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[David Comay <1915480@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

The following code in DeviceManager's fill_dhcp_udp_checksums assumes
IPv6 is always enabled:

iptables_mgr = iptables_manager.IptablesManager(use_ipv6=True,
                                                namespace=namespace)

When iptables_mgr.apply() is later called, an attempt to add the UDP
checksum rule for DHCP is done via iptables-save/iptables-restore and if
IPv6 has been disabled on a hypervisor (eg, by setting `ipv6.disable=1`
on the kernel command line) then an many-line error occurs in the DHCP
agent logfile.

There should be a way of telling the agent that IPv6 is disabled and as
such, it should ignore trying to set up the UDP checksum rule for IPv6.
This can be easily achieved given that IptablesManager already has
support for disabling it.

We've seen this on Rocky on Ubuntu Bionic but it appears the issue still
exists on the master branch.

** Affects: neutron
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1915480

Title:
  DeviceManager's fill_dhcp_udp_checksums assumes IPv6 available

Status in neutron:
  New

Bug description:
  The following code in DeviceManager's fill_dhcp_udp_checksums assumes
  IPv6 is always enabled:

  iptables_mgr = iptables_manager.IptablesManager(use_ipv6=True,
                                                  namespace=namespace)

  When iptables_mgr.apply() is later called, an attempt to add the UDP
  checksum rule for DHCP is done via iptables-save/iptables-restore and
  if IPv6 has been disabled on a hypervisor (eg, by setting
  `ipv6.disable=1` on the kernel command line) then an many-line error
  occurs in the DHCP agent logfile.

  There should be a way of telling the agent that IPv6 is disabled and
  as such, it should ignore trying to set up the UDP checksum rule for
  IPv6. This can be easily achieved given that IptablesManager already
  has support for disabling it.

  We've seen this on Rocky on Ubuntu Bionic but it appears the issue
  still exists on the master branch.

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