support force_igmp_version=3 and force_mld_version=2 ?

[Pekka Savola <pekkas@xxxxxxxxxx>]

On Wed, 24 Sep 2008, Pekka Savola wrote:
> I've spotted some irritating IGMPv3/v2 compat problems on RHEL4, and 
> I'm working on trying to see if these are due to bugs already fixed 
> in latest kernels.

OK, I've done some tests.

1) in a RHEL4 2.6.8 kernel, the logic of timeouting seeing a V2
   querier earlier seems to be broken -- even if there are no IGMPv2
   reports or queries on the LAN for a long time, the system (as seen
   by /proc/net/igmp) doesn't go back to V3.  I tested that this works
   in 2.6.26.5 so this is OK.

2) only force_igmp_version=[12] is supported.  It might be useful to
   support "force_igmp_version=3" as well, where the system will not
   fall back to IGMPv1 or IGMPv2 compat mode even if it thinks it sees
   or has seen an IGMPv1/v2 query.

   This behaviour would be useful for example in scenarios where you
   know that the router is IGMPv3/MLDv2 capable, and you want to
   ignore queries sent by other routers, snooping switches or rogue
   hosts, or membership reports by other hosts (but Linux currently
   doesn't seem to support group-specific IGMP downgrade so this is
   not a problem right now) [see e.g. RFC4604 for more on various
   other things, e.g. warning errors, that could be added].

   What I refer to something like the follows (not tested, whitespace
   probably broken due to cut'n'pasting), or some similar changes in
   the logic where IGMP_Vx_SEEN is used (similar with MLD_V1_SEEN):

--- igmp.c.orig 2008-09-25 09:33:00.000000000 +0300
+++ igmp.c      2008-09-25 09:35:20.000000000 +0300
@@ -2,9 +2,13 @@
          (IPV4_DEVCONF_ALL(dev_net(in_dev->dev), FORCE_IGMP_VERSION) == 1 || \
           IN_DEV_CONF_GET((in_dev), FORCE_IGMP_VERSION) == 1 || \
           ((in_dev)->mr_v1_seen && \
+           IPV4_DEVCONF_ALL(dev_net(in_dev->dev), FORCE_IGMP_VERSION) != 3 && \
+           IN_DEV_CONF_GET((in_dev), FORCE_IGMP_VERSION) != 3 && \
            time_before(jiffies, (in_dev)->mr_v1_seen)))
 #define IGMP_V2_SEEN(in_dev) \
          (IPV4_DEVCONF_ALL(dev_net(in_dev->dev), FORCE_IGMP_VERSION) == 2 || \
           IN_DEV_CONF_GET((in_dev), FORCE_IGMP_VERSION) == 2 || \
           ((in_dev)->mr_v2_seen && \
+           IPV4_DEVCONF_ALL(dev_net(in_dev->dev), FORCE_IGMP_VERSION) != 3 && \
+           IN_DEV_CONF_GET((in_dev), FORCE_IGMP_VERSION) != 3 && \
            time_before(jiffies, (in_dev)->mr_v2_seen)))

--
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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