BFD S. Pallagatti, Ed.
Internet-Draft VMware
Intended status: Standards Track S. Paragiri
Expires: May 4, 2020 Individual Contributor
V. Govindan
M. Mudigonda
Cisco
G. Mirsky
ZTE Corp.
November 1, 2019
BFD for VXLAN
draft-ietf-bfd-vxlan-08
Abstract
This document describes the use of the Bidirectional Forwarding
Detection (BFD) protocol in point-to-point Virtual eXtensible Local
Area Network (VXLAN) tunnels forming up an overlay network.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Deployment . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. BFD Packet Transmission over VXLAN Tunnel . . . . . . . . . . 5
5. Reception of BFD Packet from VXLAN Tunnel . . . . . . . . . . 7
5.1. Demultiplexing of the BFD Packet . . . . . . . . . . . . 8
6. Use of the Specific VNI . . . . . . . . . . . . . . . . . . . 8
7. Echo BFD . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informational References . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
"Virtual eXtensible Local Area Network" (VXLAN) [RFC7348] provides an
encapsulation scheme that allows building 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 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 [RFC7348]. Another use is as an encapsulation for
Ethernet VPN [RFC8365].
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 as a VXLAN tunnel is terminated on a VTEP.
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VTEPs are responsible for encapsulating and decapsulating frames
exchanged among VMs.
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 [RFC5880], is
used to monitor a p2p VXLAN tunnel.
In the case where a Multicast Service Node (MSN) (as described in
Section 3.3 of [RFC8293]) resides behind a Network Virtualization
Endpoint (NVE), the mechanisms described in this document apply and
can, therefore, be used to test the connectivity from the source NVE
to the MSN.
This document describes the use of Bidirectional Forwarding Detection
(BFD) protocol to enable monitoring continuity of the path between
VXLAN VTEPs, performing as Network Virtualization Endpoints, and/or
availability of a replicator multicast service node.
2. Conventions used in this document
2.1. Terminology
BFD Bidirectional Forwarding Detection
CC Continuity Check
p2p Point-to-point
MSN Multicast Service Node
NVE Network Virtualization Endpoint
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
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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Deployment
Figure 1 illustrates the scenario with two servers, each of them
hosting two VMs. The servers host VTEPs that terminate two VXLAN
tunnels with VXLAN Network Identifier (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). 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. BFD packets intended for a VTEP MUST
NOT be forwarded to a VM as a VM may drop BFD packets leading to a
false negative. This method is applicable whether the VTEP is a
virtual or physical device.
+------------+-------------+
| 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 |
+--------------------------+
Figure 1: Reference VXLAN Domain
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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.
In such case, for VTEPs BFD Control packets of that session are
indistinguishable from data packets.
As per Section 4, the inner destination IP address SHOULD be set to
one of the loopback addresses (127/8 range for IPv4 and
0:0:0:0:0:FFFF:7F00:0/104 range for IPv6). There could be a firewall
configured on VTEP to block loopback addresses if set as the
destination IP in the inner IP header. It is RECOMMENDED to allow
addresses from the loopback range through a firewall only if it is
used as the destination IP address in the inner IP header, and the
destination UDP port is set to 3784 [RFC5881].
4. BFD Packet Transmission over VXLAN Tunnel
BFD packet MUST be encapsulated and sent to a remote VTEP as
explained in this section. Implementations SHOULD ensure that the
BFD packets follow the same lookup 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 Section 5 of [RFC7348]. The Outer IP/UDP
and VXLAN headers MUST be encoded by the sender as defined in
[RFC7348].
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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 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: VXLAN Encapsulation of BFD Control Packet
The BFD packet MUST be carried inside the inner Ethernet frame of the
VXLAN packet. The choice of Destination 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:
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Destination MAC: This MUST NOT be of one of tenant's MAC
addresses. The destination MAC address MAY be the address
associated with the destination VTEP. The MAC address MAY be
configured, or it MAY be learned via a control plane protocol.
The details of how the MAC address is obtained are outside the
scope of this document.
Source MAC: MAC address associated with the originating VTEP
IP header:
Destination IP: 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, for IPv6 - from the range
0:0:0:0:0:FFFF:7F00:0/104. 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 1 to ensure that the BFD
packet is not routed within the Layer 3 underlay network. This
addresses the scenario when the inner IP destination address is
of VXLAN gateway and there is a router in underlay which
removes the VXLAN header, then it is possible to route the
packet as VXLAN gateway address is routable address.
The fields of the UDP header and the BFD Control packet are
encoded as specified in [RFC5881].
5. Reception of BFD Packet from VXLAN Tunnel
Once a packet is received, VTEP MUST validate the packet. If the
Destination MAC of the inner Ethernet frame matches one of the MAC
addresses associated with the VTEP the packet MUST be processed
further. If the Destination MAC of the inner Ethernet frame doesn't
match any of VTEP's MAC addresses, then the processing of the
received VXLAN packet MUST follow the procedures described in
Section 4.1 [RFC7348]. If the BFD session is using the Management
VNI (Section 6), BFD Control packets with unknown MAC address MUST
NOT be forwarded to VMs.
The UDP destination port and the TTL of the inner IP packet MUST be
validated to determine if the received packet can be processed by
BFD.
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5.1. Demultiplexing of the BFD Packet
Demultiplexing of IP BFD packet has been defined in Section 3 of
[RFC5881]. Since multiple BFD sessions may be running between two
VTEPs, there needs to be a mechanism for demultiplexing received BFD
packets to the proper session. For demultiplexing packets with Your
Discriminator equal to 0, a BFD session MUST be identified using the
logical link over which the BFD Control packet is received. In the
case of VXLAN, the VNI number identifies that logical link. If BFD
packet is received with non-zero Your Discriminator, then BFD session
MUST be demultiplexed only with Your Discriminator as the key.
6. Use of the Specific 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. When the single BFD session is used to monitor the
reachability of the remote VTEP, an implementation SHOULD choose any
of the VNIs. An implementation MAY support the use of the Management
VNI as control and management channel between VTEPs. The selection
of the VNI number of the Management VNI MUST be controlled through
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.
7. Echo BFD
Support for echo BFD is outside the scope of this document.
8. IANA Considerations
This specification has no IANA action requested. This section may be
deleted before the publication.
9. Security Considerations
The document requires setting the inner IP TTL to 1, which could be
used as a DDoS attack vector. Thus the implementation MUST have
throttling in place to control the rate of BFD Control packets sent
to the control plane. On the other hand, over-aggressive throttling
of BFD Control packets may become the cause of the inability to form
and maintain BFD session at scale. Hence, throttling of BFD Control
packets SHOULD be adjusted to permit BFD to work according to its
procedures.
If the implementation supports establishing multiple BFD sessions
between the same pair of VTEPs, there SHOULD be a mechanism to
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control the maximum number of such sessions that can be active at the
same time.
Other than inner IP TTL set to 1 and limit the number of BFD sessions
between the same pair of VTEPs, this specification does not raise any
additional security issues beyond those of the specifications
referred to in the list of normative references.
10. Contributors
Reshad Rahman
rrahman@cisco.com
Cisco
11. Acknowledgments
Authors would like to thank Jeff Haas of Juniper Networks for his
reviews and feedback on this material.
Authors would also like to thank Nobo Akiya, Marc Binderberger,
Shahram Davari, Donald E. Eastlake 3rd, and Anoop Ghanwani for the
extensive reviews and the most detailed and helpful comments.
12. References
12.1. 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>.
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[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>.
[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>.
12.2. Informational References
[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>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
Authors' Addresses
Santosh Pallagatti (editor)
VMware
Email: santosh.pallagatti@gmail.com
Sudarsan Paragiri
Individual Contributor
Email: sudarsan.225@gmail.com
Vengada Prasad Govindan
Cisco
Email: venggovi@cisco.com
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Mallik Mudigonda
Cisco
Email: mmudigon@cisco.com
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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