[Bug 1916761] Re: [dvr] bound port permanent arp entries never deleted

[LIU Yulong]

** Changed in: neutron
     Assignee: Edward Hope-Morley (hopem) => LIU Yulong (dragon889)

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https://bugs.launchpad.net/bugs/1916761

Title:
  [dvr] bound port permanent arp entries never deleted

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive train series:
  New
Status in Ubuntu Cloud Archive ussuri series:
  New
Status in Ubuntu Cloud Archive victoria series:
  New
Status in neutron:
  In Progress
Status in neutron package in Ubuntu:
  New
Status in neutron source package in Focal:
  New
Status in neutron source package in Groovy:
  New
Status in neutron source package in Hirsute:
  New

Bug description:
  With Openstack Ussuri using dvr-snat I do the following:

    * create port P1 with address A1 and create vm on node C1 with this port
    * associate floating ip with P1 and ping it
    * observe REACHABLE arp entry for A1 in qrouter arp cache
    * so far so good
    * restart the neutron-l3-agent
    * observe REACHABLE arp entry for A1 is now PERMANENT
    * delete vm and port
    * create port P2 with address A1 and create vm on node C1 with this port
    * vm is unreachable since arp cache contains PERMANENT entry for old port P1 mac/ip combo

  If I don't restart the l3-agent, once I have deleted the port it's arp
  entry does REACHABLE -> STALE and will either be replaced or timeout
  as expected but once it is set to PERMANENT it will never disappear
  which means any future use of that ip address (by a port with a
  different mac) will not work until that entry is manually deleted.

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