path: root/net
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authorBob Arendt <rda@rincon.com>2010-09-13 12:56:03 -0700
committerDavid S. Miller <davem@davemloft.net>2010-09-13 12:56:51 -0700
commit7998156344b0d93de61ff8e5d75e96500e43a571 (patch)
treeac9d61004b6332c745f20cae58ea130868981701 /net
parent3429769bc67c7a48b3c01b2452b32171b3450202 (diff)
ipv4: force_igmp_version ignored when a IGMPv3 query received
After all these years, it turns out that the /proc/sys/net/ipv4/conf/*/force_igmp_version parameter isn't fully implemented. *Symptom*: When set force_igmp_version to a value of 2, the kernel should only perform multicast IGMPv2 operations (IETF rfc2236). An host-initiated Join message will be sent as a IGMPv2 Join message. But if a IGMPv3 query message is received, the host responds with a IGMPv3 join message. Per rfc3376 and rfc2236, a IGMPv2 host should treat a IGMPv3 query as a IGMPv2 query and respond with an IGMPv2 Join message. *Consequences*: This is an issue when a IGMPv3 capable switch is the querier and will only issue IGMPv3 queries (which double as IGMPv2 querys) and there's an intermediate switch that is only IGMPv2 capable. The intermediate switch processes the initial v2 Join, but fails to recognize the IGMPv3 Join responses to the Query, resulting in a dropped connection when the intermediate v2-only switch times it out. *Identifying issue in the kernel source*: The issue is in this section of code (in net/ipv4/igmp.c), which is called when an IGMP query is received (from mainline 2.6.36-rc3 gitweb): ... A IGMPv3 query has a length >= 12 and no sources. This routine will exit after line 880, setting the general query timer (random timeout between 0 and query response time). This calls igmp_gq_timer_expire(): ... .. which only sends a v3 response. So if a v3 query is received, the kernel always sends a v3 response. IGMP queries happen once every 60 sec (per vlan), so the traffic is low. A IGMPv3 query *is* a strict superset of a IGMPv2 query, so this patch properly short circuit's the v3 behaviour. One issue is that this does not address force_igmp_version=1. Then again, I've never seen any IGMPv1 multicast equipment in the wild. However there is a lot of v2-only equipment. If it's necessary to support the IGMPv1 case as well: 837 if (len == 8 || IGMP_V2_SEEN(in_dev) || IGMP_V1_SEEN(in_dev)) { Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index a1ad0e7180d..1fdcacd36ce 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -834,7 +834,7 @@ static void igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
int mark = 0;
- if (len == 8) {
+ if (len == 8 || IGMP_V2_SEEN(in_dev)) {
if (ih->code == 0) {
/* Alas, old v1 router presents here. */