On Fri, Dec 15, 2017 at 5:55 PM, Stephen Hemminger
<stephen@xxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 15 Dec 2017 15:37:39 +0200
> Adrian P <adrian27oradea@xxxxxxxxx> wrote:
>
>> Hello,
>>
>> I have a strange issue with a linux bridge created by
>> openstack-neutron (pike release). This linux bridge is hosted in a
>> vmware VM running latest CentOS 7, with a single network interface in
>> promiscuous mode.
>>
>> From openstack neutron perspective, the networking setup is simple: a
>> single flat external provider network, with a single cirros VM
>> instance connected to it.
>>
>> Therefore, in the linux bridge running in the vmware host, I have 3 interfaces:
>>
>> # brctl show
>> bridge name bridge id STP enabled interfaces
>> brq025a9a94-58 8000.005056a6b378 no ens160
>> tap2eb4cad6-cd
>> <----- neutron DHCP agent tap interface
>> tap6d31a191-9f
>> <----- cirros VM instance tap interface
>>
>> The ens160 is the "physical" CentOS 7 host interface, that is in
>> promiscuous mode.
>>
>> The tap2eb4cad6-cd tap interface is the neutron DHCP agent interface,
>> and the tap6d31a191-9f tap interface is used by the cirros VM
>> instance.
>>
>> The problem is the following:
>>
>> With a tcpdump, I am able to see the arp request (ARP, Request who-has
>> 10.20.21.1 tell 10.20.21.233) going out from the cirros VM instance on
>> tap interface tap6d31a191-9f, and well as on the bridge itself
>> (brq025a9a94-58). However, the reply back to the arp request (Reply
>> 10.20.21.1 is-at 00:17:08:c4:52:80) does not reach the cirros VM
>> instance anymore. With tcpdump, I am able to see the arp reply back
>> packets in the bridge (brq025a9a94-58), however they do not show up
>> anymore on the cirros VM instance tap interface tap6d31a191-9f.
>>
>> To me it seems that for whatever reason, the bridge does not forward
>> the arp reply back packets to the cirros VM tap interface, and I do
>> not understand why. The strange thing is that after a while, for
>> apparently no reason, a single arp reply back packet gets through the
>> bridge and the tap interface, and the arp table gets updated with
>> correct IP address in the cirros VM instance. However, if I clean up
>> the arp table in the cirros VM instance, it takes again 10 to 15
>> minutes of continuously sending arp requests, until a single arp reply
>> back packets gets through.
>>
>> I was banging my head to the table for a few days with this issue, and
>> finally, for apparent no reason, I manually configured the bridge max
>> aging time to 0, to convert it in a hub, and from that moment
>> everything started to work without any issue. Still, I do no
>> understand why is this happening, and obviously I cannot manually set
>> up the bridge aging time to 0 all the time in all the bridges
>> openstack neutron creates automatically.
>>
>> Any thoughts?
>>
>> Many thanks in advance.
>>
>> Best regards,
>> Adrian
>
> Does each tap instance and the ens160 have a different and valid Ethernet
> address? Also make sure the these are in the bridge forwarding table.
Yes, they have valid Ethernet addresses, and they do show up in the
forwarding table twice, see below:
# ip addr
<...>
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master
brq025a9a94-58 state UP qlen 1000
link/ether 00:50:56:a6:b3:78 brd ff:ff:ff:ff:ff:ff
inet6 fe80::250:56ff:fea6:b378/64 scope link
valid_lft forever preferred_lft forever
4: tap2eb4cad6-cd@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
qdisc noqueue master brq025a9a94-58 state UP qlen 1000
link/ether 8a:b2:15:4c:96:55 brd ff:ff:ff:ff:ff:ff link-netnsid 0
5: brq025a9a94-58: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc
noqueue state UP qlen 1000
link/ether 00:50:56:a6:b3:78 brd ff:ff:ff:ff:ff:ff
inet 10.20.21.249/24 brd 10.20.21.255 scope global brq025a9a94-58
valid_lft forever preferred_lft forever
inet6 fe80::803d:d0ff:fe2e:3ae4/64 scope link
valid_lft forever preferred_lft forever
6: tap6d31a191-9f: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc
pfifo_fast master brq025a9a94-58 state UNKNOWN qlen 1000
link/ether fe:16:3e:9a:04:95 brd ff:ff:ff:ff:ff:ff
inet6 fe80::fc16:3eff:fe9a:495/64 scope link
valid_lft forever preferred_lft forever
# brctl showmacs brq025a9a94-58
port no mac addr is local? ageing timer
1 00:50:56:a6:b3:78 yes 0.00
1 00:50:56:a6:b3:78 yes 0.00
2 8a:b2:15:4c:96:55 yes 0.00
2 8a:b2:15:4c:96:55 yes 0.00
3 fe:16:3e:9a:04:95 yes 0.00
3 fe:16:3e:9a:04:95 yes 0.00
