Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!tinman.cis.ohio-state.edu!bob From: bob@tinman.cis.ohio-state.edu (Bob Sutterfield) Newsgroups: news.admin Subject: Re: usenet distributions Summary: some musings on directed broadcast Message-ID: Date: 14 Jul 89 14:14:33 GMT References: <316@mplex.UUCP> <464@moegate.UUCP> <3387@epimass.EPI.COM> Sender: news@tut.cis.ohio-state.edu Reply-To: Bob Sutterfield Organization: The Ohio State University Dept of Computer & Information Science Lines: 108 In-reply-to: fff@mplex.UUCP's message of 12 Jul 89 01:12:42 GMT Distribution: In article <316@mplex.UUCP> fff@mplex.UUCP (Fred Fierling) writes: I would like to post an article for distribution in West Germany only, but our /usr/lib/news/distributions file only has codes for local, na, usa, world, etc. There must be more distribution codes than this. Where do I find them? -- Fred Fierling Tel: 604 875-1461 Microplex Systems Ltd, 265 East 1st Ave uunet!mplex!fff Fax: 604 875-9029 Vancouver, BC, V5T 1A7, Canada In article <464@moegate.UUCP> soley@moegate.UUCP (Norman S. Soley) writes I doubt that there is an master list anywhere. That's right - distributions are just things that two consenting sites put into their corresponding sys file lines. Also there is no easy way to post to a distribution you are not part of, this is one of the reasons why many of the usenet sites in Toronto get the usa distribution. In article <3387@epimass.EPI.COM> jbuck@epimass.EPI.COM (Joe Buck) writes: You cannot post to a distribution that your site is not a member of. How would your article reach West Germany if you specified that no sites other than West German sites should receive it and you don't have a direct link to a German site? The only way is to mail your article to someone in West Germany and ask him or her to post the article for you with a German distribution. This sort of issue has been examined before, though in a different context. Still, very similar problems and solutions arose. Suppose we consider a news distribution to be similar to a hardware network that supports broadcasts. Then machines not "attached" to that distribution have problems receiving, and sending, "broadcasts" on that network. RFC 947 discusses multi-network broadcasting within an internet context, developed as a mechanism to support the Chronus operating system. It uses a forwarder/repeater mechanism, and discusses the problem of using link-level repeaters - the equivalent of machines along the way passing a distribution. RFC 947 refers the reader to RFCs 919 (UDP broadcasting) and 940 (IP subnetting) as well. 919 notes: ...This case is the same as local-network broadcasts; the datagram is routed by normal mechanisms until it reaches a gateway attached to the destination IP network, at which point it is broadcast. This class of broadcasting is also known as "directed broadcasting", or quaintly as sending a "letter bomb". ... Most of the complexity in supporting broadcasts lies in gateways. If a gateway receives a directed broadcast for a network to which it is not connected, it simply forwards it using the usual mechanism. Otherwise, it must do some additional work. The "letter bomb" analogy seems particularly apropos in the Usenet environment :-) How might one build a news repeater? Suppose sites A and B maintain a news link, and sites B and C do likewise. Suppose their sys files look like: A: A:dist1,dist3:: B:dist1,dist3:F: B: A:dist1,dist3:F: B:dist1,dist2:: C:dist2,dist3:F: C: B:dist2,dist3:F: C:dist2,dist3:: dist3 would pass through B without appearing in their local spool for the local readership - effectively, a news repeater. The A-B and B-C links would still carry the dist3 traffic, and B would need to be a willing party to the arrangement. But B wouldn't be a part of the dist3 "hardware network". Of course, this can't be done in the news world for both social and technical reasons. Socially: it wouldn't be polite to pass traffic through an intermediary that wasn't receiving the benefit of that traffic for its own users (though if they were willing and either friendly or well paid, they could make the service available). Also, being able to scream somewhere else (a ventriloquist posting?) would be quite impolite, because it would be stirring things up without waiting around for the repercussions. Technically: before an article can be gathered up to be sent along to other neighbors in the same distribution, it must exist in the news spool area of the machine doing the collecting. This is a lot more participation in the transmission process than is required of a typical IP router or Ethernet repeater, though those packet forwarders must have the packet in memory while shuffling it onto the other interface. All this is why sites that wish to exchange a distribution must have a direct connection - like setting up a link from your site in Canada to some site (any site!) in Germany that's on the de distribution. Perhaps distributions can be considered as protocol families, which can only be understood and forwarded by routers that are knowledgeable about that protocol - e.g. a DECnet packet will see a TCP or XNS router as a firebreak between it and other DECnet networks. Oh well, those are just some of my musings about analogies that can perhaps be stretched too far :-)