Date: Mon, 21 Aug 1995 11:29:51 PDT From: Bill Fenner <fenner@parc.xerox.com> To: davidg@root.com Cc: hackers@freebsd.org Subject: Re: Multicast on PPP devices Message-ID: <95Aug21.113005pdt.177475@crevenia.parc.xerox.com> In-Reply-To: Your message of "Mon, 21 Aug 95 11:18:54 PDT." <199508211818.LAA00148@corbin.Root.COM>
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In message <199508211818.LAA00148@corbin.Root.COM> you write: > It was changed to allow the local IPaddr of a point-to-point interface to >be shared, thus routing has to be based on the destination. Do you have a >suggestion on how to keep this functionality and not break multicasts over >point-to-point links? The problem is that multicasts are forwarded based on source address. There is a table mapping (Source, Group) -> (iif, oiflist) where iif is the expected incoming interface, and the oiflist is the list of outgoing interfaces. If this is changed to (S, G, iif) -> (oiflist), with the current architecture of the code, you can easily create forwarding loops. The key to the problem is that the multicast forwarding code treats input packets and output packets the same; in fact, if you are a member of a group on an interface, and you output a packet on that interface, that packet is looped around to the IP input queue, and forwarded from the ip_input() side. In any case, this problem is fermenting in the back of my mind, but I certainly don't have an immediate solution. I'm afraid that the solution is changing the architecture, which I'm certainly not up to at the moment. Bill
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