** Description changed:

  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)
+                                                 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.
+ 
+ =================================
+ Ubuntu SRU details:
+ 
+ [Impact]
+ See above.
+ 
+ [Test Case]
+ Deploy openstack on a hypervisor with IPv6 disabled.
+ Create a network which has a subnetwork with DHCP enabled.
+ Search the `neutron-dhcp-agent.log` (with debug log enabled) and check if 
there are any `ip6tables-restore` commands.
+ 
+ [Regression Potential]
+ Minimal.
+ Users which were relying on the setting to always be true could be affected.

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

Title:
  DeviceManager's fill_dhcp_udp_checksums assumes IPv6 available

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