Path: utzoo!attcan!uunet!lll-winken!ncis.llnl.gov!helios.ee.lbl.gov!nosc!ucsd!rutgers!elbereth.rutgers.edu!aramis.rutgers.edu!geneva.rutgers.edu!hedrick From: hedrick@geneva.rutgers.edu (Charles Hedrick) Newsgroups: comp.protocols.tcp-ip Subject: Re: Reverse Path Forwarding (or broadcasting with subnets) Message-ID: Date: 21 Jan 89 02:48:13 GMT References: <13316@dcatla.UUCP> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 18 As far as I know, cisco routers (the only ones I know in detail) do not implement RFC922 (reverse path forwarding for broadcasts). If they did, I would disable it. There are two many machines that still don't know about subnets. Thus it is very hard to know when a host really wants a site-wide broadcast as compared to one on the local subnet. I also think 922 may be overly optimistic about preventing loops. But this is just a guess. At any rate, I think if you want to do a wide-area broadcast, you should be looking at IP multicasting, not at network-wide broadcasts. Multicasting is still viewed as experimental, and is not widely implemented. However I think you'd stand a much greater chance of getting router vendors to implement that than the RFC 922 scheme. On the other hand, if I were doing a product which I wanted to sell to people other than network wizards (i.e. people whose network contains systems may be a year or two behind the latest proposals), I'd not assume any kind of broadcasting outside of the local physical network. Also, beware of the various odd configurations that people sometimes create, such as multiple networks or subnets on a single cable.