Active OAM for use in Geneve

Introduction Geneve 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 , utilize specially constructed packets injected into the network. OAM protocols such as ICMP/ICMPv6 ( and respectively), Bidirectional Forwarding Detection (BFD) , and Simple Two-way Active Measurement Protocol (STAMP) 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:

In-band OAM is an active or hybrid OAM method, as defined in , that traverses the same set of links and interfaces and receives the same Quality of Service treatment as the monitored object. In this context, the monitored object refers to either the Geneve tunnel as a whole or a specific tenant flow within a given Geneve tunnel.

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 the tenant-facing interface of the Network Virtualization Edge (NVE) or another device acting as a Geneve tunnel endpoint. Testing end-to-end between tenants is out of scope. For simplicity, this document uses an NVE to represent the Geneve tunnel endpoint. 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), 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.

Conventions used in this document

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 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

The Applicability of Active OAM Protocols in Geneve Networks

Requirements for 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 same fate as the data traffic of the monitored Geneve tunnel. Specifically, the OAM test packets MUST be in-band with the monitored traffic and follow the same overlay and transport path as packets carrying data payloads in the forward direction, i.e., from the ingress toward the egress endpoint(s) of the OAM test.

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 .

Requirement 2: The encapsulation of OAM control messages and data packets in the underlay network MUST be indistinguishable from each other from the underlay network IP forwarding point of view.
Requirement 3: The presence of an OAM control message in a Geneve packet MUST be unambiguously identifiable to Geneve functionality, such as 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, 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:

Requirement 5: There MUST be a way to encode entropy information into the underlay forwarding scheme so that OAM packets take the same dataflow paths as the transit traffic flows.

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 by the system that supports this specification 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 ICMP echo request/reply 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. An example of the realization of that scenario is discussed in .

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

Active 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. describes the use of IP encapsulation for BFD.

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 version. For IPv6, the address MUST be selected from the Dummy IPv6 Range for IPv6 .
: Source IP: IP address of the NVE.
: TTL or Hop Limit: MUST be set to 255 per . The receiver of an active OAM Geneve packet with IP/UDP encapsulation MUST drop packets whose TTL/Hop Limit is not 255.

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.