Very Computer

In Linux 2.1 a more generic and better solution has been implemented for
PF_PACKET sockets (the sucessor of SOCK_PACKET):

[Here is the part of the new rewriten man pages that describe it]

 MULTICAST AND PROMISCUOUS MODE SUPPORT
       Linux 2.2 supports a new way to configure  physical  layer
       multicasting  and promiscuous mode over packet sockets. It
       works by calling setsockopt(2)  on  a  packet  socket  for
       SOL_PACKET and one of the options PACKET_ADD_MEMBERSHIP or
       PACKET_DROP_MEMBERSHIP.  They both expects  a  packet_mreq
       structure as argument:

              struct packet_mreq
              {
                   int       mr_ifindex;       /* interface index */
                   unsigned short mr_type;     /* mreq type as defined below */
                   unsigned short mr_alen;     /* address length */
                   unsigned char  mr_address[8];    /* physical layer address */
              };

       mr_interface  contains  the interface index for the inter-
       face whose status should be changed.   Valid  options  for
       mr_type  are PACKET_MR_MULTICAST to bind the socket to the
       physical layer multicast group specified in mr_address and
       mr_alen,  PACKET_MR_PROMISC  to enable promiscuous mode on
       the interface to receive all packets on  a  shared  media,
       PACKET_MR_ALLMULTI  sets the socket up to receive all mul-
       ticast    packets    arriving    at     the     interface.
       PACKET_DROP_MEMBERSHIP removes the binding or setting.

-Andi

I forgot. Of course you can use the low level SIOCADDMULTI/SIOCDELMULTI
ioctls too. They are probably the most appropiate for a packet socket.
They get a standard ifreq structure as argument.

-Andi