Internet DRAFT - draft-dt-nvo3-encap
draft-dt-nvo3-encap
INTERNET-DRAFT Sami Boutros(Ed.)
Intended Status: Informational VMware
Ignas Bagdonas Sam Aldrin
Equinix Google
Matthew Bocci Uri Elzur
Nokia Ilango Ganga
Intel
Pankaj Garg Rajeev Manur
Microsoft Broadcom
Tal Mizrahi David Mozes
Marvell Mellanox
Erik Nordmark Michael Smith
Arista Networks Cisco
Expires: September 13, 2017 March 12, 2017
NVO3 Encapsulation Considerations
draft-dt-nvo3-encap-01
Abstract
As communicated by 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 recommend Geneve with few modifications as the common
encapsulation, more details are described in section 7.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 4
2. Design Team Goals . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Issues with current Encapsulations . . . . . . . . . . . . . . 5
5.1 Geneve . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2 GUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.3 VXLAN-GPE . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Common Encapsulation Considerations . . . . . . . . . . . . . . 6
6.1 Current Encapsulations . . . . . . . . . . . . . . . . . . . 6
6.2 Useful Extensions Use cases . . . . . . . . . . . . . . . . 6
6.2.1. Telemetry extensions. . . . . . . . . . . . . . . . . . 6
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6.2.2. Security/Integrity extensions . . . . . . . . . . . . . 7
6.2.3. Group Base Policy . . . . . . . . . . . . . . . . . . . 7
6.3 Hardware Considerations . . . . . . . . . . . . . . . . . . 8
6.4 Extension Size . . . . . . . . . . . . . . . . . . . . . . . 8
6.5 Extension Ordering . . . . . . . . . . . . . . . . . . . . . 9
6.6 TLV vs Bit Fields . . . . . . . . . . . . . . . . . . . . . 9
6.7 Control Plane Considerations . . . . . . . . . . . . . . . . 10
6.8 Split NVE . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.9 Larger VNI Considerations . . . . . . . . . . . . . . . . . 11
7. Design team recommendations . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1 Normative References . . . . . . . . . . . . . . . . . . . 14
10.2 Informative References . . . . . . . . . . . . . . . . . . 14
11. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 14
11.2. Extensibility . . . . . . . . . . . . . . . . . . . . . . 14
11.2.1. Native Extensibility Support . . . . . . . . . . . . 14
11.2.2. Extension Parsing . . . . . . . . . . . . . . . . . . 15
11.2.3. Critical Extensions . . . . . . . . . . . . . . . . . 15
11.2.4. Maximal Header Length . . . . . . . . . . . . . . . . 15
11.3. Encapsulation Header . . . . . . . . . . . . . . . . . . 15
11.3.1. Virtual Network Identifier (VNI) . . . . . . . . . . 15
11.3.2. Next Protocol . . . . . . . . . . . . . . . . . . . . 16
11.3.3. Other Header Fields . . . . . . . . . . . . . . . . . 16
11.4. Comparison Summary . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses (In alphabetical order) . . . . . . . . . . . . 17
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1. Problem Statement
As communicated by 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 drafts describing three encapsulations being adopted
by the working group:
- draft-ietf-nvo3-geneve-03
- draft-ietf-nvo3-gue-04
- draft-ietf-nvo3-vxlan-gpe-02
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 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 WG Chairs, the design team should take one of the
proposed encapsulations and enhance it to address the technical
concerns. Backwards compatibility with the chosen encapsulation and
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.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
4. Abbreviations
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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
Transit device Underlay network devices between NVE(s).
5. Issues with current Encapsulations
As summarized by 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
- Fork-lift upgrade from widely deployed VXLAN (no backwards
compatibility mechanisms)
- 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
- There were a significant number of objections related to the
complexity of implementation in hardware, similar to those noted for
Geneve above.
- In addition, there were concerns raised that GUE does not support a
sufficient number of extensions due to its reliance on a limited
flags field, which is already almost 45% allocated.
5.3 VXLAN-GPE
- GPE is not day-1 backwards compatible with VXLAN. Although the
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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.
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).
- 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 extension is 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 TLV 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.
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This includes not only tasks like debugging, troubleshooting, as well
as network planning and network 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 from 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, 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 in-bound
telemetry mechanism in extensions 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. Extensions are needed to use any
sophisticated security.
The possibility of VNI spoofing with an NVO3 protocol is exacerbated
by the use of UDP. Systems typically have no restrictions on
applications being able to send to any UDP port so an unprivileged
application can trivially spoof for instance, VXLAN packets,
including using arbitrary VNIs.
One can envision HMAC-like support in some NVO3 extension to
authenticate the header and the outer IP addresses, thereby
preventing attackers from injecting packets with spoofed VNIs.
An other aspect of security is payload security. Essentially this is
to make packets that look like IP|UDP|NVO3 Encap|DTLS
Extension|payload. This is nice since we still have the UDP header
for ECMP, the NVO3 header is in plain text so it can by 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
for DTLS).
6.2.3. Group Base 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 [VXLAN-GBP]. This allows
various forms of policy such as access control and QoS to be applied
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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.
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 an transit
devices 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
order for some hardware implementations.
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
for both NICs doing e.g. TCP offload and transit devices and NVEs
applying policy/ACLs to the inner payload.
6.4 Extension Size
Extension header length has a significant impact to hardware and
software implementations. A total header length that is too small
will unnecessarily constrained software flexibility. A total header
length that is too large will place a nontrivial cost on hardware
implementations. Thus, the design team recommends that there be a
minimum and maximum total extension header length selected. The
maximum total header length is determined by the bits 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.
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Single Extension size should always be 4 bytes aligned.
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 Extension Ordering
In order to support hardware nodes at the tunnel endpoint or at the
transit that can process one or few extensions TLVs in TCAM. A
control plane in such a deployment can signal a capability to ensure
a specific TLV will always appear in a specific order for example the
first one in the packet.
The order of the TLVs should be HW friendly for both the sender and
the receiver and possibly the transit node too.
A transit node may need to process some extensions like telemetry
and/or OAM inband extensions.
6.6 TLV vs 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-field 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 TLV with restrictions on the size and alignment, observing that
individual TLVs can have a fixed length, and support in the control
plane such that an NVE will only receive options that to 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 they need more effort, But transit devices would have
issues with future GUE bits being defined for future options as well.
A benefit of TLVs from a HW perspective is that they are self
describing i.e., all the information is in the TLV. In a Bit fields
approach the hardware needs to look up the bit to determine the
length of the data associated with the bit through some separate
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table, which would add hardware complexity.
There are use cases where multiple modules of software are running on
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 does 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.
6.7 Control Plane Considerations
Given that we want to allow large flexibility and extensibility for
e.g. software NVEs, yet be able to support key extensions in less
flexible e.g. hardware NVEs, it is useful to consider the control
plane. By control plane in this context we mean both protocols such
as EVPN and others, and also deployment specific configuration.
If each NVE can express in the control plane that they only care
about particular extensions (could be a single extension, or a few),
and the source NVEs only include requested 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
minimal hardware requirements.
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 extensions are included in
the packet. However, 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 in this approach different NVEs could desire different
(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
extensions.
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
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prevent the need for dropping unknown extensions, since they would
not be included to targets that do not support them.
The control planes defined today need to add the ability to describe
the different encapsulations. Thus perhaps EVPN, and any other
control plane protocol that the IETF defines, should have a way to
enumerate the supported NVO3 extensions and their order.
6.8 Split NVE
If the working group sees a need for having the hosts send and
receive options in a split NVE case, 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 Ether type 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 VNI 32-bits or larger. The
benefit of 24-bit VNI would be to avoid unnecessary changes with
existing proposals and implementations that are almost all, if not
all, are using 24-bit VNI. If we need a larger VNI, an extension can
be used to support that.
7. Design team recommendations
We concluded that Geneve is most suitable as a starting point for
proposed standard for network virtualization, for the following
reasons:
1. We studied whether VNI should be in base header or in extensions
and whether it should be 24-bit or 32-bit. The design team agreed
that VNI is critical information for network virtualization and MUST
be present in all packets. Design team also agreed that 24-bit VNI
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matches the existing widely used encapsulation format i.e. VxLAN and
NVGRE and hence more suitable to use going forward.
2. Geneve has the total options length that allow 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 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
header length in VxLAN-GPE and hence 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 guidance, 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 for efficiency, as well Bit-fields are
not flexible enough to address the requirement of variable length 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 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
receiver NVE to easily decide whether to process options or not. For
example a UUID based packet trace and how an optional extension such
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as that can be ignored by 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 option 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 to authenticate the Geneve packet header and secure the
Geneve packet payload by software or hardware tunnel endpoints. As
well, a Group Based Policy extension TLV can be carried.
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
implementation in software or hardware to handle. For example, there
may be some critical information such as secure hash that must be
processed in certain order at lowest latency.
A control plane can negotiate a subset of option TLVs and certain TLV
ordering, as well can limit the total number of option TLVs present
in the packet, for example, to allow hardware capable of processing
fewer options. Hence, the control planes need to have the ability to
describe the supported TLVs subset and their order.
The Geneve draft could specify that the subset and order of option
TLVs should be configurable for each remote NVE in the absence of a
protocol control plane.
8. Acknowledgements
Tom Herbert provided the motivation for the Security/Integrity
extension.
9. Security Considerations
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This document does not introduce any additional security constraints.
10. References
10.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2 Informative References
[Geneve] Generic Network Virtualization Encapsulation [I-D.ietf-nvo3-
geneve]
[GUE] Generic UDP Encapsulation [I-D.ietf-nvo3-gue]
[NSH] Network Service Header [I-D.ietf-sfc-nsh]
[VXLAN-GPE] Virtual eXtensible Local Area Network - Generic Protocol
Extension [I-D.ietf-nvo3-vxlan-gpe]
[VXLAN-GBP] VXLAN Group Policy Option - [I-D.draft-smith-vxlan-group-
policy-03]
11. Appendix A
11.1. 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 3.2 below.
11.2. Extensibility
11.2.1. 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) [I-
D.ietf-sfc-nsh] 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
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that NSH-over-VXLAN-GPE implies an additional overhead of the 8-
octets NSH header, in addition to the VXLAN-GPE header.
11.2.2. 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.
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.
11.2.3. Critical Extensions
The Geneve encapsulation header includes the 'C' field, which
indicates whether the current Geneve header includes critical
options, which must be parsed by the tunnel endpoint. If the endpoint
is not able to process the critical option, the packet is discarded.
11.2.4. 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.
11.3. Encapsulation Header
11.3.1. 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
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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].
11.3.2. 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
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.
11.3.3. 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-nvo3-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.
11.4. 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 |
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+----------------+----------------+----------------+----------------+
| 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 |
+----------------+----------------+----------------+----------------+
Figure 1: NVO3 Encapsulation Comparison
Authors' Addresses (In alphabetical order)
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Sam Aldrin
Google
Email: aldrin.ietf@gmail.com
Ignas Bagdonas
Equinix
Email: ibagdona.ietf@gmail.com
Matthew Bocci
Nokia
Email: matthew.bocci@nokia.com
Sami Boutros
VMware
Email: sboutros@vmware.com
Uri Elzur
Intel
Email: uri.elzur@intel.com
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
Mellanox
Email: davidm@mellanox.com
Erik Nordmark
Arista Networks
Email: nordmark@sonic.net
Michael Smith
Cisco
Email: michsmit@cisco.com
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