On Tue, 9 Sep 2008, Bernhard Schmidt wrote:

Working (all-hosts):
sendmsg(3, {msg_name(28)={sa_family=AF_INET6, sin6_port=htons(58), inet_pton(AF_INET6, "ff02::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, msg_iov(1)=[{"\200\0\0\0\25S\0\3\0\305\305H\212/\r\0\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36\37 !\"#$%&'()*+,-./01234567"..., 64}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_IPV6, cmsg_type=, ...}, msg_flags=0}, MSG_CONFIRM) = 64

Non-working (RIPng group):
sendmsg(3, {msg_name(28)={sa_family=AF_INET6, sin6_port=htons(58), inet_pton(AF_INET6, "ff02::9", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, msg_iov(1)=[{"\200\0\0\0MS\0\0012\305\305HCA\r\0\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36\37 !\"#$%&'()*+,-./01234567"..., 64}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_IPV6, cmsg_type=, ...}, msg_flags=0}, 0) = -1 EINVAL (Invalid argument)
sendmsg(3, {msg_name(28)={sa_family=AF_INET6, sin6_port=htons(58), inet_pton(AF_INET6, "ff02::9", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, msg_iov(1)=[{"\200\0\0\0MS\0\0012\305\305H\36F\r\0\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36\37 !\"#$%&'()*+,-./01234567"..., 64}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_IPV6, cmsg_type=, ...}, msg_flags=0}, 0) = -1 EINVAL (Invalid argument)

I wonder if it's relevant that msg_iov in working case has MSG_CONFIRM 
but in non-working case this is zero?  I guess not but apart from the 
contents of msg_iov, that's the only difference..

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings