[Bug 2051935] Re: [OVN] SNAT only happens for subnets directly connected to a router

[Brian Haley]

I just tested Ihar's patch using 0.0.0.0/0 for snat, along with Ales'
OVN change and various seemed to work - fixed to fixed, fip to fip and
others.

The only thing I couldn't do is associated a floating IP to a VM on a
nested network:

$ openstack floating ip set --port e9bca1a2-4672-482a-a3e6-a01dc4671a83 63711dab-40a3-4da3-b4d2-b48c9889b472
ResourceNotFound: 404: Client Error for url: http://172.16.0.158:9696/networking/v2.0/floatingips/63711dab-40a3-4da3-b4d2-b48c9889b472, External network 53133eed-dd5a-4f64-9187-92cfaf609489 is not reachable from subnet 35b38c51-6225-401d-982a-0f51a2c327b3.  Therefore, cannot associate Port e9bca1a2-4672-482a-a3e6-a01dc4671a83 with a Floating IP.

I think we already have a bug open for that, I think the API is looking
at the router's interfaces and barfing, should be more forgiving.

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https://bugs.launchpad.net/bugs/2051935

Title:
  [OVN] SNAT only happens for subnets directly connected to a router

Status in neutron:
  In Progress
Status in neutron package in Ubuntu:
  New

Bug description:
  I am trying to achieve the following scenario:

  I have a VM attached to a router w/o external gateway (called project-
  router) but with a default route which send all the traffic to another
  router (transit router) which has an external gateway with snat
  enabled and it is connected to a transit network 192.168.100.0/24

  My VM is  on 172.16.100.0/24, traffic hits the project-router thanks
  to the default route gets redirected to the transit-router correctly,
  here it gets into the external gateway but w/o being snat.

  This is because in ovn I see that SNAT on this router is only enabled
  for logical ip in 192.168.100.0/24 which is the subnet directly
  connected to the router

  # ovn-nbctl lr-nat-list neutron-6d1e6bb7-3949-43d1-8dac-dc55155b9ad8
  TYPE             EXTERNAL_IP        EXTERNAL_PORT    LOGICAL_IP            EXTERNAL_MAC         LOGICAL_PORT
  snat             147.22.16.207                       192.168.100.0/24

  But I would like that this router snat all the traffic that hits it,
  even when coming from a subnet not directly connected to it.

  I can achieve this by setting in ovn the snat for 0.0.0.0/0

  # ovn-nbctl lr-nat-add neutron-6d1e6bb7-3949-43d1-8dac-dc55155b9ad8
  snat 147.22.16.207 0.0.0.0/0

  # ovn-nbctl lr-nat-list neutron-6d1e6bb7-3949-43d1-8dac-dc55155b9ad8
  TYPE             EXTERNAL_IP        EXTERNAL_PORT    LOGICAL_IP            EXTERNAL_MAC         LOGICAL_PORT
  snat             147.22.16.207                       0.0.0.0/0
  snat             147.22.16.207                       192.168.100.0/24

  But this workaround can be wiped if I run the neutron-ovn-db-sync-util
  on any of the neutron-api unit.

  Is there a way to achieve this via OpenStack? If not does it make
  sense to have this as a new feature?

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