[ovs-discuss] Fwd: 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 Container2 broadcasts the ARP announcement with its IP address:
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 from Container2 standpoint

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, from which grARP is being sent belongs to the 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 as that leads to duplicate IP
addresses on Container2 and prevents it from using this IP?

Attaching the pcap captured on eth1 interface of Container2 for completeness
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