Securing OpenStack networking services

This section discusses OpenStack Networking configuration best practices as they apply to project network security within your OpenStack deployment.

Project network services workflow

OpenStack Networking provides users self services of network resources and configurations. It is important that cloud architects and operators evaluate their design use cases in providing users the ability to create, update, and destroy available network resources.

Networking resource policy engine

A policy engine and its configuration file, policy.json, within OpenStack Networking provides a method to provide finer grained authorization of users on project networking methods and objects. The OpenStack Networking policy definitions affect network availability, network security and overall OpenStack security. Cloud architects and operators should carefully evaluate their policy towards user and project access to administration of network resources. For a more detailed explanation of OpenStack Networking policy definition, please refer to the Authentication and authorization section in the OpenStack Administrator Guide.


It is important to review the default networking resource policy, as this policy can be modified to suit your security posture.

If your deployment of OpenStack provides multiple external access points into different security domains it is important that you limit the project’s ability to attach multiple vNICs to multiple external access points—this would bridge these security domains and could lead to unforeseen security compromise. It is possible mitigate this risk by utilizing the host aggregates functionality provided by OpenStack Compute or through splitting the project VMs into multiple project projects with different virtual network configurations.

Security groups

The OpenStack Networking service provides security group functionality using a mechanism that is more flexible and powerful than the security group capabilities built into OpenStack Compute. Thus, nova.conf should always disable built-in security groups and proxy all security group calls to the OpenStack Networking API when using OpenStack Networking. Failure to do so results in conflicting security policies being simultaneously applied by both services. To proxy security groups to OpenStack Networking, use the following configuration values:

  • firewall_driver must be set to nova.virt.firewall.NoopFirewallDriver so that nova-compute does not perform iptables-based filtering itself.

  • security_group_api must be set to neutron so that all security group requests are proxied to the OpenStack Networking service.

A security group is a container for security group rules. Security groups and their rules allow administrators and projects the ability to specify the type of traffic and direction (ingress/egress) that is allowed to pass through a virtual interface port. When a virtual interface port is created in OpenStack Networking it is associated with a security group. For further details on the default behavior of port security groups, reference the Networking Security Group Behavior documentation. Rules can be added to the default security group in order to change the behavior on a per-deployment basis.

When using the OpenStack Compute API to modify security groups, the updated security group applies to all virtual interface ports on an instance. This is due to the OpenStack Compute security group APIs being instance-based rather than port-based, as found in OpenStack Networking.


Quotas provide the ability to limit the number of network resources available to projects. You can enforce default quotas for all projects. The /etc/neutron/neutron.conf includes these options for quota:

# resource name(s) that are supported in quota features
quota_items = network,subnet,port

# default number of resource allowed per tenant, minus for unlimited
#default_quota = -1

# number of networks allowed per tenant, and minus means unlimited
quota_network = 10

# number of subnets allowed per tenant, and minus means unlimited
quota_subnet = 10

# number of ports allowed per tenant, and minus means unlimited
quota_port = 50

# number of security groups allowed per tenant, and minus means unlimited
quota_security_group = 10

# number of security group rules allowed per tenant, and minus means unlimited
quota_security_group_rule = 100

# default driver to use for quota checks
quota_driver = neutron.quota.ConfDriver

OpenStack Networking also supports per-project quotas limit through a quota extension API. To enable per-project quotas, you must set the quota_driver option in neutron.conf.

quota_driver = neutron.db.quota.driver.DbQuotaDriver

Mitigate ARP spoofing

When using flat networking, you cannot assume that projects which share the same layer 2 network (or broadcast domain) are fully isolated from each other. These projects may be vulnerable to ARP spoofing, risking the possibility of man-in-the-middle attacks.

If using a version of Open vSwitch that supports ARP field matching, you can help mitigate this risk by enabling the prevent_arp_spoofing option for the Open vSwitch agent. This option prevents instances from performing spoof attacks; it does not protect them from spoof attacks. Note that this setting is expected to be removed in Ocata, with the behavior becoming permanently active.

For example, in /etc/neutron/plugins/ml2/openvswitch_agent.ini:

prevent_arp_spoofing = True

Plug-ins other than Open vSwitch may also include similar mitigation measures; it is recommended you enable this feature, where appropriate.


Even with prevent_arp_spoofing enabled, flat networking does not provide a complete level of project isolation, as all project traffic is still sent to the same VLAN.