Multicast problems between 2.4.20 and 2.4.21?

Multicast problems between 2.4.20 and 2.4.21?

[Frank Lind]

Hi,

Was there ever a resolution to the multicast issues with kernels beyond 
2.4.20?

I have a very similar problem that has shown up with code which works 
fine prior with  2.4.20-6smp (Redhat 9) and then stops working for later 
kernels. I ran into this upgrading a machine to RedHat Enterprise 
(2.4.21-9.ELsmp) but it also happens under Fedora (2.6.5-1.358smp). I 
was going to try some separate kernel compiles and also a different 
distribution when I get a chance to try to localize the change. I 
haven't been able to find a clear reason why this is happening yet. I 
was wondering if anyone had any additional insights beyond what showed 
up in the kernel mailing lists so far (i.e. Any changes in Multicast 
code between 2.4.20 and 2.4.22/23)?

I am able to get the multicasting to work under these kernels by 
changing my bind calls to use the INADDR_ANY instead of binding to the 
address and port I'm using for the multicast group. I haven't found good 
documentation that this is the "correct" way to do this but I ran into 
some comments for multicast under ipv6 which made me think it was worth 
a try. This substitution gets the machines multicasting but I've had 
some problems that appear to be the switch selectively deciding to 
deliver data or not depending on if certain machines connect to the 
multicast group. (This needs more testing but basically if a machine 
using the 2.4.20 kernel joins then some of the newer kernel machines 
stop getting packets for reasons I don't understand yet).

I noted it was asked why the network switch might matter. There is a 
note from HP on their Procurve switches indicates that certain IP 
addresses are not IGMP filtered. In particular 224.0.0.x gets no IGMP 
filtering :

http://www.hp.com/rnd/pdfs/IGMP_Tech_Note.pdf

I got bit by this one a while back in that my network was getting 
flooded despite using IGMP in the code.

-- Frank

-- 
Frank D. Lind			email: flind@haystack.mit.edu	
MIT Haystack Observatory	WWW: http://www.haystack.mit.edu
Route 40			tel: 781 981 5570
Westford, MA  01886  USA	fax: 781 981 5766

Re: Multicast problems between 2.4.20 and 2.4.21?

[Martin Knoblauch]

--- Frank Lind <flind@haystack.mit.edu> wrote:
> Hi,
> 
> Was there ever a resolution to the multicast issues with kernels
> beyond 
> 2.4.20?
>
Hi Frank,

 no real resolution in my case, just a gross hack :-) With help from
some network folks and a lot of experiments we found out that somehow
IGMPv3 did cause the problems. The new protocol was introduced in
2.4.20 or 2.4.21.

 The problem only shows up when using MC groups different from
224.0.0.1. Assuming the correctness of the IGMPv3 code, the suspects
were the switch (some CISCO 6000, with the latest - v3 capable-
Firmware) or the network card (tg3). *I* am almost sure it is not the
card. Exchanging the driver from a "working" kernel into the new kernel
(and vice versa) did not change anything. The new kernel did not work
with the old driver, and the old kernel worked fine with the new
driver. So it is likely the switch.

 Solution for me was to force IGMPv2 instead of v3. The patch for taht
looks like:

--- ../../../linux-2.4.23/net/ipv4/igmp.c       Fri Nov 28 19:26:21
2003
+++ ./igmp.c    Fri Jan  9 16:59:21 2004
@@ -124,8 +124,13 @@

 #define IGMP_V1_SEEN(in_dev) ((in_dev)->mr_v1_seen && \
                time_before(jiffies, (in_dev)->mr_v1_seen))
+#if 0
 #define IGMP_V2_SEEN(in_dev) ((in_dev)->mr_v2_seen && \
                time_before(jiffies, (in_dev)->mr_v2_seen))
+#else
+#define IGMP_V2_SEEN(in_dev) (1)
+#endif
+

 The same problem occured on another cluster (again tg3 cards - maybe
there is something ...) and an HP/Procurve-41xx switch. Here we just
switched to using 224.0.0.1 to solve the problem (we could not reboot
to use a patched kernel).

B^hCheers
Martin

=====
------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de

Re: Multicast problems between 2.4.20 and 2.4.21?

[David S. Miller]

You don't need a patch to force IGMPv2, there is a sysctl
available now in 2.4.x for this purpose.

Re: Multicast problems between 2.4.20 and 2.4.21?

[Martin Knoblauch]

--- "David S. Miller" <davem@redhat.com> wrote:
> 
> You don't need a patch to force IGMPv2, there is a sysctl
> available now in 2.4.x for this purpose.
> 
> 
David,

  what is the name of the sysctl, and when was it added to 2.4? What
about 2.6.x?

Thanks
Martin

=====
------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de

Re: Multicast problems between 2.4.20 and 2.4.21?

[Frank Lind]

Hi Martin,

/sbin/sysctl -w net.ipv4.conf.eth1.force_igmp_version=2

the above worked for me. I think it was added in 2.4.25 and 2.6.2.

-- Frank


Martin Knoblauch wrote:

>--- "David S. Miller" <davem@redhat.com> wrote:
>  
>
>>You don't need a patch to force IGMPv2, there is a sysctl
>>available now in 2.4.x for this purpose.
>>
>>
>>    
>>
>David,
>
>  what is the name of the sysctl, and when was it added to 2.4? What
>about 2.6.x?
>
>Thanks
>Martin
>
>=====
>------------------------------------------------------
>Martin Knoblauch
>email: k n o b i AT knobisoft DOT de
>www:   http://www.knobisoft.de
>
>!DSPAM:40b38d3220961361122433!
>
>
>  
>


-- 
Frank D. Lind			email: flind@haystack.mit.edu	
MIT Haystack Observatory	WWW: http://www.haystack.mit.edu
Route 40			tel: 781 981 5570
Westford, MA  01886  USA	fax: 781 981 5766

Re: Multicast problems between 2.4.20 and 2.4.21?

[David S. Miller]

On Tue, 25 May 2004 11:15:10 -0700 (PDT)
Martin Knoblauch <knobi@knobisoft.de> wrote:

>   what is the name of the sysctl, and when was it added to 2.4? What
> about 2.6.x?

/proc/sys/net/ipv4/conf/${DEV}/force_igmp_version

Replace ${DEV} with a specific device name, "default", or "all"
as desired.

It got added to 2.4.25 I believe, and yes 2.6.x has it too.

Re: Multicast problems between 2.4.20 and 2.4.21?

[Martin Knoblauch]

--- "David S. Miller" <davem@redhat.com> wrote:
> On Tue, 25 May 2004 11:15:10 -0700 (PDT)
> Martin Knoblauch <knobi@knobisoft.de> wrote:
> 
> >   what is the name of the sysctl, and when was it added to 2.4?
> What
> > about 2.6.x?
> 
> /proc/sys/net/ipv4/conf/${DEV}/force_igmp_version
> 
> Replace ${DEV} with a specific device name, "default", or "all"
> as desired.
> 
> It got added to 2.4.25 I believe, and yes 2.6.x has it too.
> 
> 

 cool. What value does one put in? Is it just 0/1, or do you specify
the protocol version you want to force?

Cheers
Martin


=====
------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de