BFD S. Pallagatti, Ed.
Internet-Draft Rtbrick
Intended status: Standards Track S. Paragiri
Expires: June 29, 2019 Juniper Networks
V. Govindan
M. Mudigonda
Cisco
G. Mirsky
ZTE Corp.
December 26, 2018
BFD for VXLAN
draft-ietf-bfd-vxlan-06
Abstract
This document describes the use of the Bidirectional Forwarding
Detection (BFD) protocol in Virtual eXtensible Local Area Network
(VXLAN) overlay networks.
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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 . . . . . . . . . . . . . . . . . . 4
3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Deployment . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. BFD Packet Transmission over VXLAN Tunnel . . . . . . . . . . 6
5.1. BFD Packet Encapsulation in VXLAN . . . . . . . . . . . . 7
6. Reception of BFD packet from VXLAN Tunnel . . . . . . . . . . 8
6.1. Demultiplexing of the BFD packet . . . . . . . . . . . . 8
7. Use of reserved VNI . . . . . . . . . . . . . . . . . . . . . 9
8. Echo BFD . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
13.1. Normative References . . . . . . . . . . . . . . . . . . 10
13.2. Informational References . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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 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, discussed in section 3 [RFC7348], by providing Layer 2
overlay scheme on a Layer 3 network. 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 VTEPs in hypervisors. However, the
concepts are equally applicable to non-virtualized hosts attached to
VTEPs in switches.
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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 VXLAN
Tunnel End Point (VTEP) (hypervisor/TOR). VTEPs (hypervisor/TOR) are
responsible for encapsulating and decapsulating frames exchanged
among VMs.
Ability to monitor path continuity, i.e., perform proactive
continuity check (CC) for these tunnels, is important. The
asynchronous mode of BFD, as defined in [RFC5880], can be used to
monitor a VXLAN tunnel. Use of [I-D.ietf-bfd-multipoint] is for
future study.
Also, BFD in VXLAN can be used to monitor the particular service
nodes that are designated to handle Layer 2 broadcast properly,
unknown unicast, and multicast traffic. Such nodes, discussed in
details in [RFC8293], are often referred to as "replicators", are
usually virtual VTEPs and can be monitored by physical VTEPs to
minimize BUM traffic directed to the unavailable replicator.
This document describes the use of Bidirectional Forwarding Detection
(BFD) protocol VXLAN to enable monitoring continuity of the path
between Network Virtualization Edges (NVEs) and/or availability of a
replicator service node using BFD.
In this document, the terms NVE and VTEP are used interchangeably.
2. Conventions used in this document
2.1. Terminology
BFD - Bidirectional Forwarding Detection
CC - Continuity Check
NVE - Network Virtualization Edge
TOR - Top of Rack
VM - Virtual Machine
VTEP - VXLAN Tunnel End Point
VXLAN - Virtual eXtensible Local Area Network
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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. Use cases
The primary use case of BFD for VXLAN is for continuity check of a
tunnel. By exchanging BFD control packets between VTEPs, an operator
exercises the VXLAN path in both the underlay and overlay thus
ensuring the VXLAN path availability and VTEPs reachability. BFD
failure detection can be used for maintenance. There are other use
cases such as the following:
Layer 2 VMs:
Deployments might have VMs with only L2 capabilities and not
have an IP address assigned or, in other cases, VMs are
assigned IP address but are restricted to communicate only
within their subnet. BFD being an L3 protocol can be used as a
tunnel CC mechanism, where BFD will start and terminate at the
NVEs, e.g., VTEPs.
It is possible to aggregate the CC sessions for multiple
tenants by running a BFD session between the VTEPs over VxLAN
tunnel.
Fault localization:
It is also possible that VMs are L3 aware and can host a BFD
session. In these cases, BFD sessions can be established among
VMs for CC. Also, BFD sessions can be created among VTEPs for
tunnel CC. Having a hierarchical OAM model helps localize
faults though it requires additional consideration of, for
example, coordination of BFD intervals across the OAM layers
Service node reachability:
The service node is responsible for sending BUM traffic. In
case a service node tunnel terminates at a VTEP, and that VTEP
might not even host VM. BFD session between TOR/hypervisor and
service node can be used to monitor service node reachability.
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4. 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 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). The
implementation SHOULD have a reasonable upper bound on the number of
BFD sessions that can be created between the same pair of VTEPs. No
BFD packets intended for a Hypervisor VTEP should 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.
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+------------+-------------+
| Server 1 |
| |
| +----+----+ +----+----+ |
| |VM1-1 | |VM1-2 | |
| |VNI 100 | |VNI 200 | |
| | | | | |
| +---------+ +---------+ |
| Hypervisor VTEP (IP1) |
+--------------------------+
|
|
|
| +-------------+
| | Layer 3 |
|---| Network |
| |
+-------------+
|
|
+-----------+
|
|
+------------+-------------+
| Hypervisor VTEP (IP2) |
| +----+----+ +----+----+ |
| |VM2-1 | |VM2-2 | |
| |VNI 100 | |VNI 200 | |
| | | | | |
| +---------+ +---------+ |
| Server 2 |
+--------------------------+
Figure 1: Reference VXLAN domain
5. BFD Packet Transmission over VXLAN Tunnel
BFD packet MUST be encapsulated and sent to a remote VTEP as
explained in Section 5.1. Implementations SHOULD ensure that the BFD
packets follow the same lookup path as VXLAN data packets within the
sender system.
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5.1. BFD Packet Encapsulation in VXLAN
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].
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 Message ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: VXLAN Encapsulation of BFD Control Message
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The BFD packet MUST be carried inside the inner MAC frame of the
VXLAN packet. The inner MAC frame carrying the BFD payload has the
following format:
Ethernet Header:
Destination MAC: This MUST be the dedicated MAC TBA (Section 9)
or the MAC address of the destination VTEP. The details of how
the MAC address of the destination VTEP is obtained are outside
the scope of this document.
Source MAC: MAC address of the originating VTEP
IP header:
Source IP: IP address of the originating VTEP.
Destination IP: IP address of the terminating VTEP.
TTL: MUST be set to 1 to ensure that the BFD packet is not
routed within the L3 underlay network.
The fields of the UDP header and the BFD control packet are
encoded as specified in [RFC5881] for p2p VXLAN tunnels.
6. Reception of BFD packet from VXLAN Tunnel
Once a packet is received, VTEP MUST validate the packet as described
in Section 4.1 of [RFC7348]. If the Destination MAC of the inner MAC
frame matches the dedicated MAC or the MAC address of the VTEP the
packet MUST be processed further.
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. BFD packet with inner MAC set to VTEP or dedicated MAC address
MUST NOT be forwarded to VMs.
To ensure BFD detects the proper configuration of VXLAN Network
Identifier (VNI) in a remote VTEP, a lookup SHOULD be performed with
the MAC-DA and VNI as key in the Virtual Forwarding Instance (VFI)
table of the originating/terminating VTEP to exercise the VFI
associated with the VNI.
6.1. 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
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packets to the proper session. The procedure for demultiplexing
packets with Your Discriminator equal to 0 is different from
[RFC5880]. For such packets, the BFD session MUST be identified
using the inner headers, i.e., the source IP, the destination IP, and
the source UDP port number present in the IP header carried by the
payload of the VXLAN encapsulated packet. The VNI of the packet
SHOULD be used to derive interface-related information for
demultiplexing the packet. If BFD packet is received with non-zero
Your Discriminator, then BFD session MUST be demultiplexed only with
Your Discriminator as the key.
7. Use of reserved 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 in common. When the single BFD session is used to
monitor reachability of the remote VTEP, an implementation SHOULD use
a VNI of 0.
8. Echo BFD
Support for echo BFD is outside the scope of this document.
9. IANA Considerations
IANA has assigned TBA as a dedicated MAC address from the IANA 48-bit
unicast MAC address registry to be used as the Destination MAC
address of the inner Ethernet of VXLAN when carrying BFD control
packets.
10. 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. Throttling MAY be relaxed for BFD packets
based on port number.
The implementation SHOULD have a reasonable upper bound on the number
of BFD sessions that can be created between the same pair of VTEPs.
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.
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11. Contributors
Reshad Rahman
rrahman@cisco.com
Cisco
12. 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.
13. References
13.1. Normative References
[I-D.ietf-bfd-multipoint]
Katz, D., Ward, D., Networks, J., and G. Mirsky, "BFD for
Multipoint Networks", draft-ietf-bfd-multipoint-19 (work
in progress), December 2018.
[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>.
[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>.
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[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>.
13.2. 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)
Rtbrick
Email: santosh.pallagatti@gmail.com
Sudarsan Paragiri
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, California 94089-1206
USA
Email: sparagiri@juniper.net
Vengada Prasad Govindan
Cisco
Email: venggovi@cisco.com
Mallik Mudigonda
Cisco
Email: mmudigon@cisco.com
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Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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