Internet Engineering Task Force (IETF) X. Min

Internet Engineering Task Force (IETF) X. Min
Request for Comments: 9521 ZTE Corp.
Category: Standards Track G. Mirsky
ISSN: 2070-1721 Ericsson
S. Pallagatti
VMware
J. Tantsura
Nvidia
S. Aldrin
Google
January 2024

Bidirectional Forwarding Detection (BFD) for Generic Network
Virtualization Encapsulation (Geneve)

Abstract

This document describes the use of the Bidirectional Forwarding
Detection (BFD) protocol in point-to-point Generic Network
Virtualization Encapsulation (Geneve) unicast tunnels used to make up
an overlay network.

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/rfc9521.

Copyright Notice

Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
2. Conventions Used in This Document
2.1. Abbreviations
2.2. Requirements Language
3. BFD Packet Transmission over a Geneve Tunnel
4. BFD Encapsulation with the Inner Ethernet/IP/UDP Header
4.1. Demultiplexing a BFD Packet When the Payload Is Ethernet
5. BFD Encapsulation with the Inner IP/UDP Header
5.1. Demultiplexing a BFD Packet When the Payload Is IP
6. Security Considerations
7. IANA Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses

1. Introduction

"Geneve: Generic Network Virtualization Encapsulation" [RFC8926]
provides an encapsulation scheme that allows building an overlay
network of tunnels by decoupling the address space of the attached
virtual hosts from that of the network.

This document describes the use of the Bidirectional Forwarding
Detection (BFD) protocol [RFC5880] to enable monitoring the
continuity of the path between two Geneve tunnel endpoints, which may
be a Network Virtualization Edge (NVE) or another device acting as a
Geneve tunnel endpoint. Specifically, the asynchronous mode of BFD,
as defined in [RFC5880], is used to monitor a point-to-point (P2P)
Geneve tunnel. The support for the BFD Echo function is outside the
scope of this document. For simplicity, an NVE is used to represent
the Geneve tunnel endpoint. A Tenant System (TS) is used to
represent the physical or virtual device attached to a Geneve tunnel
endpoint from the outside. A Virtual Access Point (VAP) is the NVE
side of the interface between the NVE and the TS, and a VAP is a
logical network port (virtual or physical) into a specific virtual
network. For detailed definitions and descriptions of NVE, TS, and
VAP, please refer to [RFC7365] and [RFC8014].

The use cases and the deployment of BFD for Geneve are mostly
consistent with what's described in Sections 1 and 3 of [RFC8971].
One exception is the usage of the Management Virtual Network
Identifier (VNI), which is described in [GENEVE-OAM] and is outside
the scope of this document.

As specified in Section 4.2 of [RFC8926], Geneve MUST be used with
congestion controlled traffic or within a Traffic-Managed Controlled
Environment (TMCE) to avoid congestion; that requirement also applies
to BFD traffic. Specifically, considering the complexity and
immaturity of the BFD congestion control mechanism, BFD for Geneve
MUST be used within a TMCE unless BFD is really congestion
controlled. As an alternative to a real congestion control, an
operator of a TMCE deploying BFD for Geneve is required to provision
the rates at which BFD is transmitted to avoid congestion and false
failure detection.

2. Conventions Used in This Document

2.1. Abbreviations

BFD: Bidirectional Forwarding Detection

FCS: Frame Check Sequence

Geneve: Generic Network Virtualization Encapsulation

NVE: Network Virtualization Edge

TMCE: Traffic-Managed Controlled Environment

TS: Tenant System

VAP: Virtual Access Point

VNI: Virtual Network Identifier

VXLAN: Virtual eXtensible Local Area Network

2.2. 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.

3. BFD Packet Transmission over a Geneve Tunnel

Since the Geneve data packet payload may be either an Ethernet frame
or an IP packet, this document defines two formats of BFD packet
encapsulation in Geneve. The BFD session is originated and
terminated at the VAP of an NVE. The selection of the BFD packet
encapsulation is based on how the VAP encapsulates the data packets.
If the payload is IP, then BFD over IP is carried in the payload. If
the payload is Ethernet, then BFD over IP over Ethernet is carried in
the payload. This occurs in the same manner as BFD over IP in the IP
payload case, regardless of what the Ethernet payload might normally
carry.

4. BFD Encapsulation with the Inner Ethernet/IP/UDP Header

If the VAP that originates the BFD packets is used to encapsulate
Ethernet data frames, then the BFD packets are encapsulated in Geneve
as described below. The Geneve packet formats over IPv4 and IPv6 are
defined in Sections 3.1 and 3.2 of [RFC8926], respectively. The
outer IP/UDP and Geneve headers are encoded by the sender as defined
in [RFC8926]. Note that the outer IP header and the inner IP header
may not be of the same address family. In other words, an outer IPv6
header accompanied by an inner IPv4 header and an outer IPv4 header
accompanied by an inner IPv6 header are both possible.

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 IPvX Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Outer UDP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Geneve Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner Ethernet Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner IPvX Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner UDP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Ethernet FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Geneve Encapsulation of a BFD Control Packet with the Inner
Ethernet/IP/UDP Header

The BFD packet MUST be carried inside the inner Ethernet frame of the
Geneve packet. The inner Ethernet frame carrying the BFD Control
packet has the following format:

Inner Ethernet Header:
Destination MAC: Media Access Control (MAC) address of a VAP of
the terminating NVE.

Source MAC: MAC address of a VAP of the originating NVE.

IP Header:
Source IP: IP address of a VAP of the originating NVE. If the
VAP of the originating NVE has no IP address, then the IP
address 0.0.0.0 for IPv4 or ::/128 for IPv6 MUST be used.

Destination IP: IP address of a VAP of the terminating NVE. If
the VAP of the terminating NVE has no IP address, then the IP
address 127.0.0.1 for IPv4 or ::1/128 for IPv6 MUST be used.

TTL or Hop Limit: The TTL for IPv4 or Hop Limit for IPv6 MUST be
set to 255 in accordance with [RFC5881], which specifies the
IPv4/IPv6 single-hop BFD.

The fields of the UDP header and the BFD Control packet are
encoded as specified in [RFC5881].

When the BFD packets are encapsulated in Geneve in this way, the
Geneve header defined in [RFC8926] follows the value set below.

* The Opt Len field MUST be set as consistent with the Geneve
specification ([RFC8926]) depending on whether or not Geneve
options are present in the frame. The use of Geneve options with
BFD is beyond the scope of this document.

* The O bit MUST be set to 1, which indicates this packet contains a
control message.

* The C bit MUST be set to 0, which indicates there isn't any
critical option.

* The Protocol Type field MUST be set to 0x6558 (Ethernet frame).

* The Virtual Network Identifier (VNI) field MUST be set to the VNI
number that the originating VAP is mapped to.

4.1. Demultiplexing a BFD Packet When the Payload Is Ethernet

Once a packet is received, the NVE validates the packet as described
in [RFC8926]. When the payload is Ethernet, the Protocol Type field
equals 0x6558. The destination MAC address of the inner Ethernet
frame matches the MAC address of a VAP, which is mapped to the same
VNI as the received VNI. Then, the destination IP, the UDP
destination port, and the TTL or Hop Limit of the inner IP packet
MUST be validated to determine whether the received packet can be
processed by BFD (i.e., the three field values of the inner IP packet
MUST be in compliance with what's defined in Section 4 of this
document, as well as Section 4 of [RFC5881]). If the validation
fails, the received packet MUST NOT be processed by BFD.

In BFD over Geneve, a BFD session is originated and terminated at a
VAP. Usually one NVE owns multiple VAPs. Since multiple BFD
sessions may be running between two NVEs, there needs to be a
mechanism for demultiplexing received BFD packets to the proper
session. Furthermore, due to the fact that [RFC8014] allows for
N-to-1 mapping between VAPs and VNIs at one NVE, multiple BFD
sessions between two NVEs for the same VNI are allowed. Also, note
that a BFD session can only be established between two VAPs that are
mapped to the same VNI and that use the same way to encapsulate data
packets.

If the BFD packet is received with the value of the Your
Discriminator field set to 0, then the BFD session SHOULD be
identified using the VNI number and the inner Ethernet/IP header.
The inner Ethernet/IP header stands for the source MAC, the source
IP, the destination MAC, and the destination IP. An implementation
MAY use the inner UDP port source number to aid in demultiplexing
incoming BFD Control packets. If it fails to identify the BFD
session, the incoming BFD Control packets MUST be dropped, and an
exception event indicating the failure should be reported to the
management.

If the BFD packet is received with a non-zero Your Discriminator,
then the BFD session MUST be demultiplexed only with the Your
Discriminator as the key.

5. BFD Encapsulation with the Inner IP/UDP Header

If the VAP that originates the BFD packets is used to encapsulate IP
data packets, then the BFD packets are encapsulated in Geneve as
described below. The Geneve packet formats over IPv4 and IPv6 are
defined in Sections 3.1 and 3.2 of [RFC8926], respectively. The
outer IP/UDP and Geneve headers are encoded by the sender as defined
in [RFC8926]. Note that the outer IP header and the inner IP header
may not be of the same address family. In other words, an outer IPv6
header accompanied by an inner IPv4 header and an outer IPv4 header
accompanied by an inner IPv6 header are both possible.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Ethernet Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Outer IPvX Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Outer UDP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Geneve Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner IPvX Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner UDP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Geneve Encapsulation of a BFD Control Packet with the
Inner IP/UDP Header

The BFD packet MUST be carried inside the inner IP packet of the
Geneve packet. The inner IP packet carrying the BFD Control packet
has the following format:

Inner IP Header:
Source IP: IP address of a VAP of the originating NVE.

Destination IP: IP address of a VAP of the terminating NVE.

TTL or Hop Limit: The TTL for IPv4 or Hop Limit for IPv6 MUST be
set to 255 in accordance with [RFC5881], which specifies the
IPv4/IPv6 single-hop BFD.

The fields of the UDP header and the BFD Control packet are
encoded as specified in [RFC5881].

When the BFD packets are encapsulated in Geneve in this way, the
Geneve header defined in [RFC8926] follows the value set below.

* The Opt Len field MUST be set as consistent with the Geneve
specification ([RFC8926]) depending on whether or not Geneve
options are present in the frame. The use of Geneve options with
BFD is beyond the scope of this document.

* The O bit MUST be set to 1, which indicates this packet contains a
control message.

* The C bit MUST be set to 0, which indicates there isn't any
critical option.

* The Protocol Type field MUST be set to 0x0800 (IPv4) or 0x86DD
(IPv6), depending on the address family of the inner IP packet.

* The Virtual Network Identifier (VNI) field MUST be set to the VNI
number that the originating VAP is mapped to.

5.1. Demultiplexing a BFD Packet When the Payload Is IP

Once a packet is received, the NVE validates the packet as described
in [RFC8926]. When the payload is IP, the Protocol Type field equals
0x0800 or 0x86DD. The destination IP address of the inner IP packet
matches the IP address of a VAP, which is mapped to the same VNI as
the received VNI. Then, the UDP destination port and the TTL or Hop
Limit of the inner IP packet MUST be validated to determine whether
or not the received packet can be processed by BFD (i.e., the two
field values of the inner IP packet MUST be in compliance with what's
defined in Section 5 of this document as well as Section 4 of
[RFC5881]). If the validation fails, the received packet MUST NOT be
processed by BFD.

If the BFD packet is received with the value of the Your
Discriminator field set to 0, then the BFD session SHOULD be
identified using the VNI number and the inner IP header. The inner
IP header stands for the source IP and the destination IP. An
implementation MAY use the inner UDP port source number to aid in
demultiplexing incoming BFD Control packets. If it fails to identify
the BFD session, the incoming BFD Control packets MUST be dropped,
and an exception event indicating the failure should be reported to
the management.

If the BFD packet is received with a non-zero Your Discriminator,
then the BFD session MUST be demultiplexed only with the Your
Discriminator as the key.

6. Security Considerations

Security issues discussed in [RFC8926] and [RFC5880] apply to this
document. Particularly, the BFD is an application that is run at the
two Geneve tunnel endpoints. The IP underlay network and/or the
Geneve option can provide security between the peers, which are
subject to the issue of overload described below. The BFD introduces
no security vulnerabilities when run in this manner. Considering
Geneve does not have any inherent security mechanisms, BFD
authentication as specified in [RFC5880] is RECOMMENDED to be
utilized.

This document supports establishing multiple BFD sessions between the
same pair of NVEs. For each BFD session over a pair of VAPs residing
in the same pair of NVEs, there SHOULD be a mechanism to control the
maximum number of such sessions that can be active at the same time.
Particularly, assuming an example that each NVE of the pair of NVEs
has N VAPs using Ethernet as the payload, then there could be N
squared BFD sessions running between the pair of NVEs. Considering N
could be a high number, the N squared BFD sessions could result in
overload of the NVE. In this case, it's recommended that N BFD
sessions covering all N VAPs are run for the pair of NVEs. Generally
speaking, the number of BFD sessions is supposed to be enough as long
as all VAPs of the pair of NVEs are covered.

7. IANA Considerations

This document has no IANA actions.

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.

[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.

[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>.

[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.17487/RFC8926, November 2020,
<https://www.rfc-editor.org/info/rfc8926>.

8.2. Informative References

[GENEVE-OAM]
Mirsky, G., Boutros, S., Black, D., and S. Pallagatti,
"OAM for use in GENEVE", Work in Progress, Internet-Draft,
draft-ietf-nvo3-geneve-oam-09, 6 December 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-nvo3-
geneve-oam-09>.

[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>.

[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>.

[RFC8971] Pallagatti, S., Ed., Mirsky, G., Ed., Paragiri, S.,
Govindan, V., and M. Mudigonda, "Bidirectional Forwarding
Detection (BFD) for Virtual eXtensible Local Area Network
(VXLAN)", RFC 8971, DOI 10.17487/RFC8971, December 2020,
<https://www.rfc-editor.org/info/rfc8971>.

Acknowledgements

The authors would like to acknowledge Reshad Rahman, Jeffrey Haas,
and Matthew Bocci for their guidance on this work.

The authors would like to acknowledge David Black for his explanation
on the mapping relation between VAPs and VNIs.

The authors would like to acknowledge Stewart Bryant, Anoop Ghanwani,
Jeffrey Haas, Reshad Rahman, Matthew Bocci, Andrew Alston, Magnus
Westerlund, Paul Kyzivat, Sheng Jiang, Carl Wallace, Roman Danyliw,
John Scudder, Donald Eastlake 3rd, Éric Vyncke, Zaheduzzaman Sarker,
and Lars Eggert for their thorough review and very helpful comments.

Authors' Addresses

Xiao Min
ZTE Corp.
Nanjing
China
Phone: +86 18061680168
Email: [email protected]

Greg Mirsky
Ericsson
United States of America
Email: [email protected]

Santosh Pallagatti
VMware
India
Email: [email protected]

Jeff Tantsura
Nvidia
United States of America
Email: [email protected]

Sam Aldrin
Google
United States of America
Email: [email protected]