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[Boden R <bodenvmw@xxxxxxxxx>]

Public bug reported:

Using neutron master with devstack all-in-one installation.

Under specific circumstances, the neutron dhcp agent (with dnsmasq
driver) will incorrectly create a new interface device rather than
reusing the existing one if the network's namespace is accidentally
deleted.

1. Neutron net created.
2. Neutron subnet created for network in step #1 with dhcp enabled.
3. Network dhcp namespace accidentally deleted.
4. New subnet added to network in #1 with dhcp enabled.
--> DHCP agent incorrectly creates a new interface device rather than reusing the existing. The initial iface is now "orphaned".


The script below reproduces the error on my devstack all-in-one:

------------
#!/bin/bash

source ~/devstack/openrc admin admin

neutron net-create dhcp-net

echo "Interfaces before..."
sudo ovs-vsctl show

neutron subnet-create dhcp-net 192.168.1.0/24 --name dhcp-subnet1

sleep 2

for ns in `sudo ip netns list | grep qdhcp-*`; do
   echo "Deleting namespace $ns"
   sudo ip netns delete ${ns}
done

neutron subnet-create dhcp-net 192.168.2.0/24 --name dhcp-subnet2

sleep 2

neutron net-delete dhcp-net

sleep 2

echo "Interfaces after..."
sudo ovs-vsctl show
------------


Sample ovs output from running the script:
--------
...
Interfaces before...
0b073a08-021d-49d9-b176-5008bf87ae39
    Manager "tcp:127.0.0.1:6632"
    Bridge br-int
        Port br-int
            Interface br-int
                type: internal
    ovs_version: "2.0.2"
...
Interfaces after...
0b073a08-021d-49d9-b176-5008bf87ae39
    Manager "tcp:127.0.0.1:6632"
    Bridge br-int
        Port br-int
            Interface br-int
                type: internal
        Port "tapcf35e3b7-06"
            Interface "tapcf35e3b7-06"
    ovs_version: "2.0.2"
--------

As shown in the output, a port device is left over, even after the
network + subnets are deleted.

** Affects: neutron
     Importance: Undecided
     Assignee: Boden R (boden)
         Status: New

** Changed in: neutron
     Assignee: (unassigned) => Boden R (boden)

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https://bugs.launchpad.net/bugs/1567049

Title:
  DHCP agent not reusing iface device when namespace is missing

Status in neutron:
  New

Bug description:
  Using neutron master with devstack all-in-one installation.

  Under specific circumstances, the neutron dhcp agent (with dnsmasq
  driver) will incorrectly create a new interface device rather than
  reusing the existing one if the network's namespace is accidentally
  deleted.

  1. Neutron net created.
  2. Neutron subnet created for network in step #1 with dhcp enabled.
  3. Network dhcp namespace accidentally deleted.
  4. New subnet added to network in #1 with dhcp enabled.
  --> DHCP agent incorrectly creates a new interface device rather than reusing the existing. The initial iface is now "orphaned".

  
  The script below reproduces the error on my devstack all-in-one:

  ------------
  #!/bin/bash

  source ~/devstack/openrc admin admin

  neutron net-create dhcp-net

  echo "Interfaces before..."
  sudo ovs-vsctl show

  neutron subnet-create dhcp-net 192.168.1.0/24 --name dhcp-subnet1

  sleep 2

  for ns in `sudo ip netns list | grep qdhcp-*`; do
     echo "Deleting namespace $ns"
     sudo ip netns delete ${ns}
  done

  neutron subnet-create dhcp-net 192.168.2.0/24 --name dhcp-subnet2

  sleep 2

  neutron net-delete dhcp-net

  sleep 2

  echo "Interfaces after..."
  sudo ovs-vsctl show
  ------------

  
  Sample ovs output from running the script:
  --------
  ...
  Interfaces before...
  0b073a08-021d-49d9-b176-5008bf87ae39
      Manager "tcp:127.0.0.1:6632"
      Bridge br-int
          Port br-int
              Interface br-int
                  type: internal
      ovs_version: "2.0.2"
  ...
  Interfaces after...
  0b073a08-021d-49d9-b176-5008bf87ae39
      Manager "tcp:127.0.0.1:6632"
      Bridge br-int
          Port br-int
              Interface br-int
                  type: internal
          Port "tapcf35e3b7-06"
              Interface "tapcf35e3b7-06"
      ovs_version: "2.0.2"
  --------

  As shown in the output, a port device is left over, even after the
  network + subnets are deleted.

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