On Friday 30 January 2009 19:49:48 Kenny Chang wrote:

Hi all,

We've been having some issues with multicast packet loss, we were wondering
if anyone knows anything about the behavior we're seeing.

I didn't work much on multicast, but i have heavy unicast udp streaming (PEP 
for satellite).

First thing to check
net.core.wmem_max = 131071
net.core.wmem_default = 124928
net.ipv4.udp_mem = 379008       505344  758016

Usually they are too small by default.

next
netstat -s

Important part
Udp:
    1263992126 packets received
    260196 packets to unknown port received.
    627001 packet receive errors
    74235906 packets sent
    RcvbufErrors: 56683
    SndbufErrors: 4295851


in your case     SndbufErrors matter.