On Fri, Sep 7, 2018 at 6:56 AM Andre Naujoks <nauts...@gmail.com> wrote: > On 9/7/18 1:15 PM, Alan Bateman wrote: > > On 07/09/2018 10:49, Decke, Hendrik (K-GERFA/A) wrote: > >> > >> Hello, > >> > >> it seems one of our external developers (Andre Naujoks, CC) found a > >> bug while binding a IPv6 multicast UDP-socket for one of our projects. > >> > >> > >> > >> Since this seems to be a fundamental bug (from our perspective), we > >> address this directly to this mailing list. > >> > >> (reproducible in OpenJDK 8-11, Windows and Linux) > >> > > This bug was submitted this week on this issue: > > https://bugs.openjdk.java.net/browse/JDK-8210493 > > > > Have you tried joining the mullticast group, specifying the network > > interface, rather than binding to the multicast address? > > Hi Alan. > > First of all, thank you for the quick reply. I was not aware, that there > was actually a bug opened for that issue. > > The join is not the problem at this point. We need to bind the socket to > the address to avoid receiving traffic from all multicast groups, that > are joined on the system. Since a join joins the system (not the socket) > to the group, all sockets bound to a port, which receive multicast > traffic will receive all of that traffic, no matter the destination > address. The bind prevents that. IP_MULTICAST_ALL sadly only works for > IPv4 and the patch I tried to get IPV6_MULTICAST_ALL upstream into the > kernel was even more sadly (almost) ignored. see > https://marc.info/?l=linux-netdev&m=152344460530252&w=2
Hi Andre, I spoke with a colleague about this kernel patch. They said first of all that multicast filtering is pretty complex in the kernel with a lot of subtle behaviors. But, they also said that it may have been ignored because of the format of the patch, perhaps even accidentally/automatically. The proposed patch has an "RFC" tag, and such patches apparently need to be in "git-format-patch" mode. Lastly, they said that since the time that the post was made, IP_MULTICAST_ALL (for IPv4 only of course) has changed a little bit in that "it only allows receipt of all multicast groups if a specific list of multicast groups has not already been set", so it may need to be updated accordingly. FWIW they didn't mention seeing any actual problems with the content of the patch, though I'm not sure how thoroughly they reviewed it. So, while I myself am not a Linux kernel contributor, I do suspect that if you reposted an updated version of the patch, in the correct format, it will enter the patch queue and may be more actively discussed. For more information, see [1]. [1] https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#the-canonical-patch-format -- - DML
