(App programmer seeking expert network advice!)I have a VLAN XX which extends across an entire site, many different switches. I have many hosts all multi-casting. The vast majority are sending data to my 3 main hosts which receive the multi-casted data. These three receivers are ALL on the same local Cisco 2960G switch with a couple senders. Works great until I reboot or power-off ANY one of the 3 receivers. Then the remaining receivers lose data from all of my senders EXCEPT those that are on the local 2960G. (Same situation applies when I kill the mcasting receive APP) Looking at the traffic I see the "drop membership" at which point I lose the remote senders. I also see a "membership query" from the router, both of which I expected. After about a minute one or the other of the remaining receivers responds and the receivers now get all the multicasted data just like normal. I cannot have the 1 minute loss of data acq. Here is my "dumb applications programmer" question. Should my mcasting receive app be sending out an "add membership request"? It doesn't seem as tho it should in that how would I detect the loss of some senders? I have the local senders talking normally. I would have expected the os kernel to have responded to the membership query as it knows the app has a multicasting socket that hasn't been closed. Also, what mechanism is responding after a minute to let the router know that I have receivers still in the multicasting group? Can I define a static membership somewhere so I can "force" the multicasted data to the remaining receivers? Thanks.