FWaaS changes to support Distributed Virtual Router(DVR)


Problem description

As we move to the DVR model, current L3 based services such as FWaaS that rely on seeing both sides of the traffic on the same namespace router are broken. The reference implementation of FWaaS is built on iptables and is stateful in that connections are tracked. DVR by intent distributes the routing functionality across instances on compute nodes and all traffic is no longer routed through a centralized router to achieve goals of scalability.

Proposed change

To maintain FWaaS functionality in the context of a DVR deployment the first step (which is being targeted in this proposal) is to ensure that we can preserve current perimeter Firewall functionality (North - South) and ensure that the manner in which rules are applied does not break normal DVR East - West traffic flow.

DVR[1] classifies North - South traffic into two categories:

Default SNAT use case - traffic flowing out to the external network will go through the Network/Service Node, and the SNAT Namespace hosted there, to get out. Response traffic will again go thru the SNAT Namespace for translation and is then directly switched to the appropriate VM in a Compute Node.

VMs with Floating IPs(FIP) use case - traffic flowing out will go through the Internal Router for routing and translation and then through the FIP Namespace on the Compute Node to the external network through its br-ex. And on the incoming traffic, again the flow is through the br-ex on the Compute Node, then the FIP Namespace and through the Internal Router which also handles translation to the VM.

DVR runs L3Agent on the Network Node as well as on the Compute Nodes. Since the FWaaS Agent runs in the context of the L3Agent, the FWaaS Plugin to Agent messaging is already available. In the context of both of the above use cases, FWaaS Agent on the Network/Service Node should install the Firewall Rules in the SNAT Namespace, and the FWaaS Agent in the Compute Nodes should install the Firewall Rules in the IR Namespace to be applied on traffic flowing through the FIP Namespace (to ensure that there is no effect on East - West flows). In this manner, the FWaaS requirement of seeing traffic on both directions is satisfied for both of these use cases. FWaaS Agent can use the agent_mode configuration option to determine whether it is on a Network/Service node or Compute node to make the determination on how to install the rules.

The SNAT interfaces are prefixed with ‘sq-‘ in the SNAT namespace. The interface of interest in the IR namespace has the prefix ‘rfp-‘. The API’s being added as part of DVR support in the L3Agent[2] will be used by the FWaaS Agent to make this determination for inserting the Firewall Rules appropriately.


None. This is required as DVR - FWaaS integration will be broken.

Data model impact

No impact, the changes are on the Agent/iptables Driver.

REST API impact

No new REST API is introduced.

Security impact

The effort is to minimize the Security impact as DVR functionality breaks FWaaS. Coverage for North - South traffic but no support for East - West traffic which will be addressed as a separate proposal post Juno.

Notifications impact

None to existing.

Other end user impact

No Support for FWaaS on East - West traffic.

Performance Impact


Other deployer impact

Deployers should be aware that this only targets North - South functionality.

Developer impact




Primary assignee: skandasw / badveli_vishnuus / (TBD) Other contributors: TBD

Work Items

  • FWaaS Agent changes to recognize agent_mode to identify appropriate Namespace and interface.
  • Corresponding FWaaS driver changes.


Patches awaiting merge on [1].


Unit tests, Tempest API tests.

Documentation Impact

DVR and FWaaS documentation changes to reflect requirements.