IGMP: Inhibit reports for local multicast groups
The range of addresses between 224.0.0.0 and 224.0.0.255 inclusive, is
reserved for the use of routing protocols and other low-level topology
discovery or maintenance protocols, such as gateway discovery and
group membership reporting. Multicast routers should not forward any
multicast datagram with destination addresses in this range,
regardless of its TTL.
Currently, IGMP reports are generated for this reserved range of
addresses even though a router will ignore this information since it
has no purpose. However, the presence of reserved group addresses in
an IGMP membership report uses up network bandwidth and can also
obscure addresses of interest when inspecting membership reports using
packet inspection or debug messages.
Although the RFCs for the various version of IGMP (e.g.RFC 3376 for
v3) do not specify that the reserved addresses be excluded from
membership reports, it should do no harm in doing so. In particular
there should be no adverse effect in any IGMP snooping functionality
since 224.0.0.x is specifically excluded as per RFC 4541 (IGMP and MLD
Snooping Switches Considerations) section 2.1.2. Data Forwarding
Rules:
2) Packets with a destination IP (DIP) address in the 224.0.0.X
range which are not IGMP must be forwarded on all ports.
IGMP reports for local multicast groups can now be optionally
inhibited by means of a system control variable (by setting the value
to zero) e.g.:
echo 0 > /proc/sys/net/ipv4/igmp_link_local_mcast_reports
To retain backwards compatibility the previous behaviour is retained
by default on system boot or reverted by setting the value back to
non-zero e.g.:
echo 1 > /proc/sys/net/ipv4/igmp_link_local_mcast_reports
Signed-off-by: Philip Downey <pdowney@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 9fdfd9d..d38b8b6 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -110,6 +110,9 @@
#define IP_MAX_MEMBERSHIPS 20
#define IP_MAX_MSF 10
+/* IGMP reports for link-local multicast groups are enabled by default */
+int sysctl_igmp_llm_reports __read_mostly = 1;
+
#ifdef CONFIG_IP_MULTICAST
/* Parameter names and values are taken from igmp-v2-06 draft */
@@ -437,6 +440,8 @@
if (pmc->multiaddr == IGMP_ALL_HOSTS)
return skb;
+ if (ipv4_is_local_multicast(pmc->multiaddr) && !sysctl_igmp_llm_reports)
+ return skb;
isquery = type == IGMPV3_MODE_IS_INCLUDE ||
type == IGMPV3_MODE_IS_EXCLUDE;
@@ -545,6 +550,9 @@
for_each_pmc_rcu(in_dev, pmc) {
if (pmc->multiaddr == IGMP_ALL_HOSTS)
continue;
+ if (ipv4_is_local_multicast(pmc->multiaddr) &&
+ !sysctl_igmp_llm_reports)
+ continue;
spin_lock_bh(&pmc->lock);
if (pmc->sfcount[MCAST_EXCLUDE])
type = IGMPV3_MODE_IS_EXCLUDE;
@@ -678,7 +686,11 @@
if (type == IGMPV3_HOST_MEMBERSHIP_REPORT)
return igmpv3_send_report(in_dev, pmc);
- else if (type == IGMP_HOST_LEAVE_MESSAGE)
+
+ if (ipv4_is_local_multicast(group) && !sysctl_igmp_llm_reports)
+ return 0;
+
+ if (type == IGMP_HOST_LEAVE_MESSAGE)
dst = IGMP_ALL_ROUTER;
else
dst = group;
@@ -851,6 +863,8 @@
if (group == IGMP_ALL_HOSTS)
return false;
+ if (ipv4_is_local_multicast(group) && !sysctl_igmp_llm_reports)
+ return false;
rcu_read_lock();
for_each_pmc_rcu(in_dev, im) {
@@ -957,6 +971,9 @@
continue;
if (im->multiaddr == IGMP_ALL_HOSTS)
continue;
+ if (ipv4_is_local_multicast(im->multiaddr) &&
+ !sysctl_igmp_llm_reports)
+ continue;
spin_lock_bh(&im->lock);
if (im->tm_running)
im->gsquery = im->gsquery && mark;
@@ -1181,6 +1198,8 @@
#ifdef CONFIG_IP_MULTICAST
if (im->multiaddr == IGMP_ALL_HOSTS)
return;
+ if (ipv4_is_local_multicast(im->multiaddr) && !sysctl_igmp_llm_reports)
+ return;
reporter = im->reporter;
igmp_stop_timer(im);
@@ -1213,6 +1232,8 @@
#ifdef CONFIG_IP_MULTICAST
if (im->multiaddr == IGMP_ALL_HOSTS)
return;
+ if (ipv4_is_local_multicast(im->multiaddr) && !sysctl_igmp_llm_reports)
+ return;
if (in_dev->dead)
return;
@@ -1518,6 +1539,9 @@
for_each_pmc_rtnl(in_dev, im) {
if (im->multiaddr == IGMP_ALL_HOSTS)
continue;
+ if (ipv4_is_local_multicast(im->multiaddr) &&
+ !sysctl_igmp_llm_reports)
+ continue;
/* a failover is happening and switches
* must be notified immediately
