Date: Mon, 18 Jun 2007 19:05:06 +0100 From: "Bruce M. Simpson" <bms@incunabulum.net> To: Daniel Eischen <deischen@freebsd.org> Cc: Ian FREISLICH <ianf@clue.co.za>, current@freebsd.org Subject: Re: Multicast problems Message-ID: <4676C952.5000607@incunabulum.net> In-Reply-To: <Pine.GSO.4.64.0706181344060.24865@sea.ntplx.net> References: <E1I0E3b-0000kk-Ky@clue.co.za> <46765CB9.9020105@incunabulum.net> <Pine.GSO.4.64.0706180833080.23884@sea.ntplx.net> <4676C30E.7040300@incunabulum.net> <Pine.GSO.4.64.0706181344060.24865@sea.ntplx.net>
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Daniel Eischen wrote: > > I think in that case, the first non-loopback interface with IFF_MULTICAST > should be chosen. I think the loopback interface should be chosen in the > absence of any other interface with IFF_MULTICAST set. Our code does > rely > on this as well. > That seems correct. The code to do this would belong in the conditional for INADDR_ANY in both the ASM and SSM join paths, if the route lookup fails. If we get a bad interface address from userland we still need to return an error as code should not be relying on the presence of the RFC 1724 hack. I see that the pre-4.x rc scripts added a 224/4 route before this code was introduced. The new multicast API shouldn't try to second-guess userland code in this way as it allows an interface index to be specified explicitly. The nature of IGMP is such that it requires application joins to bind to an IPv4 interface. There are tweaks in IGMPv2 to workaround the possible lack of a protocol address e.g. during system bringup, however binding to an interface is still necessary. IPv6 (MLDv1 and MLDv2) utterly side-steps this issue by making it mandatory for interfaces to have a protocol address, even if that is a link-local address, for multicast joins to work. The condition we've seen is a side-effect of ip_multicast_if() being removed. Support for scoped addresses in the IPv4 stack will mean this code has to change again. BMS
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