Non-DHCP VLAN Network ARP Problem with OVN

Lazuardi Nasution mrxlazuardin at
Sun Feb 14 15:37:10 UTC 2021


One of our OpenStack clusters has a VLAN based network without DHCP
enabled. The cluster uses OVN for SDN.That network has to be like it since
it will be used for migrating the VMs from other platforms. I have untick
the DHCP enable feature on creating that network at Horizon. After the
network and subnet are created, I find that the DHCP port is still created
even though it is in a down state. I try to delete that port but after some
time, that port is back again.

When that DHCP port exists, we find that some VMs inside this OpenStack
cluster resolve the MAC address of the IP of that disabled DHCP port to the
MAC address of the DHCP port. The problem is coming since that IP is used
to an existing VM/server outside this OpenStack cluster at the same VLAN,
but it only happens for some VMs. Before this finding, I really disregard
the existence of the DHCP port since it is down and I don't enable the DHCP
feature. After that, I realize that it is a serious problem.

My questions are how to completely disable the DHCP feature for such a
network, including its DHCP port? How can DHCP disabled networks with a
down DHCP port still respond to the ARP request and why does it happen only
for some VMs?

Best regards,
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