[ovs-discuss] OVS bridge VS. Linux bridge: 2 libvirt's VMs both using OVS inside testlab

[Igor Podlesny]

The VMs have:
  - a virtio_net Ethernet adapter;
  - OVS installed and its bridge configured atop of that Eth. adapter.

When those VMs are connected to Linux "standard" bridge everything
works flawlessly: VMs can ping the hypervisor bridge by its IP, and
ping each other just fine.

When connecting a single one of them to the hypervisor's own
OVS-bridge no issues were spotted as well.
But simultaneous launch of both VMs is where it's gonna break. In this
example a ping from one VM to another echoed back but only once:

box-64-69% ping 192.168.64.70
PING 192.168.64.70 (192.168.64.70) 56(84) bytes of data.
64 bytes from 192.168.64.70: icmp_seq=1 ttl=64 time=4.88 ms
^C
--- 192.168.64.70 ping statistics ---
5 packets transmitted, 1 received, 80% packet loss, time 58ms
rtt min/avg/max/mdev = 4.879/4.879/4.879/0.000 ms

A set of q-ns arises:
  - Is it due to a loop? Enabling, say, RSTP across all 3 involved OVS
bridges doesn't change anything.
  - How to debug it?
  - And why does it differ from "standard" Linux bridge?

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