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[OpenStack Infra <1876094@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/725369
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=f951871430ba59a148b8cb88e0d1b9e517c0a52e
Submitter: Zuul
Branch:    master

commit f951871430ba59a148b8cb88e0d1b9e517c0a52e
Author: Harald Jensås <hjensas@xxxxxxxxxx>
Date:   Mon May 4 20:01:35 2020 +0200

    Use dhcp-host tag support when supported
    
    In dnsmasq 2.81 there is a regression (see [1] for details).
    Prior versions of dnsmasq would select a host record where:
    a) no address is present in the host record.
    b) an address matching address family of the client request
       is present in the host record.
    
    dnsmasq 2.81 will also use a host record where a only an address
    not matching the address family of the client request is present.
    
    The same issue is also backported to the dnsmasq-2.79-11.el8.x86_64
    which is e.g. in RHEL 8.2 and Centos 8.
    
    dnsmasq version 2.81 also adds support for using tag's on host
    records. When a dhcpv6 request is received, dnsmasq automatically
    sets the tag 'dhcpv6'.
    
    This change adds a runtime check, testing for dnsmasq host entry
    tag support. And adds 'tag:dhcpv6' to all IPv6 host records when
    dnsmasq supports this.
    
    Adding the tag makes dnsmasq prefer the tagged host for dhcpv6
    requests, i.e it's a workaround fix for the regression issue.
    
    [1] http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2020q2/014051.html
    
    Closes-Bug: #1876094
    Change-Id: Ie654c84137914226bdc3e31e16219345c2efaac9


** Changed in: neutron
       Status: In Progress => Fix Released

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

Title:
  Dnsmasq 2.81 broke neutron's DHCP service

Status in neutron:
  Fix Released

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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