IBM mainframe
version (FAL) allows up to 2,048. I'm aware of the performance
penalties once you exceed the network's MTU, but I was
wondering if there was a generally agreed upon maximum
(I'll guess there isn't).
As I recall from a few years ago, isn't this the reason the BSD
rwhod packets have a built in limit of information on up to 41-users.
Richard Stevens
Health Systems International, New Haven, CT
stevens@hsi.uu.net
... { uunet | yale } ! hsi ! stevenschris@GYRE.UMD.EDU (Chris Torek) (09/22/88)
4.3BSD has a default size limit of 2048 bytes, but this can be changed with a `setsockopt' call. Rwhod packets are limited not by this size, but by the Ethernet MTU, as 4BSD will not fragment a UDP broadcast packet (unless you tweak your kernel). Chris
slevy@UC.MSC.UMN.EDU ("Stuart Levy") (09/26/88)
Speaking of fragmenting broadcasts, can anyone explain the rationale for not doing this? Is it just BSD IP which refuses to fragment them or is it widely held to be a Bad Thing? I don't find mention of fragmentation in RFC 919. Stuart Levy, slevy@uc.msc.umn.edu