Comment 14 for bug 1876094

Reviewed: https://review.opendev.org/726079
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=38afccc28a49c383c4649bcd385271cbb4b4c3a6
Submitter: Zuul
Branch: stable/ussuri

commit 38afccc28a49c383c4649bcd385271cbb4b4c3a6
Author: Harald Jensås <email address hidden>
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
    (cherry picked from commit f951871430ba59a148b8cb88e0d1b9e517c0a52e)