Date: Tue, 18 May 1999 07:39:17 -0400 From: "Andrew Chalupka" <andcha@nortelnetworks.com> To: net@freebsd.org Subject: RE: RAW IP socket for IGMP packet.. Message-ID: <C51ED84B6F47D211917A0000F8BCBD11E7257B@zcard00g.ca.nortel.com>
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The problem here is that IGMP packets (and any other IP packets addressed to
a multicast group), are also addressed to a group address *at the data link
layer*. Normally, the kernel takes care of telling the data link layer to
accept group-addressed frames when you join a mcast group. However, simply
creating a raw socket with IPPROTO_IGMP is probably not sufficient to do
that.
Your best bet is to use libpcap to grab the IGMP packets.
Andrew
> -----Original Message-----
> From: Youngsu Chae [SMTP:yschae@cc.gatech.edu]
> Sent: Tuesday, May 18, 1999 4:44 AM
> To: net@freebsd.org
> Subject: RAW IP socket for IGMP packet..
>
> Hi all,
>
> I've been struggling with raw ip socket to pick up IP/IGMP packet.
> As I understand from the 'raw_ip.c' source code, if the following three
> conditions are satisfied
>
> 1) open a raw ip socket with protocol value as IPPROTO_IGMP,
> 2) do not bind local address,
> 3) do not specify foreign address,
>
> then, the socket should get all the IP/IGMP packets with whatever
> destination group addresses.
> But, I couldn't get any IGMP packets..
> The only way I can get the IP/IGMP packet is to subscribe to a specific
> group.
> That gives me only the IGMP packets destined to the group.
> How can I get all IGMP packets with raw ip socket?
> I've also tested with protocol value IPPROTO_IP(0).
> In this case it should pick up all IP packets except TCP/UDP (those
> packets are handled only in kernel).
> It picks up ICMP packets but not IGMPs.
>
>
> The following is the code for opening raw IP socket for IGMP..
> /* get an IGMP socket */
> if ((igmp_socket = socket(AF_INET,SOCK_RAW,IPPROTO_IGMP)) < 0){
> panic ("socket() failed!");
> }
>
> k_hdr_include(TRUE); /* turn on header include option */
> k_set_rcvbuf(256*1024,48*1024); /* lots of input buffering */
> k_set_ttl(1); /* restrict multicasts to one hop */
> k_set_loop(FALSE); /* disable multicast loopback */
>
>
> Thanks,
>
> Y.Chae
>
>
>
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