Open Virtual Network (OVN)

Overview

Open Virtual Network (OVN) can be deployed to provide networking services as part of an OpenStack cloud.

Note

There are feature gaps from ML2/OVS and deploying legacy ML2/OVS with the OpenStack Charms is still available.

OVN charms:

• neutron-api-plugin-ovn

• ovn-central

• ovn-chassis

• ovn-dedicated-chassis

Note

OVN is supported by Charmed OpenStack starting with OpenStack Train. OVN is the default configuration in the OpenStack Base bundle reference implementation.

Deployment

OVN makes use of Public Key Infrastructure (PKI) to authenticate and authorize control plane communication. The charm requires a Certificate Authority to be present in the model as represented by the certificates relation. Certificates must be managed by Vault.

Note

For Vault deployment instructions see the vault charm. For certificate management information read the Managing TLS certificates section of this guide.

To deploy OVN:

juju config neutron-api manage-neutron-plugin-legacy-mode=false

juju deploy neutron-api-plugin-ovn
juju deploy ovn-central -n 3 --config source=cloud:bionic-ussuri
juju deploy ovn-chassis

juju add-relation neutron-api-plugin-ovn:certificates vault:certificates
juju add-relation neutron-api-plugin-ovn:neutron-plugin \
    neutron-api:neutron-plugin-api-subordinate
juju add-relation neutron-api-plugin-ovn:ovsdb-cms ovn-central:ovsdb-cms
juju add-relation ovn-central:certificates vault:certificates
juju add-relation ovn-chassis:ovsdb ovn-central:ovsdb
juju add-relation ovn-chassis:certificates vault:certificates
juju add-relation ovn-chassis:nova-compute nova-compute:neutron-plugin

The OVN components used for the data plane is deployed by the ovn-chassis subordinate charm. A subordinate charm is deployed together with a principle charm, nova-compute in the example above.

If you require a dedicated software gateway you may deploy the data plane components as a principle charm through the use of the ovn-dedicated-chassis charm.

Note

For a concrete example take a look at the OpenStack Base bundle.

High availability

OVN is HA by design; take a look at the OVN section of the Infrastructure high availability page.

Configuration

OVN integrates with OpenStack through the OVN ML2 driver. On OpenStack Ussuri and onwards the OVN ML2 driver is maintained as an in-tree driver in Neutron. On OpenStack Train it is maintained separately as per the networking-ovn plugin.

General Neutron configuration is still done through the neutron-api charm, and the subset of configuration specific to OVN is done through the neutron-api-plugin-ovn charm.

Hardware offloading support

It is possible to configure chassis to prepare network interface cards (NICs) for use with hardware offloading and make them available to OpenStack.

Caution

This feature is to be considered Tech Preview. OVN has more stringent requirements for match/action support in the hardware than for example Neutron ML2+OVS. Make sure to acquire hardware with appropriate support.

Depending on hardware vendor, it may be required to install third party drivers (DKMS) in order to successfully use this feature.

Hardware offload support makes use of SR-IOV as an underlying mechanism to accelerate the data path between a virtual machine instance and the NIC hardware. But as opposed to traditional SR-IOV support the accelerated ports can be connected to the Open vSwitch integration bridge which allows instances to take part in regular tenant networks. The NIC also supports hardware offloading of tunnel encapsulation and decapsulation.

With OVN the Layer3 routing features are implemented as flow rules in Open vSwitch. This in turn may allow Layer 3 routing to also be offloaded to NICs with appropriate driver and firmware support.

Prerequisites

• Ubuntu 22.04 LTS or later

• Linux kernel >= 5.15

• Open vSwitch 2.17

• OVN 22.03

• OpenStack Yoga or later

Please refer to the SR-IOV for networking support section for information on kernel configuration.

Charm configuration

The below example bundle excerpt will enable hardware offloading for an OVN deployment.

applications:
  ovn-chassis:
    charm: cs:ovn-chassis
    options:
      enable-hardware-offload: true
      sriov-numvfs:  "enp3s0f0:32 enp3s0f1:32"
  neutron-api:
    charm: cs:neutron-api
    options:
      enable-hardware-offload: true
  nova-compute:
    charm: cs:nova-compute
    options:
      pci-passthrough-whitelist: '{"address": "*:03:*", "physical_network": null}'

Caution

After deploying the above example the machines hosting ovn-chassis units must be rebooted for the changes to take effect.

Boot an instance

Now we can tell OpenStack to boot an instance and attach it to an hardware offloaded port. This must be done in two stages, first we create a port with vnic-type ‘direct’ and binding-profile with ‘switchdev’ capabilities. Then we create an instance connected to the newly created port:

openstack port create --network my-network --vnic-type direct \
    --binding-profile '{"capabilities": ["switchdev"]}' direct_port1
openstack server create --flavor my-flavor --key-name my-key \
    --nic port-id=direct_port1 my-instance

Validate that traffic is offloaded

The traffic control monitor command can be used to observe updates to filters which is one of the mechanisms used to program the NIC switch hardware. Look for the ‘in_hw’ and ‘not_in_hw’ labels.

sudo tc monitor

replaced filter dev eth62 ingress protocol ip pref 3 flower chain 0 handle 0x9
  dst_mac fa:16:3e:b2:20:82
  src_mac fa:16:3e:b9:db:c8
  eth_type ipv4
  ip_proto tcp
  ip_tos 67deeb90
  dst_ip 10.42.0.17/28
  tcp_flags 22
  ip_flags nofrag
  in_hw
    action order 1: tunnel_key set
    src_ip 0.0.0.0
    dst_ip 10.6.12.8
    key_id 4
    dst_port 6081
    csum pipe
    index 15 ref 1 bind 1

    action order 2: mirred (Egress Redirect to device genev_sys_6081) stolen
    index 18 ref 1 bind 1
    cookie d4885b4d38419f7fd7ae77a11bc78b0b

Open vSwitch has a rich set of tools to monitor traffic flows and you can use the data path control tools to monitor offloaded flows.

sudo ovs-appctl dpctl/dump-flows type=offloaded

tunnel(tun_id=0x4,src=10.6.12.3,dst=10.6.12.7,tp_dst=6081,geneve({class=0x102,type=0x80,len=4,0x20007/0x7fffffff}),flags(+key)),recirc_id(0),in_port(2),eth(src=fa:16:3e:f8:52:5c,dst=00:00:00:00:00:00/01:00:00:00:00:00),eth_type(0x0800),ipv4(proto=6,frag=no),tcp_flags(psh|ack), packets:2, bytes:204, used:5.710s, actions:7
tunnel(tun_id=0x4,src=10.6.12.3,dst=10.6.12.7,tp_dst=6081,geneve({class=0x102,type=0x80,len=4,0x20007/0x7fffffff}),flags(+key)),recirc_id(0),in_port(2),eth(src=fa:16:3e:f8:52:5c,dst=00:00:00:00:00:00/01:00:00:00:00:00),eth_type(0x0800),ipv4(proto=6,frag=no),tcp_flags(ack), packets:3, bytes:230, used:5.710s, actions:7
tunnel(tun_id=0x4,src=10.6.12.8,dst=10.6.12.7,tp_dst=6081,geneve({class=0x102,type=0x80,len=4,0x60007/0x7fffffff}),flags(+key)),recirc_id(0),in_port(2),eth(src=fa:16:3e:b2:20:82,dst=00:00:00:00:00:00/01:00:00:00:00:00),eth_type(0x0800),ipv4(proto=6,frag=no),tcp_flags(syn|ack), packets:0, bytes:0, used:6.740s, actions:7
tunnel(tun_id=0x4,src=10.6.12.8,dst=10.6.12.7,tp_dst=6081,geneve({class=0x102,type=0x80,len=4,0x60007/0x7fffffff}),flags(+key)),recirc_id(0),in_port(2),eth(src=fa:16:3e:b2:20:82,dst=00:00:00:00:00:00/01:00:00:00:00:00),eth_type(0x0800),ipv4(proto=6,frag=no),tcp_flags(ack), packets:180737, bytes:9400154, used:0.000s, actions:7
recirc_id(0),in_port(6),eth(src=26:8a:07:82:a7:2f,dst=01:80:c2:00:00:0e),eth_type(0x88cc), packets:5, bytes:990, used:14.340s, actions:drop
recirc_id(0),in_port(7),eth(src=fa:16:3e:b9:db:c8,dst=fa:16:3e:b2:20:82),eth_type(0x0800),ipv4(dst=10.42.0.16/255.255.255.240,proto=6,tos=0/0x3,frag=no),tcp_flags(syn), packets:0, bytes:0, used:6.910s, actions:set(tunnel(tun_id=0x4,dst=10.6.12.8,ttl=64,tp_dst=6081,key6(bad key length 1, expected 0)(01)geneve({class=0x102,type=0x80,len=4,0x70006}),flags(key))),2
recirc_id(0),in_port(7),eth(src=fa:16:3e:b9:db:c8,dst=fa:16:3e:b2:20:82),eth_type(0x0800),ipv4(dst=10.42.0.16/255.255.255.240,proto=6,tos=0/0x3,frag=no),tcp_flags(ack), packets:935904, bytes:7504070178, used:0.590s, actions:set(tunnel(tun_id=0x4,dst=10.6.12.8,ttl=64,tp_dst=6081,key6(bad key length 1, expected 0)(01)geneve({class=0x102,type=0x80,len=4,0x70006}),flags(key))),2
recirc_id(0),in_port(7),eth(src=fa:16:3e:b9:db:c8,dst=fa:16:3e:b2:20:82),eth_type(0x0800),ipv4(dst=10.42.0.16/255.255.255.240,proto=6,tos=0/0x3,frag=no),tcp_flags(psh|ack), packets:3873, bytes:31053714, used:0.590s, actions:set(tunnel(tun_id=0x4,dst=10.6.12.8,ttl=64,tp_dst=6081,key6(bad key length 1, expected 0)(01)geneve({class=0x102,type=0x80,len=4,0x70006}),flags(key))),2

SR-IOV for networking support

Single root I/O virtualization (SR-IOV) enables splitting a single physical network port into multiple virtual network ports known as virtual functions (VFs). The division is done at the PCI level which allows attaching the VF directly to a virtual machine instance, bypassing the networking stack of the hypervisor hosting the instance.

The main use case for this feature is to support applications with high bandwidth requirements. For such applications the normal plumbing through the userspace virtio driver in QEMU will consume too much resources from the host.

It is possible to configure chassis to prepare network interface cards (NICs) for use with SR-IOV and make them available to OpenStack.

Prerequisites

To use the feature you need to use a NIC with support for SR-IOV.

Machines need to be pre-configured with appropriate kernel command-line parameters. The charm does not handle this facet of configuration and it is expected that the user configure this either manually or through the bare metal provisioning layer (for example MAAS). Example:

intel_iommu=on iommu=pt probe_vf=0

Charm configuration

Enable SR-IOV, map physical network name ‘physnet2’ to the physical port named ‘enp3s0f0’ and create 4 virtual functions on it:

juju config neutron-api enable-sriov=true
juju config ovn-chassis enable-sriov=true
juju config ovn-chassis sriov-device-mappings=physnet2:enp3s0f0
juju config ovn-chassis sriov-numvfs=enp3s0f0:4

Caution

After deploying the above example the machines hosting ovn-chassis units must be rebooted for the changes to take effect.

After enabling the virtual functions you should take note of the vendor_id and product_id of the virtual functions:

juju run --application ovn-chassis 'lspci -nn | grep "Virtual Function"'

03:10.0 Ethernet controller [0200]: Intel Corporation 82599 Ethernet Controller Virtual Function [8086:10ed] (rev 01)
03:10.2 Ethernet controller [0200]: Intel Corporation 82599 Ethernet Controller Virtual Function [8086:10ed] (rev 01)
03:10.4 Ethernet controller [0200]: Intel Corporation 82599 Ethernet Controller Virtual Function [8086:10ed] (rev 01)
03:10.6 Ethernet controller [0200]: Intel Corporation 82599 Ethernet Controller Virtual Function [8086:10ed] (rev 01)

In the above example vendor_id is ‘8086’ and product_id is ‘10ed’.

Add mapping between physical network name, physical port and Open vSwitch bridge:

juju config ovn-chassis ovn-bridge-mappings=physnet2:br-ex
juju config ovn-chassis bridge-interface-mappings br-ex:a0:36:9f:dd:37:a8

Note

The above configuration allows OVN to configure an ‘external’ port on one of the chassis for providing DHCP and metadata to instances connected directly to the network through SR-IOV.

For OpenStack to make use of the VFs the neutron-sriov-agent needs to talk to RabbitMQ:

juju add-relation ovn-chassis:amqp rabbitmq-server:amqp

OpenStack Nova also needs to know which PCI devices it is allowed to pass through to instances:

juju config nova-compute pci-passthrough-whitelist='{"vendor_id":"8086", "product_id":"10ed", "physical_network":"physnet2"}'

Boot an instance

Now we can tell OpenStack to boot an instance and attach it to an SR-IOV port. This must be done in two stages, first we create a port with vnic-type ‘direct’ and then we create an instance connected to the newly created port:

openstack port create --network my-network --vnic-type direct my-port
openstack server create --flavor my-flavor --key-name my-key \
   --nic port-id=my-port my-instance

DPDK support

It is possible to configure chassis to use experimental DPDK userspace network acceleration.

Note

Currently instances are required to be attached to a external network (also known as provider network) for connectivity. OVN supports distributed DHCP for provider networks. For OpenStack workloads use of Nova config drive is required to provide metadata to instances.

Prerequisites

To use the feature you need to use a supported CPU architecture and network interface card (NIC) hardware. Please consult the DPDK supported hardware page.

Machines need to be pre-configured with appropriate kernel command-line parameters. The charm does not handle this facet of configuration and it is expected that the user configure this either manually or through the bare metal provisioning layer (for example MAAS).

Example:

default_hugepagesz=1G hugepagesz=1G hugepages=64 intel_iommu=on iommu=pt

For the communication between the host userspace networking stack and the guest virtual NIC driver to work the instances need to be configured to use hugepages. For OpenStack this can be accomplished by Customizing instance huge pages allocations.

Example:

openstack flavor set m1.large --property hw:mem_page_size=large

By default, the charm will configure Open vSwitch/DPDK to consume one processor core + 1G of RAM from each NUMA node on the unit being deployed. This can be tuned using the dpdk-socket-memory and dpdk-socket-cores configuration options.

Note

Please check that the value of dpdk-socket-memory is large enough to accommodate the MTU size being used. For more information please refer to DPDK shared memory calculations

The userspace kernel driver can be configured using the dpdk-driver configuration option. See config.yaml for more details.

Note

Changing dpdk related configuration options will trigger a restart of Open vSwitch, and subsequently interrupt instance connectivity.

Charm configuration

The below example bundle excerpt will enable the use of DPDK for an OVN deployment.

ovn-chassis-dpdk:
  options:
    enable-dpdk: True
    bridge-interface-mappings: br-ex:00:53:00:00:00:42
ovn-chassis:
  options:
    enable-dpdk: False
    bridge-interface-mappings: br-ex:bond0
    prefer-chassis-as-gw: True

Caution

As configured by the charms, the units configured to use DPDK will not participate in the overlay network and will also not be able to provide services such as external DHCP to SR-IOV enabled units in the same deployment.

As such it is important to have at least one other named ovn-chassis application in the deployment with enable-dpdk set to ‘False’ and the prefer-chassis-as-gw configuration option set to ‘True’. Doing so will inform the CMS (Cloud Management System) that shared services such as gateways and external DHCP services should not be scheduled to the DPDK-enabled nodes.

DPDK bonding

Once Network interface cards are bound to DPDK they will be invisible to the standard Linux kernel network stack and subsequently it is not possible to use standard system tools to configure bonding.

For DPDK interfaces the charm supports configuring bonding in Open vSwitch. This is accomplished through the dpdk-bond-mappings and dpdk-bond-config configuration options. Example:

ovn-chassis-dpdk:
  options:
    enable-dpdk: True
    bridge-interface-mappings: br-ex:dpdk-bond0
    dpdk-bond-mappings: "dpdk-bond0:00:53:00:00:00:42 dpdk-bond0:00:53:00:00:00:51"
    dpdk-bond-config: ":balance-slb:off:fast"
ovn-chassis:
  options:
    enable-dpdk: False
    bridge-interface-mappings: br-ex:bond0
    prefer-chassis-as-gw: True

In this example, the network interface cards associated with the two MAC addresses provided will be used to build a bond identified by a port named ‘dpdk-bond0’ which will be attached to the ‘br-ex’ bridge.

Internal DNS resolution

OVN supports Neutron internal DNS resolution. To configure this:

Caution

At the time of this writing the internal DNS support does not include reverse lookup (PTR-records) of instance IP addresses, only forward lookup (A and AAAA-records) of instance names. This is tracked in LP #1857026.

juju config neutron-api enable-ml2-dns=true
juju config neutron-api dns-domain=openstack.example.
juju config neutron-api-plugin-ovn dns-servers="1.1.1.1 8.8.8.8"

Note

The value for the dns-domain configuration option must not be set to ‘openstack.local.’ as that will effectively disable the feature.

It is also important to end the string with a ‘.’ (dot).

When you set enable-ml2-dns to ‘true’ and set a value for dns-domain, Neutron will add details such as instance name and DNS domain name to each individual Neutron port associated with instances. The OVN ML2 driver will populate the DNS table of the Northbound and Southbound databases:

# ovn-sbctl list DNS
_uuid               : 2e149fa8-d27f-4106-99f5-a08f60c443bf
datapaths           : [b25ed99a-89f1-49cc-be51-d215aa6fb073]
external_ids        : {dns_id="4c79807e-0755-4d17-b4bc-eb57b93bf78d"}

records             : {"c-1"="192.0.2.239", "c-1.openstack.example"="192.0.2.239"}

On the chassis, OVN creates flow rules to redirect UDP port 53 packets (DNS) to the local ovn-controller process:

cookie=0xdeaffed, duration=77.575s, table=22, n_packets=0, n_bytes=0, idle_age=77, priority=100,udp6,metadata=0x2,tp_dst=53 actions=controller(userdata=00.00.00.06.00.00.00.00.00.01.de.10.00.00.00.64,pause),resubmit(,23)
cookie=0xdeaffed, duration=77.570s, table=22, n_packets=0, n_bytes=0, idle_age=77, priority=100,udp,metadata=0x2,tp_dst=53 actions=controller(userdata=00.00.00.06.00.00.00.00.00.01.de.10.00.00.00.64,pause),resubmit(,23)

The local ovn-controller process then decides if it should respond to the DNS query directly or if it needs to be forwarded to the real DNS server.

External connectivity

Interface and network to bridge mapping is done through the ovn-chassis charm.

OVN provides a more flexible way of configuring external Layer3 networking than the legacy ML2+DVR configuration as OVN does not require every node (Chassis in OVN terminology) in a deployment to have direct external connectivity. This plays nicely with Layer3-only datacenter fabrics (RFC 7938).

East/West traffic is distributed by default. North/South traffic is highly available by default. Liveness detection is done using the Bidirectional Forwarding Detection (BFD) protocol.

Networks for use with external Layer3 connectivity should have mappings on chassis located in the vicinity of the datacenter border gateways. Having two or more chassis with mappings for a Layer3 network will have OVN automatically configure highly available routers with liveness detection provided by the Bidirectional Forwarding Detection (BFD) protocol.

Chassis without direct external mapping to a external Layer3 network will forward traffic through a tunnel to one of the chassis acting as a gateway for that network.

Networks for use with external Layer2 connectivity should have mappings present on all chassis with potential to host the consuming payload.

Note

It is not necessary nor recommended to add mapping for external Layer3 networks to all chassis. Doing so will create a scaling problem at the physical network layer that needs to be resolved with globally shared Layer2 (does not scale) or tunneling at the top-of-rack switch layer (adds complexity) and is generally not a recommended configuration.

Example configuration with explicit bridge-interface-mappings:

juju config neutron-api flat-network-providers=physnet1
juju config ovn-chassis ovn-bridge-mappings=physnet1:br-provider
juju config ovn-chassis \
    bridge-interface-mappings='br-provider:00:00:5e:00:00:42 \
                               br-provider:00:00:5e:00:00:51'
openstack network create --external --share --provider-network-type flat \
                         --provider-physical-network physnet1 ext-net
openstack subnet create --network ext-net \
                        --subnet-range 192.0.2.0/24 \
                        --no-dhcp --gateway 192.0.2.1 \
                        ext

It is also possible to influence the scheduling of routers on a per named ovn-chassis application basis. The benefit of this method is that you do not need to provide MAC addresses when configuring Layer3 connectivity in the charm. For example:

juju config ovn-chassis-border \
   ovn-bridge-mappings=physnet1:br-provider \
   bridge-interface-mappings=br-provider:bond0 \
   prefer-chassis-as-gw=true

juju config ovn-chassis \
   ovn-bridge-mappings=physnet1:br-provider \
   bridge-interface-mappings=br-provider:bond0 \

In the above example units of the ovn-chassis-border application with appropriate bridge mappings will be eligible for router scheduling.

Usage

Create networks, routers and subnets through the OpenStack API or CLI as you normally would.

The OVN ML2 driver will translate the OpenStack network constructs into high level logical rules in the OVN Northbound database.

The ovn-northd daemon in turn translates this into data in the Southbound database.

The local ovn-controller daemon on each chassis consumes these rules and programs flows in the local Open vSwitch database.

Information queries

The OVN databases are configured to use the Clustered Database Service Model. In this configuration only the leader processes transactions and the administrative client tools are configured to require a connection to the leader to operate.

The leader of the Northbound and Southbound databases does not have to coincide with the charm leader, so before querying databases you must consult the output of juju status to check which unit is the leader of the database you want to query. Example:

juju status ovn-central

Unit            Workload  Agent  Machine  Public address  Ports              Message
ovn-central/0*  active    idle   0/lxd/5  10.246.114.39   6641/tcp,6642/tcp  Unit is ready (leader: ovnnb_db)
ovn-central/1   active    idle   1/lxd/4  10.246.114.15   6641/tcp,6642/tcp  Unit is ready (northd: active)
ovn-central/2   active    idle   2/lxd/2  10.246.114.27   6641/tcp,6642/tcp  Unit is ready (leader: ovnsb_db)

In the above example ‘ovn-central/0’ is the leader for the Northbound DB, ‘ovn-central/1’ has the active ovn-northd daemon and ‘ovn-central/2’ is the leader for the Southbound DB.

OVSDB Cluster status

The cluster status as conveyed through juju status is updated each time a hook is run, in some circumstances it may be necessary to get an immediate view of the current cluster status.

To get an immediate view of the database clusters:

juju run --application ovn-central 'ovn-appctl -t \
    /var/run/ovn/ovnnb_db.ctl cluster/status OVN_Northbound'
juju run --application ovn-central 'ovn-appctl -t \
    /var/run/ovn/ovnsb_db.ctl cluster/status OVN_Southbound'

Querying DBs

To query the individual databases:

juju run --unit ovn-central/0 'ovn-nbctl show'
juju run --unit ovn-central/2 'ovn-sbctl show'
juju run --unit ovn-central/2 'ovn-sbctl lflow-list'

As an alternative you may provide the administrative client tools with command-line arguments for path to certificates and IP address of servers so that you can run the client from anywhere:

ovn-nbctl \
   -p /etc/ovn/key_host \
   -C /etc/ovn/ovn-central.crt \
   -c /etc/ovn/cert_host \
   --db ssl:10.246.114.39:6641,ssl:10.246.114.15:6641,ssl:10.246.114.27:6641 \
   show

Note that for remote administrative write access to the Southbound DB you must use port number ‘16642’. This is due to OVN RBAC being enabled on the standard ‘6642’ port:

ovn-sbctl \
   -p /etc/ovn/key_host \
   -C /etc/ovn/ovn-central.crt \
   -c /etc/ovn/cert_host \
   --db ssl:10.246.114.39:16642,ssl:10.246.114.15:16642,ssl:10.246.114.27:16642 \
   show

Data plane flow tracing

SSH into one of the chassis units to get access to various diagnostic tools:

juju ssh ovn-chassis/0

sudo ovs-vsctl show

sudo ovs-ofctl -O OpenFlow13 dump-flows br-int

sudo ovs-appctl -t ovs-vswitchd \
   ofproto/trace br-provider \
   in_port=enp3s0f0,icmp,nw_src=192.0.2.1,nw_dst=192.0.2.100

sudo ovn-trace \
   -p /etc/ovn/key_host \
   -C /etc/ovn/ovn-chassis.crt \
   -c /etc/ovn/cert_host \
   --db ssl:10.246.114.39:6642,ssl:10.246.114.15:6642,ssl:10.246.114.27:6642 \
   --ovs ext-net 'inport=="provnet-dde76bc9-0620-44f7-b99a-99cfc66e1095" && \
   eth.src==30:e1:71:5c:7a:b5 && \
   eth.dst==fa:16:3e:f7:15:73 && \
   ip4.src==10.172.193.250 && \
   ip4.dst==10.246.119.8 && \
   icmp4.type==8 && \
   ip.ttl == 64'

Note

OVN makes use of OpenFlow 1.3 or newer and as such the charm configures bridges to use these protocols. To be able to successfully use the ovs-ofctl command you must specify the OpenFlow version as shown in the example above.

You may issue the ovs-vsctl list bridge command to show what protocols are enabled on the bridges.

Migration from Neutron ML2+OVS to ML2+OVN

MTU considerations

When migrating from ML2+OVS to ML2+OVN there will be a change of encapsulation for the tunnels in the overlay network to geneve. A side effect of the change of encapsulation is that the packets transmitted on the physical network get larger.

You must examine the existing configuration of network equipment, physical links on hypervisors and configuration of existing virtual project networks to determine if there is room for this growth.

Making room for the growth could be accomplished by increasing the MTU configuration on the physical network equipment and hypervisor physical links. If this can be done then steps #1 and #9 below can be skipped, where it is shown how to reduce the MTU on all existing cloud instances.

Remember to take any other encapsulation used in your physical network equipment into account when calculating the MTU (VLAN tags, MPLS labels etc.).

Encapsulation types and their overhead:

Encapsulation	Overhead	Difference from Geneve
Geneve	38 Bytes	0 Bytes
VXLAN	30 Bytes	8 Bytes
GRE	22 Bytes	16 bytes

Confirmation of migration actions

Many of the actions used for the migration require a confirmation from the operator by way of the i-really-mean-it parameter.

This parameter accepts the values ‘true’ or ‘false’. If ‘false’ the requested operation will either not be performed, or will be performed in dry-run mode, if ‘true’ the requested operation will be performed.

In the examples below the parameter will not be listed, this is deliberate to avoid accidents caused by cutting and pasting the wrong command into a terminal.

Prepare for migration

This section contains the preparation steps that will ensure minimal instance down time during the migration. Ensure that you have studied them in advance of the actual migration.

Important

Allow for at least 24 hours to pass between the completion of the preparation steps and the commencement of the actual migration steps. This is particularly necesseary because depending on your physical network configuration, it may be required to reduce the MTU size on all cloud instances as part of the migration.

1. Reduce MTU on all instances in the cloud if required

   Please refer to the MTU considerations section above.

   • Instances using DHCP can be controlled centrally by the cloud operator by overriding the MTU advertised by the DHCP server.

     juju config neutron-gateway instance-mtu=1300
     
     juju config neutron-openvswitch instance-mtu=1300
     

   • Instances using IPv6 RA or SLAAC will automatically adjust their MTU as soon as OVN takes over announcing the RAs.

   • Any instances not using DHCP must be configured manually by the end user of the instance.

2. Confirm cloud subnet configuration

   • Confirm that all subnets have IP addresses available for allocation.

     During the migration OVN may create a new port in subnets and allocate an IP address to it. Depending on the type of network, this port will be used for either the OVN metadata service or for the SNAT address assigned to an external router interface.

     Warning

     If a subnet has no free IP addresses for allocation the migration will fail.

   • Confirm that all subnets have a valid DNS server configuration.

     OVN handles instance access to DNS differently to how ML2+OVS does. Please refer to the Internal DNS resolution paragraph in this document for details.

     When the subnet dns_nameservers attribute is empty the OVN DHCP server will provide instances with the DNS addresses specified in the neutron-api-plugin-ovn dns-servers configuration option. If any of your subnets have the dns_nameservers attribute set to the IP address ML2+OVS used for instance DNS (usually the .2 address of the project subnet) you will need to remove this configuration.

3. Make a fresh backup copy of the Neutron database

4. Deploy the OVN components and Vault

   In your Juju model you can have a charm deployed multiple times using different application names. In the text below this will be referred to as “named application”. One example where this is common is for deployments with Octavia where it is common to use a separate named application for neutron-openvswtich for use with the Octavia units.

   In addition to the central components you should deploy an ovn-chassis named application for every neutron-openvswitch named application in your deployment. For every neutron-gateway named application you should deploy an ovn-dedicated-chassis named application to the same set of machines.

   At this point in time each hypervisor or gateway will have a Neutron Open vSwitch (OVS) agent managing the local OVS instance. Network loops may occur if an ovn-chassis unit is started as it will also attempt to manage OVS. To avoid this, deploy ovn-chassis (or ovn-dedicated-chassis) in a paused state by setting the new-units-paused configuration option to ‘true’:

   juju deploy ovn-central \
      --series focal \
      -n 3 \
      --to lxd:0,lxd:1,lxd:2
   
   juju deploy ovn-chassis \
      --series focal \
      --config new-units-paused=true \
      --config bridge-interface-mappings='br-provider:00:00:5e:00:00:42' \
      --config ovn-bridge-mappings=physnet1:br-provider
   
   juju deploy ovn-dedicated-chassis \
      --series focal \
      --config new-units-paused=true \
      --config bridge-interface-mappings='br-provider:00:00:5e:00:00:51' \
      --config ovn-bridge-mappings=physnet1:br-provider \
      -n 2 \
      --to 3,4
   
   juju deploy --series focal mysql-router vault-mysql-router
   juju deploy --series focal vault
   
   juju add-relation vault-mysql-router:db-router \
      mysql-innodb-cluster:db-router
   juju add-relation vault-mysql-router:shared-db vault:shared-db
   
   juju add-relation ovn-central:certificates vault:certificates
   
   juju add-relation ovn-chassis:certificates vault:certificates
   juju add-relation ovn-chassis:ovsdb ovn-central:ovsdb
   juju add-relation nova-compute:neutron-plugin ovn-chassis:nova-compute
   

   The values to use for the bridge-interface-mappings and ovn-bridge-mappings configuration options can be found by looking at what is set for the data-port and bridge-mappings configuration options on the neutron-openvswitch and/or neutron-gateway applications.

   Note

   In the above example the placement given with the --to parameter to juju is just an example. Your deployment may also have multiple named applications of the neutron-openvswitch charm and/or mutliple applications related to the neutron-openvswitch named applications. You must tailor the commands to fit with your deployments topology.

5. Unseal Vault (see the vault charm), set up TLS certificates (see Managing TLS certificates), and validate that the services on ovn-central units are running as expected. Please refer to the Usage section for more information.

Perform migration

6. Change firewall driver to ‘openvswitch’

   To be able to successfully clean up after the Neutron agents on hypervisors we need to instruct the neutron-openvswitch charm to use the ‘openvswitch’ firewall driver. This is accomplished by setting the firewall-driver configuration option to ‘openvswitch’.

   juju config neutron-openvswitch firewall-driver=openvswitch
   

7. Pause neutron-openvswitch and/or neutron-gateway units.

   If your deployments have two neutron-gateway units and four neutron-openvswitch units the sequence of commands would be:

   juju run-action neutron-gateway/0 pause
   juju run-action neutron-gateway/1 pause
   juju run-action neutron-openvswitch/0 pause
   juju run-action neutron-openvswitch/1 pause
   juju run-action neutron-openvswitch/2 pause
   juju run-action neutron-openvswitch/3 pause
   

8. Deploy the Neutron OVN plugin application

   juju deploy neutron-api-plugin-ovn \
      --series focal \
      --config dns-servers=="1.1.1.1 8.8.8.8"
   
   juju add-relation neutron-api-plugin-ovn:neutron-plugin \
      neutron-api:neutron-plugin-api-subordinate
   juju add-relation neutron-api-plugin-ovn:certificates \
      vault:certificates
   juju add-relation neutron-api-plugin-ovn:ovsdb-cms ovn-central:ovsdb-cms
   

   The values to use for the dns-servers configuration option can be found by looking at what is set for the dns-servers configuration option on the neutron-openvswitch and/or neutron-gateway applications.

   Note

   The plugin will not be activated until the neutron-api manage-neutron-plugin-legacy-mode configuration option is changed in step 9.

9. Adjust MTU on overlay networks (if required)

   Now that 24 hours have passed since we reduced the MTU on the instances running in the cloud as described in step 1, we can update the MTU setting for each individual Neutron network:

   juju run-action --wait neutron-api-plugin-ovn/0 migrate-mtu
   

10. Enable the Neutron OVN plugin

    juju config neutron-api manage-neutron-plugin-legacy-mode=false
    

    Wait for the deployment to settle.

11. Pause the Neutron API units

    juju run-action neutron-api/0 pause
    juju run-action neutron-api/1 pause
    juju run-action neutron-api/2 pause
    

    Wait for the deployment to settle.

12. Perform initial synchronization of the Neutron and OVN databases

    juju run-action --wait neutron-api-plugin-ovn/0 migrate-ovn-db
    

13. (Optional) Perform Neutron database surgery to update network_type of overlay networks to ‘geneve’.

    At the time of this writing the Neutron OVN ML2 driver will assume that all chassis participating in a network are using the ‘geneve’ tunnel protocol and it will ignore the value of the network_type field in any non-physical network in the Neutron database. It will also ignore the segmentation_id field and let OVN assign the VNIs.

    The Neutron API currently does not support changing the type of a network, so when doing a migration the above described behaviour is actually a welcome one.

    However, after the migration is done and all the primary functions are working, i.e. packets are forwarded. The end user of the cloud will be left with the false impression of their existing ‘gre’ or ‘vxlan’ typed networks still being operational on said tunnel protocols, while in reality ‘geneve’ is used under the hood.

    The end user will also run into issues with modifying any existing networks with openstack network set throwing error messages about networks of type ‘gre’ or ‘vxlan’ not being supported.

    After running this action said networks will have their network_type field changed to ‘geneve’ which will fix the above described problems.

    juju run-action --wait neutron-api-plugin-ovn/0 offline-neutron-morph-db
    

14. Resume the Neutron API units

    juju run-action neutron-api/0 resume
    juju run-action neutron-api/1 resume
    juju run-action neutron-api/2 resume
    

    Wait for the deployment to settle.

15. Migrate hypervisors and gateways

    The final step of the migration is to clean up after the Neutron agents on the hypervisors/gateways and enable the OVN services so that they can reprogram the local Open vSwitch.

    This can be done one gateway / hypervisor at a time or all at once to your discretion.

    Note

    During the migration instances running on a non-migrated hypervisor will not be able to reach instances on the migrated hypervisors.

    Caution

    When migrating a cloud with Neutron ML2+OVS+DVR+SNAT topology care should be taken to take into account on which hypervisors essential agents are running to minimize downtime for any instances on other hypervisors with dependencies on them.

    juju run-action --wait neutron-openvswitch/0 cleanup
    juju run-action --wait ovn-chassis/0 resume
    
    juju run-action --wait neutron-gateway/0 cleanup
    juju run-action --wait ovn-dedicated-chassis/0 resume
    

16. Post migration tasks

    Remove the now redundant Neutron ML2+OVS agents from hypervisors and any dedicated gateways as well as the neutron-gateway and neutron-openvswitch applications from the Juju model:

    juju run --application neutron-gateway '\
       apt remove -y neutron-dhcp-agent neutron-l3-agent \
       neutron-metadata-agent neutron-openvswitch-agent'
    
    juju remove-application neutron-gateway
    
    juju run --application neutron-openvswitch '\
       apt remove -y neutron-dhcp-agent neutron-l3-agent \
       neutron-metadata-agent neutron-openvswitch-agent'
    
    juju remove-application neutron-openvswitch
    

    Remove the now redundant Neutron ML2+OVS agents from the Neutron database:

    openstack network agent list
    openstack network agent delete ...