Internet DRAFT - draft-ietf-nvo3-arch
draft-ietf-nvo3-arch
Internet Engineering Task Force D. Black
Internet-Draft EMC
Intended status: Informational J. Hudson
Expires: October 23, 2016 Independent
L. Kreeger
Cisco
M. Lasserre
Independent
T. Narten
IBM
April 21, 2016
An Architecture for Data Center Network Virtualization Overlays (NVO3)
draft-ietf-nvo3-arch-06
Abstract
This document presents a high-level overview architecture for
building data center network virtualization overlay (NVO3) networks.
The architecture is given at a high-level, showing the major
components of an overall system. An important goal is to divide the
space into individual smaller components that can be implemented
independently and with clear interfaces and interactions with other
components. It should be possible to build and implement individual
components in isolation and have them work with other components with
no changes to other components. That way implementers have
flexibility in implementing individual components and can optimize
and innovate within their respective components without requiring
changes to other components.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 23, 2016.
Black, et al. Expires October 23, 2016 [Page 1]
Internet-Draft NVO3 Architecture April 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. VN Service (L2 and L3) . . . . . . . . . . . . . . . . . 5
3.1.1. VLAN Tags in L2 Service . . . . . . . . . . . . . . . 7
3.1.2. TTL Considerations . . . . . . . . . . . . . . . . . 7
3.2. Network Virtualization Edge (NVE) . . . . . . . . . . . . 7
3.3. Network Virtualization Authority (NVA) . . . . . . . . . 9
3.4. VM Orchestration Systems . . . . . . . . . . . . . . . . 9
4. Network Virtualization Edge (NVE) . . . . . . . . . . . . . . 11
4.1. NVE Co-located With Server Hypervisor . . . . . . . . . . 11
4.2. Split-NVE . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.1. Tenant VLAN handling in Split-NVE Case . . . . . . . 12
4.3. NVE State . . . . . . . . . . . . . . . . . . . . . . . . 13
4.4. Multi-Homing of NVEs . . . . . . . . . . . . . . . . . . 14
4.5. VAP . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Tenant System Types . . . . . . . . . . . . . . . . . . . . . 15
5.1. Overlay-Aware Network Service Appliances . . . . . . . . 15
5.2. Bare Metal Servers . . . . . . . . . . . . . . . . . . . 15
5.3. Gateways . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3.1. Gateway Taxonomy . . . . . . . . . . . . . . . . . . 16
5.3.1.1. L2 Gateways (Bridging) . . . . . . . . . . . . . 16
5.3.1.2. L3 Gateways (Only IP Packets) . . . . . . . . . . 17
5.4. Distributed Inter-VN Gateways . . . . . . . . . . . . . . 17
5.5. ARP and Neighbor Discovery . . . . . . . . . . . . . . . 18
6. NVE-NVE Interaction . . . . . . . . . . . . . . . . . . . . . 18
7. Network Virtualization Authority . . . . . . . . . . . . . . 20
7.1. How an NVA Obtains Information . . . . . . . . . . . . . 20
7.2. Internal NVA Architecture . . . . . . . . . . . . . . . . 21
7.3. NVA External Interface . . . . . . . . . . . . . . . . . 21
8. NVE-to-NVA Protocol . . . . . . . . . . . . . . . . . . . . . 22
Black, et al. Expires October 23, 2016 [Page 2]
Internet-Draft NVO3 Architecture April 2016
8.1. NVE-NVA Interaction Models . . . . . . . . . . . . . . . 23
8.2. Direct NVE-NVA Protocol . . . . . . . . . . . . . . . . . 23
8.3. Propagating Information Between NVEs and NVAs . . . . . . 24
9. Federated NVAs . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Inter-NVA Peering . . . . . . . . . . . . . . . . . . . . 27
10. Control Protocol Work Areas . . . . . . . . . . . . . . . . . 28
11. NVO3 Data Plane Encapsulation . . . . . . . . . . . . . . . . 28
12. Operations and Management . . . . . . . . . . . . . . . . . . 28
13. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
16. Security Considerations . . . . . . . . . . . . . . . . . . . 29
17. Informative References . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
This document presents a high-level architecture for building data
center network virtualization overlay (NVO3) networks. The
architecture is given at a high-level, showing the major components
of an overall system. An important goal is to divide the space into
smaller individual components that can be implemented independently
and with clear interfaces and interactions with other components. It
should be possible to build and implement individual components in
isolation and have them work with other components with no changes to
other components. That way implementers have flexibility in
implementing individual components and can optimize and innovate
within their respective components without necessarily requiring
changes to other components.
The motivation for overlay networks is given in "Problem Statement:
Overlays for Network Virtualization" [RFC7364]. "Framework for DC
Network Virtualization" [RFC7365] provides a framework for discussing
overlay networks generally and the various components that must work
together in building such systems. This document differs from the
framework document in that it doesn't attempt to cover all possible
approaches within the general design space. Rather, it describes one
particular approach.
2. Terminology
This document uses the same terminology as [RFC7365]. In addition,
the following terms are used:
NV Domain A Network Virtualization Domain is an administrative
construct that defines a Network Virtualization Authority (NVA),
the set of Network Virtualization Edges (NVEs) associated with
that NVA, and the set of virtual networks the NVA manages and
Black, et al. Expires October 23, 2016 [Page 3]
Internet-Draft NVO3 Architecture April 2016
supports. NVEs are associated with a (logically centralized) NVA,
and an NVE supports communication for any of the virtual networks
in the domain.
NV Region A region over which information about a set of virtual
networks is shared. The degenerate case of a single NV Domain
corresponds to an NV region corresponding to that domain. The
more interesting case occurs when two or more NV Domains share
information about part or all of a set of virtual networks that
they manage. Two NVAs share information about particular virtual
networks for the purpose of supporting connectivity between
tenants located in different NV Domains. NVAs can share
information about an entire NV domain, or just individual virtual
networks.
Tenant System Identifier (TSI) Interface to a Virtual Network as
presented to a Tenant System. The TSI logically connects to the
NVE via a Virtual Access Point (VAP). To the Tenant System, the
TSI is like a Network Interface Card (NIC); the TSI presents
itself to a Tenant System as a normal network interface.
VLAN Unless stated otherwise, the terms VLAN and VLAN Tag are used
in this document denote a C-VLAN [IEEE-802.1Q] and the terms are
used interchangeably to improve readability.
3. Background
Overlay networks are an approach for providing network virtualization
services to a set of Tenant Systems (TSs) [RFC7365]. With overlays,
data traffic between tenants is tunneled across the underlying data
center's IP network. The use of tunnels provides a number of
benefits by decoupling the network as viewed by tenants from the
underlying physical network across which they communicate.
Tenant Systems connect to Virtual Networks (VNs), with each VN having
associated attributes defining properties of the network, such as the
set of members that connect to it. Tenant Systems connected to a
virtual network typically communicate freely with other Tenant
Systems on the same VN, but communication between Tenant Systems on
one VN and those external to the VN (whether on another VN or
connected to the Internet) is carefully controlled and governed by
policy. The NVO3 architecture does not impose any restrictions to
the application of policy controls even within a VN.
A Network Virtualization Edge (NVE) [RFC7365] is the entity that
implements the overlay functionality. An NVE resides at the boundary
between a Tenant System and the overlay network as shown in Figure 1.
Black, et al. Expires October 23, 2016 [Page 4]
Internet-Draft NVO3 Architecture April 2016
An NVE creates and maintains local state about each Virtual Network
for which it is providing service on behalf of a Tenant System.
+--------+ +--------+
| Tenant +--+ +----| Tenant |
| System | | (') | System |
+--------+ | ................ ( ) +--------+
| +-+--+ . . +--+-+ (_)
| | NVE|--. .--| NVE| |
+--| | . . | |---+
+-+--+ . . +--+-+
/ . .
/ . L3 Overlay . +--+-++--------+
+--------+ / . Network . | NVE|| Tenant |
| Tenant +--+ . .- -| || System |
| System | . . +--+-++--------+
+--------+ ................
|
+----+
| NVE|
| |
+----+
|
|
=====================
| |
+--------+ +--------+
| Tenant | | Tenant |
| System | | System |
+--------+ +--------+
Figure 1: NVO3 Generic Reference Model
The following subsections describe key aspects of an overlay system
in more detail. Section 3.1 describes the service model (Ethernet
vs. IP) provided to Tenant Systems. Section 3.2 describes NVEs in
more detail. Section 3.3 introduces the Network Virtualization
Authority, from which NVEs obtain information about virtual networks.
Section 3.4 provides background on Virtual Machine (VM) orchestration
systems and their use of virtual networks.
3.1. VN Service (L2 and L3)
A Virtual Network provides either L2 or L3 service to connected
tenants. For L2 service, VNs transport Ethernet frames, and a Tenant
System is provided with a service that is analogous to being
Black, et al. Expires October 23, 2016 [Page 5]
Internet-Draft NVO3 Architecture April 2016
connected to a specific L2 C-VLAN. L2 broadcast frames are generally
delivered to all (and multicast frames delivered to a subset of) the
other Tenant Systems on the VN. To a Tenant System, it appears as if
they are connected to a regular L2 Ethernet link. Within the NVO3
architecture, tenant frames are tunneled to remote NVEs based on the
MAC addresses of the frame headers as originated by the Tenant
System. On the underlay, NVO3 packets are forwarded between NVEs
based on the outer addresses of tunneled packets.
For L3 service, VNs transport IP datagrams, and a Tenant System is
provided with a service that only supports IP traffic. Within the
NVO3 architecture, tenant frames are tunneled to remote NVEs based on
the IP addresses of the packet originated by the Tenant System; any
L2 destination addresses provided by Tenant Systems are effectively
ignored by the NVEs and overlay network. For L3 service, the Tenant
System will be configured with an IP subnet that is effectively a
point-to-point link, i.e., having only the Tenant System and a next-
hop router address on it.
L2 service is intended for systems that need native L2 Ethernet
service and the ability to run protocols directly over Ethernet
(i.e., not based on IP). L3 service is intended for systems in which
all the traffic can safely be assumed to be IP. It is important to
note that whether an NVO3 network provides L2 or L3 service to a
Tenant System, the Tenant System does not generally need to be aware
of the distinction. In both cases, the virtual network presents
itself to the Tenant System as an L2 Ethernet interface. An Ethernet
interface is used in both cases simply as a widely supported
interface type that essentially all Tenant Systems already support.
Consequently, no special software is needed on Tenant Systems to use
an L3 vs. an L2 overlay service.
NVO3 can also provide a combined L2 and L3 service to tenants. A
combined service provides L2 service for intra-VN communication, but
also provides L3 service for L3 traffic entering or leaving the VN.
Architecturally, the handling of a combined L2/L3 service within the
NVO3 architecture is intended to match what is commonly done today in
non-overlay environments by devices providing a combined bridge/
router service. With combined service, the virtual network itself
retains the semantics of L2 service and all traffic is processed
according to its L2 semantics. In addition, however, traffic
requiring IP processing is also processed at the IP level.
The IP processing for a combined service can be implemented on a
standalone device attached to the virtual network (e.g., an IP
router) or implemented locally on the NVE (see Section 5.4 on
Distributed Gateways). For unicast traffic, NVE implementation of a
combined service may result in a packet being delivered to another TS
Black, et al. Expires October 23, 2016 [Page 6]
Internet-Draft NVO3 Architecture April 2016
attached to the same NVE (on either the same or a different VN) or
tunneled to a remote NVE, or even forwarded outside the NVO3 domain.
For multicast or broadcast packets, the combination of NVE L2 and L3
processing may result in copies of the packet receiving both L2 and
L3 treatments to realize delivery to all of the destinations
involved. This distributed NVE implementation of IP routing results
in the same network delivery behavior as if the L2 processing of the
packet included delivery of the packet to an IP router attached to
the L2 VN as a TS, with the router having additional network
attachments to other networks, either virtual or not.
3.1.1. VLAN Tags in L2 Service
An NVO3 L2 virtual network service may include encapsulated L2 VLAN
tags provided by a Tenant System, but does not use encapsulated tags
in deciding where and how to forward traffic. Such VLAN tags can be
passed through, so that Tenant Systems that send or expect to receive
them can be supported as appropriate.
The processing of VLAN tags that an NVE receives from a TS is
controlled by settings associated with the VAP. Just as in the case
with ports on Ethernet switches, a number of settings could be
imagined. For example, C-TAGs can be passed through transparently,
they could always be stripped upon receipt from a Tenant System, they
could be compared against a list of explicitly configured tags, etc.
Note that the handling of C-VIDs has additional complications, as
described in Section 4.2.1 below.
3.1.2. TTL Considerations
For L3 service, Tenant Systems should expect the TTL of the packets
they send to be decremented by at least 1. For L2 service, the TTL
on packets (when the packet is IP) is not modified. The underlay
network manages the TTLs in the outer IP encapsulation (which could
be independent from or related to the TTL in the tenant IP packets).
3.2. Network Virtualization Edge (NVE)
Tenant Systems connect to NVEs via a Tenant System Interface (TSI).
The TSI logically connects to the NVE via a Virtual Access Point
(VAP) and each VAP is associated with one Virtual Network as shown in
Figure 2. To the Tenant System, the TSI is like a NIC; the TSI
presents itself to a Tenant System as a normal network interface. On
the NVE side, a VAP is a logical network port (virtual or physical)
into a specific virtual network. Note that two different Tenant
Systems (and TSIs) attached to a common NVE can share a VAP (e.g.,
Black, et al. Expires October 23, 2016 [Page 7]
Internet-Draft NVO3 Architecture April 2016
TS1 and TS2 in Figure 2) so long as they connect to the same Virtual
Network.
| Data Center Network (IP) |
| |
+-----------------------------------------+
| |
| Tunnel Overlay |
+------------+---------+ +---------+------------+
| +----------+-------+ | | +-------+----------+ |
| | Overlay Module | | | | Overlay Module | |
| +---------+--------+ | | +---------+--------+ |
| | | | | |
NVE1 | | | | | | NVE2
| +--------+-------+ | | +--------+-------+ |
| | VNI1 VNI2 | | | | VNI1 VNI2 | |
| +-+----------+---+ | | +-+-----------+--+ |
| | VAP1 | VAP2 | | | VAP1 | VAP2|
+----+----------+------+ +----+-----------+-----+
| | | |
|\ | | |
| \ | | /|
-------+--\-------+-------------------+---------/-+-------
| \ | Tenant | / |
TSI1 |TSI2\ | TSI3 TSI1 TSI2/ TSI3
+---+ +---+ +---+ +---+ +---+ +---+
|TS1| |TS2| |TS3| |TS4| |TS5| |TS6|
+---+ +---+ +---+ +---+ +---+ +---+
Figure 2: NVE Reference Model
The Overlay Module performs the actual encapsulation and
decapsulation of tunneled packets. The NVE maintains state about the
virtual networks it is a part of so that it can provide the Overlay
Module with such information as the destination address of the NVE to
tunnel a packet to, or the Context ID that should be placed in the
encapsulation header to identify the virtual network that a tunneled
packet belongs to.
On the data center network side, the NVE sends and receives native IP
traffic. When ingressing traffic from a Tenant System, the NVE
identifies the egress NVE to which the packet should be sent, adds an
overlay encapsulation header, and sends the packet on the underlay
network. When receiving traffic from a remote NVE, an NVE strips off
the encapsulation header, and delivers the (original) packet to the
appropriate Tenant System. When the source and destination Tenant
Black, et al. Expires October 23, 2016 [Page 8]
Internet-Draft NVO3 Architecture April 2016
System are on the same NVE, no encapsulation is needed and the NVE
forwards traffic directly.
Conceptually, the NVE is a single entity implementing the NVO3
functionality. In practice, there are a number of different
implementation scenarios, as described in detail in Section 4.
3.3. Network Virtualization Authority (NVA)
Address dissemination refers to the process of learning, building and
distributing the mapping/forwarding information that NVEs need in
order to tunnel traffic to each other on behalf of communicating
Tenant Systems. For example, in order to send traffic to a remote
Tenant System, the sending NVE must know the destination NVE for that
Tenant System.
One way to build and maintain mapping tables is to use learning, as
802.1 bridges do [IEEE-802.1Q]. When forwarding traffic to multicast
or unknown unicast destinations, an NVE could simply flood traffic.
While flooding works, it can lead to traffic hot spots and can lead
to problems in larger networks (e.g., excessive amounts of flooded
traffic).
Alternatively, to reduce the scope of where flooding must take place,
or to eliminate it all together, NVEs can make use of a Network
Virtualization Authority (NVA). An NVA is the entity that provides
address mapping and other information to NVEs. NVEs interact with an
NVA to obtain any required address mapping information they need in
order to properly forward traffic on behalf of tenants. The term NVA
refers to the overall system, without regards to its scope or how it
is implemented. NVAs provide a service, and NVEs access that service
via an NVE-to-NVA protocol as discussed in Section 4.3.
Even when an NVA is present, Ethernet bridge MAC address learning
could be used as a fallback mechanism, should the NVA be unable to
provide an answer or for other reasons. This document does not
consider flooding approaches in detail, as there are a number of
benefits in using an approach that depends on the presence of an NVA.
For the rest of this document, it is assumed that an NVA exists and
will be used. NVAs are discussed in more detail in Section 7.
3.4. VM Orchestration Systems
VM orchestration systems manage server virtualization across a set of
servers. Although VM management is a separate topic from network
virtualization, the two areas are closely related. Managing the
creation, placement, and movement of VMs also involves creating,
Black, et al. Expires October 23, 2016 [Page 9]
Internet-Draft NVO3 Architecture April 2016
attaching to and detaching from virtual networks. A number of
existing VM orchestration systems have incorporated aspects of
virtual network management into their systems.
Note also, that although this section uses the term "VM" and
"hypervisor" throughout, the same issues apply to other
virtualization approaches, including Linux Containers (LXC), BSD
Jails, Network Service Appliances as discussed in Section 5.1, etc..
From an NVO3 perspective, it should be assumed that where the
document uses the term "VM" and "hypervisor", the intention is that
the discussion also applies to other systems, where, e.g., the host
operating system plays the role of the hypervisor in supporting
virtualization, and a container plays the equivalent role as a VM.
When a new VM image is started, the VM orchestration system
determines where the VM should be placed, interacts with the
hypervisor on the target server to load and start the VM and controls
when a VM should be shutdown or migrated elsewhere. VM orchestration
systems also have knowledge about how a VM should connect to a
network, possibly including the name of the virtual network to which
a VM is to connect. The VM orchestration system can pass such
information to the hypervisor when a VM is instantiated. VM
orchestration systems have significant (and sometimes global)
knowledge over the domain they manage. They typically know on what
servers a VM is running, and meta data associated with VM images can
be useful from a network virtualization perspective. For example,
the meta data may include the addresses (MAC and IP) the VMs will use
and the name(s) of the virtual network(s) they connect to.
VM orchestration systems run a protocol with an agent running on the
hypervisor of the servers they manage. That protocol can also carry
information about what virtual network a VM is associated with. When
the orchestrator instantiates a VM on a hypervisor, the hypervisor
interacts with the NVE in order to attach the VM to the virtual
networks it has access to. In general, the hypervisor will need to
communicate significant VM state changes to the NVE. In the reverse
direction, the NVE may need to communicate network connectivity
information back to the hypervisor. Example VM orchestration systems
in use today include VMware's vCenter Server, Microsoft's System
Center Virtual Machine Manager, and systems based on OpenStack and
its associated plugins (e.g., Nova and Neutron). Each can pass
information about what virtual networks a VM connects to down to the
hypervisor. The protocol used between the VM orchestration system
and hypervisors is generally proprietary.
It should be noted that VM orchestration systems may not have direct
access to all networking related information a VM uses. For example,
Black, et al. Expires October 23, 2016 [Page 10]
Internet-Draft NVO3 Architecture April 2016
a VM may make use of additional IP or MAC addresses that the VM
management system is not aware of.
4. Network Virtualization Edge (NVE)
As introduced in Section 3.2 an NVE is the entity that implements the
overlay functionality. This section describes NVEs in more detail.
An NVE will have two external interfaces:
Tenant System Facing: On the Tenant System facing side, an NVE
interacts with the hypervisor (or equivalent entity) to provide
the NVO3 service. An NVE will need to be notified when a Tenant
System "attaches" to a virtual network (so it can validate the
request and set up any state needed to send and receive traffic on
behalf of the Tenant System on that VN). Likewise, an NVE will
need to be informed when the Tenant System "detaches" from the
virtual network so that it can reclaim state and resources
appropriately.
Data Center Network Facing: On the data center network facing side,
an NVE interfaces with the data center underlay network, sending
and receiving tunneled TS packets to and from the underlay. The
NVE may also run a control protocol with other entities on the
network, such as the Network Virtualization Authority.
4.1. NVE Co-located With Server Hypervisor
When server virtualization is used, the entire NVE functionality will
typically be implemented as part of the hypervisor and/or virtual
switch on the server. In such cases, the Tenant System interacts
with the hypervisor and the hypervisor interacts with the NVE.
Because the interaction between the hypervisor and NVE is implemented
entirely in software on the server, there is no "on-the-wire"
protocol between Tenant Systems (or the hypervisor) and the NVE that
needs to be standardized. While there may be APIs between the NVE
and hypervisor to support necessary interaction, the details of such
an API are not in-scope for the IETF to work on.
Implementing NVE functionality entirely on a server has the
disadvantage that server CPU resources must be spent implementing the
NVO3 functionality. Experimentation with overlay approaches and
previous experience with TCP and checksum adapter offloads suggests
that offloading certain NVE operations (e.g., encapsulation and
decapsulation operations) onto the physical network adapter can
produce performance advantages. As has been done with checksum and/
or TCP server offload and other optimization approaches, there may be
benefits to offloading common operations onto adapters where
possible. Just as important, the addition of an overlay header can
Black, et al. Expires October 23, 2016 [Page 11]
Internet-Draft NVO3 Architecture April 2016
disable existing adapter offload capabilities that are generally not
prepared to handle the addition of a new header or other operations
associated with an NVE.
While the exact details of how to split the implementation of
specific NVE functionality between a server and its network adapters
is an implementation matter and outside the scope of IETF
standardization, the NVO3 architecture should be cognizant of and
support such separation. Ideally, it may even be possible to bypass
the hypervisor completely on critical data path operations so that
packets between a TS and its VN can be sent and received without
having the hypervisor involved in each individual packet operation.
4.2. Split-NVE
Another possible scenario leads to the need for a split NVE
implementation. An NVE running on a server (e.g. within a
hypervisor) could support NVO3 service towards the tenant, but not
perform all NVE functions (e.g., encapsulation) directly on the
server; some of the actual NVO3 functionality could be implemented on
(i.e., offloaded to) an adjacent switch to which the server is
attached. While one could imagine a number of link types between a
server and the NVE, one simple deployment scenario would involve a
server and NVE separated by a simple L2 Ethernet link. A more
complicated scenario would have the server and NVE separated by a
bridged access network, such as when the NVE resides on a ToR, with
an embedded switch residing between servers and the ToR.
For the split NVE case, protocols will be needed that allow the
hypervisor and NVE to negotiate and setup the necessary state so that
traffic sent across the access link between a server and the NVE can
be associated with the correct virtual network instance.
Specifically, on the access link, traffic belonging to a specific
Tenant System would be tagged with a specific VLAN C-TAG that
identifies which specific NVO3 virtual network instance it connects
to. The hypervisor-NVE protocol would negotiate which VLAN C-TAG to
use for a particular virtual network instance. More details of the
protocol requirements for functionality between hypervisors and NVEs
can be found in [I-D.ietf-nvo3-nve-nva-cp-req].
4.2.1. Tenant VLAN handling in Split-NVE Case
Preserving tenant VLAN tags across an NVO3 VN as described in
Section 3.1.1 poses additional complications in the split-NVE case.
The portion of the NVE that performs the encapsulation function needs
access to the specific VLAN tags that the Tenant System is using in
order to include them in the encapsulated packet. When an NVE is
implemented entirely within the hypervisor, the NVE has access to the
Black, et al. Expires October 23, 2016 [Page 12]
Internet-Draft NVO3 Architecture April 2016
complete original packet (including any VLAN tags) sent by the
tenant. In the split-NVE case, however, the VLAN tag used between
the hypervisor and offloaded portions of the NVE normally only
identify the specific VN that traffic belongs to. In order to allow
a tenant to preserve VLAN information from end to end between TS when
in the split-NVE case, additional mechanisms would be needed (e.g.
carry an additional VLAN tag by carrying both a C-Tag and an S-Tag as
specified in [IEEE-802.1Q]).
4.3. NVE State
NVEs maintain internal data structures and state to support the
sending and receiving of tenant traffic. An NVE may need some or all
of the following information:
1. An NVE keeps track of which attached Tenant Systems are connected
to which virtual networks. When a Tenant System attaches to a
virtual network, the NVE will need to create or update local
state for that virtual network. When the last Tenant System
detaches from a given VN, the NVE can reclaim state associated
with that VN.
2. For tenant unicast traffic, an NVE maintains a per-VN table of
mappings from Tenant System (inner) addresses to remote NVE
(outer) addresses.
3. For tenant multicast (or broadcast) traffic, an NVE maintains a
per-VN table of mappings and other information on how to deliver
tenant multicast (or broadcast) traffic. If the underlying
network supports IP multicast, the NVE could use IP multicast to
deliver tenant traffic. In such a case, the NVE would need to
know what IP underlay multicast address to use for a given VN.
Alternatively, if the underlying network does not support
multicast, a source NVE could use unicast replication to deliver
traffic. In such a case, an NVE would need to know which remote
NVEs are participating in the VN. An NVE could use both
approaches, switching from one mode to the other depending on
such factors as bandwidth efficiency and group membership
sparseness. [I-D.ietf-nvo3-mcast-framework] discusses the
subject of multicast handling in NVO3 in further detail.
4. An NVE maintains necessary information to encapsulate outgoing
traffic, including what type of encapsulation and what value to
use for a Context ID within the encapsulation header.
5. In order to deliver incoming encapsulated packets to the correct
Tenant Systems, an NVE maintains the necessary information to map
Black, et al. Expires October 23, 2016 [Page 13]
Internet-Draft NVO3 Architecture April 2016
incoming traffic to the appropriate VAP (i.e., Tenant System
Interface).
6. An NVE may find it convenient to maintain additional per-VN
information such as QoS settings, Path MTU information, ACLs,
etc.
4.4. Multi-Homing of NVEs
NVEs may be multi-homed. That is, an NVE may have more than one IP
address associated with it on the underlay network. Multihoming
happens in two different scenarios. First, an NVE may have multiple
interfaces connecting it to the underlay. Each of those interfaces
will typically have a different IP address, resulting in a specific
Tenant Address (on a specific VN) being reachable through the same
NVE but through more than one underlay IP address. Second, a
specific tenant system may be reachable through more than one NVE,
each having one or more underlay addresses. In both cases, NVE
address mapping functionality needs to support one-to-many mappings
and enable a sending NVE to (at a minimum) be able to fail over from
one IP address to another, e.g., should a specific NVE underlay
address become unreachable.
Finally, multi-homed NVEs introduce complexities when source unicast
replication is used to implement tenant multicast as described in
Section 4.3. Specifically, an NVE should only receive one copy of a
replicated packet.
Multi-homing is needed to support important use cases. First, a bare
metal server may have multiple uplink connections to either the same
or different NVEs. Having only a single physical path to an upstream
NVE, or indeed, having all traffic flow through a single NVE would be
considered unacceptable in highly-resilient deployment scenarios that
seek to avoid single points of failure. Moreover, in today's
networks, the availability of multiple paths would require that they
be usable in an active-active fashion (e.g., for load balancing).
4.5. VAP
The VAP is the NVE-side of the interface between the NVE and the TS.
Traffic to and from the tenant flows through the VAP. If an NVE runs
into difficulties sending traffic received on the VAP, it may need to
signal such errors back to the VAP. Because the VAP is an emulation
of a physical port, its ability to signal NVE errors is limited and
lacks sufficient granularity to reflect all possible errors an NVE
may encounter (e.g., inability reach a particular destination). Some
errors, such as an NVE losing all of its connections to the underlay,
could be reflected back to the VAP by effectively disabling it. This
Black, et al. Expires October 23, 2016 [Page 14]
Internet-Draft NVO3 Architecture April 2016
state change would reflect itself on the TS as an interface going
down, allowing the TS to implement interface error handling, e.g.,
failover, in the same manner as when a physical interfaces becomes
disabled.
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 [I-D.ietf-nvo3-nve-nva-cp-req]
(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 multi-tenancy 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 multi-tenancy, a Network Service Appliance
may explicitly support multi-tenancy. 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 NVO3 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.
Black, et al. Expires October 23, 2016 [Page 15]
Internet-Draft NVO3 Architecture April 2016
5.3. Gateways
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
reverse manner.
Gateways can be either virtual (i.e., implemented as a VM) or
physical (i.e., as 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 implemented in either a centralized
manner or distributed to co-exist with the NVEs.
5.3.1.1. 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.
Black, et al. Expires October 23, 2016 [Page 16]
Internet-Draft NVO3 Architecture April 2016
L2 VN to L2 VN: The main motivation for this type of gateway to
create separate groups of Tenant Systems using L2 VNs such that
the gateway can enforce network policies between each L2 VN.
5.3.1.2. L3 Gateways (Only IP Packets)
L3 Gateways forward IP packets based on the IP addresses present in
the packets.
L3 VN to Legacy L2: This type of gateway forwards packets on between
L3 VNs and legacy L2 networks such as VLANs or L2 VPNs. The
MAC address in any frames forwarded between the legacy L2
network would be the MAC address of the gateway.
L3 VN to Legacy L3: The type of gateway forwards packets between L3
VNs and legacy L3 networks. These legacy L3 networks could be
local the data center, in the WAN, or an L3 VPN.
L3 VN to L2 VN: This type of gateway forwards packets on between L3
VNs and L2 VNs. The MAC address in any frames forwarded
between the 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 MAC address in
any frames forwarded between the L2 VNs would be the MAC
address of the gateway.
L3 VN to L3 VN: The main motivation for this type of gateway 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 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
Black, et al. Expires October 23, 2016 [Page 17]
Internet-Draft NVO3 Architecture April 2016
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
architecture.
5.5. ARP and Neighbor Discovery
For an L2 service, strictly speaking, special processing of Address
Resolution Protocol (ARP) [RFC0826] (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
Black, et al. Expires October 23, 2016 [Page 18]
Internet-Draft NVO3 Architecture April 2016
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 (and 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
example:
o "No such TS here", upon a receipt of a tunneled packet for an
unknown TS.
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
(soft error).
o Delivered to correct NVE, but could not deliver packet to TS-X
(hard error).
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.
Black, et al. Expires October 23, 2016 [Page 19]
Internet-Draft NVO3 Architecture April 2016
7. Network Virtualization Authority
Before sending 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 Authority.
The Network Virtualization Authority (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 regards 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. The NVA can obtain information
either 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 to 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
hypervisor.
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.
Black, et al. Expires October 23, 2016 [Page 20]
Internet-Draft NVO3 Architecture April 2016
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 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
interoperability.
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 for ensuring 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
balancing, etc.
In the NVO3 architecture, an NVA is accessed through one or more IP
addresses (or IP address/port combination). If multiple IP addresses
Black, et al. Expires October 23, 2016 [Page 21]
Internet-Draft NVO3 Architecture April 2016
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, 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. A key question with
such an approach is how information would be partitioned, and how an
NVE could determine which address to use to get the information it
needs.
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-to-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-to-NVA protocol is needed. The NVE-to-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-to-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.
Black, et al. Expires October 23, 2016 [Page 22]
Internet-Draft NVO3 Architecture April 2016
While having a direct NVE-to-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-to-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
Black, et al. Expires October 23, 2016 [Page 23]
Internet-Draft NVO3 Architecture April 2016
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) are more likely to evolve over time as
experience is gained from usage and upgrades will involve fewer
nodes.
Requirements for a direct NVE-NVA protocol can be found in
[I-D.ietf-nvo3-nve-nva-cp-req]
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 from the NVA information
about where a given remote TS destination resides. NVAs in turn
obtain information from NVEs about the individual TSs attached to
those NVEs.
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 TSes for broadcast
or multicast traffic), an NVE must know where the remote TS(es)
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 an 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 shutdown, 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 verify that the information is
still correct despite the error condition. Note that such a query
Black, et al. Expires October 23, 2016 [Page 24]
Internet-Draft NVO3 Architecture April 2016
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.
Should it then need to communicate with a destination for which it
does not have mapping information, however, it will need to be able
to query the NVA on demand for the missing information on a per-
destination basis.
The NVO3 architecture will need to support a range of operations
between the NVE and NVA. Requirements for those operations can be
found in [I-D.ietf-nvo3-nve-nva-cp-req].
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
single entity.
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,
multiple data centers managed by the same administrator 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 (1 and 2)
share information about Virtual Network "1217". VM1 and VM2 both
connect to the same Virtual Network 1217, even though the two VMs are
in separate NV Domains. There are two cases to consider. In the
first case, NV Domain B (NVB) 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 1 and 2 may not share a common address space
Black, et al. Expires October 23, 2016 [Page 25]
Internet-Draft NVO3 Architecture April 2016
(i.e., require traversal through a NAT device), 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 Virtual
Network 1217 is available, and direct that traffic between the two
nodes go through IP-G. IP-G would then decapsulate received traffic
from one NV Domain, translate it appropriately for the other domain
and re-encapsulate the packet for delivery.
xxxxxx xxxxxx +-----+
+-----+ xxxxxxxx xxxxxx xxxxxxx 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
| xxxxxxxxxx | xx xx
+---+-+ | xx xx
|NVA-1| +--+--+ xx xxx
+-----+ |NVA-2| xxxx xxxx
+-----+ xxxxxxx
Figure 3: VM1 and VM2 are 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
Black, et al. Expires October 23, 2016 [Page 26]
Internet-Draft NVO3 Architecture April 2016
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
centers.
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 to for
intra- 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
tradeoffs 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
WAN links.
Black, et al. Expires October 23, 2016 [Page 27]
Internet-Draft NVO3 Architecture April 2016
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 for it 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 and 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-to-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 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
[I-D.ietf-nvo3-dataplane-requirements]. A number of encapsulations
already exist that provide a VN Context of sufficient size for NVO3.
For example, VXLAN [RFC7348] has a 24-bit VXLAN Network Identifier
(VNI). 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 and Management
The simplicity of operating and debugging overlay networks will be
critical for successful deployment. Some architectural choices can
facilitate or hinder OAM. Related OAM drafts include
[I-D.ashwood-nvo3-operational-requirement].
13. Summary
This document presents the overall architecture for Network
Virtualization Overlays (NVO3). The architecture calls for three
main areas of protocol work:
Black, et al. Expires October 23, 2016 [Page 28]
Internet-Draft NVO3 Architecture April 2016
1. A hypervisor-to-NVE protocol to support Split NVEs as discussed
in Section 4.2.
2. An NVE to NVA protocol for disseminating VN information (e.g.,
inner to outer address mappings).
3. An NVA-to-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. Acknowledgments
Helpful comments and improvements to this document have come from
Lizhong Jin, Anton Ivanov, Dennis (Xiaohong) Qin, Erik Smith, Ziye
Yang and Lucy Yong.
15. IANA Considerations
This memo includes no request to IANA.
16. 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, modified, or having its content exposed
to an inappropriate third party. In all cases, encryption between
authenticated tunnel endpoints can be used to mitigate risks.
For the control plane, between NVAs, the NVA and NVE as well as
between different components of the split-NVE approach, a combination
of authentication and encryption can be used. All entities will need
to properly authenticate with each other and enable encryption for
their interactions as appropriate to protect sensitive information.
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.
17. Informative References
Black, et al. Expires October 23, 2016 [Page 29]
Internet-Draft NVO3 Architecture April 2016
[I-D.ashwood-nvo3-operational-requirement]
Ashwood-Smith, P., Iyengar, R., Tsou, T., Sajassi, A.,
Boucadair, M., Jacquenet, C., and M. Daikoku, "NVO3
Operational Requirements", draft-ashwood-nvo3-operational-
requirement-03 (work in progress), July 2013.
[I-D.ietf-nvo3-dataplane-requirements]
Bitar, N., Lasserre, M., Balus, F., Morin, T., Jin, L.,
and B. Khasnabish, "NVO3 Data Plane Requirements", draft-
ietf-nvo3-dataplane-requirements-03 (work in progress),
April 2014.
[I-D.ietf-nvo3-mcast-framework]
Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R.
Krishnan, "A Framework for Multicast in NVO3", draft-ietf-
nvo3-mcast-framework-04 (work in progress), February 2016.
[I-D.ietf-nvo3-nve-nva-cp-req]
Kreeger, L., Dutt, D., Narten, T., and D. Black, "Network
Virtualization NVE to NVA Control Protocol Requirements",
draft-ietf-nvo3-nve-nva-cp-req-05 (work in progress),
March 2016.
[IEEE-802.1Q]
IEEE Std 802.1Q-2014, , "IEEE Standard for Local and
metropolitan area networks: Bridges and Bridged
Networks,", November 2014.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<http://www.rfc-editor.org/info/rfc826>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
Black, et al. Expires October 23, 2016 [Page 30]
Internet-Draft NVO3 Architecture April 2016
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<http://www.rfc-editor.org/info/rfc7348>.
[RFC7364] Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
Kreeger, L., and M. Napierala, "Problem Statement:
Overlays for Network Virtualization", RFC 7364,
DOI 10.17487/RFC7364, October 2014,
<http://www.rfc-editor.org/info/rfc7364>.
[RFC7365] Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
Rekhter, "Framework for Data Center (DC) Network
Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
2014, <http://www.rfc-editor.org/info/rfc7365>.
[RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network
Virtualization Using Generic Routing Encapsulation",
RFC 7637, DOI 10.17487/RFC7637, September 2015,
<http://www.rfc-editor.org/info/rfc7637>.
Authors' Addresses
David Black
EMC
Email: david.black@emc.com
Jon Hudson
Independent
Email: jon.hudson@gmail.com
Lawrence Kreeger
Cisco
Email: kreeger@cisco.com
Marc Lasserre
Independent
Email: mmlasserre@gmail.com
Black, et al. Expires October 23, 2016 [Page 31]
Internet-Draft NVO3 Architecture April 2016
Thomas Narten
IBM
Email: narten@us.ibm.com
Black, et al. Expires October 23, 2016 [Page 32]
