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NAME | DESCRIPTION | SECURITY | DESIGN DECISIONS | COLOPHON |
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ovn-architecture(7) OVN Manual ovn-architecture(7)
ovn-architecture - Open Virtual Network architecture
OVN, the Open Virtual Network, is a system to support logical
network abstraction in virtual machine and container
environments. OVN complements the existing capabilities of OVS to
add native support for logical network abstractions, such as
logical L2 and L3 overlays and security groups. Services such as
DHCP are also desirable features. Just like OVS, OVN’s design
goal is to have a production-quality implementation that can
operate at significant scale.
A physical network comprises physical wires, switches, and
routers. A virtual network extends a physical network into a
hypervisor or container platform, bridging VMs or containers into
the physical network. An OVN logical network is a network
implemented in software that is insulated from physical (and thus
virtual) networks by tunnels or other encapsulations. This allows
IP and other address spaces used in logical networks to overlap
with those used on physical networks without causing conflicts.
Logical network topologies can be arranged without regard for the
topologies of the physical networks on which they run. Thus, VMs
that are part of a logical network can migrate from one physical
machine to another without network disruption. See Logical
Networks, below, for more information.
The encapsulation layer prevents VMs and containers connected to
a logical network from communicating with nodes on physical
networks. For clustering VMs and containers, this can be
acceptable or even desirable, but in many cases VMs and
containers do need connectivity to physical networks. OVN
provides multiple forms of gateways for this purpose. See
Gateways, below, for more information.
An OVN deployment consists of several components:
• A Cloud Management System (CMS), which is OVN’s
ultimate client (via its users and administrators).
OVN integration requires installing a CMS-specific
plugin and related software (see below). OVN
initially targets OpenStack as CMS.
We generally speak of ``the’’ CMS, but one can
imagine scenarios in which multiple CMSes manage
different parts of an OVN deployment.
• An OVN Database physical or virtual node (or,
eventually, cluster) installed in a central
location.
• One or more (usually many) hypervisors. Hypervisors
must run Open vSwitch and implement the interface
described in Documentation/topics/integration.rst
in the Open vSwitch source tree. Any hypervisor
platform supported by Open vSwitch is acceptable.
• Zero or more gateways. A gateway extends a tunnel-
based logical network into a physical network by
bidirectionally forwarding packets between tunnels
and a physical Ethernet port. This allows non-
virtualized machines to participate in logical
networks. A gateway may be a physical host, a
virtual machine, or an ASIC-based hardware switch
that supports the vtep(5) schema.
Hypervisors and gateways are together called
transport node or chassis.
The diagram below shows how the major components of OVN and
related software interact. Starting at the top of the diagram, we
have:
• The Cloud Management System, as defined above.
• The OVN/CMS Plugin is the component of the CMS that
interfaces to OVN. In OpenStack, this is a Neutron
plugin. The plugin’s main purpose is to translate
the CMS’s notion of logical network configuration,
stored in the CMS’s configuration database in a
CMS-specific format, into an intermediate
representation understood by OVN.
This component is necessarily CMS-specific, so a
new plugin needs to be developed for each CMS that
is integrated with OVN. All of the components below
this one in the diagram are CMS-independent.
• The OVN Northbound Database receives the
intermediate representation of logical network
configuration passed down by the OVN/CMS Plugin.
The database schema is meant to be ``impedance
matched’’ with the concepts used in a CMS, so that
it directly supports notions of logical switches,
routers, ACLs, and so on. See ovn-nb(5) for
details.
The OVN Northbound Database has only two clients:
the OVN/CMS Plugin above it and ovn-northd below
it.
• ovn-northd(8) connects to the OVN Northbound
Database above it and the OVN Southbound Database
below it. It translates the logical network
configuration in terms of conventional network
concepts, taken from the OVN Northbound Database,
into logical datapath flows in the OVN Southbound
Database below it.
• The OVN Southbound Database is the center of the
system. Its clients are ovn-northd(8) above it and
ovn-controller(8) on every transport node below it.
The OVN Southbound Database contains three kinds of
data: Physical Network (PN) tables that specify how
to reach hypervisor and other nodes, Logical
Network (LN) tables that describe the logical
network in terms of ``logical datapath flows,’’ and
Binding tables that link logical network
components’ locations to the physical network. The
hypervisors populate the PN and Port_Binding
tables, whereas ovn-northd(8) populates the LN
tables.
OVN Southbound Database performance must scale with
the number of transport nodes. This will likely
require some work on ovsdb-server(1) as we
encounter bottlenecks. Clustering for availability
may be needed.
The remaining components are replicated onto each hypervisor:
• ovn-controller(8) is OVN’s agent on each hypervisor
and software gateway. Northbound, it connects to
the OVN Southbound Database to learn about OVN
configuration and status and to populate the PN
table and the Chassis column in Binding table with
the hypervisor’s status. Southbound, it connects to
ovs-vswitchd(8) as an OpenFlow controller, for
control over network traffic, and to the local
ovsdb-server(1) to allow it to monitor and control
Open vSwitch configuration.
• ovs-vswitchd(8) and ovsdb-server(1) are
conventional components of Open vSwitch.
CMS
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+-----------|-----------+
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| OVN/CMS Plugin |
| | |
| | |
| OVN Northbound DB |
| | |
| | |
| ovn-northd |
| | |
+-----------|-----------+
|
|
+-------------------+
| OVN Southbound DB |
+-------------------+
|
|
+------------------+------------------+
| | |
HV 1 | | HV n |
+---------------|---------------+ . +---------------|---------------+
| | | . | | |
| ovn-controller | . | ovn-controller |
| | | | . | | | |
| | | | | | | |
| ovs-vswitchd ovsdb-server | | ovs-vswitchd ovsdb-server |
| | | |
+-------------------------------+ +-------------------------------+
Information Flow in OVN
Configuration data in OVN flows from north to south. The CMS,
through its OVN/CMS plugin, passes the logical network
configuration to ovn-northd via the northbound database. In turn,
ovn-northd compiles the configuration into a lower-level form and
passes it to all of the chassis via the southbound database.
Status information in OVN flows from south to north. OVN
currently provides only a few forms of status information. First,
ovn-northd populates the up column in the northbound
Logical_Switch_Port table: if a logical port’s chassis column in
the southbound Port_Binding table is nonempty, it sets up to
true, otherwise to false. This allows the CMS to detect when a
VM’s networking has come up.
Second, OVN provides feedback to the CMS on the realization of
its configuration, that is, whether the configuration provided by
the CMS has taken effect. This feature requires the CMS to
participate in a sequence number protocol, which works the
following way:
1. When the CMS updates the configuration in the
northbound database, as part of the same transaction,
it increments the value of the nb_cfg column in the
NB_Global table. (This is only necessary if the CMS
wants to know when the configuration has been
realized.)
2. When ovn-northd updates the southbound database based
on a given snapshot of the northbound database, it
copies nb_cfg from northbound NB_Global into the
southbound database SB_Global table, as part of the
same transaction. (Thus, an observer monitoring both
databases can determine when the southbound database
is caught up with the northbound.)
3. After ovn-northd receives confirmation from the
southbound database server that its changes have
committed, it updates sb_cfg in the northbound
NB_Global table to the nb_cfg version that was pushed
down. (Thus, the CMS or another observer can determine
when the southbound database is caught up without a
connection to the southbound database.)
4. The ovn-controller process on each chassis receives
the updated southbound database, with the updated
nb_cfg. This process in turn updates the physical
flows installed in the chassis’s Open vSwitch
instances. When it receives confirmation from Open
vSwitch that the physical flows have been updated, it
updates nb_cfg in its own Chassis record in the
southbound database.
5. ovn-northd monitors the nb_cfg column in all of the
Chassis records in the southbound database. It keeps
track of the minimum value among all the records and
copies it into the hv_cfg column in the northbound
NB_Global table. (Thus, the CMS or another observer
can determine when all of the hypervisors have caught
up to the northbound configuration.)
Chassis Setup
Each chassis in an OVN deployment must be configured with an Open
vSwitch bridge dedicated for OVN’s use, called the integration
bridge. System startup scripts may create this bridge prior to
starting ovn-controller if desired. If this bridge does not exist
when ovn-controller starts, it will be created automatically with
the default configuration suggested below. The ports on the
integration bridge include:
• On any chassis, tunnel ports that OVN uses to
maintain logical network connectivity.
ovn-controller adds, updates, and removes these
tunnel ports.
• On a hypervisor, any VIFs that are to be attached
to logical networks. For instances connected
through software emulated ports such as TUN/TAP or
VETH pairs, the hypervisor itself will normally
create ports and plug them into the integration
bridge. For instances connected through representor
ports, typically used with hardware offload, the
ovn-controller may on CMS direction consult a VIF
plug provider for representor port lookup and plug
them into the integration bridge (please refer to
Documentation/topics/vif-plug-providers/vif-plug-providers.rst
for more information). In both cases the
conventions described in
Documentation/topics/integration.rst in the Open
vSwitch source tree is followed to ensure mapping
between OVN logical port and VIF. (This is pre-
existing integration work that has already been
done on hypervisors that support OVS.)
• On a gateway, the physical port used for logical
network connectivity. System startup scripts add
this port to the bridge prior to starting
ovn-controller. This can be a patch port to another
bridge, instead of a physical port, in more
sophisticated setups.
Other ports should not be attached to the integration bridge. In
particular, physical ports attached to the underlay network (as
opposed to gateway ports, which are physical ports attached to
logical networks) must not be attached to the integration bridge.
Underlay physical ports should instead be attached to a separate
Open vSwitch bridge (they need not be attached to any bridge at
all, in fact).
The integration bridge should be configured as described below.
The effect of each of these settings is documented in
ovs-vswitchd.conf.db(5):
fail-mode=secure
Avoids switching packets between isolated logical
networks before ovn-controller starts up. See
Controller Failure Settings in ovs-vsctl(8) for
more information.
other-config:disable-in-band=true
Suppresses in-band control flows for the
integration bridge. It would be unusual for such
flows to show up anyway, because OVN uses a local
controller (over a Unix domain socket) instead of a
remote controller. It’s possible, however, for some
other bridge in the same system to have an in-band
remote controller, and in that case this suppresses
the flows that in-band control would ordinarily set
up. Refer to the documentation for more
information.
The customary name for the integration bridge is br-int, but
another name may be used.
Logical Networks
Logical network concepts in OVN include logical switches and
logical routers, the logical version of Ethernet switches and IP
routers, respectively. Like their physical cousins, logical
switches and routers can be connected into sophisticated
topologies. Logical switches and routers are ordinarily purely
logical entities, that is, they are not associated or bound to
any physical location, and they are implemented in a distributed
manner at each hypervisor that participates in OVN.
Logical switch ports (LSPs) are points of connectivity into and
out of logical switches. There are many kinds of logical switch
ports. The most ordinary kind represent VIFs, that is, attachment
points for VMs or containers. A VIF logical port is associated
with the physical location of its VM, which might change as the
VM migrates. (A VIF logical port can be associated with a VM that
is powered down or suspended. Such a logical port has no location
and no connectivity.)
Logical router ports (LRPs) are points of connectivity into and
out of logical routers. A LRP connects a logical router either to
a logical switch or to another logical router. Logical routers
only connect to VMs, containers, and other network nodes
indirectly, through logical switches.
Logical switches and logical routers have distinct kinds of
logical ports, so properly speaking one should usually talk about
logical switch ports or logical router ports. However, an
unqualified ``logical port’’ usually refers to a logical switch
port.
When a VM sends a packet to a VIF logical switch port, the Open
vSwitch flow tables simulate the packet’s journey through that
logical switch and any other logical routers and logical switches
that it might encounter. This happens without transmitting the
packet across any physical medium: the flow tables implement all
of the switching and routing decisions and behavior. If the flow
tables ultimately decide to output the packet at a logical port
attached to another hypervisor (or another kind of transport
node), then that is the time at which the packet is encapsulated
for physical network transmission and sent.
Logical Switch Port Types
OVN supports a number of kinds of logical switch ports. VIF ports
that connect to VMs or containers, described above, are the most
ordinary kind of LSP. In the OVN northbound database, VIF ports
have an empty string for their type. This section describes some
of the additional port types.
A router logical switch port connects a logical switch to a
logical router, designating a particular LRP as its peer.
A localnet logical switch port bridges a logical switch to a
physical VLAN. A logical switch may have one or more localnet
ports. Such a logical switch is used in two scenarios:
• With one or more router logical switch ports, to
attach L3 gateway routers and distributed gateways
to a physical network.
• With one or more VIF logical switch ports, to
attach VMs or containers directly to a physical
network. In this case, the logical switch is not
really logical, since it is bridged to the physical
network rather than insulated from it, and
therefore cannot have independent but overlapping
IP address namespaces, etc. A deployment might
nevertheless choose such a configuration to take
advantage of the OVN control plane and features
such as port security and ACLs.
When a logical switch contains multiple localnet ports, the
following is assumed.
• Each chassis has a bridge mapping for one of the
localnet physical networks only.
• To facilitate interconnectivity between VIF ports
of the switch that are located on different chassis
with different physical network connectivity, the
fabric implements L3 routing between these adjacent
physical network segments.
Note: nothing said above implies that a chassis cannot be plugged
to multiple physical networks as long as they belong to different
switches.
A localport logical switch port is a special kind of VIF logical
switch port. These ports are present in every chassis, not bound
to any particular one. Traffic to such a port will never be
forwarded through a tunnel, and traffic from such a port is
expected to be destined only to the same chassis, typically in
response to a request it received. OpenStack Neutron uses a
localport port to serve metadata to VMs. A metadata proxy process
is attached to this port on every host and all VMs within the
same network will reach it at the same IP/MAC address without any
traffic being sent over a tunnel. For further details, see the
OpenStack documentation for networking-ovn.
LSP types vtep and l2gateway are used for gateways. See Gateways,
below, for more information.
Implementation Details
These concepts are details of how OVN is implemented internally.
They might still be of interest to users and administrators.
Logical datapaths are an implementation detail of logical
networks in the OVN southbound database. ovn-northd translates
each logical switch or router in the northbound database into a
logical datapath in the southbound database Datapath_Binding
table.
For the most part, ovn-northd also translates each logical switch
port in the OVN northbound database into a record in the
southbound database Port_Binding table. The latter table
corresponds roughly to the northbound Logical_Switch_Port table.
It has multiple types of logical port bindings, of which many
types correspond directly to northbound LSP types. LSP types
handled this way include VIF (empty string), localnet, localport,
vtep, and l2gateway.
The Port_Binding table has some types of port binding that do not
correspond directly to logical switch port types. The common is
patch port bindings, known as logical patch ports. These port
bindings always occur in pairs, and a packet that enters on
either side comes out on the other. ovn-northd connects logical
switches and logical routers together using logical patch ports.
Port bindings with types vtep, l2gateway, l3gateway, and
chassisredirect are used for gateways. These are explained in
Gateways, below.
Gateways
Gateways provide limited connectivity between logical networks
and physical ones. They can also provide connectivity between
different OVN deployments. This section will focus on the former,
and the latter will be described in details in section OVN
Deployments Interconnection.
OVN support multiple kinds of gateways.
VTEP Gateways
A ``VTEP gateway’’ connects an OVN logical network to a physical
(or virtual) switch that implements the OVSDB VTEP schema that
accompanies Open vSwitch. (The ``VTEP gateway’’ term is a
misnomer, since a VTEP is just a VXLAN Tunnel Endpoint, but it is
a well established name.) See Life Cycle of a VTEP gateway,
below, for more information.
The main intended use case for VTEP gateways is to attach
physical servers to an OVN logical network using a physical top-
of-rack switch that supports the OVSDB VTEP schema.
L2 Gateways
A L2 gateway simply attaches a designated physical L2 segment
available on some chassis to a logical network. The physical
network effectively becomes part of the logical network.
To set up a L2 gateway, the CMS adds an l2gateway LSP to an
appropriate logical switch, setting LSP options to name the
chassis on which it should be bound. ovn-northd copies this
configuration into a southbound Port_Binding record. On the
designated chassis, ovn-controller forwards packets appropriately
to and from the physical segment.
L2 gateway ports have features in common with localnet ports.
However, with a localnet port, the physical network becomes the
transport between hypervisors. With an L2 gateway, packets are
still transported between hypervisors over tunnels and the
l2gateway port is only used for the packets that are on the
physical network. The application for L2 gateways is similar to
that for VTEP gateways, e.g. to add non-virtualized machines to a
logical network, but L2 gateways do not require special support
from top-of-rack hardware switches.
L3 Gateway Routers
As described above under Logical Networks, ordinary OVN logical
routers are distributed: they are not implemented in a single
place but rather in every hypervisor chassis. This is a problem
for stateful services such as SNAT and DNAT, which need to be
implemented in a centralized manner.
To allow for this kind of functionality, OVN supports L3 gateway
routers, which are OVN logical routers that are implemented in a
designated chassis. Gateway routers are typically used between
distributed logical routers and physical networks. The
distributed logical router and the logical switches behind it, to
which VMs and containers attach, effectively reside on each
hypervisor. The distributed router and the gateway router are
connected by another logical switch, sometimes referred to as a
``join’’ logical switch. (OVN logical routers may be connected to
one another directly, without an intervening switch, but the OVN
implementation only supports gateway logical routers that are
connected to logical switches. Using a join logical switch also
reduces the number of IP addresses needed on the distributed
router.) On the other side, the gateway router connects to
another logical switch that has a localnet port connecting to the
physical network.
The following diagram shows a typical situation. One or more
logical switches LS1, ..., LSn connect to distributed logical
router LR1, which in turn connects through LSjoin to gateway
logical router GLR, which also connects to logical switch
LSlocal, which includes a localnet port to attach to the physical
network.
LSlocal
|
GLR
|
LSjoin
|
LR1
|
+----+----+
| | |
LS1 ... LSn
To configure an L3 gateway router, the CMS sets options:chassis
in the router’s northbound Logical_Router to the chassis’s name.
In response, ovn-northd uses a special l3gateway port binding
(instead of a patch binding) in the southbound database to
connect the logical router to its neighbors. In turn,
ovn-controller tunnels packets to this port binding to the
designated L3 gateway chassis, instead of processing them
locally.
DNAT and SNAT rules may be associated with a gateway router,
which provides a central location that can handle one-to-many
SNAT (aka IP masquerading). Distributed gateway ports, described
below, also support NAT.
Distributed Gateway Ports
A distributed gateway port is a logical router port that is
specially configured to designate one distinguished chassis,
called the gateway chassis, for centralized processing. A
distributed gateway port should connect to a logical switch that
has an LSP that connects externally, that is, either a localnet
LSP or a connection to another OVN deployment (see OVN
Deployments Interconnection). Packets that traverse the
distributed gateway port are processed without involving the
gateway chassis when they can be, but when needed they do take an
extra hop through it.
The following diagram illustrates the use of a distributed
gateway port. A number of logical switches LS1, ..., LSn connect
to distributed logical router LR1, which in turn connects through
the distributed gateway port to logical switch LSlocal that
includes a localnet port to attach to the physical network.
LSlocal
|
LR1
|
+----+----+
| | |
LS1 ... LSn
ovn-northd creates two southbound Port_Binding records to
represent a distributed gateway port, instead of the usual one.
One of these is a patch port binding named for the LRP, which is
used for as much traffic as it can. The other one is a port
binding with type chassisredirect, named cr-port. The
chassisredirect port binding has one specialized job: when a
packet is output to it, the flow table causes it to be tunneled
to the gateway chassis, at which point it is automatically output
to the patch port binding. Thus, the flow table can output to
this port binding in cases where a particular task has to happen
on the gateway chassis. The chassisredirect port binding is not
otherwise used (for example, it never receives packets).
The CMS may configure distributed gateway ports three different
ways. See Distributed Gateway Ports in the documentation for
Logical_Router_Port in ovn-nb(5) for details.
Distributed gateway ports support high availability. When more
than one chassis is specified, OVN only uses one at a time as the
gateway chassis. OVN uses BFD to monitor gateway connectivity,
preferring the highest-priority gateway that is online.
A logical router can have multiple distributed gateway ports,
each connecting different external networks. Load balancing is
not yet supported for logical routers with more than one
distributed gateway port configured.
Physical VLAN MTU Issues
Consider the preceding diagram again:
LSlocal
|
LR1
|
+----+----+
| | |
LS1 ... LSn
Suppose that each logical switch LS1, ..., LSn is bridged to a
physical VLAN-tagged network attached to a localnet port on
LSlocal, over a distributed gateway port on LR1. If a packet
originating on LSi is destined to the external network, OVN sends
it to the gateway chassis over a tunnel. There, the packet
traverses LR1’s logical router pipeline, possibly undergoes NAT,
and eventually ends up at LSlocal’s localnet port. If all of the
physical links in the network have the same MTU, then the
packet’s transit across a tunnel causes an MTU problem: tunnel
overhead prevents a packet that uses the full physical MTU from
crossing the tunnel to the gateway chassis (without
fragmentation).
OVN offers two solutions to this problem, the
reside-on-redirect-chassis and redirect-type options. Both
solutions require each logical switch LS1, ..., LSn to include a
localnet logical switch port LN1, ..., LNn respectively, that is
present on each chassis. Both cause packets to be sent over the
localnet ports instead of tunnels. They differ in which
packets-some or all-are sent this way. The most prominent
tradeoff between these options is that reside-on-redirect-chassis
is easier to configure and that redirect-type performs better for
east-west traffic.
The first solution is the reside-on-redirect-chassis option for
logical router ports. Setting this option on a LRP from (e.g.)
LS1 to LR1 disables forwarding from LS1 to LR1 except on the
gateway chassis. On chassis other than the gateway chassis, this
single change means that packets that would otherwise have been
forwarded to LR1 are instead forwarded to LN1. The instance of
LN1 on the gateway chassis then receives the packet and forwards
it to LR1. The packet traverses the LR1 logical router pipeline,
possibly undergoes NAT, and eventually ends up at LSlocal’s
localnet port. The packet never traverses a tunnel, avoiding the
MTU issue.
This option has the further consequence of centralizing
``distributed’’ logical router LR1, since no packets are
forwarded from LS1 to LR1 on any chassis other than the gateway
chassis. Therefore, east-west traffic passes through the gateway
chassis, not just north-south. (The naive ``fix’’ of allowing
east-west traffic to flow directly between chassis over LN1 does
not work because routing sets the Ethernet source address to
LR1’s source address. Seeing this single Ethernet source address
originate from all of the chassis will confuse the physical
switch.)
Do not set the reside-on-redirect-chassis option on a distributed
gateway port. In the diagram above, it would be set on the LRPs
connecting LS1, ..., LSn to LR1.
The second solution is the redirect-type option for distributed
gateway ports. Setting this option to bridged causes packets that
are redirected to the gateway chassis to go over the localnet
ports instead of being tunneled. This option does not change how
OVN treats packets not redirected to the gateway chassis.
The redirect-type option requires the administrator or the CMS to
configure each participating chassis with a unique Ethernet
address for the logical router by setting
ovn-chassis-mac-mappings in the Open vSwitch database, for use by
ovn-controller. This makes it more difficult to configure than
reside-on-redirect-chassis.
Set the redirect-type option on a distributed gateway port.
Using Distributed Gateway Ports For Scalability
Although the primary goal of distributed gateway ports is to
provide connectivity to external networks, there is a special use
case for scalability.
In some deployments, such as the ones using ovn-kubernetes,
logical switches are bound to individual chassises, and are
connected by a distributed logical router. In such deployments,
the chassis level logical switches are centralized on the chassis
instead of distributed, which means the ovn-controller on each
chassis doesn’t need to process flows and ports of logical
switches on other chassises. However, without any specific hint,
ovn-controller would still process all the logical switches as if
they are fully distributed. In this case, distributed gateway
port can be very useful. The chassis level logical switches can
be connected to the distributed router using distributed gateway
ports, by setting the gateway chassis (or HA chassis groups with
only a single chassis in it) to the chassis that each logical
switch is bound to. ovn-controller would then skip processing the
logical switches on all the other chassises, largely improving
the scalability, especially when there are a big number of
chassises.
Life Cycle of a VIF
Tables and their schemas presented in isolation are difficult to
understand. Here’s an example.
A VIF on a hypervisor is a virtual network interface attached
either to a VM or a container running directly on that hypervisor
(This is different from the interface of a container running
inside a VM).
The steps in this example refer often to details of the OVN and
OVN Northbound database schemas. Please see ovn-sb(5) and
ovn-nb(5), respectively, for the full story on these databases.
1. A VIF’s life cycle begins when a CMS administrator
creates a new VIF using the CMS user interface or API
and adds it to a switch (one implemented by OVN as a
logical switch). The CMS updates its own
configuration. This includes associating unique,
persistent identifier vif-id and Ethernet address mac
with the VIF.
2. The CMS plugin updates the OVN Northbound database to
include the new VIF, by adding a row to the
Logical_Switch_Port table. In the new row, name is
vif-id, mac is mac, switch points to the OVN logical
switch’s Logical_Switch record, and other columns are
initialized appropriately.
3. ovn-northd receives the OVN Northbound database
update. In turn, it makes the corresponding updates to
the OVN Southbound database, by adding rows to the OVN
Southbound database Logical_Flow table to reflect the
new port, e.g. add a flow to recognize that packets
destined to the new port’s MAC address should be
delivered to it, and update the flow that delivers
broadcast and multicast packets to include the new
port. It also creates a record in the Binding table
and populates all its columns except the column that
identifies the chassis.
4. On every hypervisor, ovn-controller receives the
Logical_Flow table updates that ovn-northd made in the
previous step. As long as the VM that owns the VIF is
powered off, ovn-controller cannot do much; it cannot,
for example, arrange to send packets to or receive
packets from the VIF, because the VIF does not
actually exist anywhere.
5. Eventually, a user powers on the VM that owns the VIF.
On the hypervisor where the VM is powered on, the
integration between the hypervisor and Open vSwitch
(described in Documentation/topics/integration.rst in
the Open vSwitch source tree) adds the VIF to the OVN
integration bridge and stores vif-id in
external_ids:iface-id to indicate that the interface
is an instantiation of the new VIF. (None of this code
is new in OVN; this is pre-existing integration work
that has already been done on hypervisors that support
OVS.)
6. On the hypervisor where the VM is powered on,
ovn-controller notices external_ids:iface-id in the
new Interface. In response, in the OVN Southbound DB,
it updates the Binding table’s chassis column for the
row that links the logical port from external_ids:
iface-id to the hypervisor. Afterward, ovn-controller
updates the local hypervisor’s OpenFlow tables so that
packets to and from the VIF are properly handled.
7. Some CMS systems, including OpenStack, fully start a
VM only when its networking is ready. To support this,
ovn-northd notices the chassis column updated for the
row in Binding table and pushes this upward by
updating the up column in the OVN Northbound
database’s Logical_Switch_Port table to indicate that
the VIF is now up. The CMS, if it uses this feature,
can then react by allowing the VM’s execution to
proceed.
8. On every hypervisor but the one where the VIF resides,
ovn-controller notices the completely populated row in
the Binding table. This provides ovn-controller the
physical location of the logical port, so each
instance updates the OpenFlow tables of its switch
(based on logical datapath flows in the OVN DB
Logical_Flow table) so that packets to and from the
VIF can be properly handled via tunnels.
9. Eventually, a user powers off the VM that owns the
VIF. On the hypervisor where the VM was powered off,
the VIF is deleted from the OVN integration bridge.
10. On the hypervisor where the VM was powered off,
ovn-controller notices that the VIF was deleted. In
response, it removes the Chassis column content in the
Binding table for the logical port.
11. On every hypervisor, ovn-controller notices the empty
Chassis column in the Binding table’s row for the
logical port. This means that ovn-controller no longer
knows the physical location of the logical port, so
each instance updates its OpenFlow table to reflect
that.
12. Eventually, when the VIF (or its entire VM) is no
longer needed by anyone, an administrator deletes the
VIF using the CMS user interface or API. The CMS
updates its own configuration.
13. The CMS plugin removes the VIF from the OVN Northbound
database, by deleting its row in the
Logical_Switch_Port table.
14. ovn-northd receives the OVN Northbound update and in
turn updates the OVN Southbound database accordingly,
by removing or updating the rows from the OVN
Southbound database Logical_Flow table and Binding
table that were related to the now-destroyed VIF.
15. On every hypervisor, ovn-controller receives the
Logical_Flow table updates that ovn-northd made in the
previous step. ovn-controller updates OpenFlow tables
to reflect the update, although there may not be much
to do, since the VIF had already become unreachable
when it was removed from the Binding table in a
previous step.
Life Cycle of a Container Interface Inside a VM
OVN provides virtual network abstractions by converting
information written in OVN_NB database to OpenFlow flows in each
hypervisor. Secure virtual networking for multi-tenants can only
be provided if OVN controller is the only entity that can modify
flows in Open vSwitch. When the Open vSwitch integration bridge
resides in the hypervisor, it is a fair assumption to make that
tenant workloads running inside VMs cannot make any changes to
Open vSwitch flows.
If the infrastructure provider trusts the applications inside the
containers not to break out and modify the Open vSwitch flows,
then containers can be run in hypervisors. This is also the case
when containers are run inside the VMs and Open vSwitch
integration bridge with flows added by OVN controller resides in
the same VM. For both the above cases, the workflow is the same
as explained with an example in the previous section ("Life Cycle
of a VIF").
This section talks about the life cycle of a container interface
(CIF) when containers are created in the VMs and the Open vSwitch
integration bridge resides inside the hypervisor. In this case,
even if a container application breaks out, other tenants are not
affected because the containers running inside the VMs cannot
modify the flows in the Open vSwitch integration bridge.
When multiple containers are created inside a VM, there are
multiple CIFs associated with them. The network traffic
associated with these CIFs need to reach the Open vSwitch
integration bridge running in the hypervisor for OVN to support
virtual network abstractions. OVN should also be able to
distinguish network traffic coming from different CIFs. There are
two ways to distinguish network traffic of CIFs.
One way is to provide one VIF for every CIF (1:1 model). This
means that there could be a lot of network devices in the
hypervisor. This would slow down OVS because of all the
additional CPU cycles needed for the management of all the VIFs.
It would also mean that the entity creating the containers in a
VM should also be able to create the corresponding VIFs in the
hypervisor.
The second way is to provide a single VIF for all the CIFs
(1:many model). OVN could then distinguish network traffic coming
from different CIFs via a tag written in every packet. OVN uses
this mechanism and uses VLAN as the tagging mechanism.
1. A CIF’s life cycle begins when a container is spawned
inside a VM by the either the same CMS that created
the VM or a tenant that owns that VM or even a
container Orchestration System that is different than
the CMS that initially created the VM. Whoever the
entity is, it will need to know the vif-id that is
associated with the network interface of the VM
through which the container interface’s network
traffic is expected to go through. The entity that
creates the container interface will also need to
choose an unused VLAN inside that VM.
2. The container spawning entity (either directly or
through the CMS that manages the underlying
infrastructure) updates the OVN Northbound database to
include the new CIF, by adding a row to the
Logical_Switch_Port table. In the new row, name is any
unique identifier, parent_name is the vif-id of the VM
through which the CIF’s network traffic is expected to
go through and the tag is the VLAN tag that identifies
the network traffic of that CIF.
3. ovn-northd receives the OVN Northbound database
update. In turn, it makes the corresponding updates to
the OVN Southbound database, by adding rows to the OVN
Southbound database’s Logical_Flow table to reflect
the new port and also by creating a new row in the
Binding table and populating all its columns except
the column that identifies the chassis.
4. On every hypervisor, ovn-controller subscribes to the
changes in the Binding table. When a new row is
created by ovn-northd that includes a value in
parent_port column of Binding table, the
ovn-controller in the hypervisor whose OVN integration
bridge has that same value in vif-id in
external_ids:iface-id updates the local hypervisor’s
OpenFlow tables so that packets to and from the VIF
with the particular VLAN tag are properly handled.
Afterward it updates the chassis column of the Binding
to reflect the physical location.
5. One can only start the application inside the
container after the underlying network is ready. To
support this, ovn-northd notices the updated chassis
column in Binding table and updates the up column in
the OVN Northbound database’s Logical_Switch_Port
table to indicate that the CIF is now up. The entity
responsible to start the container application queries
this value and starts the application.
6. Eventually the entity that created and started the
container, stops it. The entity, through the CMS (or
directly) deletes its row in the Logical_Switch_Port
table.
7. ovn-northd receives the OVN Northbound update and in
turn updates the OVN Southbound database accordingly,
by removing or updating the rows from the OVN
Southbound database Logical_Flow table that were
related to the now-destroyed CIF. It also deletes the
row in the Binding table for that CIF.
8. On every hypervisor, ovn-controller receives the
Logical_Flow table updates that ovn-northd made in the
previous step. ovn-controller updates OpenFlow tables
to reflect the update.
Architectural Physical Life Cycle of a Packet
This section describes how a packet travels from one virtual
machine or container to another through OVN. This description
focuses on the physical treatment of a packet; for a description
of the logical life cycle of a packet, please refer to the
Logical_Flow table in ovn-sb(5).
This section mentions several data and metadata fields, for
clarity summarized here:
tunnel key
When OVN encapsulates a packet in Geneve or another
tunnel, it attaches extra data to it to allow the
receiving OVN instance to process it correctly.
This takes different forms depending on the
particular encapsulation, but in each case we refer
to it here as the ``tunnel key.’’ See Tunnel
Encapsulations, below, for details.
logical datapath field
A field that denotes the logical datapath through
which a packet is being processed. OVN uses the
field that OpenFlow 1.1+ simply (and confusingly)
calls ``metadata’’ to store the logical datapath.
(This field is passed across tunnels as part of the
tunnel key.)
logical input port field
A field that denotes the logical port from which
the packet entered the logical datapath. OVN stores
this in Open vSwitch extension register number 14.
Geneve and STT tunnels pass this field as part of
the tunnel key. Ramp switch VXLAN tunnels do not
explicitly carry a logical input port, but since
they are used to communicate with gateways that
from OVN’s perspective consist of only a single
logical port, so that OVN can set the logical input
port field to this one on ingress to the OVN
logical pipeline. As for regular VXLAN tunnels,
they don’t carry input port field at all. This puts
additional limitations on cluster capabilities that
are described in Tunnel Encapsulations section.
logical output port field
A field that denotes the logical port from which
the packet will leave the logical datapath. This is
initialized to 0 at the beginning of the logical
ingress pipeline. OVN stores this in Open vSwitch
extension register number 15.
Geneve, STT and regular VXLAN tunnels pass this
field as part of the tunnel key. Ramp switch VXLAN
tunnels do not transmit the logical output port
field, and since they do not carry a logical output
port field in the tunnel key, when a packet is
received from ramp switch VXLAN tunnel by an OVN
hypervisor, the packet is resubmitted to table 8 to
determine the output port(s); when the packet
reaches table 39, these packets are resubmitted to
table 40 for local delivery by checking a
MLF_RCV_FROM_RAMP flag, which is set when the
packet arrives from a ramp tunnel.
conntrack zone field for logical ports
A field that denotes the connection tracking zone
for logical ports. The value only has local
significance and is not meaningful between chassis.
This is initialized to 0 at the beginning of the
logical ingress pipeline. OVN stores this in the
lower 16 bits of the Open vSwitch extension
register number 13.
conntrack zone fields for routers
Fields that denote the connection tracking zones
for routers. These values only have local
significance and are not meaningful between
chassis. OVN stores the zone information for north
to south traffic (for DNATting or ECMP symmetric
replies) in Open vSwitch extension register number
11 and zone information for south to north traffic
(for SNATing) in Open vSwitch extension register
number 12.
Encap ID for logical ports
A field that records an ID that indicates which
encapsulation IP should be used when sending
packets to a remote chassis, according to the
original input logical port. This is useful when
there are multiple IPs available for encapsulation.
The value only has local significance and is not
meaningful between chassis. This is initialized to
0 at the beginning of the logical ingress pipeline.
OVN stores this in the higher 16 bits of the Open
vSwitch extension register number 13.
logical flow flags
The logical flags are intended to handle keeping
context between tables in order to decide which
rules in subsequent tables are matched. These
values only have local significance and are not
meaningful between chassis. OVN stores the logical
flags in Open vSwitch extension register number 10.
VLAN ID
The VLAN ID is used as an interface between OVN and
containers nested inside a VM (see Life Cycle of a
container interface inside a VM, above, for more
information).
Initially, a VM or container on the ingress hypervisor sends a
packet on a port attached to the OVN integration bridge. Then:
1. OpenFlow table 0 performs physical-to-logical
translation. It matches the packet’s ingress port. Its
actions annotate the packet with logical metadata, by
setting the logical datapath field to identify the
logical datapath that the packet is traversing and the
logical input port field to identify the ingress port.
Then it resubmits to table 8 to enter the logical
ingress pipeline.
Packets that originate from a container nested within
a VM are treated in a slightly different way. The
originating container can be distinguished based on
the VIF-specific VLAN ID, so the physical-to-logical
translation flows additionally match on VLAN ID and
the actions strip the VLAN header. Following this
step, OVN treats packets from containers just like any
other packets.
Table 0 also processes packets that arrive from other
chassis. It distinguishes them from other packets by
ingress port, which is a tunnel. As with packets just
entering the OVN pipeline, the actions annotate these
packets with logical datapath metadata. For tunnel
types that support it, they are also annotated with
logical ingress port metadata. In addition, the
actions set the logical output port field, which is
available because in OVN tunneling occurs after the
logical output port is known. These pieces of
information are obtained from the tunnel encapsulation
metadata (see Tunnel Encapsulations for encoding
details). Then the actions resubmit to table 38 to
enter the logical egress pipeline.
2. OpenFlow tables 8 through 31 execute the logical
ingress pipeline from the Logical_Flow table in the
OVN Southbound database. These tables are expressed
entirely in terms of logical concepts like logical
ports and logical datapaths. A big part of
ovn-controller’s job is to translate them into
equivalent OpenFlow (in particular it translates the
table numbers: Logical_Flow tables 0 through 23 become
OpenFlow tables 8 through 31).
Each logical flow maps to one or more OpenFlow flows.
An actual packet ordinarily matches only one of these,
although in some cases it can match more than one of
these flows (which is not a problem because all of
them have the same actions). ovn-controller uses the
first 32 bits of the logical flow’s UUID as the cookie
for its OpenFlow flow or flows. (This is not
necessarily unique, since the first 32 bits of a
logical flow’s UUID is not necessarily unique.)
Some logical flows can map to the Open vSwitch
``conjunctive match’’ extension (see ovs-fields(7)).
Flows with a conjunction action use an OpenFlow cookie
of 0, because they can correspond to multiple logical
flows. The OpenFlow flow for a conjunctive match
includes a match on conj_id.
Some logical flows may not be represented in the
OpenFlow tables on a given hypervisor, if they could
not be used on that hypervisor. For example, if no VIF
in a logical switch resides on a given hypervisor, and
the logical switch is not otherwise reachable on that
hypervisor (e.g. over a series of hops through logical
switches and routers starting from a VIF on the
hypervisor), then the logical flow may not be
represented there.
Most OVN actions have fairly obvious implementations
in OpenFlow (with OVS extensions), e.g. next; is
implemented as resubmit, field = constant; as
set_field. A few are worth describing in more detail:
output:
Implemented by resubmitting the packet to table
37. If the pipeline executes more than one
output action, then each one is separately
resubmitted to table 37. This can be used to
send multiple copies of the packet to multiple
ports. (If the packet was not modified between
the output actions, and some of the copies are
destined to the same hypervisor, then using a
logical multicast output port would save
bandwidth between hypervisors.)
get_arp(P, A);
get_nd(P, A);
Implemented by storing arguments into OpenFlow
fields, then resubmitting to table 66, which
ovn-controller populates with flows generated
from the MAC_Binding table in the OVN Southbound
database. If there is a match in table 66, then
its actions store the bound MAC in the Ethernet
destination address field.
(The OpenFlow actions save and restore the
OpenFlow fields used for the arguments, so that
the OVN actions do not have to be aware of this
temporary use.)
put_arp(P, A, E);
put_nd(P, A, E);
Implemented by storing the arguments into
OpenFlow fields, then outputting a packet to
ovn-controller, which updates the MAC_Binding
table.
(The OpenFlow actions save and restore the
OpenFlow fields used for the arguments, so that
the OVN actions do not have to be aware of this
temporary use.)
R = lookup_arp(P, A, M);
R = lookup_nd(P, A, M);
Implemented by storing arguments into OpenFlow
fields, then resubmitting to table 67, which
ovn-controller populates with flows generated
from the MAC_Binding table in the OVN Southbound
database. If there is a match in table 67, then
its actions set the logical flow flag
MLF_LOOKUP_MAC.
(The OpenFlow actions save and restore the
OpenFlow fields used for the arguments, so that
the OVN actions do not have to be aware of this
temporary use.)
3. OpenFlow tables 37 through 41 implement the output
action in the logical ingress pipeline. Specifically,
table 37 serves as an entry point to egress pipeline.
Table 37 detects IP packets that are too big for a
corresponding interface. Table 38 produces ICMPv4
Fragmentation Needed (or ICMPv6 Too Big) errors and
deliver them back to the offending port. table 39
handles packets to remote hypervisors, table 40
handles packets to the local hypervisor, and table 41
checks whether packets whose logical ingress and
egress port are the same should be discarded.
Logical patch ports are a special case. Logical patch
ports do not have a physical location and effectively
reside on every hypervisor. Thus, flow table 40, for
output to ports on the local hypervisor, naturally
implements output to unicast logical patch ports too.
However, applying the same logic to a logical patch
port that is part of a logical multicast group yields
packet duplication, because each hypervisor that
contains a logical port in the multicast group will
also output the packet to the logical patch port.
Thus, multicast groups implement output to logical
patch ports in table 39.
Each flow in table 39 matches on a logical output port
for unicast or multicast logical ports that include a
logical port on a remote hypervisor. Each flow’s
actions implement sending a packet to the port it
matches. For unicast logical output ports on remote
hypervisors, the actions set the tunnel key to the
correct value, then send the packet on the tunnel port
to the correct hypervisor. (When the remote hypervisor
receives the packet, table 0 there will recognize it
as a tunneled packet and pass it along to table 40.)
For multicast logical output ports, the actions send
one copy of the packet to each remote hypervisor, in
the same way as for unicast destinations. If a
multicast group includes a logical port or ports on
the local hypervisor, then its actions also resubmit
to table 40. Table 39 also includes:
• A higher-priority rule to match packets
received from ramp switch tunnels, based on
flag MLF_RCV_FROM_RAMP, and resubmit these
packets to table 40 for local delivery. Packets
received from ramp switch tunnels reach here
because of a lack of logical output port field
in the tunnel key and thus these packets needed
to be submitted to table 8 to determine the
output port.
• A higher-priority rule to match packets
received from ports of type localport, based on
the logical input port, and resubmit these
packets to table 40 for local delivery. Ports
of type localport exist on every hypervisor and
by definition their traffic should never go out
through a tunnel.
• A higher-priority rule to match packets that
have the MLF_LOCAL_ONLY logical flow flag set,
and whose destination is a multicast address.
This flag indicates that the packet should not
be delivered to remote hypervisors, even if the
multicast destination includes ports on remote
hypervisors. This flag is used when
ovn-controller is the originator of the
multicast packet. Since each ovn-controller
instance is originating these packets, the
packets only need to be delivered to local
ports.
• A fallback flow that resubmits to table 40 if
there is no other match.
Flows in table 40 resemble those in table 39 but for
logical ports that reside locally rather than
remotely. For unicast logical output ports on the
local hypervisor, the actions just resubmit to table
41. For multicast output ports that include one or
more logical ports on the local hypervisor, for each
such logical port P, the actions change the logical
output port to P, then resubmit to table 41.
A special case is that when a localnet port exists on
the datapath, remote port is connected by switching to
the localnet port. In this case, instead of adding a
flow in table 39 to reach the remote port, a flow is
added in table 40 to switch the logical outport to the
localnet port, and resubmit to table 40 as if it were
unicasted to a logical port on the local hypervisor.
Table 41 matches and drops packets for which the
logical input and output ports are the same and the
MLF_ALLOW_LOOPBACK flag is not set. It also drops
MLF_LOCAL_ONLY packets directed to a localnet port. It
resubmits other packets to table 42.
4. OpenFlow tables 42 through 62 execute the logical
egress pipeline from the Logical_Flow table in the OVN
Southbound database. The egress pipeline can perform a
final stage of validation before packet delivery.
Eventually, it may execute an output action, which
ovn-controller implements by resubmitting to table 64.
A packet for which the pipeline never executes output
is effectively dropped (although it may have been
transmitted through a tunnel across a physical
network).
The egress pipeline cannot change the logical output
port or cause further tunneling.
5. Table 64 bypasses OpenFlow loopback when
MLF_ALLOW_LOOPBACK is set. Logical loopback was
handled in table 41, but OpenFlow by default also
prevents loopback to the OpenFlow ingress port. Thus,
when MLF_ALLOW_LOOPBACK is set, OpenFlow table 64
saves the OpenFlow ingress port, sets it to zero,
resubmits to table 65 for logical-to-physical
transformation, and then restores the OpenFlow ingress
port, effectively disabling OpenFlow loopback
prevents. When MLF_ALLOW_LOOPBACK is unset, table 64
flow simply resubmits to table 65.
6. OpenFlow table 65 performs logical-to-physical
translation, the opposite of table 0. It matches the
packet’s logical egress port. Its actions output the
packet to the port attached to the OVN integration
bridge that represents that logical port. If the
logical egress port is a container nested with a VM,
then before sending the packet the actions push on a
VLAN header with an appropriate VLAN ID.
Logical Routers and Logical Patch Ports
Typically logical routers and logical patch ports do not have a
physical location and effectively reside on every hypervisor.
This is the case for logical patch ports between logical routers
and logical switches behind those logical routers, to which VMs
(and VIFs) attach.
Consider a packet sent from one virtual machine or container to
another VM or container that resides on a different subnet. The
packet will traverse tables 0 to 65 as described in the previous
section Architectural Physical Life Cycle of a Packet, using the
logical datapath representing the logical switch that the sender
is attached to. At table 39, the packet will use the fallback
flow that resubmits locally to table 40 on the same hypervisor.
In this case, all of the processing from table 0 to table 65
occurs on the hypervisor where the sender resides.
When the packet reaches table 65, the logical egress port is a
logical patch port. ovn-controller implements output to the
logical patch is packet by cloning and resubmitting directly to
the first OpenFlow flow table in the ingress pipeline, setting
the logical ingress port to the peer logical patch port, and
using the peer logical patch port’s logical datapath (that
represents the logical router).
The packet re-enters the ingress pipeline in order to traverse
tables 8 to 65 again, this time using the logical datapath
representing the logical router. The processing continues as
described in the previous section Architectural Physical Life
Cycle of a Packet. When the packet reaches table 65, the logical
egress port will once again be a logical patch port. In the same
manner as described above, this logical patch port will cause the
packet to be resubmitted to OpenFlow tables 8 to 65, this time
using the logical datapath representing the logical switch that
the destination VM or container is attached to.
The packet traverses tables 8 to 65 a third and final time. If
the destination VM or container resides on a remote hypervisor,
then table 39 will send the packet on a tunnel port from the
sender’s hypervisor to the remote hypervisor. Finally table 65
will output the packet directly to the destination VM or
container.
The following sections describe two exceptions, where logical
routers and/or logical patch ports are associated with a physical
location.
Gateway Routers
A gateway router is a logical router that is bound to a physical
location. This includes all of the logical patch ports of the
logical router, as well as all of the peer logical patch ports on
logical switches. In the OVN Southbound database, the
Port_Binding entries for these logical patch ports use the type
l3gateway rather than patch, in order to distinguish that these
logical patch ports are bound to a chassis.
When a hypervisor processes a packet on a logical datapath
representing a logical switch, and the logical egress port is a
l3gateway port representing connectivity to a gateway router, the
packet will match a flow in table 39 that sends the packet on a
tunnel port to the chassis where the gateway router resides. This
processing in table 39 is done in the same manner as for VIFs.
Distributed Gateway Ports
This section provides additional details on distributed gateway
ports, outlined earlier.
The primary design goal of distributed gateway ports is to allow
as much traffic as possible to be handled locally on the
hypervisor where a VM or container resides. Whenever possible,
packets from the VM or container to the outside world should be
processed completely on that VM’s or container’s hypervisor,
eventually traversing a localnet port instance or a tunnel to the
physical network or a different OVN deployment. Whenever
possible, packets from the outside world to a VM or container
should be directed through the physical network directly to the
VM’s or container’s hypervisor.
In order to allow for the distributed processing of packets
described in the paragraph above, distributed gateway ports need
to be logical patch ports that effectively reside on every
hypervisor, rather than l3gateway ports that are bound to a
particular chassis. However, the flows associated with
distributed gateway ports often need to be associated with
physical locations, for the following reasons:
• The physical network that the localnet port is
attached to typically uses L2 learning. Any
Ethernet address used over the distributed gateway
port must be restricted to a single physical
location so that upstream L2 learning is not
confused. Traffic sent out the distributed gateway
port towards the localnet port with a specific
Ethernet address must be sent out one specific
instance of the distributed gateway port on one
specific chassis. Traffic received from the
localnet port (or from a VIF on the same logical
switch as the localnet port) with a specific
Ethernet address must be directed to the logical
switch’s patch port instance on that specific
chassis.
Due to the implications of L2 learning, the
Ethernet address and IP address of the distributed
gateway port need to be restricted to a single
physical location. For this reason, the user must
specify one chassis associated with the distributed
gateway port. Note that traffic traversing the
distributed gateway port using other Ethernet
addresses and IP addresses (e.g. one-to-one NAT) is
not restricted to this chassis.
Replies to ARP and ND requests must be restricted
to a single physical location, where the Ethernet
address in the reply resides. This includes ARP and
ND replies for the IP address of the distributed
gateway port, which are restricted to the chassis
that the user associated with the distributed
gateway port.
• In order to support one-to-many SNAT (aka IP
masquerading), where multiple logical IP addresses
spread across multiple chassis are mapped to a
single external IP address, it will be necessary to
handle some of the logical router processing on a
specific chassis in a centralized manner. Since the
SNAT external IP address is typically the
distributed gateway port IP address, and for
simplicity, the same chassis associated with the
distributed gateway port is used.
The details of flow restrictions to specific chassis are
described in the ovn-northd documentation.
While most of the physical location dependent aspects of
distributed gateway ports can be handled by restricting some
flows to specific chassis, one additional mechanism is required.
When a packet leaves the ingress pipeline and the logical egress
port is the distributed gateway port, one of two different sets
of actions is required at table 39:
• If the packet can be handled locally on the
sender’s hypervisor (e.g. one-to-one NAT traffic),
then the packet should just be resubmitted locally
to table 40, in the normal manner for distributed
logical patch ports.
• However, if the packet needs to be handled on the
chassis associated with the distributed gateway
port (e.g. one-to-many SNAT traffic or non-NAT
traffic), then table 39 must send the packet on a
tunnel port to that chassis.
In order to trigger the second set of actions, the
chassisredirect type of southbound Port_Binding has been added.
Setting the logical egress port to the type chassisredirect
logical port is simply a way to indicate that although the packet
is destined for the distributed gateway port, it needs to be
redirected to a different chassis. At table 39, packets with this
logical egress port are sent to a specific chassis, in the same
way that table 39 directs packets whose logical egress port is a
VIF or a type l3gateway port to different chassis. Once the
packet arrives at that chassis, table 40 resets the logical
egress port to the value representing the distributed gateway
port. For each distributed gateway port, there is one type
chassisredirect port, in addition to the distributed logical
patch port representing the distributed gateway port.
High Availability for Distributed Gateway Ports
OVN allows you to specify a prioritized list of chassis for a
distributed gateway port. This is done by associating multiple
Gateway_Chassis rows with a Logical_Router_Port in the
OVN_Northbound database.
When multiple chassis have been specified for a gateway, all
chassis that may send packets to that gateway will enable BFD on
tunnels to all configured gateway chassis. The current active
chassis for the gateway is the highest priority gateway chassis
that is currently viewed as active based on BFD status.
For more information on L3 gateway high availability, please
refer to
http://docs.ovn.org/en/latest/topics/high-availability.html.
Restrictions of Distributed Gateway Ports
Distributed gateway ports are used to connect to an external
network, which can be a physical network modeled by a logical
switch with a localnet port, and can also be a logical switch
that interconnects different OVN deployments (see OVN Deployments
Interconnection). Usually there can be many logical routers
connected to the same external logical switch, as shown in below
diagram.
+--LS-EXT-+
| | |
| | |
LR1 ... LRn
In this diagram, there are n logical routers connected to a
logical switch LS-EXT, each with a distributed gateway port, so
that traffic sent to external world is redirected to the gateway
chassis that is assigned to the distributed gateway port of
respective logical router.
In the logical topology, nothing can prevent an user to add a
route between the logical routers via the connected distributed
gateway ports on LS-EXT. However, the route works only if the LS-
EXT is a physical network (modeled by a logical switch with a
localnet port). In that case the packet will be delivered between
the gateway chassises through the localnet port via physical
network. If the LS-EXT is a regular logical switch (backed by
tunneling only, as in the use case of OVN interconnection), then
the packet will be dropped on the source gateway chassis. The
limitation is due the fact that distributed gateway ports are
tied to physical location, and without physical network
connection, we will end up with either dropping the packet or
transferring it over the tunnels which could cause bigger
problems such as broadcast packets being redirect repeatedly by
different gateway chassises.
With the limitation in mind, if a user do want the direct
connectivity between the logical routers, it is better to create
an internal logical switch connected to the logical routers with
regular logical router ports, which are completely distributed
and the packets don’t have to leave a chassis unless necessary,
which is more optimal than routing via the distributed gateway
ports.
ARP request and ND NS packet processing
Due to the fact that ARP requests and ND NA packets are usually
broadcast packets, for performance reasons, OVN deals with
requests that target OVN owned IP addresses (i.e., IP addresses
configured on the router ports, VIPs, NAT IPs) in a specific way
and only forwards them to the logical router that owns the target
IP address. This behavior is different than that of traditional
switches and implies that other routers/hosts connected to the
logical switch will not learn the MAC/IP binding from the request
packet.
All other ARP and ND packets are flooded in the L2 broadcast
domain and to all attached logical patch ports.
VIFs on the logical switch connected by a distributed gateway port
Typically the logical switch connected by a distributed gateway
port is for external connectivity, usually to a physical network
through a localnet port on the logical switch, or to a remote OVN
deployment through OVN Interconnection. In these cases there is
no VIF ports required on the logical switch.
While not very common, it is still possible to create VIF ports
on the logical switch connected by a distributed gateway port,
but there is a limitation that the logical ports need to reside
on the gateway chassis where the distributed gateway port resides
to get connectivity to other logical switches through the
distributed gateway port. There is no limitation for the VIFs to
connect within the logical switch, or beyond the logical switch
through other regular distributed logical router ports.
A special case is when using distributed gateway ports for
scalability purpose, as mentioned earlier in this document. The
logical switches connected by distributed gateway ports are not
for connectivity but just for regular VIFs. However, the above
limitation usually does not matter because in this use case all
the VIFs on the logical switch are located on the same chassis
with the distributed gateway port that connects the logical
switch.
Multiple localnet logical switches connected to a Logical Router
It is possible to have multiple logical switches each with a
localnet port (representing physical networks) connected to a
logical router, in which one localnet logical switch may provide
the external connectivity via a distributed gateway port and rest
of the localnet logical switches use VLAN tagging in the physical
network. It is expected that ovn-bridge-mappings is configured
appropriately on the chassis for all these localnet networks.
East West routing
East-West routing between these localnet VLAN tagged logical
switches work almost the same way as normal logical switches.
When the VM sends such a packet, then:
1. It first enters the ingress pipeline, and then egress
pipeline of the source localnet logical switch
datapath. It then enters the ingress pipeline of the
logical router datapath via the logical router port in
the source chassis.
2. Routing decision is taken.
3. From the router datapath, packet enters the ingress
pipeline and then egress pipeline of the destination
localnet logical switch datapath and goes out of the
integration bridge to the provider bridge ( belonging
to the destination logical switch) via the localnet
port. While sending the packet to provider bridge, we
also replace router port MAC as source MAC with a
chassis unique MAC.
This chassis unique MAC is configured as global ovs
config on each chassis (eg. via "ovs-vsctl set open .
external-ids:
ovn-chassis-mac-mappings="phys:aa:bb:cc:dd:ee:$i$i"").
For more details, see ovn-controller(8).
If the above is not configured, then source MAC would
be the router port MAC. This could create problem if
we have more than one chassis. This is because, since
the router port is distributed, the same (MAC,VLAN)
tuple will seen by physical network from other chassis
as well, which could cause these issues:
• Continuous MAC moves in top-of-rack switch
(ToR).
• ToR dropping the traffic, which is causing
continuous MAC moves.
• ToR blocking the ports from which MAC moves are
happening.
4. The destination chassis receives the packet via the
localnet port and sends it to the integration bridge.
Before entering the integration bridge the source mac
of the packet will be replaced with router port mac
again. The packet enters the ingress pipeline and then
egress pipeline of the destination localnet logical
switch and finally gets delivered to the destination
VM port.
External traffic
The following happens when a VM sends an external traffic (which
requires NATting) and the chassis hosting the VM doesn’t have a
distributed gateway port.
1. The packet first enters the ingress pipeline, and then
egress pipeline of the source localnet logical switch
datapath. It then enters the ingress pipeline of the
logical router datapath via the logical router port in
the source chassis.
2. Routing decision is taken. Since the gateway router or
the distributed gateway port doesn’t reside in the
source chassis, the traffic is redirected to the
gateway chassis via the tunnel port.
3. The gateway chassis receives the packet via the tunnel
port and the packet enters the egress pipeline of the
logical router datapath. NAT rules are applied here.
The packet then enters the ingress pipeline and then
egress pipeline of the localnet logical switch
datapath which provides external connectivity and
finally goes out via the localnet port of the logical
switch which provides external connectivity.
Although this works, the VM traffic is tunnelled when sent from
the compute chassis to the gateway chassis. In order for it to
work properly, the MTU of the localnet logical switches must be
lowered to account for the tunnel encapsulation.
Centralized routing for localnet VLAN tagged logical switches
connected to a Logical Router
To overcome the tunnel encapsulation problem described in the
previous section, OVN supports the option of enabling centralized
routing for localnet VLAN tagged logical switches. CMS can
configure the option options:reside-on-redirect-chassis to true
for each Logical_Router_Port which connects to the localnet VLAN
tagged logical switches. This causes the gateway chassis (hosting
the distributed gateway port) to handle all the routing for these
networks, making it centralized. It will reply to the ARP
requests for the logical router port IPs.
If the logical router doesn’t have a distributed gateway port
connecting to the localnet logical switch which provides external
connectivity, or if it has more than one distributed gateway
ports, then this option is ignored by OVN.
The following happens when a VM sends an east-west traffic which
needs to be routed:
1. The packet first enters the ingress pipeline, and then
egress pipeline of the source localnet logical switch
datapath and is sent out via a localnet port of the
source localnet logical switch (instead of sending it
to router pipeline).
2. The gateway chassis receives the packet via a localnet
port of the source localnet logical switch and sends
it to the integration bridge. The packet then enters
the ingress pipeline, and then egress pipeline of the
source localnet logical switch datapath and enters the
ingress pipeline of the logical router datapath.
3. Routing decision is taken.
4. From the router datapath, packet enters the ingress
pipeline and then egress pipeline of the destination
localnet logical switch datapath. It then goes out of
the integration bridge to the provider bridge (
belonging to the destination logical switch) via a
localnet port.
5. The destination chassis receives the packet via a
localnet port and sends it to the integration bridge.
The packet enters the ingress pipeline and then egress
pipeline of the destination localnet logical switch
and finally delivered to the destination VM port.
The following happens when a VM sends an external traffic which
requires NATting:
1. The packet first enters the ingress pipeline, and then
egress pipeline of the source localnet logical switch
datapath and is sent out via a localnet port of the
source localnet logical switch (instead of sending it
to router pipeline).
2. The gateway chassis receives the packet via a localnet
port of the source localnet logical switch and sends
it to the integration bridge. The packet then enters
the ingress pipeline, and then egress pipeline of the
source localnet logical switch datapath and enters the
ingress pipeline of the logical router datapath.
3. Routing decision is taken and NAT rules are applied.
4. From the router datapath, packet enters the ingress
pipeline and then egress pipeline of the localnet
logical switch datapath which provides external
connectivity. It then goes out of the integration
bridge to the provider bridge (belonging to the
logical switch which provides external connectivity)
via a localnet port.
The following happens for the reverse external traffic.
1. The gateway chassis receives the packet from a
localnet port of the logical switch which provides
external connectivity. The packet then enters the
ingress pipeline and then egress pipeline of the
localnet logical switch (which provides external
connectivity). The packet then enters the ingress
pipeline of the logical router datapath.
2. The ingress pipeline of the logical router datapath
applies the unNATting rules. The packet then enters
the ingress pipeline and then egress pipeline of the
source localnet logical switch. Since the source VM
doesn’t reside in the gateway chassis, the packet is
sent out via a localnet port of the source logical
switch.
3. The source chassis receives the packet via a localnet
port and sends it to the integration bridge. The
packet enters the ingress pipeline and then egress
pipeline of the source localnet logical switch and
finally gets delivered to the source VM port.
As an alternative to reside-on-redirect-chassis, OVN supports
VLAN-based redirection. Whereas reside-on-redirect-chassis
centralizes all router functionality, VLAN-based redirection only
changes how OVN redirects packets to the gateway chassis. By
setting options:redirect-type to bridged on a distributed gateway
port, OVN redirects packets to the gateway chassis using the
localnet port of the router’s peer logical switch, instead of a
tunnel.
If the logical router doesn’t have a distributed gateway port
connecting to the localnet logical switch which provides external
connectivity, or if it has more than one distributed gateway
ports, then this option is ignored by OVN.
Following happens for bridged redirection:
1. On compute chassis, packet passes though logical
router’s ingress pipeline.
2. If logical outport is gateway chassis attached router
port then packet is "redirected" to gateway chassis
using peer logical switch’s localnet port.
3. This redirected packet has destination mac as router
port mac (the one to which gateway chassis is
attached). Its VLAN id is that of localnet port (peer
logical switch of the logical router port).
4. On the gateway chassis packet will enter the logical
router pipeline again and this time it will
passthrough egress pipeline as well.
5. Reverse traffic packet flows stays the same.
Some guidelines and expections with bridged redirection:
1. Since router port mac is destination mac, hence it has
to be ensured that physical network learns it on ONLY
from the gateway chassis. Which means that
ovn-chassis-mac-mappings should be configure on all
the compute nodes, so that physical network never
learn router port mac from compute nodes.
2. Since packet enters logical router ingress pipeline
twice (once on compute chassis and again on gateway
chassis), hence ttl will be decremented twice.
3. Default redirection type continues to be overlay. User
can switch the redirect-type between bridged and
overlay by changing the value of options:redirect-type
Life Cycle of a VTEP gateway
A gateway is a chassis that forwards traffic between the OVN-
managed part of a logical network and a physical VLAN, extending
a tunnel-based logical network into a physical network.
The steps below refer often to details of the OVN and VTEP
database schemas. Please see ovn-sb(5), ovn-nb(5) and vtep(5),
respectively, for the full story on these databases.
1. A VTEP gateway’s life cycle begins with the
administrator registering the VTEP gateway as a
Physical_Switch table entry in the VTEP database. The
ovn-controller-vtep connected to this VTEP database,
will recognize the new VTEP gateway and create a new
Chassis table entry for it in the OVN_Southbound
database.
2. The administrator can then create a new Logical_Switch
table entry, and bind a particular vlan on a VTEP
gateway’s port to any VTEP logical switch. Once a VTEP
logical switch is bound to a VTEP gateway, the
ovn-controller-vtep will detect it and add its name to
the vtep_logical_switches column of the Chassis table
in the OVN_Southbound database. Note, the tunnel_key
column of VTEP logical switch is not filled at
creation. The ovn-controller-vtep will set the column
when the corresponding vtep logical switch is bound to
an OVN logical network.
3. Now, the administrator can use the CMS to add a VTEP
logical switch to the OVN logical network. To do that,
the CMS must first create a new Logical_Switch_Port
table entry in the OVN_Northbound database. Then, the
type column of this entry must be set to "vtep". Next,
the vtep-logical-switch and vtep-physical-switch keys
in the options column must also be specified, since
multiple VTEP gateways can attach to the same VTEP
logical switch. Next, the addresses column of this
logical port must be set to "unknown", it will add a
priority 0 entry in "ls_in_l2_lkup" stage of logical
switch ingress pipeline. So, traffic with unrecorded
mac by OVN would go through the Logical_Switch_Port to
physical network.
4. The newly created logical port in the OVN_Northbound
database and its configuration will be passed down to
the OVN_Southbound database as a new Port_Binding
table entry. The ovn-controller-vtep will recognize
the change and bind the logical port to the
corresponding VTEP gateway chassis. Configuration of
binding the same VTEP logical switch to a different
OVN logical networks is not allowed and a warning will
be generated in the log.
5. Beside binding to the VTEP gateway chassis, the
ovn-controller-vtep will update the tunnel_key column
of the VTEP logical switch to the corresponding
Datapath_Binding table entry’s tunnel_key for the
bound OVN logical network.
6. Next, the ovn-controller-vtep will keep reacting to
the configuration change in the Port_Binding in the
OVN_Northbound database, and updating the
Ucast_Macs_Remote table in the VTEP database. This
allows the VTEP gateway to understand where to forward
the unicast traffic coming from the extended external
network.
7. Eventually, the VTEP gateway’s life cycle ends when
the administrator unregisters the VTEP gateway from
the VTEP database. The ovn-controller-vtep will
recognize the event and remove all related
configurations (Chassis table entry and port bindings)
in the OVN_Southbound database.
8. When the ovn-controller-vtep is terminated, all
related configurations in the OVN_Southbound database
and the VTEP database will be cleaned, including
Chassis table entries for all registered VTEP gateways
and their port bindings, and all Ucast_Macs_Remote
table entries and the Logical_Switch tunnel keys.
OVN Deployments Interconnection
It is not uncommon for an operator to deploy multiple OVN
clusters, for two main reasons. Firstly, an operator may prefer
to deploy one OVN cluster for each availability zone, e.g. in
different physical regions, to avoid single point of failure.
Secondly, there is always an upper limit for a single OVN control
plane to scale.
Although the control planes of the different availability zone
(AZ)s are independent from each other, the workloads from
different AZs may need to communicate across the zones. The OVN
interconnection feature provides a native way to interconnect
different AZs by L3 routing through transit overlay networks
between logical routers of different AZs.
A global OVN Interconnection Northbound database is introduced
for the operator (probably through CMS systems) to configure
transit logical switches that connect logical routers from
different AZs. A transit switch is similar to a regular logical
switch, but it is used for interconnection purpose only.
Typically, each transit switch can be used to connect all logical
routers that belong to same tenant across all AZs.
A dedicated daemon process ovn-ic, OVN interconnection
controller, in each AZ will consume this data and populate
corresponding logical switches to their own northbound databases
for each AZ, so that logical routers can be connected to the
transit switch by creating patch port pairs in their northbound
databases. Any router ports connected to the transit switches are
considered interconnection ports, which will be exchanged between
AZs.
Physically, when workloads from different AZs communicate,
packets need to go through multiple hops: source chassis, source
gateway, destination gateway and destination chassis. All these
hops are connected through tunnels so that the packets never
leave overlay networks. A distributed gateway port is required to
connect the logical router to a transit switch, with a gateway
chassis specified, so that the traffic can be forwarded through
the gateway chassis.
A global OVN Interconnection Southbound database is introduced
for exchanging control plane information between the AZs. The
data in this database is populated and consumed by the ovn-ic, of
each AZ. The main information in this database includes:
• Datapath bindings for transit switches, which
mainly contains the tunnel keys generated for each
transit switch. Separate key ranges are reserved
for transit switches so that they will never
conflict with any tunnel keys locally assigned for
datapaths within each AZ.
• Availability zones, which are registered by ovn-ic
from each AZ.
• Gateways. Each AZ specifies chassises that are
supposed to work as interconnection gateways, and
the ovn-ic will populate this information to the
interconnection southbound DB. The ovn-ic from all
the other AZs will learn the gateways and populate
to their own southbound DB as a chassis.
• Port bindings for logical switch ports created on
the transit switch. Each AZ maintains their logical
router to transit switch connections independently,
but ovn-ic automatically populates local port
bindings on transit switches to the global
interconnection southbound DB, and learns remote
port bindings from other AZs back to its own
northbound and southbound DBs, so that logical
flows can be produced and then translated to OVS
flows locally, which finally enables data plane
communication.
• Routes that are advertised between different AZs.
If enabled, routes are automatically exchanged by
ovn-ic. Both static routes and directly connected
subnets are advertised. Options in options column
of the NB_Global table of OVN_NB database control
the behavior of route advertisement, such as
enable/disable the advertising/learning routes,
whether default routes are advertised/learned, and
blacklisted CIDRs. See ovn-nb(5) for more details.
The tunnel keys for transit switch datapaths and related port
bindings must be agreed across all AZs. This is ensured by
generating and storing the keys in the global interconnection
southbound database. Any ovn-ic from any AZ can allocate the key,
but race conditions are solved by enforcing unique index for the
column in the database.
Once each AZ’s NB and SB databases are populated with
interconnection switches and ports, and agreed upon the tunnel
keys, data plane communication between the AZs are established.
When VXLAN tunneling is enabled in an OVN cluster, due to the
limited range available for VNIs, Interconnection feature is not
supported.
A day in the life of a packet crossing AZs
1. An IP packet is sent out from a VIF on a hypervisor
(HV1) of AZ1, with destination IP belonging to a VIF
in AZ2.
2. In HV1’s OVS flow tables, the packet goes through
logical switch and logical router pipelines, and in a
logical router pipeline, the routing stage finds out
the next hop for the destination IP, which belongs to
a remote logical router port in AZ2, and the output
port, which is a chassis-redirect port located on an
interconnection gateway (GW1 in AZ1), so HV1 sends the
packet to GW1 through tunnel.
3. On GW1, it continues with the logical router pipe line
and switches to the transit switch’s pipeline through
the peer port of the chassis redirect port. In the
transit switch’s pipeline it outputs to the remote
logical port which is located on a gateway (GW2) in
AZ2, so the GW1 sends the packet to GW2 in tunnel.
4. On GW2, it continues with the transit switch pipeline
and switches to the logical router pipeline through
the peer port, which is a chassis redirect port that
is located on GW2. The logical router pipeline then
forwards the packet to relevant logical pipelines
according to the destination IP address, and figures
out the MAC and location of the destination VIF port -
a hypervisor (HV2). The GW2 then sends the packet to
HV2 in tunnel.
5. On HV2, the packet is delivered to the final
destination VIF port by the logical switch egress
pipeline, just the same way as for intra-AZ
communications.
Native OVN services for external logical ports
To support OVN native services (like DHCP/IPv6 RA/DNS lookup) to
the cloud resources which are external, OVN supports external
logical ports.
Below are some of the use cases where external ports can be used.
• VMs connected to SR-IOV nics - Traffic from these
VMs by passes the kernel stack and local
ovn-controller do not bind these ports and cannot
serve the native services.
• When CMS supports provisioning baremetal servers.
OVN will provide the native services if CMS has done the below
configuration in the OVN Northbound Database.
• A row is created in Logical_Switch_Port,
configuring the addresses column and setting the
type to external.
• ha_chassis_group column is configured.
• The HA chassis which belongs to the HA chassis
group has the ovn-bridge-mappings configured and
has proper L2 connectivity so that it can receive
the DHCP and other related request packets from
these external resources.
• The Logical_Switch of this port has a localnet
port.
• Native OVN services are enabled by configuring the
DHCP and other options like the way it is done for
the normal logical ports.
It is recommended to use the same HA chassis group for all the
external ports of a logical switch. Otherwise, the physical
switch might see MAC flap issue when different chassis provide
the native services. For example when supporting native DHCPv4
service, DHCPv4 server mac (configured in options:server_mac
column in table DHCP_Options) originating from different ports
can cause MAC flap issue. The MAC of the logical router IP(s) can
also flap if the same HA chassis group is not set for all the
external ports of a logical switch.
Role-Based Access Controls for the Southbound DB
In order to provide additional security against the possibility
of an OVN chassis becoming compromised in such a way as to allow
rogue software to make arbitrary modifications to the southbound
database state and thus disrupt the OVN network, role-based
access controls (see ovsdb-server(1) for additional details) are
provided for the southbound database.
The implementation of role-based access controls (RBAC) requires
the addition of two tables to an OVSDB schema: the RBAC_Role
table, which is indexed by role name and maps the the names of
the various tables that may be modifiable for a given role to
individual rows in a permissions table containing detailed
permission information for that role, and the permission table
itself which consists of rows containing the following
information:
Table Name
The name of the associated table. This column
exists primarily as an aid for humans reading the
contents of this table.
Auth Criteria
A set of strings containing the names of columns
(or column:key pairs for columns containing
string:string maps). The contents of at least one
of the columns or column:key values in a row to be
modified, inserted, or deleted must be equal to the
ID of the client attempting to act on the row in
order for the authorization check to pass. If the
authorization criteria is empty, authorization
checking is disabled and all clients for the role
will be treated as authorized.
Insert/Delete
Row insertion/deletion permission; boolean value
indicating whether insertion and deletion of rows
is allowed for the associated table. If true,
insertion and deletion of rows is allowed for
authorized clients.
Updatable Columns
A set of strings containing the names of columns or
column:key pairs that may be updated or mutated by
authorized clients. Modifications to columns within
a row are only permitted when the authorization
check for the client passes and all columns to be
modified are included in this set of modifiable
columns.
RBAC configuration for the OVN southbound database is maintained
by ovn-northd. With RBAC enabled, modifications are only
permitted for the Chassis, Encap, Port_Binding, and MAC_Binding
tables, and are restricted as follows:
Chassis
Authorization: client ID must match the chassis
name.
Insert/Delete: authorized row insertion and
deletion are permitted.
Update: The columns nb_cfg, external_ids, encaps,
and vtep_logical_switches may be modified when
authorized.
Encap Authorization: client ID must match the chassis
name.
Insert/Delete: row insertion and row deletion are
permitted.
Update: The columns type, options, and ip can be
modified.
Port_Binding
Authorization: disabled (all clients are considered
authorized. A future enhancement may add columns
(or keys to external_ids) in order to control which
chassis are allowed to bind each port.
Insert/Delete: row insertion/deletion are not
permitted (ovn-northd maintains rows in this table.
Update: Only modifications to the chassis column
are permitted.
MAC_Binding
Authorization: disabled (all clients are considered
to be authorized).
Insert/Delete: row insertion/deletion are
permitted.
Update: The columns logical_port, ip, mac, and
datapath may be modified by ovn-controller.
IGMP_Group
Authorization: disabled (all clients are considered
to be authorized).
Insert/Delete: row insertion/deletion are
permitted.
Update: The columns address, chassis, datapath, and
ports may be modified by ovn-controller.
Enabling RBAC for ovn-controller connections to the southbound
database requires the following steps:
1. Creating SSL certificates for each chassis with the
certificate CN field set to the chassis name (e.g. for
a chassis with external-ids:system-id=chassis-1, via
the command "ovs-pki -u req+sign chassis-1 switch").
2. Configuring each ovn-controller to use SSL when
connecting to the southbound database (e.g. via
"ovs-vsctl set open .
external-ids:ovn-remote=ssl:x.x.x.x:6642").
3. Configuring a southbound database SSL remote with
"ovn-controller" role (e.g. via "ovn-sbctl
set-connection role=ovn-controller pssl:6642").
Encrypt Tunnel Traffic with IPsec
OVN tunnel traffic goes through physical routers and switches.
These physical devices could be untrusted (devices in public
network) or might be compromised. Enabling encryption to the
tunnel traffic can prevent the traffic data from being monitored
and manipulated.
The tunnel traffic is encrypted with IPsec. The CMS sets the
ipsec column in the northbound NB_Global table to enable or
disable IPsec encrytion. If ipsec is true, all OVN tunnels will
be encrypted. If ipsec is false, no OVN tunnels will be
encrypted.
When CMS updates the ipsec column in the northbound NB_Global
table, ovn-northd copies the value to the ipsec column in the
southbound SB_Global table. ovn-controller in each chassis
monitors the southbound database and sets the options of the OVS
tunnel interface accordingly. OVS tunnel interface options are
monitored by the ovs-monitor-ipsec daemon which configures IKE
daemon to set up IPsec connections.
Chassis authenticates each other by using certificate. The
authentication succeeds if the other end in tunnel presents a
certificate signed by a trusted CA and the common name (CN)
matches the expected chassis name. The SSL certificates used in
role-based access controls (RBAC) can be used in IPsec. Or use
ovs-pki to create different certificates. The certificate is
required to be x.509 version 3, and with CN field and
subjectAltName field being set to the chassis name.
The CA certificate, chassis certificate and private key are
required to be installed in each chassis before enabling IPsec.
Please see ovs-vswitchd.conf.db(5) for setting up CA based IPsec
authentication.
Tunnel Encapsulations
In general, OVN annotates logical network packets that it sends
from one hypervisor to another with the following three pieces of
metadata, which are encoded in an encapsulation-specific fashion:
• 24-bit logical datapath identifier, from the
tunnel_key column in the OVN Southbound
Datapath_Binding table.
• 15-bit logical ingress port identifier. ID 0 is
reserved for internal use within OVN. IDs 1 through
32767, inclusive, may be assigned to logical ports
(see the tunnel_key column in the OVN Southbound
Port_Binding table).
• 16-bit logical egress port identifier. IDs 0
through 32767 have the same meaning as for logical
ingress ports. IDs 32768 through 65535, inclusive,
may be assigned to logical multicast groups (see
the tunnel_key column in the OVN Southbound
Multicast_Group table).
When VXLAN is enabled on any hypervisor in a cluster, datapath
and egress port identifier ranges are reduced to 12-bits. This is
done because only STT and Geneve provide the large space for
metadata (over 32 bits per packet). To accommodate for VXLAN, 24
bits available are split as follows:
• 12-bit logical datapath identifier, derived from
the tunnel_key column in the OVN Southbound
Datapath_Binding table.
• 12-bit logical egress port identifier. IDs 0
through 2047 are used for unicast output ports. IDs
2048 through 4095, inclusive, may be assigned to
logical multicast groups (see the tunnel_key column
in the OVN Southbound Multicast_Group table). For
multicast group tunnel keys, a special mapping
scheme is used to internally transform from
internal OVN 16-bit keys to 12-bit values before
sending packets through a VXLAN tunnel, and back
from 12-bit tunnel keys to 16-bit values when
receiving packets from a VXLAN tunnel.
• No logical ingress port identifier.
The limited space available for metadata when VXLAN tunnels are
enabled in a cluster put the following functional limitations
onto features available to users:
• The maximum number of networks is reduced to 4096.
• The maximum number of ports per network is reduced
to 2048.
• ACLs matching against logical ingress port
identifiers are not supported.
• OVN interconnection feature is not supported.
In addition to functional limitations described above, the
following should be considered before enabling it in your
cluster:
• STT and Geneve use randomized UDP or TCP source
ports that allows efficient distribution among
multiple paths in environments that use ECMP in
their underlay.
• NICs are available to offload STT and Geneve
encapsulation and decapsulation.
Due to its flexibility, the preferred encapsulation between
hypervisors is Geneve. For Geneve encapsulation, OVN transmits
the logical datapath identifier in the Geneve VNI. OVN transmits
the logical ingress and logical egress ports in a TLV with class
0x0102, type 0x80, and a 32-bit value encoded as follows, from
MSB to LSB:
1 15 16
+---+------------+-----------+
|rsv|ingress port|egress port|
+---+------------+-----------+
0
Environments whose NICs lack Geneve offload may prefer STT
encapsulation for performance reasons. For STT encapsulation, OVN
encodes all three pieces of logical metadata in the STT 64-bit
tunnel ID as follows, from MSB to LSB:
9 15 16 24
+--------+------------+-----------+--------+
|reserved|ingress port|egress port|datapath|
+--------+------------+-----------+--------+
0
For connecting to gateways, in addition to Geneve and STT, OVN
supports VXLAN, because only VXLAN support is common on top-of-
rack (ToR) switches. Currently, gateways have a feature set that
matches the capabilities as defined by the VTEP schema, so fewer
bits of metadata are necessary. In the future, gateways that do
not support encapsulations with large amounts of metadata may
continue to have a reduced feature set.
This page is part of the Open Virtual Network (Daemons for Open
vSwitch that translate virtual network configurations into
OpenFlow) project. Information about the project can be found at
⟨https://www.ovn.org/⟩. If you have a bug report for this manual
page, send it to [email protected]. This page was obtained
from the project's upstream Git repository
⟨https://github.com/ovn-org/ovn⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
OVN 24.03.90 OVN Architecture ovn-architecture(7)
Pages that refer to this page: ovn-sb(5), ovn-controller(8), ovn-trace(8)
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