Bidirectional Forwarding Detection (BFD) for Virtual eXtensible Local Area Network (VXLAN)VMwaresantosh.pallagatti@gmail.comZTE Corp.gregimirsky@gmail.comIndividual Contributorsudarsan.225@gmail.comCiscovenggovi@cisco.comCiscommudigon@cisco.com
Routing
BFDBFDBFD for VXLANThis document describes the use of the Bidirectional Forwarding Detection (BFD) protocol
in point-to-point Virtual eXtensible Local Area Network (VXLAN) tunnels
used to form an overlay network.Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
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approved by the IESG are candidates for any level of Internet
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Table of Contents
. Introduction
. Conventions Used in This Document
. Abbreviations
. Requirements Language
. Deployment
. Use of the Management VNI
. BFD Packet Transmission over VXLAN Tunnel
. Reception of BFD Packet from VXLAN Tunnel
. Echo BFD
. IANA Considerations
. Security Considerations
. References
. Normative References
. Informative References
Acknowledgments
Contributors
Authors' Addresses
Introduction
"Virtual eXtensible Local Area Network (VXLAN)" provides
an encapsulation scheme that allows the building of an overlay network by
decoupling the address space of the attached virtual hosts from that of the network.
One use of VXLAN is in data centers interconnecting virtual machines (VMs)
of a tenant. VXLAN addresses the requirements of the Layer 2 and
Layer 3 data-center network infrastructure in the presence of VMs in a multi-tenant environment by
providing a Layer 2 overlay scheme on a Layer 3 network .
Another use is as an encapsulation for Ethernet VPN .
This document is written assuming the use of VXLAN for virtualized
hosts and refers to VMs and VXLAN Tunnel End Points (VTEPs) in hypervisors. However, the
concepts are equally applicable to non-virtualized hosts attached to
VTEPs in switches.
In the absence of a router in the overlay, a VM can communicate with another VM only if they are on the same VXLAN segment.
VMs are unaware of VXLAN tunnels, because a VXLAN tunnel is terminated on a VTEP.
VTEPs are responsible for encapsulating and decapsulating frames exchanged among
VMs.
The ability to monitor path continuity -- i.e., perform proactive
continuity check (CC) for point-to-point (p2p) VXLAN tunnels -- is
important.
The asynchronous mode of BFD, as defined in , is used to monitor a p2p VXLAN tunnel.
In the case where a Multicast Service Node (MSN) (as described in
) participates in VXLAN, the
mechanisms described in this
document apply and can, therefore, be used to test the continuity of the path between
the source Network Virtualization Endpoint (NVE) and the MSN.
This document describes the use of the Bidirectional Forwarding Detection (BFD) protocol
to enable monitoring continuity of the path between VXLAN VTEPs that are
performing as VNEs,
and/or between the source NVE and a replicator MSN using a Management
VXLAN Network Identifier (VNI) ().
All other uses of the specification to test toward other VXLAN endpoints are out of scope.
Conventions Used in This DocumentAbbreviations
BFD:
Bidirectional Forwarding Detection
CC:
Continuity Check
FCS:
Frame Check Sequence
MSN:
Multicast Service Node
NVE:
Network Virtualization Endpoint
p2p:
Point-to-point
VFI:
Virtual Forwarding Instance
VM:
Virtual Machine
VNI:
VXLAN Network Identifier (or VXLAN Segment ID)
VTEP:
VXLAN Tunnel End Point
VXLAN:
Virtual eXtensible Local Area Network
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
when, and only when, they appear in all capitals, as shown here.
Deployment illustrates a scenario with two servers: each hosting two VMs.
The servers host VTEPs that terminate two VXLAN tunnels with VNI number 100
and 200, respectively. Separate BFD sessions can be
established between the VTEPs (IP1 and IP2) for monitoring
each of the VXLAN tunnels (VNI 100 and 200). Using a BFD session to monitor a set of VXLAN VNIs
between the same pair of VTEPs might help to detect and localize problems caused by misconfiguration.
An implementation that supports this specification MUST
be able to control the number of BFD sessions
that can be created between the same pair of VTEPs.
This method is applicable whether the VTEP is a virtual or physical device.
Reference VXLAN Domain
+------------+-------------+
| Server 1 |
| +----+----+ +----+----+ |
| |VM1-1 | |VM1-2 | |
| |VNI 100 | |VNI 200 | |
| | | | | |
| +---------+ +---------+ |
| VTEP (IP1) |
+--------------------------+
|
| +-------------+
| | Layer 3 |
+---| Network |
+-------------+
|
+-----------+
|
+------------+-------------+
| VTEP (IP2) |
| +----+----+ +----+----+ |
| |VM2-1 | |VM2-2 | |
| |VNI 100 | |VNI 200 | |
| | | | | |
| +---------+ +---------+ |
| Server 2 |
+--------------------------+
At the same time, a service-layer BFD session may be used between the
tenants of VTEPs IP1 and IP2
to provide end-to-end fault management; this use case is outside the
scope of this document. In
such a case, for VTEPs, the BFD Control packets of that session are
indistinguishable from data packets.
For BFD Control packets encapsulated in VXLAN (),
the inner destination IP address
SHOULD be set to one of the loopback addresses from
127/8 range for IPv4 or to one of IPv4-mapped IPv6 loopback addresses from ::ffff:127.0.0.0/104 range for IPv6.
Use of the Management VNI
In most cases, a single BFD session is sufficient for the given VTEP to monitor
the reachability of a remote VTEP, regardless of the number of VNIs.
BFD control messages MUST be sent using the Management VNI, which acts
as the control and management channel between VTEPs.
An implementation MAY support operating BFD on another
(non-Management) VNI, although the implications of this are outside
the scope of this document. The selection of the VNI number
of the Management VNI MUST be controlled through a management plane. An implementation MAY use VNI number 1 as
the default value for the Management VNI. All VXLAN packets received on the Management VNI MUST be processed locally
and MUST NOT be forwarded to a tenant.
BFD Packet Transmission over VXLAN Tunnel
BFD packets MUST be encapsulated and sent to a remote VTEP as explained in this section.
Implementations SHOULD ensure that the BFD packets follow the same
forwarding path as VXLAN data packets within the sender system.
BFD packets are encapsulated in VXLAN as described below.
The VXLAN packet format is defined in
.
The value in the VNI field of the VXLAN header MUST
be set to the value selected as the Management VNI.
The outer IP/UDP and VXLAN headers MUST
be encoded by the sender, as defined in .VXLAN Encapsulation of BFD Control Packet
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 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ VXLAN Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner Ethernet Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner IPvX Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Inner UDP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer Ethernet FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The BFD packet MUST be carried inside the inner Ethernet frame of the VXLAN packet.
The choice of destination Media Access Control (MAC) and destination
IP addresses for the inner Ethernet frame MUST
ensure that the BFD Control packet is not forwarded to a tenant but is processed locally at the remote VTEP.
The inner Ethernet frame carrying the BFD Control packet has the following format:
Ethernet Header:
Destination MAC:
A Management VNI, which does not have
any tenants, will have no dedicated MAC address for decapsulated
traffic. The value 00-52-02 SHOULD be used in
this field.
Source MAC:
MAC address associated with the originating VTEP.
Ethertype:
This is set to 0x0800 if the inner IP header is
IPv4 and set to 0x86DD if the inner IP header is IPv6.
IP header:
Destination IP:
This IP address MUST NOT be of one of tenant's IP addresses.
The IP address SHOULD be selected
from the range 127/8 for IPv4 and from the range
::ffff:127.0.0.0/104 for IPv6.
Alternatively, the destination IP address MAY be set to VTEP's IP address.
Source IP:
IP address of the originating VTEP.
TTL or Hop Limit:
MUST be set to 255, in
accordance with .
The destination UDP port is set to 3784 and the fields of the
BFD Control packet are encoded as specified in .Reception of BFD Packet from VXLAN Tunnel
Once a packet is received, the VTEP MUST validate the packet.
If the packet is received on the Management VNI and is identified as a
BFD Control packet addressed to the VTEP,
then the packet can be processed further. Processing of BFD Control
packets received on a non-Management VNI
is outside the scope of this specification.
The received packet's inner IP payload is then validated according to
Sections
and in .
Echo BFDSupport for echo BFD is outside the scope of this document.IANA Considerations
IANA has assigned a single MAC address of the value 00-52-02 from the "Unassigned (small allocations)" block of the "IANA Unicast 48-bit MAC Addresses" registry as follows:
the "Usage" field is "BFD for VXLAN". The "Reference" is this document.
Security Considerations
Security issues discussed in , , and
apply to this document.
This document recommends using an address from the internal host loopback addresses
127/8 range for IPv4, or an IP4-mapped IPv6 loopback address from the
::ffff:127.0.0.0/104 range for IPv6,
as the destination IP address in the inner IP header. Using such an address prevents
the forwarding of the encapsulated BFD control message by a transient
node, in case the VXLAN tunnel is broken, in
accordance with .
The use of IPv4-mapped IPv6 addresses
has the same property as using the IPv4 network 127/8. Moreover, the IPv4-mapped
IPv6 addresses' prefix is not advertised in any routing protocol.
If the implementation supports establishing multiple BFD sessions
between the same pair of VTEPs, there SHOULD be a mechanism
to control the maximum number of such sessions that can be active
at the same time.
ReferencesNormative ReferencesRequirements for IP Version 4 RoutersThis memo defines and discusses requirements for devices that perform the network layer forwarding function of the Internet protocol suite. [STANDARDS-TRACK]Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Bidirectional Forwarding Detection (BFD)This document describes a protocol intended to detect faults in the bidirectional path between two forwarding engines, including interfaces, data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. It operates independently of media, data protocols, and routing protocols. [STANDARDS-TRACK]Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)This document describes the use of the Bidirectional Forwarding Detection (BFD) protocol over IPv4 and IPv6 for single IP hops. [STANDARDS-TRACK]Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 NetworksThis document describes Virtual eXtensible Local Area Network (VXLAN), which is used to address the need for overlay networks within virtualized data centers accommodating multiple tenants. The scheme and the related protocols can be used in networks for cloud service providers and enterprise data centers. This memo documents the deployed VXLAN protocol for the benefit of the Internet community.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Informative ReferencesA Framework for Multicast in Network Virtualization over Layer 3This document provides a framework for supporting multicast traffic in a network that uses Network Virtualization over Layer 3 (NVO3). Both infrastructure multicast and application-specific multicast are discussed. It describes the various mechanisms that can be used for delivering such traffic as well as the data plane and control plane considerations for each of the mechanisms.A Network Virtualization Overlay Solution Using Ethernet VPN (EVPN)This document specifies how Ethernet VPN (EVPN) can be used as a Network Virtualization Overlay (NVO) solution and explores the various tunnel encapsulation options over IP and their impact on the EVPN control plane and procedures. In particular, the following encapsulation options are analyzed: Virtual Extensible LAN (VXLAN), Network Virtualization using Generic Routing Encapsulation (NVGRE), and MPLS over GRE. This specification is also applicable to Generic Network Virtualization Encapsulation (GENEVE); however, some incremental work is required, which will be covered in a separate document. This document also specifies new multihoming procedures for split-horizon filtering and mass withdrawal. It also specifies EVPN route constructions for VXLAN/NVGRE encapsulations and Autonomous System Border Router (ASBR) procedures for multihoming of Network Virtualization Edge (NVE) devices.AcknowledgmentsThe authors would like to thank of
Juniper Networks for his reviews and feedback on this material.The authors would also like to thank ,
, ,
, , ,
, and for the extensive reviews
and the most detailed and constructive comments.ContributorsCiscorrahman@cisco.comAuthors' AddressesVMwaresantosh.pallagatti@gmail.comZTE Corp.gregimirsky@gmail.comIndividual Contributorsudarsan.225@gmail.comCiscovenggovi@cisco.comCiscommudigon@cisco.com