Internet Engineering Task Force (IETF) J. Gross, Ed.

Internet Engineering Task Force (IETF) J. Gross, Ed.
Request for Comments: 8926
Category: Standards Track I. Ganga, Ed.
ISSN: 2070-1721 Intel
T. Sridhar, Ed.
VMware
November 2020

Geneve: Generic Network Virtualization Encapsulation

Abstract

Network virtualization involves the cooperation of devices with a
wide variety of capabilities such as software and hardware tunnel
endpoints, transit fabrics, and centralized control clusters. As a
result of their role in tying together different elements of the
system, the requirements on tunnels are influenced by all of these
components. Therefore, flexibility is the most important aspect of a
tunneling protocol if it is to keep pace with the evolution of
technology. This document describes Geneve, an encapsulation
protocol designed to recognize and accommodate these changing
capabilities and needs.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8926.

Copyright Notice

Copyright (c) 2020 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/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction
1.1. Requirements Language
1.2. Terminology
2. Design Requirements
2.1. Control Plane Independence
2.2. Data Plane Extensibility
2.2.1. Efficient Implementation
2.3. Use of Standard IP Fabrics
3. Geneve Encapsulation Details
3.1. Geneve Packet Format over IPv4
3.2. Geneve Packet Format over IPv6
3.3. UDP Header
3.4. Tunnel Header Fields
3.5. Tunnel Options
3.5.1. Options Processing
4. Implementation and Deployment Considerations
4.1. Applicability Statement
4.2. Congestion-Control Functionality
4.3. UDP Checksum
4.3.1. Zero UDP Checksum Handling with IPv6
4.4. Encapsulation of Geneve in IP
4.4.1. IP Fragmentation
4.4.2. DSCP, ECN, and TTL
4.4.3. Broadcast and Multicast
4.4.4. Unidirectional Tunnels
4.5. Constraints on Protocol Features
4.5.1. Constraints on Options
4.6. NIC Offloads
4.7. Inner VLAN Handling
5. Transition Considerations
6. Security Considerations
6.1. Data Confidentiality
6.1.1. Inter-Data Center Traffic
6.2. Data Integrity
6.3. Authentication of NVE Peers
6.4. Options Interpretation by Transit Devices
6.5. Multicast/Broadcast
6.6. Control Plane Communications
7. IANA Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Contributors
Authors' Addresses

1. Introduction

Networking has long featured a variety of tunneling, tagging, and
other encapsulation mechanisms. However, the advent of network
virtualization has caused a surge of renewed interest and a
corresponding increase in the introduction of new protocols. The
large number of protocols in this space -- for example, ranging all
the way from VLANs [IEEE.802.1Q_2018] and MPLS [RFC3031] through the
more recent VXLAN (Virtual eXtensible Local Area Network) [RFC7348]
and NVGRE (Network Virtualization Using Generic Routing
Encapsulation) [RFC7637] -- often leads to questions about the need
for new encapsulation formats and what it is about network
virtualization in particular that leads to their proliferation. Note
that the list of protocols presented above is non-exhaustive.

While many encapsulation protocols seek to simply partition the
underlay network or bridge two domains, network virtualization views
the transit network as providing connectivity between multiple
components of a distributed system. In many ways, this system is
similar to a chassis switch with the IP underlay network playing the
role of the backplane and tunnel endpoints on the edge as line cards.
When viewed in this light, the requirements placed on the tunneling
protocol are significantly different in terms of the quantity of
metadata necessary and the role of transit nodes.

Work such as "VL2: A Scalable and Flexible Data Center Network" [VL2]
and "NVO3 Data Plane Requirements" [NVO3-DATAPLANE] have described
some of the properties that the data plane must have to support
network virtualization. However, one additional defining requirement
is the need to carry metadata (e.g., system state) along with the
packet data; example use cases of metadata are noted below. The use
of some metadata is certainly not a foreign concept -- nearly all
protocols used for network virtualization have at least 24 bits of
identifier space as a way to partition between tenants. This is
often described as overcoming the limits of 12-bit VLANs; when seen
in that context or any context where it is a true tenant identifier,
16 million possible entries is a large number. However, the reality
is that the metadata is not exclusively used to identify tenants, and
encoding other information quickly starts to crowd the space. In
fact, when compared to the tags used to exchange metadata between
line cards on a chassis switch, 24-bit identifiers start to look
quite small. There are nearly endless uses for this metadata,
ranging from storing input port identifiers for simple security
policies to sending service-based context for advanced middlebox
applications that terminate and re-encapsulate Geneve traffic.

Existing tunneling protocols have each attempted to solve different
aspects of these new requirements only to be quickly rendered out of
date by changing control plane implementations and advancements.
Furthermore, software and hardware components and controllers all
have different advantages and rates of evolution -- a fact that
should be viewed as a benefit, not a liability or limitation. This
document describes Geneve, a protocol that seeks to avoid these
problems by providing a framework for tunneling for network
virtualization rather than being prescriptive about the entire
system.

1.1. Requirements Language

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.

1.2. Terminology

The Network Virtualization over Layer 3 (NVO3) Framework [RFC7365]
defines many of the concepts commonly used in network virtualization.
In addition, the following terms are specifically meaningful in this
document:

Checksum offload: An optimization implemented by many NICs (Network
Interface Controllers) that enables computation and verification
of upper-layer protocol checksums in hardware on transmit and
receive, respectively. This typically includes IP and TCP/UDP
checksums that would otherwise be computed by the protocol stack
in software.

Clos network: A technique for composing network fabrics larger than
a single switch while maintaining non-blocking bandwidth across
connection points. ECMP is used to divide traffic across the
multiple links and switches that constitute the fabric. Sometimes
termed "leaf and spine" or "fat tree" topologies.

ECMP: Equal Cost Multipath. A routing mechanism for selecting from
among multiple best next-hop paths by hashing packet headers in
order to better utilize network bandwidth while avoiding
reordering of packets within a flow.

Geneve: Generic Network Virtualization Encapsulation. The tunneling
protocol described in this document.

LRO: Large Receive Offload. The receiver-side equivalent function
of LSO, in which multiple protocol segments (primarily TCP) are
coalesced into larger data units.

LSO: Large Segmentation Offload. A function provided by many
commercial NICs that allows data units larger than the MTU to be
passed to the NIC to improve performance, the NIC being
responsible for creating smaller segments of a size less than or
equal to the MTU with correct protocol headers. When referring
specifically to TCP/IP, this feature is often known as TSO (TCP
Segmentation Offload).

Middlebox: In the context of this document, the term "middlebox"
refers to network service functions or service interposition
appliances that typically implement tunnel endpoint functionality,
terminating and re-encapsulating Geneve traffic.

NIC: Network Interface Controller. Also called "Network Interface
Card" or "Network Adapter". A NIC could be part of a tunnel
endpoint or transit device and can either process or aid in the
processing of Geneve packets.

Transit device: A forwarding element (e.g., router or switch) along
the path of the tunnel making up part of the underlay network. A
transit device may be capable of understanding the Geneve packet
format but does not originate or terminate Geneve packets.

Tunnel endpoint: A component performing encapsulation and
decapsulation of packets, such as Ethernet frames or IP datagrams,
in Geneve headers. As the ultimate consumer of any tunnel
metadata, tunnel endpoints have the highest level of requirements
for parsing and interpreting tunnel headers. Tunnel endpoints may
consist of either software or hardware implementations or a
combination of the two. Tunnel endpoints are frequently a
component of a Network Virtualization Edge (NVE) but may also be
found in middleboxes or other elements making up an NVO3 network.

VM: Virtual Machine.

2. Design Requirements

Geneve is designed to support network virtualization use cases for
data center environments. In these situations, tunnels are typically
established to act as a backplane between the virtual switches
residing in hypervisors, physical switches, or middleboxes or other
appliances. An arbitrary IP network can be used as an underlay,
although Clos networks composed using ECMP links are a common choice
to provide consistent bisectional bandwidth across all connection
points. Many of the concepts of network virtualization overlays over
IP networks are described in the NVO3 Framework [RFC7365]. Figure 1
shows an example of a hypervisor, a top-of-rack switch for
connectivity to physical servers, and a WAN uplink connected using
Geneve tunnels over a simplified Clos network. These tunnels are
used to encapsulate and forward frames from the attached components,
such as VMs or physical links.

+---------------------+ +-------+ +------+
| +--+ +-------+---+ | |Transit|--|Top of|==Physical
| |VM|--| | | | +------+ /|Router | | Rack |==Servers
| +--+ |Virtual|NIC|---|Top of|/ +-------+\/+------+
| +--+ |Switch | | | | Rack |\ +-------+/\+------+
| |VM|--| | | | +------+ \|Transit| |Uplink| WAN
| +--+ +-------+---+ | |Router |--| |=========>
+---------------------+ +-------+ +------+
Hypervisor

()===================================()
Switch-Switch Geneve Tunnels

Figure 1: Sample Geneve Deployment

To support the needs of network virtualization, the tunneling
protocol should be able to take advantage of the differing (and
evolving) capabilities of each type of device in both the underlay
and overlay networks. This results in the following requirements
being placed on the data plane tunneling protocol:

* The data plane is generic and extensible enough to support current
and future control planes.

* Tunnel components are efficiently implementable in both hardware
and software without restricting capabilities to the lowest common
denominator.

* High performance over existing IP fabrics is maintained.

These requirements are described further in the following
subsections.

2.1. Control Plane Independence

Although some protocols for network virtualization have included a
control plane as part of the tunnel format specification (most
notably, VXLAN [RFC7348] prescribed a multicast-learning-based
control plane), these specifications have largely been treated as
describing only the data format. The VXLAN packet format has
actually seen a wide variety of control planes built on top of it.

There is a clear advantage in settling on a data format: most of the
protocols are only superficially different and there is little
advantage in duplicating effort. However, the same cannot be said of
control planes, which are diverse in very fundamental ways. The case
for standardization is also less clear given the wide variety in
requirements, goals, and deployment scenarios.

As a result of this reality, Geneve is a pure tunnel format
specification that is capable of fulfilling the needs of many control
planes by explicitly not selecting any one of them. This
simultaneously promotes a shared data format and reduces the chance
of obsolescence by future control plane enhancements.

2.2. Data Plane Extensibility

Achieving the level of flexibility needed to support current and
future control planes effectively requires an options infrastructure
to allow new metadata types to be defined, deployed, and either
finalized or retired. Options also allow for differentiation of
products by encouraging independent development in each vendor's core
specialty, leading to an overall faster pace of advancement. By far,
the most common mechanism for implementing options is the Type-
Length-Value (TLV) format.

It should be noted that, while options can be used to support non-
wirespeed control packets, they are equally important in data packets
as well for segregating and directing forwarding. (For instance, the
examples given before regarding input-port-based security policies
and terminating/re-encapsulating service interposition both require
tags to be placed on data packets.) Therefore, while it would be
desirable to limit the extensibility to only control packets for the
purposes of simplifying the datapath, that would not satisfy the
design requirements.

2.2.1. Efficient Implementation

There is often a conflict between software flexibility and hardware
performance that is difficult to resolve. For a given set of
functionality, it is obviously desirable to maximize performance.
However, that does not mean new features that cannot be run at a
desired speed today should be disallowed. Therefore, for a protocol
to be considered efficiently implementable, it is expected to have a
set of common capabilities that can be reasonably handled across
platforms as well as a graceful mechanism to handle more advanced
features in the appropriate situations.

The use of a variable-length header and options in a protocol often
raises questions about whether the protocol is truly efficiently
implementable in hardware. To answer this question in the context of
Geneve, it is important to first divide "hardware" into two
categories: tunnel endpoints and transit devices.

Tunnel endpoints must be able to parse the variable-length header,
including any options, and take action. Since these devices are
actively participating in the protocol, they are the most affected by
Geneve. However, as tunnel endpoints are the ultimate consumers of
the data, transmitters can tailor their output to the capabilities of
the recipient.

Transit devices may be able to interpret the options; however, as
non-terminating devices, transit devices do not originate or
terminate the Geneve packet. Hence, they MUST NOT modify Geneve
headers and MUST NOT insert or delete options, as that is the
responsibility of tunnel endpoints. Options, if present in the
packet, MUST only be generated and terminated by tunnel endpoints.
The participation of transit devices in interpreting options is
OPTIONAL.

Further, either tunnel endpoints or transit devices MAY use offload
capabilities of NICs, such as checksum offload, to improve the
performance of Geneve packet processing. The presence of a Geneve
variable-length header should not prevent the tunnel endpoints and
transit devices from using such offload capabilities.

2.3. Use of Standard IP Fabrics

IP has clearly cemented its place as the dominant transport
mechanism, and many techniques have evolved over time to make it
robust, efficient, and inexpensive. As a result, it is natural to
use IP fabrics as a transit network for Geneve. Fortunately, the use
of IP encapsulation and addressing is enough to achieve the primary
goal of delivering packets to the correct point in the network
through standard switching and routing.

In addition, nearly all underlay fabrics are designed to exploit
parallelism in traffic to spread load across multiple links without
introducing reordering in individual flows. These ECMP techniques
typically involve parsing and hashing the addresses and port numbers
from the packet to select an outgoing link. However, the use of
tunnels often results in poor ECMP performance, as without additional
knowledge of the protocol, the encapsulated traffic is hidden from
the fabric by design, and only tunnel endpoint addresses are
available for hashing.

Since it is desirable for Geneve to perform well on these existing
fabrics, it is necessary for entropy from encapsulated packets to be
exposed in the tunnel header. The most common technique for this is
to use the UDP source port, which is discussed further in
Section 3.3.

3. Geneve Encapsulation Details

The Geneve packet format consists of a compact tunnel header
encapsulated in UDP over either IPv4 or IPv6. A small fixed tunnel
header provides control information plus a base level of
functionality and interoperability with a focus on simplicity. This
header is then followed by a set of variable-length options to allow
for future innovation. Finally, the payload consists of a protocol
data unit of the indicated type, such as an Ethernet frame. Sections
3.1 and 3.2 illustrate the Geneve packet format transported (for
example) over Ethernet along with an Ethernet payload.

3.1. Geneve Packet Format over IPv4

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 Ethernet Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Destination MAC Address | Outer Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional Ethertype=C-Tag 802.1Q| Outer VLAN Tag Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype = 0x0800 IPv4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Outer IPv4 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |Protocol=17 UDP| Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Source IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Destination IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Outer UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = xxxx | 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 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Inner Ethernet Header (example payload):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Destination MAC Address | Inner Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional Ethertype=C-Tag 802.1Q| Inner VLAN Tag Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Payload:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype of Original Payload | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Original Ethernet Payload |
| |
~ (Note that the original Ethernet frame's preamble, start ~
| frame delimiter (SFD), and frame check sequence (FCS) are not |
| included, and the Ethernet payload need not be 4-byte aligned)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Frame Check Sequence:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Frame Check Sequence (FCS) for Outer Ethernet Frame |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Geneve Packet Format over IPv4

3.2. Geneve Packet Format over IPv6

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 Ethernet Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Destination MAC Address | Outer Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional Ethertype=C-Tag 802.1Q| Outer VLAN Tag Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype = 0x86DD IPv6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Outer IPv6 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | NxtHdr=17 UDP | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Outer Source IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Outer Destination IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Outer UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = xxxx | 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 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Inner Ethernet Header (example payload):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Destination MAC Address | Inner Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional Ethertype=C-Tag 802.1Q| Inner VLAN Tag Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Payload:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype of Original Payload | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Original Ethernet Payload |
| |
~ (Note that the original Ethernet frame's preamble, start ~
| frame delimiter (SFD), and frame check sequence (FCS) are not |
| included, and the Ethernet payload need not be 4-byte aligned)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Frame Check Sequence:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Frame Check Sequence (FCS) for Outer Ethernet Frame |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Geneve Packet Format over IPv6

3.3. UDP Header

The use of an encapsulating UDP [RFC0768] header follows the
connectionless semantics of Ethernet and IP in addition to providing
entropy to routers performing ECMP. Therefore, header fields are
interpreted as follows:

Source Port: A source port selected by the originating tunnel
endpoint. This source port SHOULD be the same for all packets
belonging to a single encapsulated flow to prevent reordering due
to the use of different paths. To encourage an even distribution
of flows across multiple links, the source port SHOULD be
calculated using a hash of the encapsulated packet headers using,
for example, a traditional 5-tuple. Since the port represents a
flow identifier rather than a true UDP connection, the entire
16-bit range MAY be used to maximize entropy. In addition to
setting the source port, for IPv6, the flow label MAY also be used
for providing entropy. For an example of using the IPv6 flow
label for tunnel use cases, see [RFC6438].

If Geneve traffic is shared with other UDP listeners on the same
IP address, tunnel endpoints SHOULD implement a mechanism to
ensure ICMP return traffic arising from network errors is directed
to the correct listener. The definition of such a mechanism is
beyond the scope of this document.

Dest Port: IANA has assigned port 6081 as the fixed well-known
destination port for Geneve. Although the well-known value should
be used by default, it is RECOMMENDED that implementations make
this configurable. The chosen port is used for identification of
Geneve packets and MUST NOT be reversed for different ends of a
connection as is done with TCP. It is the responsibility of the
control plane to manage any reconfiguration of the assigned port
and its interpretation by respective devices. The definition of
the control plane is beyond the scope of this document.

UDP Length: The length of the UDP packet including the UDP header.

UDP Checksum: In order to protect the Geneve header, options, and
payload from potential data corruption, the UDP checksum SHOULD be
generated as specified in [RFC0768] and [RFC1122] when Geneve is
encapsulated in IPv4. To protect the IP header, Geneve header,
options, and payload from potential data corruption, the UDP
checksum MUST be generated by default as specified in [RFC0768]
and [RFC8200] when Geneve is encapsulated in IPv6, except under
certain conditions, which are outlined in the next paragraph.
Upon receiving such packets with a non-zero UDP checksum, the
receiving tunnel endpoints MUST validate the checksum. If the
checksum is not correct, the packet MUST be dropped; otherwise,
the packet MUST be accepted for decapsulation.

Under certain conditions, the UDP checksum MAY be set to zero on
transmit for packets encapsulated in both IPv4 and IPv6 [RFC8200].
See Section 4.3 for additional requirements that apply when using
zero UDP checksum with IPv4 and IPv6. Disabling the use of UDP
checksums is an operational consideration that should take into
account the risks and effects of packet corruption.

3.4. Tunnel Header Fields

Ver (2 bits): The current version number is 0. Packets received by
a tunnel endpoint with an unknown version MUST be dropped.
Transit devices interpreting Geneve packets with an unknown
version number MUST treat them as UDP packets with an unknown
payload.

Opt Len (6 bits): The length of the option fields, expressed in
4-byte multiples, not including the 8-byte fixed tunnel header.
This results in a minimum total Geneve header size of 8 bytes and
a maximum of 260 bytes. The start of the payload headers can be
found using this offset from the end of the base Geneve header.

Transit devices MUST maintain consistent forwarding behavior
irrespective of the value of 'Opt Len', including ECMP link
selection.

O (1 bit): Control packet. This packet contains a control message.
Control messages are sent between tunnel endpoints. Tunnel
endpoints MUST NOT forward the payload, and transit devices MUST
NOT attempt to interpret it. Since control messages are less
frequent, it is RECOMMENDED that tunnel endpoints direct these
packets to a high-priority control queue (for example, to direct
the packet to a general purpose CPU from a forwarding Application-
Specific Integrated Circuit (ASIC) or to separate out control
traffic on a NIC). Transit devices MUST NOT alter forwarding
behavior on the basis of this bit, such as ECMP link selection.

C (1 bit): Critical options present. One or more options has the
critical bit set (see Section 3.5). If this bit is set, then
tunnel endpoints MUST parse the options list to interpret any
critical options. On tunnel endpoints where option parsing is not
supported, the packet MUST be dropped on the basis of the 'C' bit
in the base header. If the bit is not set, tunnel endpoints MAY
strip all options using 'Opt Len' and forward the decapsulated
packet. Transit devices MUST NOT drop packets on the basis of
this bit.

Rsvd. (6 bits): Reserved field, which MUST be zero on transmission
and MUST be ignored on receipt.

Protocol Type (16 bits): The type of protocol data unit appearing
after the Geneve header. This follows the Ethertype [ETYPES]
convention, with Ethernet itself being represented by the value
0x6558.

Virtual Network Identifier (VNI) (24 bits): An identifier for a
unique element of a virtual network. In many situations, this may
represent an L2 segment; however, the control plane defines the
forwarding semantics of decapsulated packets. The VNI MAY be used
as part of ECMP forwarding decisions or MAY be used as a mechanism
to distinguish between overlapping address spaces contained in the
encapsulated packet when load balancing across CPUs.

Reserved (8 bits): Reserved field, which MUST be zero on
transmission and ignored on receipt.

3.5. Tunnel Options

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Class | Type |R|R|R| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Variable-Length Option Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Geneve Option

The base Geneve header is followed by zero or more options in Type-
Length-Value format. Each option consists of a 4-byte option header
and a variable amount of option data interpreted according to the
type.

Option Class (16 bits): Namespace for the 'Type' field. IANA has
created a "Geneve Option Class" registry to allocate identifiers
for organizations, technologies, and vendors that have an interest
in creating types for options. Each organization may allocate
types independently to allow experimentation and rapid innovation.
It is expected that, over time, certain options will become well
known, and a given implementation may use option types from a
variety of sources. In addition, IANA has reserved specific
ranges for allocation by IETF Review and for Experimental Use (see
Section 7).

Type (8 bits): Type indicating the format of the data contained in
this option. Options are primarily designed to encourage future
extensibility and innovation, and standardized forms of these
options will be defined in separate documents.

The high-order bit of the option type indicates that this is a
critical option. If the receiving tunnel endpoint does not
recognize the option and this bit is set, then the packet MUST be
dropped. If this bit is set in any option, then the 'C' bit in
the Geneve base header MUST also be set. Transit devices MUST NOT
drop packets on the basis of this bit. The following figure shows
the location of the 'C' bit in the 'Type' field:

0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|C| Type |
+-+-+-+-+-+-+-+-+

Figure 5: 'C' Bit in the 'Type' Field

The requirement to drop a packet with an unknown option with the
'C' bit set applies to the entire tunnel endpoint system and not a
particular component of the implementation. For example, in a
system comprised of a forwarding ASIC and a general purpose CPU,
this does not mean that the packet must be dropped in the ASIC.
An implementation may send the packet to the CPU using a rate-
limited control channel for slow-path exception handling.

R (3 bits): Option control flags reserved for future use. These
bits MUST be zero on transmission and MUST be ignored on receipt.

Length (5 bits): Length of the option, expressed in 4-byte
multiples, excluding the option header. The total length of each
option may be between 4 and 128 bytes. A value of 0 in the
'Length' field implies an option with only an option header and no
option data. Packets in which the total length of all options is
not equal to the 'Opt Len' in the base header are invalid and MUST
be silently dropped if received by a tunnel endpoint that
processes the options.

Variable-Length Option Data: Option data interpreted according to
'Type'.

3.5.1. Options Processing

Geneve options are intended to be originated and processed by tunnel
endpoints. However, options MAY be interpreted by transit devices
along the tunnel path. Transit devices not interpreting Geneve
headers (which may or may not include options) MUST handle Geneve
packets as any other UDP packet and maintain consistent forwarding
behavior.

In tunnel endpoints, the generation and interpretation of options is
determined by the control plane, which is beyond the scope of this
document. However, to ensure interoperability between heterogeneous
devices, some requirements are imposed on options and the devices
that process them:

* Receiving tunnel endpoints MUST drop packets containing unknown
options with the 'C' bit set in the option type. Conversely,
transit devices MUST NOT drop packets as a result of encountering
unknown options, including those with the 'C' bit set.

* The contents of the options and their ordering MUST NOT be
modified by transit devices.

* If a tunnel endpoint receives a Geneve packet with an 'Opt Len'
(the total length of all options) that exceeds the options-
processing capability of the tunnel endpoint, then the tunnel
endpoint MUST drop such packets. An implementation may raise an
exception to the control plane in such an event. It is the
responsibility of the control plane to ensure the communicating
peer tunnel endpoints have the processing capability to handle the
total length of options. The definition of the control plane is
beyond the scope of this document.

When designing a Geneve option, it is important to consider how the
option will evolve in the future. Once an option is defined, it is
reasonable to expect that implementations may come to depend on a
specific behavior. As a result, the scope of any future changes must
be carefully described upfront.

Architecturally, options are intended to be self descriptive and
independent. This enables parallelism in options processing and
reduces implementation complexity. However, the control plane may
impose certain ordering restrictions, as described in Section 4.5.1.

Unexpectedly significant interoperability issues may result from
changing the length of an option that was defined to be a certain
size. A particular option is specified to have either a fixed
length, which is constant, or a variable length, which may change
over time or for different use cases. This property is part of the
definition of the option and is conveyed by the 'Type'. For fixed-
length options, some implementations may choose to ignore the
'Length' field in the option header and instead parse based on the
well-known length associated with the type. In this case, redefining
the length will impact not only the parsing of the option in question
but also any options that follow. Therefore, options that are
defined to be a fixed length in size MUST NOT be redefined to a
different length. Instead, a new 'Type' should be allocated. Actual
definition of the option type is beyond the scope of this document.
The option type and its interpretation should be defined by the
entity that owns the option class.

Options may be processed by NIC hardware utilizing offloads (e.g.,
LSO and LRO) as described in Section 4.6. Careful consideration
should be given to how the offload capabilities outlined in
Section 4.6 impact an option's design.

4. Implementation and Deployment Considerations

4.1. Applicability Statement

Geneve is a UDP-based network virtualization overlay encapsulation
protocol designed to establish tunnels between NVEs over an existing
IP network. It is intended for use in public or private data center
environments, for deploying multi-tenant overlay networks over an
existing IP underlay network.

As a UDP-based protocol, Geneve adheres to the UDP usage guidelines
as specified in [RFC8085]. The applicability of these guidelines is
dependent on the underlay IP network and the nature of the Geneve
payload protocol (for example, TCP/IP, IP/Ethernet).

Geneve is intended to be deployed in a data center network
environment operated by a single operator or an adjacent set of
cooperating network operators that fits with the definition of
controlled environments in [RFC8085]. A network in a controlled
environment can be managed to operate under certain conditions,
whereas in the general Internet, this cannot be done. Hence,
requirements for a tunneling protocol operating under a controlled
environment can be less restrictive than the requirements of the
general Internet.

For the purpose of this document, a traffic-managed controlled
environment (TMCE) is defined as an IP network that is traffic
engineered and/or otherwise managed (e.g., via use of traffic rate
limiters) to avoid congestion. The concept of a TMCE is outlined in
[RFC8086]. Significant portions of the text in Section 4.1 through
Section 4.3 are based on [RFC8086] as applicable to Geneve.

It is the responsibility of the operator to ensure that the
guidelines/requirements in this section are followed as applicable to
their Geneve deployment(s).

4.2. Congestion-Control Functionality

Geneve does not natively provide congestion-control functionality and
relies on the payload protocol traffic for congestion control. As
such, Geneve MUST be used with congestion-controlled traffic or
within a TMCE to avoid congestion. An operator of a TMCE may avoid
congestion through careful provisioning of their networks, rate-
limiting user data traffic, and managing traffic engineering
according to path capacity.

4.3. UDP Checksum

The outer UDP checksum SHOULD be used with Geneve when transported
over IPv4; this is to provide integrity for the Geneve headers,
options, and payload in case of data corruption (for example, to
avoid misdelivery of the payload to different tenant systems). The
UDP checksum provides a statistical guarantee that a payload was not
corrupted in transit. These integrity checks are not strong from a
coding or cryptographic perspective and are not designed to detect
physical-layer errors or malicious modification of the datagram (see
Section 3.4 of [RFC8085]). In deployments where such a risk exists,
an operator SHOULD use additional data integrity mechanisms such as
those offered by IPsec (see Section 6.2).

An operator MAY choose to disable UDP checksums and use zero UDP
checksum if Geneve packet integrity is provided by other data
integrity mechanisms, such as IPsec or additional checksums, or if
one of the conditions (a, b, or c) in Section 4.3.1 is met.

By default, UDP checksums MUST be used when Geneve is transported
over IPv6. A tunnel endpoint MAY be configured for use with zero UDP
checksum if additional requirements in Section 4.3.1 are met.

4.3.1. Zero UDP Checksum Handling with IPv6

When Geneve is used over IPv6, the UDP checksum is used to protect
IPv6 headers, UDP headers, and Geneve headers, options, and payload
from potential data corruption. As such, by default, Geneve MUST use
UDP checksums when transported over IPv6. An operator MAY choose to
configure zero UDP checksum if operating in a TMCE as stated in
Section 4.1 if one of the following conditions is met.

a. It is known that packet corruption is exceptionally unlikely
(perhaps based on knowledge of equipment types in their underlay
network) and the operator is willing to risk undetected packet
corruption.

b. It is judged through observational measurements (perhaps through
historic or current traffic flows that use non-zero checksum)
that the level of packet corruption is tolerably low and is where
the operator is willing to risk undetected corruption.

c. The Geneve payload is carrying applications that are tolerant of
misdelivered or corrupted packets (perhaps through higher-layer
checksum validation and/or reliability through retransmission).

In addition, Geneve tunnel implementations using zero UDP checksum
MUST meet the following requirements:

1. Use of UDP checksum over IPv6 MUST be the default configuration
for all Geneve tunnels.

2. If Geneve is used with zero UDP checksum over IPv6, then such a
tunnel endpoint implementation MUST meet all the requirements
specified in Section 4 of [RFC6936] and requirement 1 as
specified in Section 5 of [RFC6936] since it is relevant to
Geneve.

3. The Geneve tunnel endpoint that decapsulates the tunnel SHOULD
check that the source and destination IPv6 addresses are valid
for the Geneve tunnel that is configured to receive zero UDP
checksum and discard other packets for which such a check fails.

4. The Geneve tunnel endpoint that encapsulates the tunnel MAY use
different IPv6 source addresses for each Geneve tunnel that uses
zero UDP checksum mode in order to strengthen the decapsulator's
check of the IPv6 source address (i.e., the same IPv6 source
address is not to be used with more than one IPv6 destination
address, irrespective of whether that destination address is a
unicast or multicast address). When this is not possible, it is
RECOMMENDED to use each source address for as few Geneve tunnels
that use zero UDP checksum as is feasible.

Note that for requirements 3 and 4, the receiving tunnel endpoint
can apply these checks only if it has out-of-band knowledge that
the encapsulating tunnel endpoint is applying the indicated
behavior. One possibility to obtain this out-of-band knowledge
is through signaling by the control plane. The definition of the
control plane is beyond the scope of this document.

5. Measures SHOULD be taken to prevent Geneve traffic over IPv6 with
zero UDP checksum from escaping into the general Internet.
Examples of such measures include employing packet filters at the
gateways or edge of the Geneve network and/or keeping logical or
physical separation of the Geneve network from networks carrying
general Internet traffic.

The above requirements do not change the requirements specified in
either [RFC8200] or [RFC6936].

The use of the source IPv6 address in addition to the destination
IPv6 address, plus the recommendation against reuse of source IPv6
addresses among Geneve tunnels, collectively provide some mitigation
for the absence of UDP checksum coverage of the IPv6 header. A
traffic-managed controlled environment that satisfies at least one of
the three conditions listed at the beginning of this section provides
additional assurance.

4.4. Encapsulation of Geneve in IP

As an IP-based tunneling protocol, Geneve shares many properties and
techniques with existing protocols. The application of some of these
are described in further detail, although, in general, most concepts
applicable to the IP layer or to IP tunnels generally also function
in the context of Geneve.

4.4.1. IP Fragmentation

It is RECOMMENDED that Path MTU Discovery (see [RFC1191] and
[RFC8201]) be used to prevent or minimize fragmentation. The use of
Path MTU Discovery on the transit network provides the encapsulating
tunnel endpoint with soft-state information about the link that it
may use to prevent or minimize fragmentation depending on its role in
the virtualized network. The NVE can maintain this state (the MTU
size of the tunnel link(s) associated with the tunnel endpoint), so
if a tenant system sends large packets that, when encapsulated,
exceed the MTU size of the tunnel link, the tunnel endpoint can
discard such packets and send exception messages to the tenant
system(s). If the tunnel endpoint is associated with a routing or
forwarding function and/or has the capability to send ICMP messages,
the encapsulating tunnel endpoint MAY send ICMP fragmentation needed
[RFC0792] or Packet Too Big [RFC4443] messages to the tenant
system(s). When determining the MTU size of a tunnel link, the
maximum length of options MUST be assumed as options may vary on a
per-packet basis. Recommendations and guidance for handling
fragmentation in similar overlay encapsulation services like
Pseudowire Emulation Edge-to-Edge (PWE3) are provided in Section 5.3
of [RFC3985].

Note that some implementations may not be capable of supporting
fragmentation or other less common features of the IP header, such as
options and extension headers. Some of the issues associated with
MTU size and fragmentation in IP tunneling and use of ICMP messages
are outlined in Section 4.2 of [INTAREA-TUNNELS].

4.4.2. DSCP, ECN, and TTL

When encapsulating IP (including over Ethernet) packets in Geneve,
there are several considerations for propagating Differentiated
Services Code Point (DSCP) and Explicit Congestion Notification (ECN)
bits from the inner header to the tunnel on transmission and the
reverse on reception.

[RFC2983] provides guidance for mapping DSCP between inner and outer
IP headers. Network virtualization is typically more closely aligned
with the Pipe model described, where the DSCP value on the tunnel
header is set based on a policy (which may be a fixed value, one
based on the inner traffic class or some other mechanism for grouping
traffic). Aspects of the Uniform model (which treats the inner and
outer DSCP values as a single field by copying on ingress and egress)
may also apply, such as the ability to re-mark the inner header on
tunnel egress based on transit marking. However, the Uniform model
is not conceptually consistent with network virtualization, which
seeks to provide strong isolation between encapsulated traffic and
the physical network.

[RFC6040] describes the mechanism for exposing ECN capabilities on IP
tunnels and propagating congestion markers to the inner packets.
This behavior MUST be followed for IP packets encapsulated in Geneve.

Though either the Uniform or Pipe models could be used for handling
TTL (or Hop Limit in case of IPv6) when tunneling IP packets, the
Pipe model is more consistent with network virtualization. [RFC2003]
provides guidance on handling TTL between inner IP header and outer
IP tunnels; this model is similar to the Pipe model and is
RECOMMENDED for use with Geneve for network virtualization
applications.

4.4.3. Broadcast and Multicast

Geneve tunnels may either be point-to-point unicast between two
tunnel endpoints or utilize broadcast or multicast addressing. It is
not required that inner and outer addressing match in this respect.
For example, in physical networks that do not support multicast,
encapsulated multicast traffic may be replicated into multiple
unicast tunnels or forwarded by policy to a unicast location
(possibly to be replicated there).

With physical networks that do support multicast, it may be desirable
to use this capability to take advantage of hardware replication for
encapsulated packets. In this case, multicast addresses may be
allocated in the physical network corresponding to tenants,
encapsulated multicast groups, or some other factor. The allocation
of these groups is a component of the control plane and, therefore,
is beyond the scope of this document.

When physical multicast is in use, devices with heterogeneous
capabilities may be present in the same group. Some options may only
be interpretable by a subset of the devices in the group. Other
devices can safely ignore such options unless the 'C' bit is set to
mark the unknown option as critical. The requirements outlined in
Section 3.4 apply for critical options.

In addition, [RFC8293] provides examples of various mechanisms that
can be used for multicast handling in network virtualization overlay
networks.

4.4.4. Unidirectional Tunnels

Generally speaking, a Geneve tunnel is a unidirectional concept. IP
is not a connection-oriented protocol, and it is possible for two
tunnel endpoints to communicate with each other using different paths
or to have one side not transmit anything at all. As Geneve is an
IP-based protocol, the tunnel layer inherits these same
characteristics.

It is possible for a tunnel to encapsulate a protocol, such as TCP,
that is connection oriented and maintains session state at that
layer. In addition, implementations MAY model Geneve tunnels as
connected, bidirectional links, for example, to provide the
abstraction of a virtual port. In both of these cases,
bidirectionality of the tunnel is handled at a higher layer and does
not affect the operation of Geneve itself.

4.5. Constraints on Protocol Features

Geneve is intended to be flexible for use with a wide range of
current and future applications. As a result, certain constraints
may be placed on the use of metadata or other aspects of the protocol
in order to optimize for a particular use case. For example, some
applications may limit the types of options that are supported or
enforce a maximum number or length of options. Other applications
may only handle certain encapsulated payload types, such as Ethernet
or IP. These optimizations can be implemented either globally
(throughout the system) or locally (for example, restricted to
certain classes of devices or network paths).

These constraints may be communicated to tunnel endpoints either
explicitly through a control plane or implicitly by the nature of the
application. As Geneve is defined as a data plane protocol that is
control plane agnostic, definition of such mechanisms is beyond the
scope of this document.

4.5.1. Constraints on Options

While Geneve options are flexible, a control plane may restrict the
number of option TLVs as well as the order and size of the TLVs
between tunnel endpoints to make it simpler for a data plane
implementation in software or hardware to handle (see [NVO3-ENCAP]).
For example, there may be some critical information, such as a secure
hash, that must be processed in a certain order to provide the lowest
latency, or there may be other scenarios where the options must be
processed in a given order due to protocol semantics.

A control plane may negotiate a subset of option TLVs and certain TLV
ordering; it may also limit the total number of option TLVs present
in the packet, for example, to accommodate hardware capable of
processing fewer options. Hence, a control plane needs to have the
ability to describe the supported TLV subset and its ordering to the
tunnel endpoints. In the absence of a control plane, alternative
configuration mechanisms may be used for this purpose. Such
mechanisms are beyond the scope of this document.

4.6. NIC Offloads

Modern NICs currently provide a variety of offloads to enable the
efficient processing of packets. The implementation of many of these
offloads requires only that the encapsulated packet be easily parsed
(for example, checksum offload). However, optimizations such as LSO
and LRO involve some processing of the options themselves since they
must be replicated/merged across multiple packets. In these
situations, it is desirable not to require changes to the offload
logic to handle the introduction of new options. To enable this,
some constraints are placed on the definitions of options to allow
for simple processing rules:

* When performing LSO, a NIC MUST replicate the entire Geneve header
and all options, including those unknown to the device, onto each
resulting segment unless an option allows an exception.
Conversely, when performing LRO, a NIC may assume that a binary
comparison of the options (including unknown options) is
sufficient to ensure equality and MAY merge packets with equal
Geneve headers.

* Options MUST NOT be reordered during the course of offload
processing, including when merging packets for the purpose of LRO.

* NICs performing offloads MUST NOT drop packets with unknown
options, including those marked as critical, unless explicitly
configured to do so.

There is no requirement that a given implementation of Geneve employ
the offloads listed as examples above. However, as these offloads
are currently widely deployed in commercially available NICs, the
rules described here are intended to enable efficient handling of
current and future options across a variety of devices.

4.7. Inner VLAN Handling

Geneve is capable of encapsulating a wide range of protocols;
therefore, a given implementation is likely to support only a small
subset of the possibilities. However, as Ethernet is expected to be
widely deployed, it is useful to describe the behavior of VLANs
inside encapsulated Ethernet frames.

As with any protocol, support for inner VLAN headers is OPTIONAL. In
many cases, the use of encapsulated VLANs may be disallowed due to
security or implementation considerations. However, in other cases,
the trunking of VLAN frames across a Geneve tunnel can prove useful.
As a result, the processing of inner VLAN tags upon ingress or egress
from a tunnel endpoint is based upon the configuration of the tunnel
endpoint and/or control plane and is not explicitly defined as part
of the data format.

5. Transition Considerations

Viewed exclusively from the data plane, Geneve is compatible with
existing IP networks as it appears to most devices as UDP packets.
However, as there are already a number of tunneling protocols
deployed in network virtualization environments, there is a practical
question of transition and coexistence.

Since Geneve builds on the base data plane functionality provided by
the most common protocols used for network virtualization (VXLAN and
NVGRE), it should be straightforward to port an existing control
plane to run on top of it with minimal effort. With both the old and
new packet formats supporting the same set of capabilities, there is
no need for a hard transition; tunnel endpoints directly
communicating with each other can use any common protocol, which may
be different even within a single overall system. As transit devices
are primarily forwarding packets on the basis of the IP header, all
protocols appear to be similar, and these devices do not introduce
additional interoperability concerns.

To assist with this transition, it is strongly suggested that
implementations support simultaneous operation of both Geneve and
existing tunneling protocols, as it is expected to be common for a
single node to communicate with a mixture of other nodes.
Eventually, older protocols may be phased out as they are no longer
in use.

6. Security Considerations

As it is encapsulated within a UDP/IP packet, Geneve does not have
any inherent security mechanisms. As a result, an attacker with
access to the underlay network transporting the IP packets has the
ability to snoop on, alter, or inject packets. Compromised tunnel
endpoints or transit devices may also spoof identifiers in the tunnel
header to gain access to networks owned by other tenants.

Within a particular security domain, such as a data center operated
by a single service provider, the most common and highest-performing
security mechanism is isolation of trusted components. Tunnel
traffic can be carried over a separate VLAN and filtered at any
untrusted boundaries.

When crossing an untrusted link, such as the general Internet, VPN
technologies such as IPsec [RFC4301] should be used to provide
authentication and/or encryption of the IP packets formed as part of
Geneve encapsulation (see Section 6.1.1).

Geneve does not otherwise affect the security of the encapsulated
packets. As per the guidelines of BCP 72 [RFC3552], the following
sections describe potential security risks that may be applicable to
Geneve deployments and approaches to mitigate such risks. It is also
noted that not all such risks are applicable to all Geneve deployment
scenarios, i.e., only a subset may be applicable to certain
deployments. An operator has to make an assessment based on their
network environment, determine the risks that are applicable to their
specific environment, and use appropriate mitigation approaches as
applicable.

6.1. Data Confidentiality

Geneve is a network virtualization overlay encapsulation protocol
designed to establish tunnels between NVEs over an existing IP
network. It can be used to deploy multi-tenant overlay networks over
an existing IP underlay network in a public or private data center.
The overlay service is typically provided by a service provider, such
as a cloud service provider or a private data center operator. This
may or not may be the same provider as an underlay service provider.
Due to the nature of multi-tenancy in such environments, a tenant
system may expect data confidentiality to ensure its packet data is
not tampered with (i.e., active attack) in transit or is a target of
unauthorized monitoring (i.e., passive attack), for example, by other
tenant systems or underlay service provider. A compromised network
node or a transit device within a data center may passively monitor
Geneve packet data between NVEs or route traffic for further
inspection. A tenant may expect the overlay service provider to
provide data confidentiality as part of the service, or a tenant may
bring its own data confidentiality mechanisms like IPsec or TLS to
protect the data end to end between its tenant systems. The overlay
provider is expected to provide cryptographic protection in cases
where the underlay provider is not the same as the overlay provider
to ensure the payload is not exposed to the underlay.

If an operator determines data confidentiality is necessary in their
environment based on their risk analysis -- for example, in multi-
tenant environments -- then an encryption mechanism SHOULD be used to
encrypt the tenant data end to end between the NVEs. The NVEs may
use existing well-established encryption mechanisms, such as IPsec,
DTLS, etc.

6.1.1. Inter-Data Center Traffic

A tenant system in a customer premises (private data center) may want
to connect to tenant systems on their tenant overlay network in a
public cloud data center, or a tenant may want to have its tenant
systems located in multiple geographically separated data centers for
high availability. Geneve data traffic between tenant systems across
such separated networks should be protected from threats when
traversing public networks. Any Geneve overlay data leaving the data
center network beyond the operator's security domain SHOULD be
secured by encryption mechanisms, such as IPsec or other VPN
technologies, to protect the communications between the NVEs when
they are geographically separated over untrusted network links.
Specification of data protection mechanisms employed between data
centers is beyond the scope of this document.

The principles described in Section 4 regarding controlled
environments still apply to the geographically separated data center
usage outlined in this section.

6.2. Data Integrity

Geneve encapsulation is used between NVEs to establish overlay
tunnels over an existing IP underlay network. In a multi-tenant data
center, a rogue or compromised tenant system may try to launch a
passive attack, such as monitoring the traffic of other tenants, or
an active attack, such as trying to inject unauthorized Geneve
encapsulated traffic such as spoofing, replay, etc., into the
network. To prevent such attacks, an NVE MUST NOT propagate Geneve
packets beyond the NVE to tenant systems and SHOULD employ packet-
filtering mechanisms so as not to forward unauthorized traffic
between tenant systems in different tenant networks. An NVE MUST NOT
interpret Geneve packets from tenant systems other than as frames to
be encapsulated.

A compromised network node or a transit device within a data center
may launch an active attack trying to tamper with the Geneve packet
data between NVEs. Malicious tampering of Geneve header fields may
cause the packet from one tenant to be forwarded to a different
tenant network. If an operator determines there is a possibility of
such a threat in their environment, the operator may choose to employ
data integrity mechanisms between NVEs. In order to prevent such
risks, a data integrity mechanism SHOULD be used in such environments
to protect the integrity of Geneve packets, including packet headers,
options, and payload on communications between NVE pairs. A
cryptographic data protection mechanism, such as IPsec, may be used
to provide data integrity protection. A data center operator may
choose to deploy any other data integrity mechanisms as applicable
and supported in their underlay networks, although non-cryptographic
mechanisms may not protect the Geneve portion of the packet from
tampering.

6.3. Authentication of NVE Peers

A rogue network device or a compromised NVE in a data center
environment might be able to spoof Geneve packets as if it came from
a legitimate NVE. In order to mitigate such a risk, an operator
SHOULD use an authentication mechanism, such as IPsec, to ensure that
the Geneve packet originated from the intended NVE peer in
environments where the operator determines spoofing or rogue devices
are potential threats. Other simpler source checks, such as ingress
filtering for VLAN/MAC/IP addresses, reverse path forwarding checks,
etc., may be used in certain trusted environments to ensure Geneve
packets originated from the intended NVE peer.

6.4. Options Interpretation by Transit Devices

Options, if present in the packet, are generated and terminated by
tunnel endpoints. As indicated in Section 2.2.1, transit devices may
interpret the options. However, if the packet is protected by
encryption from tunnel endpoint to tunnel endpoint (for example,
through IPsec), transit devices will not have visibility into the
Geneve header or options in the packet. In such cases, transit
devices MUST handle Geneve packets as any other IP packet and
maintain consistent forwarding behavior. In cases where options are
interpreted by transit devices, the operator MUST ensure that transit
devices are trusted and not compromised. The definition of a
mechanism to ensure this trust is beyond the scope of this document.

6.5. Multicast/Broadcast

In typical data center networks where IP multicasting is not
supported in the underlay network, multicasting may be supported
using multiple unicast tunnels. The same security requirements as
described in the above sections can be used to protect Geneve
communications between NVE peers. If IP multicasting is supported in
the underlay network and the operator chooses to use it for multicast
traffic among tunnel endpoints, then the operator in such
environments may use data protection mechanisms, such as IPsec with
multicast extensions [RFC5374], to protect multicast traffic among
Geneve NVE groups.

6.6. Control Plane Communications

A Network Virtualization Authority (NVA) as outlined in [RFC8014] may
be used as a control plane for configuring and managing the Geneve
NVEs. The data center operator is expected to use security
mechanisms to protect the communications between the NVA and NVEs and
to use authentication mechanisms to detect any rogue or compromised
NVEs within their administrative domain. Data protection mechanisms
for control plane communication or authentication mechanisms between
the NVA and NVEs are beyond the scope of this document.

7. IANA Considerations

IANA has allocated UDP port 6081 in the "Service Name and Transport
Protocol Port Number Registry" [IANA-SN] as the well-known
destination port for Geneve:

Service Name: geneve
Transport Protocol(s): UDP
Assignee: IESG <[email protected]>
Contact: IETF Chair <[email protected]>
Description: Generic Network Virtualization Encapsulation (Geneve)
Reference: [RFC8926]
Port Number: 6081

In addition, IANA has created a new subregistry titled "Geneve Option
Class" for option classes. This registry has been placed under a new
"Network Virtualization Overlay (NVO3)" heading in the IANA protocol
registries [IANA-PR]. The "Geneve Option Class" registry consists of
16-bit hexadecimal values along with descriptive strings, assignee/
contact information, and references. The registration rules for the
new registry are (as defined by [RFC8126]):

+===============+=========================+
| Range | Registration Procedures |
+===============+=========================+
| 0x0000-0x00FF | IETF Review |
+---------------+-------------------------+
| 0x0100-0xFEFF | First Come First Served |
+---------------+-------------------------+
| 0xFF00-0xFFFF | Experimental Use |
+---------------+-------------------------+

Table 1: Geneve Option Class Registry
Ranges

8. References

8.1. Normative References

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.

[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.

[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.

[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
DOI 10.17487/RFC2003, October 1996,
<https://www.rfc-editor.org/info/rfc2003>.

[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>.

[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.

[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/info/rfc6040>.

[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.

[RFC7365] Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
Rekhter, "Framework for Data Center (DC) Network
Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
2014, <https://www.rfc-editor.org/info/rfc7365>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[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>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.

8.2. Informative References

[ETYPES] IANA, "IEEE 802 Numbers",
<https://www.iana.org/assignments/ieee-802-numbers>.

[IANA-PR] IANA, "Protocol Registries",
<https://www.iana.org/protocols>.

[IANA-SN] IANA, "Service Name and Transport Protocol Port Number
Registry", <https://www.iana.org/assignments/service-
names-port-numbers>.

[IEEE.802.1Q_2018]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks--Bridges and Bridged Networks",
DOI 10.1109/IEEESTD.2018.8403927, IEEE 802.1Q-2018, July
2018, <http://ieeexplore.ieee.org/servlet/
opac?punumber=8403925>.

[INTAREA-TUNNELS]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://tools.ietf.org/html/draft-ietf-intarea-tunnels-
10>.

[NVO3-DATAPLANE]
Bitar, N., Lasserre, M., Balus, F., Morin, T., Jin, L.,
and B. Khasnabish, "NVO3 Data Plane Requirements", Work in
Progress, Internet-Draft, draft-ietf-nvo3-dataplane-
requirements-03, 15 April 2014,
<https://tools.ietf.org/html/draft-ietf-nvo3-dataplane-
requirements-03>.

[NVO3-ENCAP]
Boutros, S., "NVO3 Encapsulation Considerations", Work in
Progress, Internet-Draft, draft-ietf-nvo3-encap-05, 17
February 2020,
<https://tools.ietf.org/html/draft-ietf-nvo3-encap-05>.

[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, DOI 10.17487/RFC2983, October 2000,
<https://www.rfc-editor.org/info/rfc2983>.

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.

[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.

[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>.

[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.

[RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast
Extensions to the Security Architecture for the Internet
Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008,
<https://www.rfc-editor.org/info/rfc5374>.

[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.

[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>.

[RFC8014] Black, D., Hudson, J., Kreeger, L., Lasserre, M., and T.
Narten, "An Architecture for Data-Center Network
Virtualization over Layer 3 (NVO3)", RFC 8014,
DOI 10.17487/RFC8014, December 2016,
<https://www.rfc-editor.org/info/rfc8014>.

[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE-
in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086,
March 2017, <https://www.rfc-editor.org/info/rfc8086>.

[RFC8293] Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R.
Krishnan, "A Framework for Multicast in Network
Virtualization over Layer 3", RFC 8293,
DOI 10.17487/RFC8293, January 2018,
<https://www.rfc-editor.org/info/rfc8293>.

[VL2] "VL2: A Scalable and Flexible Data Center Network", ACM
SIGCOMM Computer Communication Review,
DOI 10.1145/1594977.1592576, August 2009,
<https://dl.acm.org/doi/10.1145/1594977.1592576>.

Acknowledgements

The authors wish to acknowledge Puneet Agarwal, David Black, Sami
Boutros, Scott Bradner, Martín Casado, Alissa Cooper, Roman Danyliw,
Bruce Davie, Anoop Ghanwani, Benjamin Kaduk, Suresh Krishnan, Mirja
Kühlewind, Barry Leiba, Daniel Migault, Greg Mirksy, Tal Mizrahi,
Kathleen Moriarty, Magnus Nyström, Adam Roach, Sabrina Tanamal, Dave
Thaler, Éric Vyncke, Magnus Westerlund, and many other members of the
NVO3 Working Group for their reviews, comments, and suggestions.

The authors would like to thank Sam Aldrin, Alia Atlas, Matthew
Bocci, Benson Schliesser, and Martin Vigoureux for their guidance
throughout the process.

Contributors

The following individuals were authors of an earlier version of this
document and made significant contributions:

Pankaj Garg
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
United States of America

Email: [email protected]

Chris Wright
Red Hat Inc.
1801 Varsity Drive
Raleigh, NC 27606
United States of America

Email: [email protected]

Kenneth Duda
Arista Networks
5453 Great America Parkway
Santa Clara, CA 95054
United States of America

Email: [email protected]

Dinesh G. Dutt
Independent

Email: [email protected]

Jon Hudson
Independent

Email: [email protected]

Ariel Hendel
Facebook, Inc.
1 Hacker Way
Menlo Park, CA 94025
United States of America

Email: [email protected]

Authors' Addresses

Jesse Gross (editor)

Email: [email protected]

Ilango Ganga (editor)
Intel Corporation
2200 Mission College Blvd.
Santa Clara, CA 95054
United States of America

Email: [email protected]

T. Sridhar (editor)
VMware, Inc.
3401 Hillview Ave.
Palo Alto, CA 94304
United States of America

Email: [email protected]