Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site umcp-cs.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!zehntel!hplabs!hao!seismo!umcp-cs!chris From: chris@umcp-cs.UUCP (Chris Torek) Newsgroups: net.unix-wizards Subject: Re: Problems in datagram socket between 4.2 BSD Message-ID: <1561@umcp-cs.UUCP> Date: Tue, 4-Dec-84 21:51:02 EST Article-I.D.: umcp-cs.1561 Posted: Tue Dec 4 21:51:02 1984 Date-Received: Thu, 6-Dec-84 06:30:04 EST References: <1197@kaist.UUCP> Distribution: net.bugs.4bsd Organization: U of Maryland, Computer Science Dept., College Park, MD Lines: 34 > We have connected two 4.2BSD with serial I/O routines from Harvard. > Operations using TCP(or stream socket) work well, > but operations using UDP(or datagram socket) - talk, rwho, dsh - > do not work. If the size of data to receive is large, > the local machine seems not to get the data from > the remote machine. In case of the command rwho, > it works well only when the remote machine has up to nine users. > It does not receive at all if more than nine users. I don't know why you'd have problems with talk or dsh, but rwho uses broadcast UDP packets, and these are not allowed to fragment. We weren't sure why this was so -- perhaps to reduce the load on anyone receiving uninteresting broadcast packets -- but we went ahead and removed the restriction, and things work fine. The restriction is in sys/netinet/ip_output.c, where you will find a set of lines looking something like this: /* don't allow broadcast messages to be fragmented */ if (ip->ip_len > ifp->if_mtu) { error = EMSGSIZE; goto bad; } If you simply remove this check, the kernel will merrily fragment broadcast messages, and you can ``rwho'' with a practially infinite number of users. (Whether you can run anything else with as many users is an entirely different question.) -- (This line accidently left nonblank.) In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690 UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris CSNet: chris@umcp-cs ARPA: chris@maryland