ipv4: implement igmp_qrv sysctl to tune igmp robustness variable

As in IPv6 people might increase the igmp query robustness variable to
make sure unsolicited state change reports aren't lost on the network. Add
and document this new knob to igmp code.

RFCs allow tuning this parameter back to first IGMP RFC, so we also use
this setting for all counters, including source specific multicast.

Also take over sysctl value when upping the interface and don't reuse
the last one seen on the interface.

Cc: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index cfc71ac0f764..db2383cb1df9 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -844,6 +844,11 @@ igmp_max_memberships - INTEGER
 
         conf/all/*        is special, changes the settings for all interfaces
 
+igmp_qrv - INTEGER
+         Controls the IGMP query robustness variable (see RFC2236 8.1).
+         Default: 2 (as specified by RFC2236 8.1)
+         Minimum: 1 (as specified by RFC6636 4.5)
+
 log_martians - BOOLEAN
         Log packets with impossible addresses to kernel log.
         log_martians for the interface will be enabled if at least one of