.. _config-ovsfwdriver: =================================== Open vSwitch Native Firewall Driver =================================== Historically, Open vSwitch (OVS) could not interact directly with *iptables* to implement security groups. Thus, the OVS agent and Compute service use a Linux bridge between each instance (VM) and the OVS integration bridge ``br-int`` to implement security groups. The Linux bridge device contains the *iptables* rules pertaining to the instance. In general, additional components between instances and physical network infrastructure cause scalability and performance problems. To alleviate such problems, the OVS agent includes an optional firewall driver that natively implements security groups as flows in OVS rather than the Linux bridge device and *iptables*. This increases scalability and performance. Configuring heterogeneous firewall drivers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ L2 agents can be configured to use differing firewall drivers. There is no requirement that they all be the same. If an agent lacks a firewall driver configuration, it will default to what is configured on its server. This also means there is no requirement that the server has any firewall driver configured at all, as long as the agents are configured correctly. Prerequisites ~~~~~~~~~~~~~ The native OVS firewall implementation requires kernel and user space support for *conntrack*, thus requiring minimum versions of the Linux kernel and Open vSwitch. All cases require Open vSwitch version 2.5 or newer. * Kernel version 4.3 or newer includes *conntrack* support. * Kernel version 3.3, but less than 4.3, does not include *conntrack* support and requires building the OVS modules. It also requires the conntrack kernel module(s) to be loaded, which varies depending on the kernel version. * Kernel version 4.19 or newer requires the *nf_conntrack* module. * Kernel versions 4.18 or older require the *nf_conntrack_ipv4* and *nf_conntrack_ipv6* modules. Enable the native OVS firewall driver ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * On nodes running the Open vSwitch agent, edit the ``openvswitch_agent.ini`` file and enable the firewall driver. .. code-block:: ini [securitygroup] firewall_driver = openvswitch For more information, see the :doc:`/contributor/internals/openvswitch_firewall` and the `video `_. Using GRE tunnels inside VMs with OVS firewall driver ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If GRE tunnels from VM to VM are going to be used, the native OVS firewall implementation requires ``nf_conntrack_proto_gre`` module to be loaded in the kernel on nodes running the Open vSwitch agent. It can be loaded with the command: .. code-block:: console # modprobe nf_conntrack_proto_gre Some Linux distributions have files that can be used to automatically load kernel modules at boot time, for example, ``/etc/modules``. Check with your distribution for further information. This isn't necessary to use ``gre`` tunnel network type Neutron. Differences between OVS and iptables firewall drivers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Both OVS and iptables firewall drivers should always behave in the same way if the same rules are configured for the security group. But in some cases that is not true and there may be slight differences between those drivers. +-------------------------------------+----------------+----------------------+ | Case | OVS | iptables | +=====================================+================+======================+ | Traffic marked as INVALID by | Blocked | Allowed because it | | conntrack but matching some of the | | first matches SG | | SG rules (please check [1]_ and | | rule, never reaches | | [2]_ for details) | | rule to drop invalid | | | | packets | +-------------------------------------+----------------+----------------------+ | Multicast traffic sent in the group | Allowed always | Blocked, | | 224.0.0.X | | Can be enabled by SG | | (please check [3]_ for details) | | rule. | +-------------------------------------+----------------+----------------------+ Open Flow rules processing considerations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The native Open vSwitch firewall driver increases the number of Open Flow rules to be installed in the integration bridge, that could be up to thousands of entries, depending on the number or rules, rule type and number of ports in the compute node. By default, these rules are written into the integration bridge in batches. The ``_constants.AGENT_RES_PROCESSING_STEP`` constant defines how many rules are written in a single operation. It is set to 100. As seen in `LP#1934917 `_, during the Open Flow processing (that could be better displayed during the OVS agent initial transient period), there could be some inconsistencies in the port rules. In order to avoid them, the configuration variable ``OVS.openflow_processed_per_port`` allows to process all Open Flow rules related to a single port in a single transaction. The following script provides a tool to measure, in each deployment, the processing time when using ``OVS.openflow_processed_per_port`` or the default ``_constants.AGENT_RES_PROCESSING_STEP``: .. code-block:: bash # (1) Create a network with a single IPv4 subnet openstack network create net-scale openstack subnet create --subnet-range 10.250.0.0/16 --network net-scale snet-scale # (2) Create 400 ports bound to one host for i in {1..400} do openstack port create \ --security-group \ --device-owner testing:scale \ --binding-profile host_id= \ --network net-scale test-large-scale-port-$i done # (3) Create 1000 security group rules, belonging to the same security # group for i in {3000..4000} do curl -g -i -X POST http://controller:9696/v2.0/security-group-rules \ -H "User-Agent: python-neutronclient" -H "Content-Type: application/json" \ -H "Accept: application/json" -H "X-Auth-Token: " \ -d '{ "security_group_rule": { "direction": "ingress", "protocol": "tcp", "ethertype": "IPv4", "port_range_max": "'$i'", "port_range_min": "3000", "security_group_id": } }' 2>&1 > /dev/null done # (4) Setup the port to the host # "grep" the test port list into file port_list. $ for p in `openstack port list -f value -c id -c name -c mac_address -c fixed_ips | grep test-large-scale-port` do mac=`echo $p | cut -f3 -d" "` ip_addr=`echo $p | cut -f7 -d" " | cut -f2 -d"'"` dev_id=`echo $p | cut -f1 -d" " | cut -b 1-11` dev_name="tp-$dev_id" echo "===" $mac "===" $ip_addr "===" $dev_id "===" $dev_name ovs-vsctl --may-exist add-port br-int ${dev_name} -- set Interface \ ${dev_name} type=internal \ -- set Interface ${dev_name} external-ids:attached-mac="${mac}" \ -- set Interface ${dev_name} external-ids:iface-id="${p}" \ -- set Interface ${dev_name} external-ids:iface-status=active sleep 0.2 ip link set dev ${dev_name} address ${mac} ip addr add ${ip_addr} dev ${dev_name} ip link set ${dev_name} up done # (5) Restart the OVS agent and check that all flows are in place. # (6) Check the OVS agent restart time, checking the "iteration" time and # number. Permitted ethertypes ~~~~~~~~~~~~~~~~~~~~ The OVS Firewall blocks traffic that does not have either the IPv4 or IPv6 ethertypes at present. This is a behavior change compared to the "iptables_hybrid" firewall, which only operates on IP packets and thus does not address other ethertypes. With the configuration option ``permitted_ethertypes`` it is possible to define a set of allowed ethertypes. Any traffic with these allowed ethertypes with destination to a local port or generated from a local port and MAC address, will be allowed. References ~~~~~~~~~~ .. [1] https://bugs.launchpad.net/neutron/+bug/1460741 .. [2] https://bugs.launchpad.net/neutron/+bug/1896587 .. [3] https://bugs.launchpad.net/neutron/+bug/1889631