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Reviewed:  https://review.opendev.org/c/openstack/neutron/+/799197
Committed: https://opendev.org/openstack/neutron/commit/be7d0bb6abc893e53dfc864c52506928b1d38fa3
Submitter: "Zuul (22348)"
Branch:    master

commit be7d0bb6abc893e53dfc864c52506928b1d38fa3
Author: Hemanth Nakkina <hemanth.nakkina@xxxxxxxxxxxxx>
Date:   Fri Jul 2 17:01:55 2021 +0530

    Update arp entry of snat port on qrouter ns
    
    In some cases, the arp entry of snat port is not updated
    in qrouter namespace. l3-agent calls get_ports_by_subnet()
    while setting arps for the subnet. And the snat port is
    not returned if it is still unbound. One of the scenario
    this is observed is when router is created, external
    gateway set and internal subnet attached to router in
    quick succession.
    
    This patch retrieves snat port details from router info
    as well and updates arp entry for snat port.
    
    Closes-Bug: #1933092
    Change-Id: I7ee797b4b930306cf6360922d855f8b24f1b813d


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

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https://bugs.launchpad.net/bugs/1933092

Title:
  snat arp entry missing in qrouter namespace

Status in neutron:
  Fix Released

Bug description:
  In one of the cloud environment, the FIP attached to the Octavia
  Loadbalancer VIP is not reachable. After analysis, we found the ARP
  entry for SNAT IP is missing in the qrouter namespace where Amphora VM
  is running. And so the return packets are not forwarded from qrouter
  to snat on active l3-agent node.

  Version:
  Ubuntu Ussuri packages (16.3.2 point release)
  DVR+SNAT+L3HA enabled

  Expectation is to have PERMANENT arp entry for snat ip on qrouter namespace on all compute nodes
  192.168.33.238 dev qr-4ee692e0-7a lladdr fa:16:3e:25:6a:73 used 38/38/38 probes 0 PERMANENT

  How to reproduce:

  Attaching a script to simulate the problem (without octavia) with following steps
  1. network/subnet/router is created, network attached to router
  2. verify if qrouter on all compute nodes has arp entries related to snat ip
  3. if arp entries exists, delete network/subnet/router
  4. Repeat steps 1,2,3 until missing arp entry is observed.

  I am able to reproduce missing arp entry sometimes in 3rd loop and
  sometimes in 6th loop.

  Observed arp entries for snat ip is updated at the following places
  [1] [2] but get_snat_interfaces() and get_ports_by_subnet() are not
  updated with snat ip in non-working cases.

  [1] https://opendev.org/openstack/neutron/src/commit/dfd04115b059c2263cdd8ac44ccc2ec47614bcc3/neutron/agent/l3/dvr_local_router.py#L570
  [2] https://opendev.org/openstack/neutron/src/commit/dfd04115b059c2263cdd8ac44ccc2ec47614bcc3/neutron/agent/l3/dvr_local_router.py#L317

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