On Sun, May 4, 2014 at 3:53 PM, Stephen Hemminger
<step...@networkplumber.org> wrote:
> On Mon, 5 May 2014 07:29:34 +1000
> Jon Maxwell <jmaxwel...@gmail.com> wrote:
>
>> 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 <jmaxw...@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))
>
> Ok, but please shorten the message to a single line without excess wordage.
> Plus flapping to mean means link going up and down. Maybe use same message
> as BSD?
Isn't this normal mac move? Any message will be confusing.
VMs can spoof their src macs and trigger this warning.
I don't think it's worth adding it just to debug the learning on the
external interface.
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