OAM for use in GENEVE

Introduction Geneve is intended to support various scenarios of network virtualization. In addition to carrying multiple protocols, e.g., Ethernet, IPv4/IPv6, the Geneve message includes metadata. Operations, Administration, and Maintenance (OAM) protocols support fault management and performance monitoring functions necessary for comprehensive network operation. Active OAM protocols, as defined in , use specially constructed packets that are injected into the network. To ensure that a performance metric or a detected failure are related to a particular Geneve flow, it is critical that these OAM test packets share fate with overlay data packets for that flow when traversing the underlay network. A set of general requirements for active OAM protocols in the Geneve overlay network is listed in . IP encapsulation conforms to these requirements and is a suitable encapsulation of active OAM protocols in a Geneve overlay network. Active OAM in a Geneve overlay network are exchanged between two Geneve tunnel endpoints, which may be an NVE (Network Virtualization Edge) or another device acting as a Geneve tunnel endpoint. For simplicity, an NVE is used to represent the Geneve tunnel endpoint. Please refer to and 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) that could be used in combination with various values of the Protocol Type field in the Geneve header, i.e., Ethertypes for IPv4 or IPv6. The analysis and definition of other types of OAM encapsulation in Geneve are outside the scope of this document.

Conventions used in this document

In-band OAM is an active OAM or hybrid OAM method () that traverses the same set of links and interfaces receiving the same QoS treatment as the monitored object, i.e., a Geneve tunnel as a whole or a particular tenant flow within given Geneve tunnel.

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.

Acronyms Geneve: Generic Network Virtualization Encapsulation NVO3: Network Virtualization Overlays OAM: Operations, Administration, and Maintenance VNI: Virtual Network Identifier

Active OAM Protocols in Geneve Networks 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:

Requirement#1: Geneve OAM test packets MUST share the fate with data traffic of the monitored Geneve tunnel, i.e., be in-band () with the monitored traffic, follow the same overlay and transport path as packets with data payload, in the forward direction, i.e. from ingress toward egress endpoint(s) of the OAM test.

An OAM protocol MAY be used to monitor the particular Geneve tunnel as a whole. In that case, test packets could be in-band relative to a sub-set of tenant flows transported over the Geneve tunnel. If the goal is to monitor the condition experienced by the flow of a particular tenant, the test packets MUST be in-band with that specific flow in the Geneve tunnel. Both scenarios are discussed in detail in .

Requirement#2: The encapsulation of OAM control messages and data packets in the underlay network MUST be indistinguishable from each other from an underlay network IP forwarding point of view.
Requirement#3: The presence of an OAM control message in the Geneve packet MUST be unambiguously identifiable to Geneve functionality, e.g., at endpoints of Geneve tunnels.
Requirement#4: OAM test packets MUST NOT be forwarded to a tenant system.

A test packet generated by an active OAM protocol, either for a defect detection or performance measurement, according to Requirement#1, MUST be in-band () with the tunnel or data flow being monitored. In an environment 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, i.e., traverses the same set of nodes and links, as a data packet of the monitored flow. Thus, the following requirement to support OAM packet fate-sharing with the data flow:

Requirement#5: It MUST be possible to express entropy for underlay Equal Cost Multipath in the Geneve encapsulation of OAM packets.

Defect Detection and Troubleshooting in Geneve Network with Active OAM This section considers two scenarios where active OAM is used to detect and localize defects in a Geneve network. presents an example of a Geneve domain.

An example of a Geneve domain 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 () 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 . 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 ) 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 . 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.

OAM Encapsulation in Geneve Active OAM over a Management VNI in the Geneve network uses an IP encapsulation. Protocols such as BFD and STAMP use UDP transport. The destination UDP port number in the inner UDP header () identifies the OAM protocol. This approach is well-known and has been used, for example, in MPLS networks . 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.

An Example of Geneve IP/UDP Encapsulation of an Active OAM Packet Inner IP header:

: Destination IP: The IP address MUST be set to the loopback address 127.0.0.1/32 for IPv4, or the loopback address ::1/128 for IPv6 .
: Source IP: IP address of the NVE.
: TTL or Hop Limit: MUST be set to 255 per .

Echo Request and Echo Reply in Geneve Tunnel ICMP and ICMPv6 ( and respectively) 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 .

IANA Considerations This document has no requirements for IANA. This section can be removed before the publication.

Security Considerations As part of a Geneve network, active OAM inherits the security considerations discussed in . 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 , and any packet received with an inner TTL / Hop Count other than 255 MUST be discarded.

Acknowledgments The authors express their appreciation to Donald E. Eastlake 3rd for his suggestions that improved the readability of the document.