NVO3 Encapsulation Considerations
draft-ietf-nvo3-encap-07
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Sami Boutros
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Donald Eastlake
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NVO3 Workgroup S. Boutros, Ed.
Internet-Draft Ciena
Intended Status: Informational D. Eastlake, Ed.
Futurewei
Expires: January 28, 2022 July 29, 2021
NVO3 Encapsulation Considerations
draft-ietf-nvo3-encap-07
Abstract
As communicated by the WG Chairs, the IETF NVO3 chairs and Routing
Area director have chartered a design team to take forward the
encapsulation discussion and see if there is potential to design a
common encapsulation that addresses the various technical concerns.
There are implications of different encapsulations in real
environments consisting of both software and hardware implementations
and spanning multiple data centers. For example, OAM functions such
as path MTU discovery become challenging with multiple encapsulations
along the data path.
The design team recommends Geneve with a few modifications as the
common encapsulation. This document provides more details,
particularly in Section 7.
Status of This Document
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the authors or the IDR Working Group mailing list <nvo3@ietf.org>.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
https://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
Shadow Directories can be accessed at
https://www.ietf.org/shadow.html.
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Copyright Notice
Copyright (c) 2021 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.
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Table of Contents
1. Introduction............................................4
2. Design Team Goals.......................................4
3. Terminology.............................................5
4. Abbreviations and Acronyms..............................5
5. Issues with Current Encapsulations......................6
5.1. Geneve................................................6
5.2. GUE (Generic UDP Encapsulation).......................6
5.3. VXLAN-GPE.............................................6
6. Common Encapsulation Considerations.....................7
6.1. Current Encapsulations................................7
6.2. Useful Extensions Use Cases...........................7
6.2.1. Telemetry Extensions................................7
6.2.2. Security/Integrity Extensions.......................8
6.2.3 Group Based Policy...................................8
6.3. Hardware Considerations...............................9
6.4. Extension Size........................................9
6.5. Ordering of Extension Headers........................10
6.6. TLV versus Bit Fields................................10
6.7. Control Plane Considerations.........................11
6.8. Split NVE............................................12
6.9. Larger VNI Considerations............................12
7. Design Team Recommendations............................14
8. Acknowledgements.......................................17
9. Security Considerations................................17
10. IANA Considerations...................................17
11. References............................................18
11.1 Normative References.................................18
11.2 Informative References...............................18
Appendix A: Encapsulations Comparison.....................20
A.1. Overview.............................................20
A.2. Extensibility........................................20
A.2.1. Native Extensibility Support.......................20
A.2.2. Extension Parsing..................................20
A.2.3. Critical Extensions................................21
A.2.4. Maximal Header Length..............................21
A.3. Encapsulation Header.................................21
A.3.1. Virtual Network Identifier (VNI)...................21
A.3.2. Next Protocol......................................21
A.3.3. Other Header Fields................................22
A.4. Comparison Summary...................................23
Contributors..............................................25
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1. Introduction
As communicated by the WG Chairs, the NVO3 WG Charter states that it
may produce requirements for network virtualization data planes based
on encapsulation of virtual network traffic over an IP-based underlay
data plane. Such requirements should consider OAM and security.
Based on these requirements the WG will select, extend, and/or
develop one or more data plane encapsulation format(s).
This has led to WG drafts and an RFC describing three encapsulations
as follows:
- [RFC8926] Geneve: Generic Network Virtualization Encapsulation
- [I-D.ietf-intarea-gue] Generic UDP Encapsulation
- [I-D.ietf-nvo3-vxlan-gpe] Generic Protocol Extension for VXLAN
(VXLAN-GPE)
Discussion on the list and in face-to-face meetings has identified a
number of technical problems with each of these encapsulations.
Furthermore, there was clear consensus at the 96th IETF meeting in
Berlin that it is undesirable for the working group to progress more
than one data plane encapsulation. Although consensus could not be
reached on the list, the overall consensus was for a single
encapsulation [RFC2418], Section 3.3.
Nonetheless there has been resistance to converging on a single
encapsulation format.
2. Design Team Goals
As communicated by the WG Chairs, the design team (DT) should take
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 are
goals. The DT should specifically avoid a design that is burdensome
on hardware implementations but should allow future extensibility.
The chosen design should also operate well with ICMP and in ECMP
environments. If further extensibility is required, then it should
be done in such a manner that it does not require the consent of an
entity outside of the IETF.
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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
DT NVO3 encapsulation Design Team
EVPN Ethernet VPN [RFC8365]
GUE Generic UDP Encapsulation [I-D.ietf-intarea-gue]
NVO3 Network Virtualization Overlays over Layer 3
OAM Operations, Administration, and Maintenance
TLV Type, Length, and Value
VNI Virtual Network Identifier
NVE Network Virtualization Edge
NVA Network Virtualization Authority
NIC Network interface card
TCAM Ternary Content-Addressable Memory
Transit device - Underlay network devices between NVE(s).
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5. Issues with Current Encapsulations
The following subsections describe issues with current encapsulations
as summarized by the WG Chairs:
5.1. Geneve
- Can't be implemented cost-effectively in all use cases because
variable length header and order of the TLVs makes is 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.
5.2. GUE (Generic UDP Encapsulation)
- There were a significant number of objections to GUE
[I-D.ietf-intarea-gue] related to the complexity of implementation in
hardware, similar to those noted for Geneve above.
5.3. VXLAN-GPE
- 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 is the same.
- GPE is insufficiently extensible. Numerous extensions and options
have been designed for GUE and Geneve. Note that these have not yet
been validated by the WG.
- Security, e.g., of the VNI, has not been addressed by GPE.
Although a shim header could be used for security and other
extensions, this has not been defined yet and its implications on
offloading in NICs are not understood.
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6. Common Encapsulation Considerations
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.
6.2. Useful Extensions Use Cases
Non vendor specific TLVs MUST follow the standardization process.
The following use cases for extensions shows 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
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inserted along the path. Both approaches are often not feasible from
an operational perspective, be it that access to the end-system is
not feasible, or that the diversity of parameters and associated
probe packets to be created is simply too large. An extension
providing an in-band telemetry mechanism [I-D.ietf-ippm-ioam-data] is
an alternative in those cases.
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 HMAC-like support 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 is
to make packets that look like IP|UDP|NVO3 Encap|DTLS/IPSEC-ESP
Extension|payload. This is desireable 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).
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
[I-D.smith-vxlan-group-policy]. 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.
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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.
We note that 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 option 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/ACLs to the inner payload.
6.4. Extension Size
Extension header length has a significant impact on hardware and
software implementations. A total header length that is too small
will unnecessarily constrain software flexibility. A 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 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 the minimum total header length which would then become the
de facto maximum total header length. The recommended minimum total
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 the transit device
also.
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 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 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 different options.
However, general TLV of arbitrary order, size, and repetition of the
same order is 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 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.
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
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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. This 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 for, e.g., 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 (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 it can provide useful functionality with simplified
hardware requirements for the target NVE.
Note that 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.)
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
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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.
The WG should consider developing a separate draft on guidance for
option processing and control plane participation. 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. So, having the control plane negotiate the
constraints is the most appropriate and flexible way to address these
requirements.
6.8. Split NVE
If the working group sees a need for having the hosts 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 we need to do this with other encapsulations it can be done by
defining an Ethertype for other encapsulations so that it can be
carried over Ethernet and 802.1Q.
If we 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.
6.9. Larger VNI Considerations
We discussed whether we should make the VNI 32-bits or larger. The
benefit of a 24-bit VNI would be to avoid unnecessary changes with
existing proposals and implementations that are almost all, if not
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all, using 24-bit VNI. If we need a larger VNI, an extension can be
used to support that.
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7. Design Team Recommendations
We concluded that Geneve is most suitable as a starting point for a
proposed standard for network virtualization, for the following
reasons:
1. We studied 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.
The design team agreed that VNI is critical information for network
virtualization and MUST be present in all packets. The design team
also agreed that a 24-bit VNI 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. We considered the option of using NSH [RFC8300] with VXLAN-GPE
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. 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). We
explored whether it would make sense to either use NSH for this, or
define a new NVO3 options header. However, we observed that 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 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. We compared the TLV vs bit fields style extension and it was
deemed that parsing both TLV and 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
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OAM, Telemetry, and security extensions, for variable length option
and different subtypes of the same option. While TLV 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
dataplane implementation to handle.
5. We briefly discussed the multi-vendor NVE case, and the need to
allow vendors to put their own extensions in the NVE header. This is
possible with TLVs.
6. We also agreed that the C bit in Geneve is helpful to allow 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 remains 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 in telemetry defined extension TLV from
switches. It is also possible to add security extension TLVs like
HMAC and DTLS/IPSEC 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.
8. There are already implementations of Geneve options deployed in
production networks as of this writing. There are 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
have also defined some option TLV(s) for Geneve.
9. The DT has addressed the usage models while considering the
requirements and implementations in general that includes software
and hardware.
There seems to be interest to standardize some well-known secure
option TLVs to secure the header and payload to guarantee
encapsulation header integrity and tenant data privacy. The
design team recommends that the working group consider
standardizing such option(s).
We recommend the following enhancements to Geneve to make it more
suitable to hardware and yet provide the flexibility for software:
We would propose a text such as, while TLV 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
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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 draft 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.
We recommend that Geneve 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).
We request that Geneve 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, we recommend that Geneve increase the Single TLV option
length to 256.
We request that Geneve address Requirements for OAM considerations
for alternate marking and for performance measurements that need a
2 bit field in the header and clarify the need for the current OAM
bit in the Geneve Header.
We recommend that the WG work on security options for Geneve.
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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, and
Anoop Ghanwani for his extensive comments.
9. Security Considerations
This document does not introduce any additional security constraints.
10. IANA Considerations
This document requires no IANA actions.
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11. References
11.1 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>.
11.2 Informative References
[I-D.herbert-gue-extensions] Herbert, T., Yong, L., and F. Templin,
"Extensions for Generic UDP Encapsulation",
draft-herbert-gue-extensions-01 (work in progress), October
2016.
[I-D.ietf-intarea-gue] Herbert, T., Yong, L., and O. Zia, "Generic
UDP Encapsulation", draft-ietf-intarea-gue (work in
progress), October 2019.
[I-D.ietf-ippm-ioam-data] F. Brockers, S. Bhandari, T. Mizrahi, "Data
Fields for In-situ OAM", draft-ietf-ippm-ioam-data (work in
progress), June 2021.
[I-D.ietf-nvo3-vxlan-gpe] Maino, F., Kreeger, L., and U. Elzur,
"Generic Protocol Extension for VXLAN",
draft-ietf-nvo3-vxlan-gpe (work in progress), March 2021.
[I-D.smith-vxlan-group-policy] Smith, M. and L. Kreeger, "VXLAN Group
Policy Option", draft-smith-vxlan-group-policy-05 (work in
progress), October 2018.
[INT] P4.org, "In-band Network Telemetry (INT) Dataplane
Specification", November 2020,
https://p4.org/p4-spec/docs/INT_v2_1.pdf
[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
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10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[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>.
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Appendix A: Encapsulations Comparison
A.1. Overview
This section presents a comparison of the three NVO3 encapsulation
proposals, Geneve, GUE, and 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 [I-D.ietf-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). It should be noted 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 [I-D.herbert-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.
The length field simplifies the parsing of 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 [I-D.herbert-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 [I-D.herbert-gue-extensions].
A.3.2. Next Protocol
The 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
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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 [I-D.ietf-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.
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 [I-D.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.
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A.4. Comparison Summary
The following table summarizes the comparison between the three NVO3
encapsulations:
+----------------+----------------+----------------+----------------+
| | Geneve | GUE | VXLAN-GPE |
+----------------+----------------+----------------+----------------+
| Outer transport| UDP/IP | UDP/IP | UDP/IP |
+----------------+----------------+----------------+----------------+
| Base header | 8 octets | 4 octets | 8 octets |
| length | | | (16 octets |
| | | | using NSH) |
+----------------+----------------+----------------+----------------+
| Extensibility |Variable length |Extension fields| No native ext- |
| | options | | ensibility. |
| | | | Extensible |
| | | | using 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 | - | 27 bits |
+----------------+----------------+----------------+----------------+
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Figure 1: 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 Marvell Email: talmi@marvell.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
Ignas Bagdonas Equinix Email: ibagdona.ietf@gmail.com
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Authors' Addresses
Sami Boutros (editor)
Ciena
USA
Email: sboutros@ciena.com
Donald E. Eastlake, 3rd (editor)
Futurewei Technologies
2386 Panoramic Circle
Apopka, FL 32703
USA
Tel: +1-508-333-2270
Email: d3e3e3@gmail.com
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