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.
