Date: Mon, 1 Jan 1996 11:20:02 -0800 (PST) From: "Garrett A. Wollman" <wollman@lcs.mit.edu> To: freebsd-bugs Subject: kern/923: Multicast problems on point-to-point interfaces Message-ID: <199601011920.LAA03430@freefall.freebsd.org>
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The following reply was made to PR kern/923; it has been noted by GNATS. From: "Garrett A. Wollman" <wollman@lcs.mit.edu> To: marquard@austin.ibm.com Cc: FreeBSD-gnats-submit@freebsd.org, Bill Fenner <fenner@parc.xerox.com> Subject: kern/923: Multicast problems on point-to-point interfaces Date: Mon, 1 Jan 1996 14:16:48 -0500 <<On Sat, 30 Dec 1995 16:26:55 -0600, marquard@austin.ibm.com said: > In attempting to run mrouted for multicast routing, I noted > that tun0 has IFF_MULTICAST set, and tun0 along with a tunnel > to a remote site should make mrouted work. > Here's the mrouted configuration file I used: > # mrouted configuration > phyint 9.3.240.156 > tunnel 9.3.240.156 129.35.128.45 Actually, this doesn't make any sense. You should either disable the physical interface (`phyint x.x.x.x disabled') and just use a tunnel, or otherwise don't use a tunnel and run mrouted on the other side of the phyint. (Otherwise, you will duplicate all your multicast traffic.) This is not the cause of your problem, however. > In the case of a point to point link like tun0, we check the > DESTINATION address rather than the source address of the > interface. It seems to me we should either check the source, > or both the source and destination, but not just the > destination. You have hit on a thorny problem. The code is written in the way it is in order to support a ``half-router'' model of IP forwarding. Never mind that this breaks the IP reference model; a number of people complained about it not working last year, and so pains were taken to make it work despite the problems. You have hit upon one of the most serious problems resulting from allowing half-router support: the IP model requires that an IP address /uniquely/ name an interface, and the half-router support breaks that completely. We are unlikely to get the multicast people to change their software, because they are just following the rules. > This should catch both the source and destination address of > point to point links. This might be a workable solution, except in the half-router case. I might just tell the half-router people ``Go away, you're broken'', but I'm not sure I want to do that. -GAWollman -- Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ... wollman@lcs.mit.edu | Shashish is the bonding of hearts in spite of distance. Opinions not those of| It is a bond more powerful than absence. We like people MIT, LCS, ANA, or NSA| who like Shashish. - Claude McKenzie + Florent Vollant
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