Xref: utzoo comp.protocols.tcp-ip:7965 comp.protocols.nfs:319 Path: utzoo!utgpu!watmath!att!tut.cis.ohio-state.edu!cs.utexas.edu!sun-barr!texsun!newstop!east!hinode!geoff From: geoff@hinode.East.Sun.COM (Geoff Arnold @ Sun BOS - R.H. coast near the top) Newsgroups: comp.protocols.tcp-ip,comp.protocols.nfs Subject: How to get an urgent message to an arbitrary system Message-ID: <681@east.East.Sun.COM> Date: 8 Aug 89 21:51:17 GMT Sender: news@east.East.Sun.COM Reply-To: geoff@hinode.East.Sun.COM (Geoff Arnold @ Sun BOS - R.H. coast near the top) Followup-To: comp.protocols.tcp-ip Organization: Sun Microsystems, Billerica MA Lines: 37 One of the questions I am often asked about PC-NFS is "how come there's no way for me to find out when a particular file server is going down? Unix users get notified." I point out that (at least on SunOS) the mechanism used is "rwall", which is an RPC service, and that for size reasons we can't afford to embed a version of rpc.rwalld in PC-NFS. This explanation is reasonable, but unsatisfactory. My reaction was to say "let's ask the NIC for a UDP port so that we can use it to send unsolicited messages to PCs running PC-NFS." That would certainly do the trick. However, a moment's thought reveals that the problem is bigger than just PC-NFS. Surprisingly, there is at present no simple ubiquitous message protocol to fulfil this function. rwall is fine for SunOS and other ONC licensees, but what about other systems? Do I have to rely upon SMTP? That's incompatible with the idea of broadcasting a simple message such as "The backbone will be down for five minutes at 12:00 to replace a bridge." This could be trivially simple or slightly more involved (but still simple). The trivial approach is to dedicate a UDP port for unsolicited system messages. Anyone could send one, in a single datagram, and the listener process would be responsible for delivering it as seemed appropriate for the system (dialog box, console message, etc.) A more complete approach would be to define a formal protocol so that it would be possible to convey information about the coding of the message, message length (so that TCP could be used instead) and so forth. [If the spec exceeds one page, it's too complicated.] Comments? Geoff Geoff Arnold, Internet: geoff@East.Sun.COM PCDS Group, Sun Microsystems Inc. --------------------------------------------------------------------------- Just think: If Unix had been developed in England, we'd all be using BCPL...