netdev - Re: Multicast socket behaviour?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 13 Aug 2008 07:19:50 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Daniel Ng <daniel_ng11@...os.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Multicast socket behaviour?

On Wed, Aug 13, 2008 at 08:21:58AM +0000, Daniel Ng wrote:
> Hi,
> 
> The below C code registers the socket with the multicast group 'HELLO_GROUP':
> 
>     mreq.imr_multiaddr.s_addr=inet_addr(HELLO_GROUP);
>     mreq.imr_address.s_addr=htonl(INADDR_ANY);
> 
>     mreq.imr_ifindex = if_nametoindex("ppp1");
> 
>     if (setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0) {
>         perror("setsockopt");
>         exit(1);
>     }
> 
> I understand that if 'INADDR_ANY' is used, it is up to the kernel to decide 
> what action to take.
> 
> >From my experiments, it seems that the interface corresponding to the 
> highest '224.0.0.0' entry in the routing table is used.
> 
> Would someone please explain why this is so? 
> 
> How difficult would it be to have the kernel join the HELLO_GROUP on *all* 
> available multicast-capable interfaces? Why isn't this currently implemented?
> 
> I'm using 2.6.14.
> 
> Cheers,
> Daniel
> 

I had this same confusion on netdev a few weeks ago:
http://marc.info/?l=linux-netdev&m=121580189427089&w=2

Its working as it should, allbeit somewhat counter-intuitively.  Although there
may be a bug in your kernel, you're several releases back.

Neil


-- 
/****************************************************
 * Neil Horman <nhorman@...driver.com>
 * Software Engineer, Red Hat
 ****************************************************/
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html