|
NAME | DESCRIPTION | SECURITY | DESIGN DECISIONS | COLOPHON |
|
ovn-architecture(7) Open vSwitch Manual ovn-architecture(7)
ovn-architecture - Open Virtual Network architecture
OVN, the Open Virtual Network, is a system to support virtual network
abstraction. OVN complements the existing capabilities of OVS to add
native support for virtual network abstractions, such as virtual 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.
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 IntegrationGuide.rst in the OVS 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
|
|
+-----------|-----------+
| | |
| 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. The hypervisor itself, or the
integration between Open vSwitch and the hypervisor
(described in IntegrationGuide.rst) takes care of this.
(This is not part of OVN or new to OVN; 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
A logical network implements the same concepts as physical networks,
but they are insulated from the physical network with tunnels or
other encapsulations. This allows logical networks to have separate
IP and other address spaces that overlap, without conflicting, with
those used for physical networks. Logical network topologies can be
arranged without regard for the topologies of the physical networks
on which they run.
Logical network concepts in OVN include:
· Logical switches, the logical version of Ethernet
switches.
· Logical routers, the logical version of IP routers.
Logical switches and routers can be connected into
sophisticated topologies.
· Logical datapaths are the logical version of an
OpenFlow switch. Logical switches and routers are both
implemented as logical datapaths.
· Logical ports represent the points of connectivity in
and out of logical switches and logical routers. Some
common types of logical ports are:
· Logical ports representing VIFs.
· Localnet ports represent the points of
connectivity between logical switches and the
physical network. They are implemented as OVS
patch ports between the integration bridge and
the separate Open vSwitch bridge that underlay
physical ports attach to.
· Logical patch ports represent the points of
connectivity between logical switches and
logical routers, and in some cases between peer
logical routers. There is a pair of logical
patch ports at each such point of connectivity,
one on each side.
· Localport ports represent the points of local
connectivity between logical switches and VIFs.
These ports are present in every chassis (not
bound to any particular one) and traffic from
them will never go through a tunnel. A localport
is expected to only generate traffic destined
for a local destination, typically in response
to a request it received. One use case is how
OpenStack Neutron uses a localport port for
serving metadata to VM’s residing on every
hypervisor. A metadata proxy process is attached
to this port on every host and all VM’s within
the same network will reach it at the same
IP/MAC address without any traffic being sent
over a tunnel. Further details can be seen at
https://docs.openstack.org/developer/networking-ovn/design/metadata_api.html.
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
IntegrationGuide.rst) 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. Although VXLAN tunnels do not explicitly
carry a logical input port, OVN only uses VXLAN 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.
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 and STT tunnels pass this field as part of the
tunnel key. VXLAN tunnels do not transmit the logical
output port field. Since VXLAN tunnels do not carry a
logical output port field in the tunnel key, when a
packet is received from VXLAN tunnel by an OVN
hypervisor, the packet is resubmitted to table 8 to
determine the output port(s); when the packet reaches
table 32, these packets are resubmitted to table 33 for
local delivery by checking a MLF_RCV_FROM_VXLAN flag,
which is set when the packet arrives from a VXLAN
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 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 DNATting in Open vSwitch extension
register number 11 and zone information for SNATing in
Open vSwitch extension register number 12.
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 and 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 three pieces of
information are obtained from the tunnel encapsulation
metadata (see Tunnel Encapsulations for encoding details).
Then the actions resubmit to table 33 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 32.
If the pipeline executes more than one output action,
then each one is separately resubmitted to table 32.
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.)
3.
OpenFlow tables 32 through 47 implement the output action in
the logical ingress pipeline. Specifically, table 32 handles
packets to remote hypervisors, table 33 handles packets to
the local hypervisor, and table 34 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 33, 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 32.
Each flow in table 32 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 33.) 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 33. Table 32 also includes:
· A higher-priority rule to match packets received from
VXLAN tunnels, based on flag MLF_RCV_FROM_VXLAN, and
resubmit these packets to table 33 for local
delivery. Packets received from VXLAN 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 33 for
local delivery. Ports of type localport exist on
every hypervisor and by definition their traffic
should never go out through a tunnel.
· A fallback flow that resubmits to table 33 if there
is no other match.
Flows in table 33 resemble those in table 32 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 34. 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 34.
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 32 to reach the remote port, a flow is added in table
33 to switch the logical outport to the localnet port, and
resubmit to table 33 as if it were unicasted to a logical
port on the local hypervisor.
Table 34 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 resubmits other
packets to table 40.
4.
OpenFlow tables 40 through 63 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 34, 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 32, the packet will use the fallback flow that
resubmits locally to table 33 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. The implementation in table 65 differs depending
on the OVS version, although the observed behavior is meant to be the
same:
· In OVS versions 2.6 and earlier, table 65 outputs to an
OVS patch port that represents the logical patch port.
The packet re-enters the OpenFlow flow table from the
OVS patch port’s peer in table 0, which identifies the
logical datapath and logical input port based on the
OVS patch port’s OpenFlow port number.
· In OVS versions 2.7 and later, the packet is cloned and
resubmitted 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 reachs 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 32 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 32 that sends the packet on a
tunnel port to the chassis where the gateway router resides. This
processing in table 32 is done in the same manner as for VIFs.
Gateway routers are typically used in 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. On the other side, the gateway
router connects to another logical switch that has a localnet port
connecting to the physical network.
When using gateway routers, DNAT and SNAT rules are associated with
the gateway router, which provides a central location that can handle
one-to-many SNAT (aka IP masquerading).
Distributed Gateway Ports
Distributed gateway ports are logical router patch ports that
directly connect distributed logical routers to logical switches with
localnet ports.
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 on that hypervisor to the physical network.
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, where the packet will enter the
integration bridge through a localnet port.
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 32:
· 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 33,
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 32 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 32, packets with this logical egress port are sent to a
specific chassis, in the same way that table 32 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 33 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 master 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.openvswitch.org/en/latest/topics/high-availability.
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 correponding 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.
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.
Role-Based Access Controls for the Soutbound 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
resstricted 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: disabled (all clients are considered to
be authorized. Future: add a "creating chassis name"
column to this table and use it for authorization
checking.
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.
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 -B 1024 -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").
Tunnel Encapsulations
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).
For hypervisor-to-hypervisor traffic, OVN supports only Geneve and
STT encapsulations, for the following reasons:
· Only STT and Geneve support the large amounts of
metadata (over 32 bits per packet) that OVN uses (as
described above).
· 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 vSwitch (a distributed virtual
multilayer switch) project. Information about the project can be
found at ⟨http://openvswitch.org/⟩. If you have a bug report for
this manual page, send it to bugs@openvswitch.org. This page was
obtained from the project's upstream Git repository
⟨https://github.com/openvswitch/ovs.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2018-02-01.) 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 man-pages@man7.org
Open vSwitch 2.8.90 OVN Architecture ovn-architecture(7)
Pages that refer to this page: ovn-sb(5), ovn-controller(8), ovn-trace(8)
|
HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
|
|