[ovs-discuss] ovs gratuitous arp (grARP) and duplicated IP

[Roman Dodin]

Hi all,
I have an issue in my lab setup where I have two containers: container1 and
container2
Container1 has OVS installed inside and a qemu VM which is connected with
its tap1 interface to the OVS bridge named *vr-ovs-tap1*
To the same *vr-ovs-tap1* OVS bridge I have container's *eth1* interface
connected:

[image: image.png]

ovs-vsctl show
5f076880-7c79-4e45-8fba-dd0ed58c2002
    Bridge vr-ovs-tap1
        datapath_type: netdev
        Port vr-ovs-tap1
            Interface vr-ovs-tap1
                type: internal
        Port eth1
            Interface eth1
        Port tap1
            Interface tap1
    ovs_version: "2.13.1"

The problem starts when I configure IP address in container2, let's say I
add 192.168.1.1/24 IP address on interface *eth1 *of container2.
Container2 sends broadcast ARPs to ensure that this address is available.

11 76.741180 EquipTra_ff:00:00 Broadcast ARP 60 Who has 192.168.1.1? (ARP
Probe)

Then it sends ARP announcement
12 78.740426 EquipTra_ff:00:00 Broadcast ARP 60 ARP Announcement for
192.168.1.1

And right after that announcement, OVS replies with grARP for the same IP,
which makes it a duplicate

13 78.804164 fa:c2:db:b4:bc:49 EquipTra_ff:00:00 ARP 42 Gratuitous ARP for
192.168.1.1 (Reply) (duplicate use of 192.168.1.1 detected!)

MAC fa:c2:db:b4:bc:49 belongs to OVS bridge:

6: vr-ovs-tap1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc
fq_codel state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether fa:c2:db:b4:bc:49 brd ff:ff:ff:ff:ff:ff

What is the proper way to fix this behaviour that leads to duplicate IP
addresses?

Attaching the pcap for completeness
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