On Sun, 2004-10-03 at 06:23 -0500, Brian Fahrlander wrote: > OK, I've been working a lot a sleeping a little; I think my head is > now clear enough to respond to this: > > > On Sat, 2004-10-02 at 06:49, Ted Kaczmarek wrote: > > On Fri, 2004-10-01 at 12:25 -0400, Deron Meranda wrote: > > > Is this the correct behavior, or a bug? (seeing this in both FC2 > > > as well as EL3) > > > > > > I wrote an application which registers itself in a couple IPv6 > > > multicast groups on an ethernet interface. A "netstat -A inet6 -g" > > > then shows the group membership, such as > > > > > > IPv6/IPv4 Group Memberships > > > Interface RefCnt Group > > > --------------- ------ --------------------- > > > lo 1 ff02::1 > > > eth0 1 ff02::eb42:8740 > > > eth0 1 ff02::f6b6:d980 > > > eth0 1 ff02::1:ff13:7276 > > > eth0 1 ff02::1 > > > > > > If I then leave the application running, but do > > > an "ifdown eth0" then "ifup eth0", I get this, > > > > > > IPv6/IPv4 Group Memberships > > > Interface RefCnt Group > > > --------------- ------ --------------------- > > > lo 1 ff02::1 > > > eth0 1 ff02::1:ff13:7276 > > > eth0 1 ff02::1 > > > > > > Are group memberships supposed to be preserved across > > > up/down cycling? If not, then what's the proper way for an > > > application to detect that this has occurred so it can re-register? > > > Note that the app can still successfully SEND packets to the > > > group, but obviously, it no longer receives any packets. > > > > > > up/down cycling of what? > > Most switches will and should flush all tables on a port state change. > > I am assuming you are in a switch that is doing igmp snooping as well. > > What you probably need is for your app to detect link loss and send a > > new join when the link comes back. I have seen what I consider many > > broken applications that have this same issue. You may want to read up > > on how igmp and Pim work, and how the network equipment you are using > > implements it. Some vendors allow for you to manually join a group, this > > will force that port to always get the multicast data for that group. > > > > Also if come up with a good negative ack model , which is really the > > proper approach, it should recover in a relatively fast time on any > > up/down cycling assuming the network gear is set up right and working > > properly. > > > CAUGHT YA! You're using Multicast on Linux. After all these > years, I've finally found the 'one guy' actually using what, to me, is > the coolest feature of Linux: multicast with no artificial limitations. > > 1. What are ya using it for? (Hope it's not just NTP) > > 2. How can I get involved? > > 3. Why does the topic seem all-but-dead? > > 4. Does any software really _work_ with multicast other than NTP? Vlc, squid, quagga and probably many more. One of the coolest things I set up was vlc streaming video through a quagga box using htb qdisc to add priority to the video stream. Add some queues for some other flows and watch the qdisc do its job. I did extensive testing of qos on many vendors products, the Linux qos was by far the most robust. Ted
