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[Slawek Kaplonski <1876094@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

With dnsmasq 2.81 DHCP for instances connected to network with both IPv4 and IPv6 dhcp-stateful networks will not work as it should. Dnsmasq is processing "host" file's entries from the bottom to the top and as neutron always places first IPv4 and then IPv6 addresses for same MAC, DHCP for IPv4 will not work now.
Details are in Harald's email: http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2020q2/014038.html

Basically it's not Neutron's fault but regression in dnsmasq, but we can
workaround it by changing how we generate host file. If it will be one
line per mac address, like:

fa:16:3e:b2:5f:a2,host-10-0-0-72.openstacklocal,[fd05:321f:2d56:1::b5]
fa:16:3e:08:f4:1f,host-10-0-0-2.openstacklocal,10.0.0.2,[fd05:321f:2d56:1::2]
fa:16:3e:9d:76:87,host-10-0-0-31.openstacklocal,10.0.0.31,[fd05:321f:2d56:1::8]
fa:16:3e:9f:f9:a5,host-10-0-0-60.openstacklocal,10.0.0.60,[fd05:321f:2d56:1::30a]
fa:16:3e:8c:47:e5,host-10-0-0-1.openstacklocal,10.0.0.1

then it should works fine in both dnsmasq 2.81 and older versions.

** Affects: neutron
     Importance: Undecided
     Assignee: Slawek Kaplonski (slaweq)
         Status: New


** Tags: l3-ipam-dhcp

** Changed in: neutron
     Assignee: (unassigned) => Slawek Kaplonski (slaweq)

** Tags added: l3-ipam-dhcp

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https://bugs.launchpad.net/bugs/1876094

Title:
  Dnsmasq 2.81 broke neutron's DHCP service

Status in neutron:
  New

Bug description:
  With dnsmasq 2.81 DHCP for instances connected to network with both IPv4 and IPv6 dhcp-stateful networks will not work as it should. Dnsmasq is processing "host" file's entries from the bottom to the top and as neutron always places first IPv4 and then IPv6 addresses for same MAC, DHCP for IPv4 will not work now.
  Details are in Harald's email: http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2020q2/014038.html

  Basically it's not Neutron's fault but regression in dnsmasq, but we
  can workaround it by changing how we generate host file. If it will be
  one line per mac address, like:

  fa:16:3e:b2:5f:a2,host-10-0-0-72.openstacklocal,[fd05:321f:2d56:1::b5]
  fa:16:3e:08:f4:1f,host-10-0-0-2.openstacklocal,10.0.0.2,[fd05:321f:2d56:1::2]
  fa:16:3e:9d:76:87,host-10-0-0-31.openstacklocal,10.0.0.31,[fd05:321f:2d56:1::8]
  fa:16:3e:9f:f9:a5,host-10-0-0-60.openstacklocal,10.0.0.60,[fd05:321f:2d56:1::30a]
  fa:16:3e:8c:47:e5,host-10-0-0-1.openstacklocal,10.0.0.1

  then it should works fine in both dnsmasq 2.81 and older versions.

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