5. Tenant System Types
This section describes a number of special Tenant System types and
how they fit into an NVO3 system.
5.1. Overlay-Aware Network Service Appliances
Some Network Service Appliances [NVE-NVA] (virtual or physical)
provide tenant-aware services. That is, the specific service they
provide depends on the identity of the tenant making use of the
service. For example, firewalls are now becoming available that
support multitenancy where a single firewall provides virtual
firewall service on a per-tenant basis, using per-tenant
configuration rules and maintaining per-tenant state. Such
appliances will be aware of the VN an activity corresponds to while
processing requests. Unlike server virtualization, which shields VMs
from needing to know about multitenancy, a Network Service Appliance
may explicitly support multitenancy. In such cases, the Network
Service Appliance itself will be aware of network virtualization and
either embed an NVE directly or implement a split-NVE as described in
Section 4.2. Unlike server virtualization, however, the Network
Service Appliance may not be running a hypervisor, and the VM
orchestration system may not interact with the Network Service
Appliance. The NVE on such appliances will need to support a control
plane to obtain the necessary information needed to fully participate
in an NV Domain.
5.2. Bare Metal Servers
Many data centers will continue to have at least some servers
operating as non-virtualized (or "bare metal") machines running a
traditional operating system and workload. In such systems, there
will be no NVE functionality on the server, and the server will have
no knowledge of NVO3 (including whether overlays are even in use).
In such environments, the NVE functionality can reside on the first-
hop physical switch. In such a case, the network administrator would
(manually) configure the switch to enable the appropriate NVO3
functionality on the switch port connecting the server and associate
that port with a specific virtual network. Such configuration would
typically be static, since the server is not virtualized and, once
configured, is unlikely to change frequently. Consequently, this
scenario does not require any protocol or standards work.
Gateways on VNs relay traffic onto and off of a virtual network.
Tenant Systems use gateways to reach destinations outside of the
local VN. Gateways receive encapsulated traffic from one VN, remove
the encapsulation header, and send the native packet out onto the
data-center network for delivery. Outside traffic enters a VN in a
Gateways can be either virtual (i.e., implemented as a VM) or
physical (i.e., a standalone physical device). For performance
reasons, standalone hardware gateways may be desirable in some cases.
Such gateways could consist of a simple switch forwarding traffic
from a VN onto the local data-center network or could embed router
functionality. On such gateways, network interfaces connecting to
virtual networks will (at least conceptually) embed NVE (or split-
NVE) functionality within them. As in the case with Network Service
Appliances, gateways may not support a hypervisor and will need an
appropriate control-plane protocol to obtain the information needed
to provide NVO3 service.
Gateways handle several different use cases. For example, one use
case consists of systems supporting overlays together with systems
that do not (e.g., bare metal servers). Gateways could be used to
connect legacy systems supporting, e.g., L2 VLANs, to specific
virtual networks, effectively making them part of the same virtual
network. Gateways could also forward traffic between a virtual
network and other hosts on the data-center network or relay traffic
between different VNs. Finally, gateways can provide external
connectivity such as Internet or VPN access.
5.3.1. Gateway Taxonomy
As can be seen from the discussion above, there are several types of
gateways that can exist in an NVO3 environment. This section breaks
them down into the various types that could be supported. Note that
each of the types below could be either implemented in a centralized
manner or distributed to coexist with the NVEs.
220.127.116.11. L2 Gateways (Bridging)
L2 Gateways act as Layer 2 bridges to forward Ethernet frames based
on the MAC addresses present in them.
L2 VN to Legacy L2: This type of gateway bridges traffic between L2
VNs and other legacy L2 networks such as VLANs or L2 VPNs.
L2 VN to L2 VN: The main motivation for this type of gateway is to
create separate groups of Tenant Systems using L2 VNs such that
the gateway can enforce network policies between each L2 VN.
18.104.22.168. L3 Gateways (Only IP Packets)
L3 Gateways forward IP packets based on the IP addresses present in
L3 VN to Legacy L2: This type of gateway forwards packets between L3
VNs and legacy L2 networks such as VLANs or L2 VPNs. The original
sender's destination MAC address in any frames that the gateway
forwards from a legacy L2 network would be the MAC address of the
L3 VN to Legacy L3: This type of gateway forwards packets between L3
VNs and legacy L3 networks. These legacy L3 networks could be
local to the data center, be in the WAN, or be an L3 VPN.
L3 VN to L2 VN: This type of gateway forwards packets between L3 VNs
and L2 VNs. The original sender's destination MAC address in any
frames that the gateway forwards from a L2 VN would be the MAC
address of the gateway.
L2 VN to L2 VN: This type of gateway acts similar to a traditional
router that forwards between L2 interfaces. The original sender's
destination MAC address in any frames that the gateway forwards
from any of the L2 VNs would be the MAC address of the gateway.
L3 VN to L3 VN: The main motivation for this type of gateway is to
create separate groups of Tenant Systems using L3 VNs such that
the gateway can enforce network policies between each L3 VN.
5.4. Distributed Inter-VN Gateways
The relaying of traffic from one VN to another deserves special
consideration. Whether traffic is permitted to flow from one VN to
another is a matter of policy and would not (by default) be allowed
unless explicitly enabled. In addition, NVAs are the logical place
to maintain policy information about allowed inter-VN communication.
Policy enforcement for inter-VN communication can be handled in (at
least) two different ways. Explicit gateways could be the central
point for such enforcement, with all inter-VN traffic forwarded to
such gateways for processing. Alternatively, the NVA can provide
such information directly to NVEs by either providing a mapping for a
target Tenant System (TS) on another VN or indicating that such
communication is disallowed by policy.
When inter-VN gateways are centralized, traffic between TSs on
different VNs can take suboptimal paths, i.e., triangular routing
results in paths that always traverse the gateway. In the worst
case, traffic between two TSs connected to the same NVE can be hair-
pinned through an external gateway. As an optimization, individual
NVEs can be part of a distributed gateway that performs such
relaying, reducing or completely eliminating triangular routing. In
a distributed gateway, each ingress NVE can perform such relaying
activity directly so long as it has access to the policy information
needed to determine whether cross-VN communication is allowed.
Having individual NVEs be part of a distributed gateway allows them
to tunnel traffic directly to the destination NVE without the need to
take suboptimal paths.
The NVO3 architecture supports distributed gateways for the case of
inter-VN communication. Such support requires that NVO3 control
protocols include mechanisms for the maintenance and distribution of
policy information about what type of cross-VN communication is
allowed so that NVEs acting as distributed gateways can tunnel
traffic from one VN to another as appropriate.
Distributed gateways could also be used to distribute other
traditional router services to individual NVEs. The NVO3
architecture does not preclude such implementations but does not
define or require them as they are outside the scope of the NVO3
5.5. ARP and Neighbor Discovery
Strictly speaking, for an L2 service, special processing of the
Address Resolution Protocol (ARP) [RFC826] and IPv6 Neighbor
Discovery (ND) [RFC4861] is not required. ARP requests are
broadcast, and an NVO3 can deliver ARP requests to all members of a
given L2 virtual network just as it does for any packet sent to an L2
broadcast address. Similarly, ND requests are sent via IP multicast,
which NVO3 can support by delivering via L2 multicast. However, as a
performance optimization, an NVE can intercept ARP (or ND) requests
from its attached TSs and respond to them directly using information
in its mapping tables. Since an NVE will have mechanisms for
determining the NVE address associated with a given TS, the NVE can
leverage the same mechanisms to suppress sending ARP and ND requests
for a given TS to other members of the VN. The NVO3 architecture
supports such a capability.
6. NVE-NVE Interaction
Individual NVEs will interact with each other for the purposes of
tunneling and delivering traffic to remote TSs. At a minimum, a
control protocol may be needed for tunnel setup and maintenance. For
example, tunneled traffic may need to be encrypted or integrity
protected, in which case it will be necessary to set up appropriate
security associations between NVE peers. It may also be desirable to
perform tunnel maintenance (e.g., continuity checks) on a tunnel in
order to detect when a remote NVE becomes unreachable. Such generic
tunnel setup and maintenance functions are not generally
NVO3-specific. Hence, the NVO3 architecture expects to leverage
existing tunnel maintenance protocols rather than defining new ones.
Some NVE-NVE interactions may be specific to NVO3 (in particular, be
related to information kept in mapping tables) and agnostic to the
specific tunnel type being used. For example, when tunneling traffic
for TS-X to a remote NVE, it is possible that TS-X is not presently
associated with the remote NVE. Normally, this should not happen,
but there could be race conditions where the information an NVE has
learned from the NVA is out of date relative to actual conditions.
In such cases, the remote NVE could return an error or warning
indication, allowing the sending NVE to attempt a recovery or
otherwise attempt to mitigate the situation.
The NVE-NVE interaction could signal a range of indications, for
o "No such TS here", upon a receipt of a tunneled packet for an
o "TS-X not here, try the following NVE instead" (i.e., a redirect)
o "Delivered to correct NVE but could not deliver packet to TS-X"
When an NVE receives information from a remote NVE that conflicts
with the information it has in its own mapping tables, it should
consult with the NVA to resolve those conflicts. In particular, it
should confirm that the information it has is up to date, and it
might indicate the error to the NVA so as to nudge the NVA into
following up (as appropriate). While it might make sense for an NVE
to update its mapping table temporarily in response to an error from
a remote NVE, any changes must be handled carefully as doing so can
raise security considerations if the received information cannot be
authenticated. That said, a sending NVE might still take steps to
mitigate a problem, such as applying rate limiting to data traffic
towards a particular NVE or TS.
7. Network Virtualization Authority (NVA)
Before sending traffic to and receiving traffic from a virtual
network, an NVE must obtain the information needed to build its
internal forwarding tables and state as listed in Section 4.3. An
NVE can obtain such information from a Network Virtualization
The NVA is the entity that is expected to provide address mapping and
other information to NVEs. NVEs can interact with an NVA to obtain
any required information they need in order to properly forward
traffic on behalf of tenants. The term "NVA" refers to the overall
system, without regard to its scope or how it is implemented.
7.1. How an NVA Obtains Information
There are two primary ways in which an NVA can obtain the address
dissemination information it manages: from the VM orchestration
system and/or directly from the NVEs themselves.
On virtualized systems, the NVA may be able to obtain the address-
mapping information associated with VMs from the VM orchestration
system itself. If the VM orchestration system contains a master
database for all the virtualization information, having the NVA
obtain information directly from the orchestration system would be a
natural approach. Indeed, the NVA could effectively be co-located
with the VM orchestration system itself. In such systems, the VM
orchestration system communicates with the NVE indirectly through the
However, as described in Section 4, not all NVEs are associated with
hypervisors. In such cases, NVAs cannot leverage VM orchestration
protocols to interact with an NVE and will instead need to peer
directly with them. By peering directly with an NVE, NVAs can obtain
information about the TSs connected to that NVE and can distribute
information to the NVE about the VNs those TSs are associated with.
For example, whenever a Tenant System attaches to an NVE, that NVE
would notify the NVA that the TS is now associated with that NVE.
Likewise, when a TS detaches from an NVE, that NVE would inform the
NVA. By communicating directly with NVEs, both the NVA and the NVE
are able to maintain up-to-date information about all active tenants
and the NVEs to which they are attached.
7.2. Internal NVA Architecture
For reliability and fault tolerance reasons, an NVA would be
implemented in a distributed or replicated manner without single
points of failure. How the NVA is implemented, however, is not
important to an NVE so long as the NVA provides a consistent and
well-defined interface to the NVE. For example, an NVA could be
implemented via database techniques whereby a server stores address-
mapping information in a traditional (possibly replicated) database.
Alternatively, an NVA could be implemented in a distributed fashion
using an existing (or modified) routing protocol to maintain and
distribute mappings. So long as there is a clear interface between
the NVE and NVA, how an NVA is architected and implemented is not
important to an NVE.
A number of architectural approaches could be used to implement NVAs
themselves. NVAs manage address bindings and distribute them to
where they need to go. One approach would be to use the Border
Gateway Protocol (BGP) [RFC4364] (possibly with extensions) and route
reflectors. Another approach could use a transaction-based database
model with replicated servers. Because the implementation details
are local to an NVA, there is no need to pick exactly one solution
technology, so long as the external interfaces to the NVEs (and
remote NVAs) are sufficiently well defined to achieve
7.3. NVA External Interface
Conceptually, from the perspective of an NVE, an NVA is a single
entity. An NVE interacts with the NVA, and it is the NVA's
responsibility to ensure that interactions between the NVE and NVA
result in consistent behavior across the NVA and all other NVEs using
the same NVA. Because an NVA is built from multiple internal
components, an NVA will have to ensure that information flows to all
internal NVA components appropriately.
One architectural question is how the NVA presents itself to the NVE.
For example, an NVA could be required to provide access via a single
IP address. If NVEs only have one IP address to interact with, it
would be the responsibility of the NVA to handle NVA component
failures, e.g., by using a "floating IP address" that migrates among
NVA components to ensure that the NVA can always be reached via the
one address. Having all NVA accesses through a single IP address,
however, adds constraints to implementing robust failover, load
In the NVO3 architecture, an NVA is accessed through one or more IP
addresses (or an IP address/port combination). If multiple IP
addresses are used, each IP address provides equivalent
functionality, meaning that an NVE can use any of the provided
addresses to interact with the NVA. Should one address stop working,
an NVE is expected to failover to another. While the different
addresses result in equivalent functionality, one address may respond
more quickly than another, e.g., due to network conditions, load on
the server, etc.
To provide some control over load balancing, NVA addresses may have
an associated priority. Addresses are used in order of priority,
with no explicit preference among NVA addresses having the same
priority. To provide basic load balancing among NVAs of equal
priorities, NVEs could use some randomization input to select among
equal-priority NVAs. Such a priority scheme facilitates failover and
load balancing, for example, by allowing a network operator to
specify a set of primary and backup NVAs.
It may be desirable to have individual NVA addresses responsible for
a subset of information about an NV Domain. In such a case, NVEs
would use different NVA addresses for obtaining or updating
information about particular VNs or TS bindings. Key questions with
such an approach are how information would be partitioned and how an
NVE could determine which address to use to get the information it
Another possibility is to treat the information on which NVA
addresses to use as cached (soft-state) information at the NVEs, so
that any NVA address can be used to obtain any information, but NVEs
are informed of preferences for which addresses to use for particular
information on VNs or TS bindings. That preference information would
be cached for future use to improve behavior, e.g., if all requests
for a specific subset of VNs are forwarded to a specific NVA
component, the NVE can optimize future requests within that subset by
sending them directly to that NVA component via its address.
8. NVE-NVA Protocol
As outlined in Section 4.3, an NVE needs certain information in order
to perform its functions. To obtain such information from an NVA, an
NVE-NVA protocol is needed. The NVE-NVA protocol provides two
functions. First, it allows an NVE to obtain information about the
location and status of other TSs with which it needs to communicate.
Second, the NVE-NVA protocol provides a way for NVEs to provide
updates to the NVA about the TSs attached to that NVE (e.g., when a
TS attaches or detaches from the NVE) or about communication errors
encountered when sending traffic to remote NVEs. For example, an NVE
could indicate that a destination it is trying to reach at a
destination NVE is unreachable for some reason.
While having a direct NVE-NVA protocol might seem straightforward,
the existence of existing VM orchestration systems complicates the
choices an NVE has for interacting with the NVA.
8.1. NVE-NVA Interaction Models
An NVE interacts with an NVA in at least two (quite different) ways:
o NVEs embedded within the same server as the hypervisor can obtain
necessary information entirely through the hypervisor-facing side
of the NVE. Such an approach is a natural extension to existing
VM orchestration systems supporting server virtualization because
an existing protocol between the hypervisor and VM orchestration
system already exists and can be leveraged to obtain any needed
information. Specifically, VM orchestration systems used to
create, terminate, and migrate VMs already use well-defined
(though typically proprietary) protocols to handle the
interactions between the hypervisor and VM orchestration system.
For such systems, it is a natural extension to leverage the
existing orchestration protocol as a sort of proxy protocol for
handling the interactions between an NVE and the NVA. Indeed,
existing implementations can already do this.
o Alternatively, an NVE can obtain needed information by interacting
directly with an NVA via a protocol operating over the data-center
underlay network. Such an approach is needed to support NVEs that
are not associated with systems performing server virtualization
(e.g., as in the case of a standalone gateway) or where the NVE
needs to communicate directly with the NVA for other reasons.
The NVO3 architecture will focus on support for the second model
above. Existing virtualization environments are already using the
first model, but they are not sufficient to cover the case of
standalone gateways -- such gateways may not support virtualization
and do not interface with existing VM orchestration systems.
8.2. Direct NVE-NVA Protocol
An NVE can interact directly with an NVA via an NVE-NVA protocol.
Such a protocol can be either independent of the NVA internal
protocol or an extension of it. Using a purpose-specific protocol
would provide architectural separation and independence between the
NVE and NVA. The NVE and NVA interact in a well-defined way, and
changes in the NVA (or NVE) do not need to impact each other. Using
a dedicated protocol also ensures that both NVE and NVA
implementations can evolve independently and without dependencies on
each other. Such independence is important because the upgrade path
for NVEs and NVAs is quite different. Upgrading all the NVEs at a
site will likely be more difficult in practice than upgrading NVAs
because of their large number -- one on each end device. In
practice, it would be prudent to assume that once an NVE has been
implemented and deployed, it may be challenging to get subsequent NVE
extensions and changes implemented and deployed, whereas an NVA (and
its associated internal protocols) is more likely to evolve over time
as experience is gained from usage and upgrades will involve fewer
Requirements for a direct NVE-NVA protocol can be found in [NVE-NVA].
8.3. Propagating Information Between NVEs and NVAs
Information flows between NVEs and NVAs in both directions. The NVA
maintains information about all VNs in the NV Domain so that NVEs do
not need to do so themselves. NVEs obtain information from the NVA
about where a given remote TS destination resides. NVAs, in turn,
obtain information from NVEs about the individual TSs attached to
While the NVA could push information relevant to every virtual
network to every NVE, such an approach scales poorly and is
unnecessary. In practice, a given NVE will only need and want to
know about VNs to which it is attached. Thus, an NVE should be able
to subscribe to updates only for the virtual networks it is
interested in receiving updates for. The NVO3 architecture supports
a model where an NVE is not required to have full mapping tables for
all virtual networks in an NV Domain.
Before sending unicast traffic to a remote TS (or TSs for broadcast
or multicast traffic), an NVE must know where the remote TS(s)
currently reside. When a TS attaches to a virtual network, the NVE
obtains information about that VN from the NVA. The NVA can provide
that information to the NVE at the time the TS attaches to the VN,
either because the NVE requests the information when the attach
operation occurs or because the VM orchestration system has initiated
the attach operation and provides associated mapping information to
the NVE at the same time.
There are scenarios where an NVE may wish to query the NVA about
individual mappings within a VN. For example, when sending traffic
to a remote TS on a remote NVE, that TS may become unavailable (e.g.,
because it has migrated elsewhere or has been shut down, in which
case the remote NVE may return an error indication). In such
situations, the NVE may need to query the NVA to obtain updated
mapping information for a specific TS or to verify that the
information is still correct despite the error condition. Note that
such a query could also be used by the NVA as an indication that
there may be an inconsistency in the network and that it should take
steps to verify that the information it has about the current state
and location of a specific TS is still correct.
For very large virtual networks, the amount of state an NVE needs to
maintain for a given virtual network could be significant. Moreover,
an NVE may only be communicating with a small subset of the TSs on
such a virtual network. In such cases, the NVE may find it desirable
to maintain state only for those destinations it is actively
communicating with. In such scenarios, an NVE may not want to
maintain full mapping information about all destinations on a VN.
However, if it needs to communicate with a destination for which it
does not have mapping information, it will need to be able to query
the NVA on demand for the missing information on a per-destination
The NVO3 architecture will need to support a range of operations
between the NVE and NVA. Requirements for those operations can be
found in [NVE-NVA].
9. Federated NVAs
An NVA provides service to the set of NVEs in its NV Domain. Each
NVA manages network virtualization information for the virtual
networks within its NV Domain. An NV Domain is administered by a
In some cases, it will be necessary to expand the scope of a specific
VN or even an entire NV Domain beyond a single NVA. For example, an
administrator managing multiple data centers may wish to operate all
of its data centers as a single NV Region. Such cases are handled by
having different NVAs peer with each other to exchange mapping
information about specific VNs. NVAs operate in a federated manner
with a set of NVAs operating as a loosely coupled federation of
individual NVAs. If a virtual network spans multiple NVAs (e.g.,
located at different data centers), and an NVE needs to deliver
tenant traffic to an NVE that is part of a different NV Domain, it
still interacts only with its NVA, even when obtaining mappings for
NVEs associated with a different NV Domain.
Figure 3 shows a scenario where two separate NV Domains (A and B)
share information about a VN. VM1 and VM2 both connect to the same
VN, even though the two VMs are in separate NV Domains. There are
two cases to consider. In the first case, NV Domain B does not allow
NVE-A to tunnel traffic directly to NVE-B. There could be a number
of reasons for this. For example, NV Domains A and B may not share a
common address space (i.e., traversal through a NAT device is
required), or for policy reasons, a domain might require that all
traffic between separate NV Domains be funneled through a particular
device (e.g., a firewall). In such cases, NVA-2 will advertise to
NVA-1 that VM1 on the VN is available and direct that traffic between
the two nodes be forwarded via IP-G (an IP Gateway). IP-G would then
decapsulate received traffic from one NV Domain, translate it
appropriately for the other domain, and re-encapsulate the packet for
xxxxxx xxxx +-----+
+-----+ xxxxxx xxxxxx xxxxxx xxxxx | VM2 |
| VM1 | xx xx xxx xx |-----|
|-----| xx x xx x |NVE-B|
|NVE-A| x x +----+ x x +-----+
+--+--+ x NV Domain A x |IP-G|--x x |
+-------x xx--+ | x xx |
x x +----+ x NV Domain B x |
+---x xx xx x---+
| xxxx xx +->xx xx
| xxxxxxxx | xx xx
+---+-+ | xx xx
|NVA-1| +--+--+ xx xxx
+-----+ |NVA-2| xxxx xxxx
Figure 3: VM1 and VM2 in Different NV Domains
NVAs at one site share information and interact with NVAs at other
sites, but only in a controlled manner. It is expected that policy
and access control will be applied at the boundaries between
different sites (and NVAs) so as to minimize dependencies on external
NVAs that could negatively impact the operation within a site. It is
an architectural principle that operations involving NVAs at one site
not be immediately impacted by failures or errors at another site.
(Of course, communication between NVEs in different NV Domains may be
impacted by such failures or errors.) It is a strong requirement
that an NVA continue to operate properly for local NVEs even if
external communication is interrupted (e.g., should communication
between a local and remote NVA fail).
At a high level, a federation of interconnected NVAs has some
analogies to BGP and Autonomous Systems. Like an Autonomous System,
NVAs at one site are managed by a single administrative entity and do
not interact with external NVAs except as allowed by policy.
Likewise, the interface between NVAs at different sites is well
defined so that the internal details of operations at one site are
largely hidden to other sites. Finally, an NVA only peers with other
NVAs that it has a trusted relationship with, i.e., where a VN is
intended to span multiple NVAs.
Reasons for using a federated model include:
o Provide isolation among NVAs operating at different sites at
different geographic locations.
o Control the quantity and rate of information updates that flow
(and must be processed) between different NVAs in different data
o Control the set of external NVAs (and external sites) a site peers
with. A site will only peer with other sites that are cooperating
in providing an overlay service.
o Allow policy to be applied between sites. A site will want to
carefully control what information it exports (and to whom) as
well as what information it is willing to import (and from whom).
o Allow different protocols and architectures to be used for intra-
NVA vs. inter-NVA communication. For example, within a single
data center, a replicated transaction server using database
techniques might be an attractive implementation option for an
NVA, and protocols optimized for intra-NVA communication would
likely be different from protocols involving inter-NVA
communication between different sites.
o Allow for optimized protocols rather than using a one-size-fits-
all approach. Within a data center, networks tend to have lower
latency, higher speed, and higher redundancy when compared with
WAN links interconnecting data centers. The design constraints
and trade-offs for a protocol operating within a data-center
network are different from those operating over WAN links. While
a single protocol could be used for both cases, there could be
advantages to using different and more specialized protocols for
the intra- and inter-NVA case.
9.1. Inter-NVA Peering
To support peering between different NVAs, an inter-NVA protocol is
needed. The inter-NVA protocol defines what information is exchanged
between NVAs. It is assumed that the protocol will be used to share
addressing information between data centers and must scale well over
10. Control Protocol Work Areas
The NVO3 architecture consists of two major distinct entities: NVEs
and NVAs. In order to provide isolation and independence between
these two entities, the NVO3 architecture calls for well-defined
protocols for interfacing between them. For an individual NVA, the
architecture calls for a logically centralized entity that could be
implemented in a distributed or replicated fashion. While the IETF
may choose to define one or more specific architectural approaches to
building individual NVAs, there is little need to pick exactly one
approach to the exclusion of others. An NVA for a single domain will
likely be deployed as a single vendor product; thus, there is little
benefit in standardizing the internal structure of an NVA.
Individual NVAs peer with each other in a federated manner. The NVO3
architecture calls for a well-defined interface between NVAs.
Finally, a hypervisor-NVE protocol is needed to cover the split-NVE
scenario described in Section 4.2.
11. NVO3 Data-Plane Encapsulation
When tunneling tenant traffic, NVEs add an encapsulation header to
the original tenant packet. The exact encapsulation to use for NVO3
does not seem to be critical. The main requirement is that the
encapsulation support a Context ID of sufficient size. A number of
encapsulations already exist that provide a VN Context of sufficient
size for NVO3. For example, Virtual eXtensible Local Area Network
(VXLAN) [RFC7348] has a 24-bit VXLAN Network Identifier (VNI).
Network Virtualization using Generic Routing Encapsulation (NVGRE)
[RFC7637] has a 24-bit Tenant Network ID (TNI). MPLS-over-GRE
provides a 20-bit label field. While there is widespread recognition
that a 12-bit VN Context would be too small (only 4096 distinct
values), it is generally agreed that 20 bits (1 million distinct
values) and 24 bits (16.8 million distinct values) are sufficient for
a wide variety of deployment scenarios.
12. Operations, Administration, and Maintenance (OAM)
The simplicity of operating and debugging overlay networks will be
critical for successful deployment.
Overlay networks are based on tunnels between NVEs, so the
Operations, Administration, and Maintenance (OAM) [RFC6291] framework
for overlay networks can draw from prior IETF OAM work for tunnel-
based networks, specifically L2VPN OAM [RFC6136]. RFC 6136 focuses
on Fault Management and Performance Management as fundamental to
L2VPN service delivery, leaving the Configuration Management,
Accounting Management, and Security Management components of the Open
Systems Interconnection (OSI) Fault, Configuration, Accounting,
Performance, and Security (FCAPS) taxonomy [M.3400] for further
study. This section does likewise for NVO3 OAM, but those three
areas continue to be important parts of complete OAM functionality
The relationship between the overlay and underlay networks is a
consideration for fault and performance management -- a fault in the
underlay may manifest as fault and/or performance issues in the
overlay. Diagnosing and fixing such issues are complicated by NVO3
abstracting the underlay network away from the overlay network (e.g.,
intermediate nodes on the underlay network path between NVEs are
hidden from overlay VNs).
NVO3-specific OAM techniques, protocol constructs, and tools are
needed to provide visibility beyond this abstraction to diagnose and
correct problems that appear in the overlay. Two examples are
underlay-aware traceroute [TRACEROUTE-VXLAN] and ping protocol
constructs for overlay networks [VXLAN-FAILURE] [NVO3-OVERLAY].
NVO3-specific tools and techniques are best viewed as complements to
(i.e., not as replacements for) single-network tools that apply to
the overlay and/or underlay networks. Coordination among the
individual network tools (for the overlay and underlay networks) and
NVO3-aware, dual-network tools is required to achieve effective
monitoring and fault diagnosis. For example, the defect detection
intervals and performance measurement intervals ought to be
coordinated among all tools involved in order to provide consistency
and comparability of results.
For further discussion of NVO3 OAM requirements, see [NVO3-OAM].
This document presents the overall architecture for NVO3. The
architecture calls for three main areas of protocol work:
1. A hypervisor-NVE protocol to support split-NVEs as discussed in
2. An NVE-NVA protocol for disseminating VN information (e.g., inner
to outer address mappings)
3. An NVA-NVA protocol for exchange of information about specific
virtual networks between federated NVAs
It should be noted that existing protocols or extensions of existing
protocols are applicable.
14. Security Considerations
The data plane and control plane described in this architecture will
need to address potential security threats.
For the data plane, tunneled application traffic may need protection
against being misdelivered, being modified, or having its content
exposed to an inappropriate third party. In all cases, encryption
between authenticated tunnel endpoints (e.g., via use of IPsec
[RFC4301]) and enforcing policies that control which endpoints and
VNs are permitted to exchange traffic can be used to mitigate risks.
For the control plane, a combination of authentication and encryption
can be used between NVAs, between the NVA and NVE, as well as between
different components of the split-NVE approach. All entities will
need to properly authenticate with each other and enable encryption
for their interactions as appropriate to protect sensitive
Leakage of sensitive information about users or other entities
associated with VMs whose traffic is virtualized can also be covered
by using encryption for the control-plane protocols and enforcing
policies that control which NVO3 components are permitted to exchange
Control-plane elements such as NVEs and NVAs need to collect
performance and other data in order to carry out their functions.
This data can sometimes be unexpectedly sensitive, for example,
allowing non-obvious inferences of activity within a VM. This
provides a reason to minimize the data collected in some environments
in order to limit potential exposure of sensitive information. As