Internet DRAFT - draft-ietf-nvo3-encap
draft-ietf-nvo3-encap
NVO3 Working Group S. Boutros, Ed.
Internet-Draft Ciena Corporation
Intended status: Informational D. Eastlake, Ed.
Expires: 22 August 2024 Futurewei Technologies
19 February 2024
Network Virtualization Overlays (NVO3) Encapsulation Considerations
draft-ietf-nvo3-encap-12
Abstract
The IETF Network Virtualization Overlays (NVO3) Working Group
developed considerations for a common encapsulation that addresses
various network virtualization overlay technical concerns. This
document provides a record, for the benefit of the IETF community, of
the considerations arrived at starting from the output of an NVO3
encapsulation design team. These considerations may be helpful with
future deliberations by working groups over the choice of
encapsulation formats.
There are implications of having different encapsulations in real
environments consisting of both software and hardware implementations
and within and spanning multiple data centers. For example, OAM
functions such as path MTU discovery become challenging with multiple
encapsulations along the data path.
Based on these considerations, the Working Group determined that
Geneve with a few modifications as the common encapsulation. This
document provides more details, particularly in Section 7.
Status of This Memo
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This Internet-Draft will expire on 22 August 2024.
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Copyright Notice
Copyright (c) 2024 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Design Team and Working Group Process . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Abbreviations and Acronyms . . . . . . . . . . . . . . . . . 4
5. Encapsulation Issues and Background . . . . . . . . . . . . . 5
5.1. Geneve . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Generic UDP Encapsulation (GUE) . . . . . . . . . . . . . 6
5.3. Generic Protocol Extension (GPE) for VXLAN . . . . . . . 7
6. Common Encapsulation Considerations . . . . . . . . . . . . . 8
6.1. Current Encapsulations . . . . . . . . . . . . . . . . . 9
6.2. Useful Extensions Use Cases . . . . . . . . . . . . . . . 9
6.2.1. Telemetry Extensions . . . . . . . . . . . . . . . . 9
6.2.2. Security/Integrity Extensions . . . . . . . . . . . . 10
6.2.3. Group Based Policy . . . . . . . . . . . . . . . . . 10
6.3. Hardware Considerations . . . . . . . . . . . . . . . . . 10
6.4. Extension Size . . . . . . . . . . . . . . . . . . . . . 11
6.5. Ordering of Extension Headers . . . . . . . . . . . . . . 12
6.6. TLV versus Bit Fields . . . . . . . . . . . . . . . . . . 12
6.7. Control Plane Considerations . . . . . . . . . . . . . . 13
6.8. Split NVE . . . . . . . . . . . . . . . . . . . . . . . . 14
6.9. Larger VNI Considerations . . . . . . . . . . . . . . . . 15
7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11. Normative References . . . . . . . . . . . . . . . . . . . . 18
12. Informative References . . . . . . . . . . . . . . . . . . . 18
Appendix A. Encapsulation Comparison . . . . . . . . . . . . . . 21
A.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 21
A.2. Extensibility . . . . . . . . . . . . . . . . . . . . . . 21
A.2.1. Native Extensibility Support . . . . . . . . . . . . 21
A.2.2. Extension Parsing . . . . . . . . . . . . . . . . . . 21
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A.2.3. Critical Extensions . . . . . . . . . . . . . . . . . 22
A.2.4. Maximal Header Length . . . . . . . . . . . . . . . . 22
A.3. Encapsulation Header . . . . . . . . . . . . . . . . . . 22
A.3.1. Virtual Network Identifier (VNI) . . . . . . . . . . 22
A.3.2. Next Protocol . . . . . . . . . . . . . . . . . . . . 22
A.3.3. Other Header Fields . . . . . . . . . . . . . . . . . 23
A.4. Comparison Summary . . . . . . . . . . . . . . . . . . . 23
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
The NVO3 Working Group is chartered to gather requirements and
develop solutions for network virtualization data planes based on
encapsulation of virtual network traffic over an IP-based underlay
data plane. Requirements include due consideration for OAM and
security. Based on these requirements the WG was to select, extend,
and/or develop one or more data plane encapsulation format(s).
This led to WG drafts and an RFC describing three encapsulations as
follows:
* [RFC8926] Geneve: Generic Network Virtualization Encapsulation
* [ietf_intarea_gue] Generic UDP Encapsulation
* [nvo3_vxlan_gpe] Generic Protocol Extension for VXLAN (VXLAN-GPE)
Discussion on the list and in face-to-face meetings identified a
number of technical problems with each of these encapsulations.
Furthermore, there was clear consensus at the 96th IETF meeting in
Berlin that, to maximize interoperability, the working group should
progress only one data plane encapsulation. In order to overcome a
deadlock on the encapsulation decision, the WG consensus was to form
a Design Team [RFC2418] to resolve this issue and provide initial
considerations.
2. Design Team and Working Group Process
The Design Team was to select one of the proposed encapsulations and
enhance it to address the technical concerns. The simple evolution
of deployed networks as well as applicability to all locations in the
NVO3 architecture were goals. The Design Team was to specifically
avoid selecting a design that is burdensome on hardware
implementations but should allow future extensibility. The selected
design also needed to operate well with ICMP and in Equal Cost Multi-
Path (ECMP) environments. If further extensibility is required, then
it should be done in such a manner that it does not require the
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consent of an entity outside of the IETF.
The output of the Design Team was then prcoessed through the working
group resulting in working group consensus for this document.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. Abbreviations and Acronyms
The following abbreviations and acronyms are used in this document:
ACL - Access Control List
DT - NVO3 encapsulation Design Team
ECMP - Equal Cost Multi-Path
EVPN - Ethernet VPN [RFC8365]
Geneve - Generic Network Virtualization Encapsulation [RFC8926]
GPE - Generic Protocol Extension
GUE - Generic UDP Encapsulation [ietf_intarea_gue]
HMAC - Hash based keyed Message Authentication Code [RFC2104]
IEEE - Institute for Electrical and Electronic Engineers
(www.ieee.org)
NIC - Network Interface Card (refers to network interface hardware
which is not necessarily a discrete "card")
NSH - Network Service Header [RFC8300]
NVA - Network Virtualization Authority
NVE - Network Virtual Edge (device)
NVO3 - Network Virtualization Overlays over Layer 3
OAM - Operations, Administration, and Maintenance [RFC6291]
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PWE3 - Pseudowire Emulation Edge to Edge
TCAM - Ternary Content-Addressable Memory
TLV - Type, Length, and Value
Transit device - Underlay network devices between NVE(s).
UUID - Universally Unique Identifier
VNI - Virtual Network Identifier
VXLAN - Virtual eXtensible LAN [RFC7348]
5. Encapsulation Issues and Background
The following subsections describe issues with current encapsulations
as discussed by the NVO3 WG. Numerous extensions and options have
been designed for GUE and Geneve which may help resolve some of these
issues but have not yet been validated by the WG.
Also included are diagrams and information on the candidate
encapsulations. These are mostly copied from other documents. Since
each protocol is assumed to be sent over UDP, an initial UDP Header
is shown which would be preceded by an IPv4 or IPv6 Header.
5.1. Geneve
The Geneve packet format, taken from [RFC8926], is shown in Figure 1
below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Outer UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port = 6081 Geneve |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Geneve Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver| Opt Len |O|C| Rsvd. | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Virtual Network Identifier (VNI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Variable-Length Options ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Geneve Header
The type of payload being carried is indicated by an Ethertype
[RFC7042] in the Protocol Type field in the Geneve Header; Ethernet
itself is represented by Ethertype 0x6558. See [RFC8926] for details
concerning UDP header fields. The O bit indicates an OAM packet.
The C bit is the "Critical" bit which means that the options must be
processed or the packet discarded.
Issues with Geneve [RFC8926] are as follows:
* Can't be implemented cost-effectively in all use cases because
variable length header and order of the TLVs makes it costly (in
terms of number of gates) to implement in hardware.
* Header doesn't fit into largest commonly available parse buffer
(256 bytes in NIC). Cannot justify doubling buffer size unless it
is mandatory for hardware to process additional option fields.
Selection of Geneve despite these issues may be the result of the
Geneve design effort assuming that the Geneve header would typically
be delivered to a server and parsed in software.
5.2. Generic UDP Encapsulation (GUE)
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Dest port = 6080 GUE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GUE Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |C| Hlen | Proto/ctype | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Extensions Fields (optional) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: GUE Header
The type of payload being carried is indicated by an IANA Internet
protocol number in the Proto/ctype field. The C bit indicates a
Control packet.
Issues with GUE [ietf_intarea_gue] are as follows:
* There were a significant number of objections to GUE related to
the complexity of implementation in hardware, similar to those
noted for Geneve above, such as the variable length and possible
high maximum length of the header.
5.3. Generic Protocol Extension (GPE) for VXLAN
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Outer UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Dest Port = 4790 GPE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
VXLAN-GPE Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|Ver|I|P|B|O| Reserved | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VXLAN Network Identifier (VNI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: GPE Header
The type of payload being carried is indicated by the Next Protocol
field using a VXLAN-GPE-specific registry. The I bit indicates that
the VNI is valid. The P bit indicates that the Next Protocol field
is valid. The B bit indicates the packet is an ingress replicated
Broadcast, Unknown Unicast, or Multicast packet. The O bit indicates
an OAM packet.
Issues with VXLAN-GPE [nvo3_vxlan_gpe] are as follows:
* GPE is not day-1 backwards compatible with VXLAN [RFC7348].
Although the frame format is similar, it uses a different UDP
port, so would require changes to existing implementations even if
the rest of the GPE frame were the same.
* GPE is insufficiently extensible. It adds a Next Protocol field
and some flag bits to the VXLAN header but is not otherwise
extensible.
* Security, e.g., of the VNI, as discussed in Section 6.2.2, has not
been addressed by GPE. Although a shim header could be added for
security and to support other extensions, this has not been
defined yet. More study would be needed to understand the
implication of such a shim on offloading in NICs.
6. Common Encapsulation Considerations
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6.1. Current Encapsulations
Appendix A includes a detailed comparison between the three proposed
encapsulations. The comparison indicates several common properties
but also three major differences among the encapsulations:
* Extensibility: Geneve and GUE were defined with built-in
extensibility, while VXLAN-GPE is not inherently extensible. Note
that any of the three encapsulations can be extended using the
Network Service Header (NSH [RFC8300]).
* Extension method: Geneve is extensible using Type/Length/Value
(TLV) fields, while GUE uses a small set of possible extensions,
and a set of flags that indicate which extensions are present.
* Length field: Geneve and GUE include a Length field, indicating
the length of the encapsulation header, while VXLAN-GPE does not
include such a field. Thus it may be harder to skip the
encapsulation header with VXLAN-GPE
6.2. Useful Extensions Use Cases
Non-vendor specific extensions, such as TLVs, MUST follow the
standardization process. The following use cases for extensions show
that there is a strong requirement to support variable length
extensions with possible different subtypes.
6.2.1. Telemetry Extensions
In several scenarios it is beneficial to make information about the
path a packet took through the network or through a network device as
well as associated telemetry information available to the operator.
This includes not only tasks like debugging, troubleshooting, and
network planning and optimization but also policy or service level
agreement compliance checks.
Packet scheduling algorithms, especially for balancing traffic across
equal cost paths or links, often leverage information contained
within the packet, such as protocol number, IP address, or MAC
address. Probe packets would thus either need to be sent between the
exact same endpoints with the exact same parameters, or probe packets
would need to be artificially constructed as "fake" packets and
inserted along the path. Both approaches are often not feasible from
an operational perspective because access to the end-system is not
feasible or the diversity of parameters and associated probe packets
to be created is simply too large. An extension providing an in-band
telemetry mechanism [RFC9197] is an alternative in those cases.
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6.2.2. Security/Integrity Extensions
Since the currently proposed NVO3 encapsulations do not protect their
headers, a single bit corruption in the VNI field could deliver a
packet to the wrong tenant. Extension headers are needed to use any
sophisticated security.
The possibility of VNI spoofing with an NVO3 protocol is exacerbated
by using UDP. Systems typically have no restrictions on applications
being able to send to any UDP port so an unprivileged application can
trivially spoof VXLAN [RFC7348] packets for instance, including using
arbitrary VNIs.
One can envision support of an HMAC-like Message Authentication Code
(MAC) [RFC2104] in an NVO3 extension to authenticate the header and
the outer IP addresses, thereby preventing attackers from injecting
packets with spoofed VNIs.
Another aspect of security is payload security. Essentially this
makes packets that look like the following:
IP|UDP|NVO3 Encap|DTLS/IPsec-ESP Extension|payload.
This is desirable since we still have the UDP header for ECMP, the
NVO3 header is in plain text so it can be read by network elements,
and different security or other payload transforms can be supported
on a single UDP port (we don't need a separate UDP port for DTLS/
IPsec [RFC9147]/[RFC6071]).
6.2.3. Group Based Policy
Another use case would be to carry the Group Based Policy (GBP)
source group information within a NVO3 header extension in a similar
manner as has been implemented for VXLAN [VXLANgroup]. This allows
various forms of policy such as access control and QoS to be applied
between abstract groups rather than coupled to specific endpoint
addresses.
6.3. Hardware Considerations
Hardware restrictions should be taken into consideration along with
future hardware enhancements that may provide more flexible metadata
processing. However, the set of options that need to and will be
implemented in hardware will be a subset of what is implemented in
software, since software NVEs are likely to grow features, and hence
option support, at a more rapid rate.
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It is hard to predict which options will be implemented in which
piece of hardware and when. That depends on whether the hardware
will be in the form of
* a NIC providing increasing offload capabilities to software NVEs,
* or a switch chip being used as an NVE gateway towards non-NVO3
parts of the network,
* or even a transit device that participates in the NVO3 dataplane,
e.g., for OAM purposes.
A result of this is that it doesn't look useful to prescribe some
order of the options so that the ones that are likely to be
implemented in hardware come first; we can't decide such an order
when we define the options, however a control plane can enforce such
an order for some hardware implementation.
We do know that hardware needs to initially be able to efficiently
skip over the NVO3 header to find the inner payload. That is needed
both for NICs implementing various TCP offload mechanisms and for
transit devices and NVEs applying policy or ACLs to the inner
payload.
6.4. Extension Size
Extension header length has a significant impact on hardware and
software implementations. A maximum total header length that is too
small will unnecessarily constrain software flexibility. A maximum
total header length that is too large will place a nontrivial cost on
hardware implementations. Thus, the DT recommends that there be a
minimum and maximum total available extension header length
specified. The maximum total header length is determined by the size
of the bit field allocated for the total extension header length
field. The risk with this approach is that it may be difficult to
extend the total header size in the future. The minimum total header
length is determined by a requirement in the specifications that all
implementations must meet. The risk with this approach is that all
implementations will only implement support for the minimum total
header length which would then become the de facto maximum total
header length.
The recommended minimum total available header length is 64 bytes.
The size of an extension header should always be 4 byte aligned.
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The maximum length of a single option should be large enough to meet
the different extension use case requirements, e.g., in-band
telemetry and future use.
6.5. Ordering of Extension Headers
To support hardware nodes at the target NVE or at a transit device
that can process one or a few extension headers in TCAM, a control
plane in such a deployment can signal a capability to ensure a
specific extension header will always appear in a specific order, for
example the first one in the packet.
The order of the extension headers should be hardware friendly for
both the sender and the receiver and possibly some transit devices
also. This may requre that the extension headers and their order be
dynamically determined based on the hardware of those devices.
Transit devices don't participate in control plane communication
between the end points and are not required to process the extension
headers; however, if they do, they may need to process only a small
subset of the extension headers that will be consumed by target NVEs.
6.6. TLV versus Bit Fields
If there is a well-known initial set of options that are likely to be
implemented in software and in hardware, it can be efficient to use
the bit fields approach to indicate the presence of extensions as in
GUE. However, as described in section 6.3, if options are added over
time and different subsets of options are likely to be implemented in
different pieces of hardware, then it would be hard for the IETF to
specify which options should get the early bit fields. TLVs are a
lot more flexible, which avoids the need to determine the relative
importance of different options. However, general TLVs of arbitrary
order, size, and repetition are difficult to implement in hardware.
A middle ground is to use TLVs with restrictions on their size and
alignment, observing that individual TLVs can have a fixed length,
and to support via the control plane a method such that an NVE will
only receive options that it needs and implements. The control plane
approach can potentially be used to control the order of the TLVs
sent to a particular NVE. Note that transit devices are not likely
to participate in the control plane; hence, to the extent that they
need to participate in option processing, some other method must be
used. Transit devices would have issues with future GUE bit fields
being defined for future options as well.
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A benefit of TLVs from a hardware perspective is that they are self
describing, i.e., all the information is in the TLV. In a bit field
approach, the hardware needs to look up the bit to determine the
length of the data associated with the bit through some separate
table, which would add hardware complexity.
There are use cases where multiple modules of software are running on
an NVE. These can be modules such as a diagnostic module by one
vendor that does packet sampling and another module from a different
vendor that implements a firewall. Using a TLV format, it is easier
to have different software modules process different TLVs, which
could be standard extensions or vendor specific extensions defined by
the different vendors, without conflicting with each other. This can
help with hardware modularity as well. There are some
implementations with options that allows different software modules,
like MAC learning and security, to process different options.
6.7. Control Plane Considerations
Given that we want to allow considerable flexibility and
extensibility, e.g., for software NVEs, yet be able to support
important extensions in less flexible contexts such as hardware NVEs,
it is useful to consider the control plane. By control plane in this
section we mean both protocols, such as EVPN [RFC8365] and others,
and deployment specific configuration.
If each NVE can express in the control plane that it only supports
certain extensions (which could be a single extension, or a few), and
the source NVEs only include supported extensions in the NVO3
packets, then the target NVE can both use a simpler parser (e.g., a
TCAM might be usable to look for a single NVO3 extension) and the
depth of the inner payload in the NVO3 packet will be minimized.
Furthermore, if the target NVE cares about a few extensions and can
express in the control plane the desired order of those extensions in
the NVO3 packets, then the deployment can provide useful
functionality with simplified hardware requirements for the target
NVE.
Transit devices that are not aware of the NVO3 extensions somewhat
benefit from such an approach, since the inner payload is less deep
in the packet if no extraneous extension headers are included in the
packet. In general, a transit device is not likely to participate in
the NVO3 control plane. However, configuration mechanisms can take
into account limitations of the transit devices used in particular
deployments.
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Note that with this approach different NVEs could desire different
extensions or sets of extensions, which means that the source NVE
needs to be able to place different sets of extensions in different
NVO3 packets, and perhaps in different order. It also assumes that
underlay multicast or replication servers are not used together with
NVO3 extension headers.
There is a need to consider mandatory extensions versus optional
extensions. Mandatory extensions require the receiver to drop the
packet if the extension is unknown. A control plane mechanism can
prevent the need for dropping unknown extensions, since they would
not be included to target NVEs that do not support them.
The control planes defined today need to add the ability to describe
the different encapsulations. Thus, perhaps EVPN [RFC8365] and any
other control plane protocol that the IETF defines should have a way
to indicate the supported NVO3 extensions and their order, for each
of the encapsulations supported.
Developing a separate draft on guidance for option processing and
control plane participation should be considered. This should
provide examples/guidance on range of usage models and deployments
scenarios for specific options and ordering that are relevant for
that specific deployment. This includes end points and middle boxes
using the options. Having the control plane negotiate the
constraints is the most appropriate and flexible way to address these
requirements.
6.8. Split NVE
If there is a need for hosts to send and receive options in a split
NVE case [RFC8394], this is possible using any of the existing
extensible encapsulations (Geneve, GUE, GPE+NSH) by defining a way to
carry those over other transports. NSH can already be used over
different transports.
If this is needed with other encapsulations it can be done by
defining an Ethertype so that it can be carried over Ethernet and
[IEEE802.1Q].
If there is a need to carry other encapsulations over MPLS, it would
require an EVPN control plane to signal that other encapsulation
header + options will be present in front of the L2 packet. The VNI
can be ignored in the header, and the MPLS label will be the one used
to identify the EVPN L2 instance.
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6.9. Larger VNI Considerations
Whether we should make the VNI 32-bits or larger was one of the
topics considered. The benefit of a 24-bit VNI would be to avoid
unnecessary changes with existing proposals and implementations that
are almost all, if not all, using 24-bit VNI. If we need a larger
VNI, perhaps for a telemetry case, an extension can be used to
support that.
7. Recommendations
The Design Team (DT) reported that Geneve was most suitable as a
starting point for a proposed standard for network virtualization,
for the following reasons given below. This conclusion was supported
by the NVO3 Working Group.
1. On whether VNI should be in the base header or in an extension
header and whether it should be a 24-bit or 32-bit field (see
Section 6.9), it was agreed that VNI is critical information for
network virtualization and MUST be present in all packets. It
was also agreed that a 24-bit VNI, which is supported by Geneve,
matches the existing widely used encapsulation formats, i.e.,
VXLAN [RFC7348] and NVGRE [RFC7637], and hence is more suitable
to use going forward.
2. The Geneve header has the total options length which allows
skipping over the options for NIC offload operations and will
allow transit devices to view flow information in the inner
payload.
3. The option of using NSH [RFC8300] with VXLAN-GPE was considered
but given that NSH is targeted at service chaining and contains
service chaining information, it is less suitable for the network
virtualization use case. The other downside for VXLAN-GPE was
lack of a header length in VXLAN-GPE, which makes skipping over
the headers to process inner payload more difficult. A Total
Option Length is present in Geneve. It is not possible to skip
any options in the middle with VXLAN-GPE. In principle a split
between a base header and a header with options is interesting
(whether that options header is NSH or some new header without
ties to a service path). Whether it would make sense to either
use NSH for this, or define a new NVO3 options header was
explored. However, this makes it slightly harder to find the
inner payload since the length field is not in the NVO3 header
itself. Thus, one more field would have to be extracted to
compute the start of the inner payload. Also, if the experience
with IPv6 extension headers is a guide, there would be a risk
that key pieces of hardware might not implement the options
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header, resulting in future calls to deprecate its use. Making
the options part of the base NVO3 header has less of those
issues. Even though the implementation of any particular option
can not be predicted ahead of time, the option mechanism and
ability to skip the options is likely to be broadly implemented.
4. The TLV style and bit field style of extension were compared. It
was deemed that parsing either TLVs or bit fields is expensive
and, while bit fields may be simpler to parse, it is also more
restrictive and requires guessing which extensions will be widely
implemented so they can get early bit assignments. Given that
half the bits are already assigned in GUE, a widely deployed
extension may appear in a flag extension, and this will require
extra processing, to dig the flag from the flag extension and
then look for the extension itself. Also bit fields are not
flexible enough to address the requirements from OAM, Telemetry,
and security extensions, for variable length option and different
subtypes of the same option. While TLVs are more flexible, a
control plane can restrict the number of option TLVs as well as
the order and size of the TLVs to limit this flexibility and make
the TLVs simpler for a dataplane implementation to handle.
5. The multi-vendor NVE case was briefly discussed, as was the need
to allow vendors to put their own extensions in the NVE header.
This is possible with TLVs.
6. It was agreed that the C (Critical) bit in Geneve is helpful.
This bit indicates that the header includes options which must be
parsed or the packet discarded. It allows a receiver NVE to
easily decide whether to process options or not, for example a
UUID based packet trace, and how an optional extension such as
that can be ignored by a receiver NVE and thus make it easy for
NVE to skip over the options. Thus, the C bit should remain as
defined in Geneve.
7. There are already some extensions that are being discussed (see
section 6.2) of varying sizes. By using Geneve options it is
possible to get in-band parameters like switch id, ingress port,
egress port, internal delay, and queue size using TLV extensions
for telemetry purpose from switches. It is also possible to add
security extension TLVs like HMAC [RFC2104] and DTLS/IPsec
[RFC9147]/[RFC6071] to authenticate the Geneve packet header and
secure the Geneve packet payload by software or hardware tunnel
endpoints. A Group Based Policy extension TLV can be carried as
well.
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8. There are already implementations of Geneve options deployed in
production networks. There is as well new hardware supporting
Geneve TLV parsing. In addition, an In-band Telemetry [INT]
specification is being developed by P4.org that illustrates the
option of INT meta data carried over Geneve. OVN/OVS [OVN] have
also defined some option TLV(s) for Geneve.
9. Usage requirements (see Section 6) have been addressed while
considering the requirements and implementations in general
including software and hardware.
There seems to be interest in standardizing some well-known secure
option TLVs to secure the header and payload to guarantee
encapsulation header integrity and tenant data privacy. The working
group should consider standardizing such option(s).
The following enhancements to Geneve are recommended to make it more
suitable to hardware and yet provide flexibility for software:
* The following sort of text is recommended: while TLVs are more
flexible, a control plane can restrict the number of option TLVs
as well the order and size of the TLVs to make it simpler for a
data plane implementation in software or hardware to handle. For
example, there may be some critical information such as a secure
hash that must be processed in a certain order at lowest latency.
* A control plane can negotiate a subset of option TLVs and certain
TLV ordering, as well as limiting the total number of option TLVs
present in the packet, for example, to allow for hardware capable
of processing fewer options. Hence, the control plane needs to
have the ability to describe the supported TLVs subset and their
order.
* The Geneve documents should specify that the subset and order of
option TLVs SHOULD be configurable for each remote NVE in the
absence of a protocol control plane.
* Geneve should follow fragmentation recommendations in overlay
services like PWE3 and the L2/L3 VPN recommendations to guarantee
larger MTU for the tunnel overhead ([RFC3985] Section 5.3).
* Geneve should provide a recommendation for critical bit processing
- text could specify how critical bits can be used with control
plane specifying the critical options.
* Given that there is a telemetry option use case for a length of
256 bytes, it is recommended that Geneve increase the Single TLV
option length to 256.
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* Geneve address requirements for OAM considerations for alternate
marking and for performance measurements that need a 2 bit field
in the header should be considered and the need for the current
OAM bit in the Geneve Header clarified.
* The WG should work on security options for Geneve.
8. Acknowledgements
The authors would like to thank Tom Herbert for providing the
motivation for the Security/Integrity extension, and for his valuable
comments, T. Sridhar for his valuable comments and feedback, Anoop
Ghanwani for his extensive comments, and Ignas Bagdonas.
9. Security Considerations
This document does not introduce any additional security constraints;
however, Section 6.2.2 discusess security/integrity extensions and
this document suggests, in Section 7, that the the nvo3 WG work on
security options for Geneve.
10. IANA Considerations
This document requires no IANA actions.
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12. Informative References
[ietf_gue_extensions]
Herbert, T., Yong, L., and F. Templin, "Extensions for
Generic UDP Encapsulation", work in progress, 8 March
2019, <https://datatracker.ietf.org/doc/draft-ietf-
intarea-gue-extensions/>.
[ietf_intarea_gue]
Herbert, T., Yong, L., and O. Zia, "Generic UDP
Encapsulation", work in progress, 26 October 2019.
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[IEEE802.1Q]
802.1 WG, IEEE., "Bridges and Bridged Networks", IEEE Std
802.1Q-2014, 3 November 2014.
[INT] P4.org, "In-band Network Telemetry (INT) Dataplane
Specification", November 2020,
<https://p4.org/p4-spec/docs/INT_v2_1.pdf>.
[nvo3_vxlan_gpe]
Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
Extension for VXLAN (VXLAN-GPE)", work in progress, 4
November 2023, <https://datatracker.ietf.org/doc/draft-
ietf-nvo3-vxlan-gpe/>.
[OVN] Network, O. V., "", <https://www.openvswitch.org/>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC2418] Bradner, S., "IETF Working Group Guidelines and
Procedures", BCP 25, RFC 2418, DOI 10.17487/RFC2418,
September 1998, <https://www.rfc-editor.org/info/rfc2418>.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
DOI 10.17487/RFC6071, February 2011,
<https://www.rfc-editor.org/info/rfc6071>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
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[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,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network
Virtualization Using Generic Routing Encapsulation",
RFC 7637, DOI 10.17487/RFC7637, September 2015,
<https://www.rfc-editor.org/info/rfc7637>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
[RFC8394] Li, Y., Eastlake 3rd, D., Kreeger, L., Narten, T., and D.
Black, "Split Network Virtualization Edge (Split-NVE)
Control-Plane Requirements", RFC 8394,
DOI 10.17487/RFC8394, May 2018,
<https://www.rfc-editor.org/info/rfc8394>.
[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.17487/RFC8926, November 2020,
<https://www.rfc-editor.org/info/rfc8926>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.
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[VXLANgroup]
Smith, M. and L. Kreeger, "VXLAN Group Policy Option",
work in progress, 22 October 2018,
<https://datatracker.ietf.org/doc/html/draft-smith-vxlan-
group-policy-05>.
Appendix A. Encapsulation Comparison
A.1. Overview
This section presents a comparison of the three NVO3 encapsulation
proposals, Geneve [RFC8926], GUE [ietf_intarea_gue], and VXLAN-GPE
[nvo3_vxlan_gpe]. The three encapsulations use an outer UDP/IP
transport. Geneve and VXLAN-GPE use an 8-octet header, while GUE
uses a 4-octet header. In addition to the base header, optional
extensions may be included in the encapsulation, as discussed in
Section A.2 below.
A.2. Extensibility
A.2.1. Native Extensibility Support
The Geneve and GUE encapsulations both enable optional headers to be
incorporated at the end of the base encapsulation header.
VXLAN-GPE does not provide native support for header extensions.
However, as discussed in [nvo3_vxlan_gpe], extensibility can be
attained to some extent if the Network Service Header (NSH) [RFC8300]
is used immediately following the VXLAN-GPE header. NSH supports
either a fixed-size extension (MD Type 1), or a variable-size TLV-
based extension (MD Type 2). Note that NSH-over-VXLAN-GPE implies an
additional overhead of the 8-octets NSH header, in addition to the
VXLAN-GPE header.
A.2.2. Extension Parsing
The Geneve Variable Length Options are defined as Type/Length/Value
(TLV) extensions. Similarly, VXLAN-GPE, when using NSH, can include
NSH TLV-based extensions. In contrast, GUE defines a small set of
possible extension fields (proposed in [ietf_gue_extensions]), and a
set of flags in the GUE header that indicate for each extension type
whether it is present or not.
TLV-based extensions, as defined in Geneve, provide the flexibility
for a large number of possible extension types. Similar behavior can
be supported in NSH-over-VXLAN-GPE when using MD Type 2. The flag-
based approach taken in GUE strives to simplify implementations by
defining a small number of possible extensions used in a fixed order.
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The Geneve and GUE headers both include a length field, defining the
total length of the encapsulation, including the optional extensions.
This length field simplifies the parsing by transit devices that skip
the encapsulation header without parsing its extensions.
A.2.3. Critical Extensions
The Geneve encapsulation header includes the 'C' field, which
indicates whether the current Geneve header includes critical
options, that is to say, options which must be parsed by the target
NVE. If the endpoint is not able to process a critical option, the
packet is discarded.
A.2.4. Maximal Header Length
The maximal header length in Geneve, including options, is 260
octets. GUE defines the maximal header to be 128 octets. VXLAN-GPE
uses a fixed-length header of 8 octets, unless NSH-over-VXLAN-GPE is
used, yielding an encapsulation header of up to 264 octets.
A.3. Encapsulation Header
A.3.1. Virtual Network Identifier (VNI)
The Geneve and VXLAN-GPE headers both include a 24-bit VNI field.
GUE, on the other hand, enables the use of a 32-bit field called
VNID; this field is not included in the GUE header, but was defined
as an optional extension in [ietf_gue_extensions].
The VXLAN-GPE header includes the 'I' bit, indicating that the VNI
field is valid in the current header. A similar indicator is defined
as a flag in the GUE header [ietf_gue_extensions].
A.3.2. Next Protocol
All three encapsulation headers include a field that specifies the
type of the next protocol header, which resides after the NVO3
encapsulation header. The Geneve header includes a 16-bit field that
uses the IEEE Ethertype convention. GUE uses an 8-bit field, which
uses the IANA Internet protocol numbering. The VXLAN-GPE header
incorporates an 8-bit Next Protocol field, using a VXLAN-GPE-specific
registry, defined in [nvo3_vxlan_gpe].
The VXLAN-GPE header also includes the 'P' bit, which explicitly
indicates whether the Next Protocol field is present in the current
header.
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A.3.3. Other Header Fields
The OAM bit, which is defined in Geneve and in VXLAN-GPE, indicates
whether the current packet is an OAM packet. The GUE header includes
a similar field, but uses different terminology; the GUE 'C-bit'
specifies whether the current packet is a control packet. Note that
the GUE control bit can potentially be used in a large set of
protocols that are not OAM protocols. However, the control packet
examples discussed in [ietf_intarea_gue] are OAM-related.
Each of the three NVO3 encapsulation headers includes a 2-bit Version
field, which is currently defined to be zero.
The Geneve and VXLAN-GPE headers include reserved fields; 14 bits in
the Geneve header, and 27 bits in the VXLAN-GPE header are reserved.
A.4. Comparison Summary
The following table summarizes the comparison between the three NVO3
encapsulations. In some cases a plus sign ("+") or minus sign ("-")
is used to indicate that the header is stronger or weaker in an area
respectively.
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+----------------+----------------+----------------+----------------+
| | Geneve | GUE | VXLAN-GPE |
+----------------+----------------+----------------+----------------+
| Outer transport| UDP/IP | UDP/IP | UDP/IP |
| UDP Port Number| 6081 | 6080 | 4790 |
+----------------+----------------+----------------+----------------+
| Base header | 8 octets | 4 octets | 8 octets |
| length | | | (16 octets |
| | | | using NSH) |
+----------------+----------------+----------------+----------------+
| Extensibility |Variable length |Extension fields| No native ext- |
| | options | | ensibility. |
| | | | Might use NSH. |
+----------------+----------------+----------------+----------------+
| Extension | TLV-based | Flag-based | TLV-based |
| parsing method | | |(using NSH with |
| | | | MD Type 2) |
+----------------+----------------+----------------+----------------+
| Extension | Variable | Fixed | Variable |
| order | | | (using NSH) |
+----------------+----------------+----------------+----------------+
| Length field | + | + | - |
+----------------+----------------+----------------+----------------+
| Max Header | 260 octets | 128 octets | 8 octets |
| Length | | |(264 using NSH) |
+----------------+----------------+----------------+----------------+
| Critical exte- | + | - | - |
| nsion bit | | | |
+----------------+----------------+----------------+----------------+
| VNI field size | 24 bits | 32 bits | 24 bits |
| | | (extension) | |
+----------------+----------------+----------------+----------------+
| Next protocol | 16 bits | 8 bits | 8 bits |
| field | Ethertype | Internet prot- | New registry |
| | registry | ocol registry | |
+----------------+----------------+----------------+----------------+
| Next protocol | - | - | + |
| indicator | | | |
+----------------+----------------+----------------+----------------+
| OAM / control | OAM bit | Control bit | OAM bit |
| field | | | |
+----------------+----------------+----------------+----------------+
| Version field | 2 bits | 2 bits | 2 bits |
+----------------+----------------+----------------+----------------+
| Reserved bits | 14 bits | none | 27 bits |
+----------------+----------------+----------------+----------------+
Figure 4: NVO3 Encapsulations Comparison
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Contributors
The following co-authors have contributed to this document:.
Ilango Ganga
Intel
Email: ilango.s.ganga@intel.com
Pankaj Garg
Microsoft
Email: pankajg@microsoft.com
Rajeev Manur
Broadcom
Email: rajeev.manur@broadcom.com
Tal Mizrahi
Huawei
Email: tal.mizrahi.phd@gmail.com
David Mozes
Email: mosesster@gmail.com
Erik Nordmark
ZEDEDA
Email: nordmark@sonic.net
Michael Smith
Cisco
Email: michsmit@cisco.com
Sam Aldrin
Google
Email: aldrin.ietf@gmail.com
Authors' Addresses
Sami Boutros (editor)
Ciena Corporation
United States of America
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Email: sboutros@ciena.com
Donald E. Eastlake 3rd (editor)
Futurewei Technologies
2386 Panoramic Circle
Apopka, Florida 32703
United States of America
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
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