BFD for Geneve: Bidirectional Forwarding Detection (BFD) for Generic Network Virtualization Encapsulation (Geneve)
How two Geneve tunnel endpoints use BFD to notice quickly when the path between them stops working.
Min, X., Mirsky, G., Pallagatti, S., Tantsura, J., and S. Aldrin, "Bidirectional Forwarding Detection (BFD) for Generic Network Virtualization Encapsulation (Geneve)", RFC 9521, DOI 10.17487/RFC9521, January 2024, <https://www.rfc-editor.org/info/rfc9521>.
@misc{rfc9521,
series = {Request for Comments},
number = 9521,
howpublished = {RFC 9521},
publisher = {RFC Editor},
doi = {10.17487/RFC9521},
url = {https://www.rfc-editor.org/info/rfc9521},
author = {X. Min and G. Mirsky and S. Pallagatti and J. Tantsura and S. Aldrin},
title = {{Bidirectional Forwarding Detection (BFD) for Generic Network Virtualization Encapsulation (Geneve)}},
pagetotal = 11,
year = 2024,
month = jan,
} RFC text
Contents
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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
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: xiao.min2@zte.com.cn
Greg Mirsky
Ericsson
United States of America
Email: gregimirsky@gmail.com
Santosh Pallagatti
VMware
India
Email: santosh.pallagatti@gmail.com
Jeff Tantsura
Nvidia
United States of America
Email: jefftant.ietf@gmail.com
Sam Aldrin
Google
United States of America
Email: aldrin.ietf@gmail.com
AI ELI5
On this page
§1Why BFD for Geneve
Geneve (RFC 8926) lets operators build an overlay network of tunnels, decoupling the address space of attached virtual hosts from that of the network. Bidirectional Forwarding Detection (BFD, RFC 5880) is a protocol for monitoring whether a path between two systems is still alive.
RFC 9521 describes how to run BFD between two Geneve tunnel endpoints, which may be a Network Virtualization Edge (NVE) or another device acting as an endpoint. Only the asynchronous mode of BFD is used, and only for point-to-point (P2P) Geneve tunnels. The BFD Echo function is outside the scope of the document.
The use cases and deployment are mostly consistent with those of BFD for VXLAN in RFC 8971. One exception is the Management Virtual Network Identifier (VNI), which is left to a separate work in progress.
A tunnel can quietly break without anyone noticing. This document says how the two ends of a Geneve tunnel keep checking on each other so a break is spotted fast.
§2Terms: NVE, Tenant System and VAP
The RFC uses an NVE to stand for any Geneve tunnel endpoint. A Tenant System (TS) is the physical or virtual device attached to a tunnel endpoint from the outside. A Virtual Access Point (VAP) is the NVE side of the interface between the NVE and the TS: a logical network port, virtual or physical, into a specific virtual network.
The BFD session is originated and terminated at a VAP of an NVE, not at the NVE as a whole. Detailed definitions are left to RFC 7365 and RFC 8014.
Think of an NVE as an apartment building and each VAP as one front door into one of its private hallways. The BFD chat happens door to door.
§4BFD in an Inner Ethernet/IP/UDP Packet
Geneve payloads can be either Ethernet frames or IP packets, so the RFC defines two encapsulations. The choice follows how the originating VAP encapsulates its data packets. If the VAP carries Ethernet, the BFD Control packet rides in an inner Ethernet frame, over IP, over UDP.
The outer IP/UDP and Geneve headers are encoded as in RFC 8926. The outer and inner IP headers need not be the same address family, so an outer IPv6 header with an inner IPv4 header is allowed, and the reverse as well.
For the inner headers, the destination MAC is the MAC address of a VAP of the terminating NVE and the source MAC is that of the originating NVE. The source and destination IP addresses are those of the VAPs. If a VAP has no IP address, the source uses 0.0.0.0 (IPv4) or ::/128 (IPv6), and the destination uses 127.0.0.1 (IPv4) or ::1/128 (IPv6). The TTL or Hop Limit MUST be 255, as in the single-hop BFD of RFC 5881, which also defines the UDP and BFD Control fields.
The Geneve header values are fixed: the O bit MUST be 1 (a control message), the C bit MUST be 0 (no critical option), the Protocol Type MUST be 0x6558 (Ethernet frame), and the VNI MUST be the one the originating VAP is mapped to. Opt Len is set as usual, and the use of Geneve options with BFD is out of scope.
When the tunnel carries whole Ethernet frames, the BFD message is wrapped like a letter in an envelope, inside a bigger envelope, inside the tunnel. Each envelope has its labels filled in a set way.
- Outer Ethernet HeaderCarries the whole packet on the underlay
- Outer IPvX and UDP HeadersEncoded as in RFC 8926
- Geneve HeaderO=1, C=0, Protocol Type 0x6558
- Inner Ethernet HeaderMAC addresses of the VAPs
- Inner IPvX and UDP HeadersTTL or Hop Limit 255
- BFD Control PacketEncoded as in RFC 5881
§5BFD in an Inner IP/UDP Packet
If the originating VAP encapsulates IP data packets, the BFD Control packet is carried directly in an inner IP packet over UDP, with no inner Ethernet header. Source and destination IP are the addresses of the originating and terminating VAPs, and TTL or Hop Limit MUST again be 255. UDP and BFD fields follow RFC 5881.
The Geneve header rules match the Ethernet case, except for the Protocol Type: it MUST be 0x0800 for an inner IPv4 packet or 0x86DD for an inner IPv6 packet. The O bit is 1, the C bit is 0, and the VNI is the one the originating VAP is mapped to.
Here the tunnel carries plain IP letters, so the BFD message needs one less envelope. Only the type label on the tunnel header changes.
| Case | Inner headers | Geneve Protocol Type |
|---|---|---|
| Ethernet payload | Ethernet, IP, UDP | 0x6558 |
| IP payload | IP, UDP | 0x0800 (IPv4) or 0x86DD (IPv6) |
§7Demultiplexing Received BFD Packets
A receiving NVE first validates the packet as RFC 8926 requires. For an Ethernet payload it checks that the Protocol Type is 0x6558 and that the inner destination MAC matches a VAP mapped to the received VNI. It then validates the inner destination IP, the UDP destination port and the TTL or Hop Limit. For an IP payload the Protocol Type is 0x0800 or 0x86DD, and the checks cover the destination IP, UDP port and TTL or Hop Limit. If validation fails, the packet MUST NOT be processed by BFD.
One NVE usually owns several VAPs, and RFC 8014 allows N-to-1 mapping between VAPs and VNIs, so several BFD sessions can exist between the same two NVEs, even for the same VNI. A session can only be established between two VAPs mapped to the same VNI that encapsulate data the same way.
To find the right session, the rules depend on the Your Discriminator field. If it is 0, the session SHOULD be identified by the VNI plus the inner headers (source and destination MAC and IP for Ethernet, source and destination IP for IP). An implementation MAY also use the inner UDP source port. If no session is found, the packet MUST be dropped and an exception event should be reported to management. If Your Discriminator is non-zero, the session MUST be demultiplexed using only that value as the key.
Many pairs of doors may be chatting through the same tunnel. The receiver looks at the labels, or at a ticket number if there is one, to know which chat each message belongs to.
§6Congestion and Security
Geneve MUST be used with congestion-controlled traffic or inside a Traffic-Managed Controlled Environment (TMCE), and this also applies to BFD traffic. Because the BFD congestion control mechanism is considered complex and immature, BFD for Geneve MUST be used within a TMCE unless BFD is really congestion controlled. As an alternative, a TMCE operator is required to provision the BFD transmission rates to avoid congestion and false failure detection.
Security issues from RFC 8926 and RFC 5880 apply. Since Geneve has no inherent security mechanisms, BFD authentication as in RFC 5880 is RECOMMENDED. The document also warns about session overload: with N VAPs on each of two NVEs using Ethernet payloads, there could be N squared BFD sessions. There SHOULD be a mechanism to limit how many are active, and running N sessions that cover all the VAPs is recommended instead.
The document has no IANA actions.
Too many check-in calls can clog the line, so the rules say to keep them under control. And since the tunnel has no lock of its own, use BFD's password feature.