| Internet-Draft | Active OAM for use in GENEVE | November 2024 |
| Mirsky, et al. | Expires 1 June 2025 | [Page] |
Geneve (Generic Network Virtualization Encapsulation) is a flexible and extensible network virtualization overlay protocol designed to encapsulate network packets for transport across underlying physical networks. This document specifies the requirements and provides a framework for Operations, Administration, and Maintenance (OAM) in Geneve networks. It outlines the OAM functions necessary to monitor, diagnose, and troubleshoot Geneve overlay networks to ensure proper operation and performance. The document aims to guide the implementation of OAM mechanisms within the Geneve protocol to support network operators in maintaining reliable and efficient virtualized network environments.¶
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Geneve [RFC8926] is designed to support various scenarios of network virtualization. It encapsulates multiple protocols, such as Ethernet and IPv4/IPv6, and includes metadata within the Geneve message.¶
Operations, Administration, and Maintenance (OAM) protocols provide fault management and performance monitoring functions necessary for comprehensive network operation. Active OAM protocols, as defined in [RFC7799], utilize specially constructed packets injected into the network. OAM protocols such as ICMP/ICMPv6 ([RFC0792] and [RFC4443] respectively), Bidirectional Forwarding Detection (BFD) [RFC5880], and Simple Two-way Active Measurement Protocol (STAMP) [RFC8762] are example of active OAM protocols. To ensure that performance metrics or detected failures are accurately related to a particular Geneve flow, it is critical that these OAM test packets share fate, i.e., are in-band, with the overlay data packets of that monitored flow when traversing the underlay network. In this document "in-band OAM" is interpreted as follows:¶
Section 2.1 of this document lists the general requirements for active OAM protocols in the Geneve overlay network. IP encapsulation meets these requirements and is suitable for encapsulating active OAM protocols within a Geneve overlay network. Active OAM messages in a Geneve overlay network are exchanged between two Geneve tunnel endpoints, which may be a Network Virtualization Edge (NVE) or another device acting as a Geneve tunnel endpoint. For simplicity, this document uses an NVE to represent the Geneve tunnel endpoint. Refer to [RFC7365] and [RFC8014] for detailed definitions and descriptions of an NVE.¶
The IP encapsulation of Geneve OAM defined in this document applies to an overlay service by introducing a Management Virtual Network Identifier (VNI), which can be used in combination with various values of the Protocol Type field in the Geneve header, such as Ethertypes for IPv4 or IPv6. The analysis and definition of other types of OAM encapsulation in Geneve are outside the scope of this document.¶
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.¶
Geneve: Generic Network Virtualization Encapsulation¶
NVO3: Network Virtualization over Layer 3¶
OAM: Operations, Administration, and Maintenance¶
VNI: Virtual Network Identifier¶
BFD: Bidirectional Forwarding Detection¶
STAMP: Simple Two-way Active Measurement Protocol¶
NVE: Network Virtualization Edge¶
OAM protocols, whether part of fault management or performance monitoring, are intended to provide reliable information that can be used to detect a failure, identify the defect and localize it, thus helping to identify and apply corrective actions to minimize the negative impact on service. Several OAM protocols are used to perform these functions; these protocols require demultiplexing at the receiving instance of Geneve. To improve the accuracy of the correlation between the condition experienced by the monitored Geneve tunnel and the state of the OAM protocol the OAM encapsulation is required to comply with the following requirements:¶
An OAM protocol MAY be employed to monitor an entire Geneve tunnel. In this case, test packets could be in-band relative to a subset of tenant flows transported over the Geneve tunnel. If the goal is to monitor the conditions experienced by the flow of a particular tenant, the test packets MUST be in-band with that specific flow within the Geneve tunnel. Both scenarios are discussed in detail in Section 2.2.¶
A test packet generated by an active OAM protocol, whether for defect detection or performance measurement, MUST be in-band with the tunnel or data flow being monitored, as specified in Requirement 1. In environments where multiple paths through the domain are available, underlay transport nodes can be programmed to use characteristic information to balance the load across known paths. It is essential that test packets follow the same route - that is, traverse the same set of nodes and links as a data packet of the monitored flow. Therefore, the following requirement supports OAM packet fate-sharing with the data flow:¶
This section considers two scenarios where active OAM is used to detect and localize defects in a Geneve network. Figure 1 presents an example of a Geneve domain.¶
+--------+ +--------+
| Tenant +--+ +----| Tenant |
| VNI 28 | | | | VNI 35 |
+--------+ | ................ | +--------+
| +----+ . . +----+ |
| | NVE|--. .--| NVE| |
+--| A | . . | B |---+
+----+ . . +----+
/ . .
/ . Geneve .
+--------+ / . Network .
| Tenant +--+ . .
| VNI 35 | . .
+--------+ ................
|
+----+
| NVE|
| C |
+----+
|
|
=====================
| |
+--------+ +--------+
| Tenant | | Tenant |
| VNI 28 | | VNI 35 |
+--------+ +--------+
In the first case, consider when a communication problem between Network Virtualization Edge (NVE) device A and NVE C exists. Upon the investigation, the operator discovers that the forwarding in the IP underlay network is working accordingly. Still, the Geneve connection is unstable for all NVE A and NVE C tenants. Detection, troubleshooting, and localization of the problem can be done regardless of the VNI value.¶
In the second case, traffic on VNI 35 between NVE A and NVE B has no problems, as on VNI 28 between NVE A and NVE C. But traffic on VNI 35 between NVE A and NVE C experiences problems, for example, excessive packet loss.¶
The first case can be detected and investigated using any VNI value, whether it connects tenant systems or not; however, to conform to Requirement#4 (Section 2.1) OAM test packets SHOULD be transmitted on a VNI that doesn't have any tenants. Such a Geneve tunnel is dedicated to carrying only control and management data between the tunnel endpoints, hence it is referred to as a Geneve control channel and that VNI is referred to as the Management VNI. A configured VNI MAY be used to identify the control channel, but it is RECOMMENDED that the default value 1 be used as the Management VNI. Encapsulation of test packets using the Management VNI is discussed in Section 2.3.¶
The control channel of a Geneve tunnel MUST NOT carry tenant data. As no tenants are connected using the control channel, a system that supports this specification, MUST NOT forward a packet received over the control channel to any tenant. A packet received over the control channel MUST be forwarded if and only if it is sent onto the control channel of the concatenated Geneve tunnel. Else, it MUST be terminated locally. The Management VNI SHOULD be terminated on the tenant-facing side of the Geneve encapsulation/decapsulation functionality, not the DC-network-facing side (per definitions in Section 4 of [RFC8014]) so that Geneve encap/decap functionality is included in its scope. This approach causes an active OAM packet, e.g., an ICMP echo request, to be decapsulated in the same fashion as any other received Geneve packet. In this example, the resulting ICMP packet is handed to NVE's local management functionality for the processing which generates an ICMP echo reply. The ICMP echo reply is encapsulated in Geneve as specified in Section 2.3. for forwarding back to the NVE that sent the echo request. One advantage of this approach is that a repeated ping test could detect an intermittent problem in Geneve encap/decap hardware, which would not be tested if the Management VNI were handled as a "special case" at the DC-network-facing interface.¶
The second case is when a test packet is transmitted using the VNI value associated with the monitored service flow. By doing that, the test packet experiences network treatment as the tenant's packets. Details of that use case are outside the scope of this specification.¶
ICMP and ICMPv6 ([RFC0792] and [RFC4443] respectively) , as noted above, are examples of an active OAM protocol. They provide required on-demand defect detection and failure localization. ICMP control messages immediately follow the inner IP header encapsulated in Geneve. ICMP extensions for Geneve networks use mechanisms defined in [RFC4884].¶
Active OAM over a Management VNI in the Geneve network uses an IP encapsulation. Protocols such as BFD [RFC5880] and STAMP [RFC8762] use UDP transport. The destination UDP port number in the inner UDP header (Figure 2) identifies the OAM protocol. This approach is well-known and has been used, for example, in MPLS networks [RFC8029]. To use IP encapsulation for an active OAM protocol, the Protocol Type field of the Geneve header MUST be set to the IPv4 (0x0800) or IPv6 (0x86DD) value. [RFC9521] describes the use of IP encapsulation for BFD.¶
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 IPvX Header ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Outer UDP Header ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Geneve Header ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Inner IPvX Header ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Inner UDP Header ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Active OAM Packet ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Inner IP header:¶
This document has no requirements for IANA. This section can be removed before the publication.¶
As part of a Geneve network, active OAM inherits the security considerations discussed in [RFC8926]. Additionally, a system MUST provide control to limit the rate of Geneve OAM packets punted to the Geneve control plane for processing in order to avoid overloading that control plane.¶
OAM in GENEVE packets uses the General TTL Security Mechanism [RFC5082], and any packet received with an inner TTL / Hop Count other than 255 MUST be discarded.¶
The authors express their appreciation to Donald E. Eastlake 3rd for his suggestions that improved the readability of the document.¶