Bug 12109

Summary:	Multicast packets with TTL 0 sent out if not local listener
Product:	Networking	Reporter:	Jani Monoses (jani)
Component:	IPV4	Assignee:	Stephen Hemminger (stephen)
Status:	RESOLVED OBSOLETE
Severity:	normal	CC:	alan, thierry.guibert
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.27	Subsystem:
Regression:	No	Bisected commit-id:

Description Jani Monoses 2008-11-27 02:32:26 UTC

According to what I have read, setting the IP_MULTICAST_TTL option to 0 on a multicast sending socket should prevent it sending to the network, and be destined only for listeners on the local computer.

This only seems to work if there is a local listener on that particular group. If such a listener app is stopped other computers on the LAN get the messages, and tcpdump -v shows they have  TTL 0

I am not sure if this is intended behaviour but it is unexpected.

Comment 1 Anonymous Emailer 2008-11-27 09:34:15 UTC

Reply-To: akpm@linux-foundation.org


(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Thu, 27 Nov 2008 02:32:27 -0800 (PST) bugme-daemon@bugzilla.kernel.org wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=12109
> 
>            Summary: Multicast packets with TTL 0 sent out if not local
>                     listener
>            Product: Networking
>            Version: 2.5
>      KernelVersion: 2.6.27
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV4
>         AssignedTo: shemminger@linux-foundation.org
>         ReportedBy: jani@ubuntu.com
> 
> 
> According to what I have read, setting the IP_MULTICAST_TTL option to 0 on a
> multicast sending socket should prevent it sending to the network, and be
> destined only for listeners on the local computer.
> 
> This only seems to work if there is a local listener on that particular
> group.
> If such a listener app is stopped other computers on the LAN get the
> messages,
> and tcpdump -v shows they have  TTL 0
> 
> I am not sure if this is intended behaviour but it is unexpected.
> 
>

Comment 2 Thierry GUIBERT 2009-02-12 03:01:40 UTC

According to RFC 791 (Internet Protocol spec), page 20 any packet with a TTL = 0 must be destroyed.

I encounter the same problem on Red Hat Enterprise Linux WS release 4 (Nahant Update 5) using kernel :
Linux [hostname] 2.6.9-55.ELsmp #1 SMP Fri Apr 20 17:03:35 EDT 2007 i686 i686 i386 GNU/Linux

Comment 3 Thierry GUIBERT 2009-04-09 12:29:50 UTC

is there any fix scheduled ?

Comment 4 Alan 2012-10-30 15:37:16 UTC

If this is still seen on modern kernels then please re-open/update and report to netdev@vger.kernel.org