| 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
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.
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"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. 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.
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
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.
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
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].
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].
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:
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.
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.
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.
Support for echo BFD is outside the scope of this document.
This specification has no IANA action requested. This section may be deleted before the publication.
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 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.
Reshad Rahman rrahman@cisco.com Cisco
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.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC5880] | Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010. |
| [RFC5881] | Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, DOI 10.17487/RFC5881, June 2010. |
| [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. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [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. |
| [RFC8365] | Sajassi, A., Drake, J., 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. |