yahoo-eng-team team mailing list archive

[Sebastian Lohff <2063459@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

When creating a network with two subnets the DHCP agent will choose any
subnet that has a gateway_ip (which is allocated and set by default). In
cases where only one of the subnets is attached to a router (which the
DHCP agent needs to access resources outside of the internal network
like an upstream DNS server), the DHCP agent will still arbitrarily
choose one of the available subnets. If it chooses the subnet not on a
router, service will be disrupted for that network namespace. The sort
order of subnet is arbitrary, but stable, but if a subnet is being added
to a network the DHCP agent might also switch over to this network.

Problem was observed with Neutron Yoga, but can be reproduced with
current upstream code.

To fix this I would propose to sort subnet gateway selection to first use
subnets that have a port that matches the gateway ip of the subnet, as they'll have a higher likelihood of being connected.

** Affects: neutron
     Importance: Undecided
         Status: In Progress

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https://bugs.launchpad.net/bugs/2063459

Title:
  DHCP agent might use default gateway of unrouted subnets

Status in neutron:
  In Progress

Bug description:
  When creating a network with two subnets the DHCP agent will choose
  any subnet that has a gateway_ip (which is allocated and set by
  default). In cases where only one of the subnets is attached to a
  router (which the DHCP agent needs to access resources outside of the
  internal network like an upstream DNS server), the DHCP agent will
  still arbitrarily choose one of the available subnets. If it chooses
  the subnet not on a router, service will be disrupted for that network
  namespace. The sort order of subnet is arbitrary, but stable, but if a
  subnet is being added to a network the DHCP agent might also switch
  over to this network.

  Problem was observed with Neutron Yoga, but can be reproduced with
  current upstream code.

  To fix this I would propose to sort subnet gateway selection to first use
  subnets that have a port that matches the gateway ip of the subnet, as they'll have a higher likelihood of being connected.

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