There has been a number incidents recently where customers running KVM have
reported that VM hosts on different Hypervisors are unreachable. Based on pcap
traces we found that the bridge was broadcasting the ARP request out onto the
network. However some NICs have an inbuilt switch which on occasions were
broadcasting the VMs ARP request back through the physical NIC on the
Hypervisor. This resulted in the bridge flapping ports and incorrectly learning
that the VMs mac address was external. As a result the ARP reply was directed
back onto the external network and VM never updated it's ARP cache. This
patch will detect port flapping and log a message so that this condition can be
detected earlier.
Signed-off-by: Jon Maxwell <jmaxwell@redhat.com>
---
net/bridge/br_fdb.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 9203d5a..c08607b 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -507,6 +507,13 @@ void br_fdb_update(struct net_bridge *br, struct
net_bridge_port *source,
source->dev->name);
} else {
/* fastpath: update of existing entry */
+ if (source->port_no != fdb->dst->port_no &&
+ net_ratelimit())
+ br_warn(br, "Port flapping detected source entry dev = %s mac = %pM,
port_no = %d\n existing entry dev = %s mac = %pM, port_no = %d\n",
+ source->dev->name,
+ addr, source->port_no,
+ fdb->dst->dev->name, addr,
+ fdb->dst->port_no);
fdb->dst = source;
fdb->updated = jiffies;
if (unlikely(added_by_user))
--
1.8.3.1