Networking services

In the initial architectural phases of designing your OpenStack Network infrastructure it is important to ensure appropriate expertise is available to assist with the design of the physical networking infrastructure, to identify proper security controls and auditing mechanisms.

OpenStack Networking adds a layer of virtualized network services which gives tenants the capability to architect their own virtual networks. Currently, these virtualized services are not as mature as their traditional networking counterparts. Consider the current state of these virtualized services before adopting them as it dictates what controls you may have to implement at the virtualized and traditional network boundaries.

L2 isolation using VLANs and tunneling

OpenStack Networking can employ two different mechanisms for traffic segregation on a per tenant/network combination: VLANs (IEEE 802.1Q tagging) or L2 tunnels using GRE encapsulation. The scope and scale of your OpenStack deployment determines which method you should utilize for traffic segregation or isolation.


VLANs are realized as packets on a specific physical network containing IEEE 802.1Q headers with a specific VLAN ID (VID) field value. VLAN networks sharing the same physical network are isolated from each other at L2, and can even have overlapping IP address spaces. Each distinct physical network supporting VLAN networks is treated as a separate VLAN trunk, with a distinct space of VID values. Valid VID values are 1 through 4094.

VLAN configuration complexity depends on your OpenStack design requirements. In order to allow OpenStack Networking to efficiently use VLANs, you must allocate a VLAN range (one for each tenant) and turn each compute node physical switch port into a VLAN trunk port.


If you intend for your network to support more than 4094 tenants VLAN is probably not the correct option for you as multiple ‘hacks’ are required to extend the VLAN tags to more than 4094 tenants.

L2 tunneling

Network tunneling encapsulates each tenant/network combination with a unique “tunnel-id” that is used to identify the network traffic belonging to that combination. The tenant’s L2 network connectivity is independent of physical locality or underlying network design. By encapsulating traffic inside IP packets, that traffic can cross Layer-3 boundaries, removing the need for preconfigured VLANs and VLAN trunking. Tunneling adds a layer of obfuscation to network data traffic, reducing the visibility of individual tenant traffic from a monitoring point of view.

OpenStack Networking currently supports both GRE and VXLAN encapsulation.

The choice of technology to provide L2 isolation is dependent upon the scope and size of tenant networks that will be created in your deployment. If your environment has limited VLAN ID availability or will have a large number of L2 networks, it is our recommendation that you utilize tunneling.

Network services

The choice of tenant network isolation affects how the network security and control boundary is implemented for tenant services. The following additional network services are either available or currently under development to enhance the security posture of the OpenStack network architecture.

Access control lists

OpenStack Compute supports tenant network traffic access controls directly when deployed with the legacy nova-network service, or may defer access control to the OpenStack Networking service.

Note, legacy nova-network security groups are applied to all virtual interface ports on an instance using iptables.

Security groups allow administrators and tenants the ability to specify the type of traffic, and direction (ingress/egress) that is allowed to pass through a virtual interface port. Security groups rules are stateful L2-L4 traffic filters.

When using the Networking service, we recommend that you enable security groups in this service and disable it in the Compute service.

L3 routing and NAT

OpenStack Networking routers can connect multiple L2 networks, and can also provide a gateway that connects one or more private L2 networks to a shared external network, such as a public network for access to the Internet.

The L3 router provides basic Network Address Translation (NAT) capabilities on gateway ports that uplink the router to external networks. This router SNATs (Static NAT) all traffic by default, and supports floating IPs, which creates a static one-to-one mapping from a public IP on the external network to a private IP on one of the other subnets attached to the router.

It is our recommendation to leverage per tenant L3 routing and Floating IPs for more granular connectivity of tenant VMs.

Quality of Service (QoS)

By default, Quality of Service (QoS) policies and rules are managed by the cloud administrator, which results in tenants being unable to create specific QoS rules, or to attach specific ports to policies. In some use cases, such as some telecommunications applications, the administrator may trust the tenants and therefore let them create and attach their own policies to ports. This can be achieved by modifying the policy.json file and specific documentation. will be released with the extension.

The Networking service (neutron) supports bandwidth-limiting QoS rules in Liberty and later. This QoS rule is named QosBandwidthLimitRule and it accepts two non-negative integers measured in kilobits per second:

  • max-kbps: bandwidth

  • max-burst-kbps: burst buffer

The QoSBandwidthLimitRule has been implemented in the neutron Open vSwitch, Linux bridge and single root input/output virtualization (SR-IOV) drivers.

In Newton, the QoS rule QosDscpMarkingRule was added. This rule marks the Differentiated Service Code Point (DSCP) value in the type of service header on IPv4 (RFC 2474) and traffic class header on IPv6 on all traffic leaving a virtual machine, where the rule is applied. This is a 6-bit header with 21 valid values that denote the drop priority of a packet as it crosses networks should it meet congestion. It can also be used by firewalls to match valid or invalid traffic against its access control list.

Port mirroring service involves sending a copy of packets entering or leaving one port to another port, which is usually different from the original destinations of the packets being mirrored. Tap-as-a-Service (TaaS) is an extension to the OpenStack networking service (neutron). It provides remote port mirroring capability for tenant virtual networks. This service has been primarily designed to help tenants (or the cloud administrator) debug complex virtual networks and gain visibility into their VMs, by monitoring the network traffic associated with them. TaaS honors tenant boundaries and its mirror sessions are capable of spanning across multiple compute and network nodes. It serves as an essential infrastructure component that can be utilized for supplying data to a variety of network analytics and security applications.

Load balancing

Another feature in OpenStack Networking is Load-Balancer-as-a-service (LBaaS). The LBaaS reference implementation is based on HA-Proxy. There are third-party plug-ins in development for extensions in OpenStack Networking to provide extensive L4-L7 functionality for virtual interface ports.


FW-as-a-Service (FWaaS) is considered an experimental feature for the Kilo release of OpenStack Networking. FWaaS addresses the need to manage and leverage the rich set of security features provided by typical firewall products which are typically far more comprehensive than what is currently provided by security groups. Both Freescale and Intel developed third-party plug-ins as extensions in OpenStack Networking to support this component in the Kilo release. For more details on the administration of FWaaS, see Firewall-as-a-Service (FWaaS) overview in the OpenStack Administrator Guide.

During the design of an OpenStack Networking infrastructure it is important that you understand the current features and limitations of available network services. Understanding the boundaries of your virtual and physical networks will assist in adding required security controls in your environment.

Network services extensions

A list of known plug-ins provided by the open source community or by SDN companies that work with OpenStack Networking is available at OpenStack neutron plug-ins and drivers wiki page.

Networking services limitations

OpenStack Networking has the following known limitations:

Overlapping IP addresses

If nodes that run either neutron-l3-agent or neutron-dhcp-agent use overlapping IP addresses, those nodes must use Linux network namespaces. By default, the DHCP and L3 agents use Linux network namespaces and run in their own respective namespaces. However, if the host does not support multiple namespaces, the DHCP and L3 agents should be run on separate hosts. This is due to the fact that there is no isloation between the IP addresses created by the L3 agent and the DHCP agent.

If network namespace support is not present, a further limitation of the L3 agent is that only a single logical router is supported.

Multi-host DHCP-agent

OpenStack Networking supports multiple L3 and DHCP agents with load balancing. However, tight coupling of the location of the virtual machine is not supported. In other words, the default Virtual Machine scheduler will not take the location of the agents into account when creating virtual machines.

No IPv6 support for L3 agents

The neutron-l3-agent, used by many plug-ins to implement L3 forwarding, supports only IPv4 forwarding.