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[Alan Pevec <1438819@xxxxxxxxxxxxxxxxxx>]

** Also affects: neutron/kilo
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1438819

Title:
  Router gets address allocation from all new gw subnets

Status in neutron:
  Fix Released
Status in neutron kilo series:
  New

Bug description:
  When a new subnet is created on an external network, all existing
  routers with gateways on the network will get a new address allocated
  from it.  This could be pretty bad for IPv4 networks where the
  addresses are scarce and therefore valuable.  In some cases, the
  entire new subnet could be consumed by router gateway ports alone.

  Adding an IP address replaces the default route on a Neutron router.
  In Kilo, Neutron now automatically allocates an IP address for the WAN
  interface on Neutron routers when a subnet on the external network is
  created. Previously, there was a check to allow a maximum of one IP
  address on a Neutron router gateway port. This check, however, was
  removed, and this patch replaces that check and allows one IPv6
  address in addition to the IPv4 address to support dual-stack.

  The combination of the automatic update of a router gateway port upon
  creation of a subnet and the absence of a check on the number of fixed
  IPs causes a change in behavior to that of Neutron in the Juno
  release.

  An issue is that creation of a subnet with a gateway IP on the
  external network replaces all default routes of Neutron routers on
  that network. This is not the behavior operators expect based on
  previous releases, and is most likely not the behavior they want - and
  as a result it could cause loss of external connectivity to tenants
  based on the network configuration.

  We need to validate a router's gateway port during creation and update
  of a router gateway port by ensuring it has no more than one v4 fixed
  IP and one v6 fixed IP.

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