RFC 9378 | IOAM Deployment | April 2023
Brockners, et al. | Informational | [Page]

Stream:
  Internet Engineering Task Force (IETF)
RFC:
  9378
Category:
  Informational
Published:
  April 2023
ISSN:
  2070-1721
Authors:
  F. Brockners, Ed.
  Cisco
  S. Bhandari, Ed.
  Thoughtspot
  D. Bernier
  Bell Canada
  T. Mizrahi, Ed.
  Huawei

# RFC 9378

# In Situ Operations, Administration, and Maintenance (IOAM) Deployment

## Abstract

In situ Operations, Administration, and Maintenance (IOAM) collects operational and telemetry information in the packet while the packet traverses a path between two points in the network. This document provides a framework for IOAM deployment and provides IOAM deployment considerations and guidance.¶

## Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9378.¶

## Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved.¶

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

## 1. Introduction

In situ Operations, Administration, and Maintenance (IOAM) collects OAM information within the packet while the packet traverses a particular network domain. The term "in situ" refers to the fact that the OAM data is added to the data packets rather than being sent within packets specifically dedicated to OAM. IOAM complements mechanisms such as Ping, Traceroute, or other active probing mechanisms. In terms of "active" or "passive" OAM, IOAM can be considered a hybrid OAM type. In situ mechanisms do not require extra packets to be sent. IOAM adds information to the already available data packets and, therefore, cannot be considered passive. In terms of the classification given in [RFC7799], IOAM could be portrayed as Hybrid Type I. IOAM mechanisms can be leveraged where mechanisms using, e.g., ICMP do not apply or do not offer the desired results. These situations could include:¶

- proving that a certain traffic flow takes a predefined path,¶
- verifying the Service Level Agreement (SLA) verification for the live data traffic,¶
- providing detailed statistics on traffic distribution paths in networks that distribute traffic across multiple paths, or¶
- providing scenarios in which probe traffic is potentially handled differently from regular data traffic by the network devices.¶

## 2. Conventions

Abbreviations used in this document:¶

BIER:
  Bit Index Explicit Replication [RFC8279]¶
Geneve:
  Generic Network Virtualization Encapsulation [RFC8926]¶
GRE:
  Generic Routing Encapsulation [RFC2784]¶
IOAM:
  In situ Operations, Administration, and Maintenance¶
MTU:
  Maximum Transmission Unit¶
NSH:
  Network Service Header [RFC8300]¶
OAM:
  Operations, Administration, and Maintenance¶
POT:
  Proof of Transit¶
VXLAN-GPE:
  Virtual eXtensible Local Area Network - Generic Protocol Extension [VXLAN-GPE]¶

## 3. IOAM Deployment: Domains and Nodes

[RFC9197] defines the scope of IOAM as well as the different types of IOAM nodes. For improved readability, this section provides a brief overview of where IOAM applies, along with explaining the main roles of nodes that employ IOAM. Please refer to [RFC9197] for further details.¶

IOAM is focused on "limited domains", as defined in [RFC8799]. IOAM is not targeted for a deployment on the global Internet. The part of the network that employs IOAM is referred to as the "IOAM-Domain". For example, an IOAM-Domain can include an enterprise campus using physical connections between devices or an overlay network using virtual connections or tunnels for connectivity between said devices. An IOAM-Domain is defined by its perimeter or edge. The operator of an IOAM-Domain is expected to put provisions in place to ensure that packets that contain IOAM data fields do not leak beyond the edge of an IOAM-Domain, e.g., using packet filtering methods. The operator should consider the potential operational impact of IOAM on mechanisms such as ECMP load-balancing schemes (e.g., load-balancing schemes based on packet length could be impacted by the increased packet size due to IOAM), path MTU (i.e., ensure that the MTU of all links within a domain is sufficiently large enough to support the increased packet size due to IOAM), and ICMP message handling.¶

An IOAM-Domain consists of "IOAM encapsulating nodes", "IOAM decapsulating nodes", and "IOAM transit nodes". The role of a node (i.e., encapsulating, transit, decapsulating) is defined within an IOAM-Namespace (see below). A node can have different roles in different IOAM-Namespaces.¶

An IOAM encapsulating node incorporates one or more IOAM Option-Types into packets that IOAM is enabled for. If IOAM is enabled for a selected subset of the traffic, the IOAM encapsulating node is responsible for applying the IOAM functionality to the selected subset.¶

An IOAM transit node updates one or more of the IOAM-Data-Fields. If both the Pre-allocated and the Incremental Trace Option-Types are present in the packet, each IOAM transit node will update at most one of these Option-Types. Note that in case both Trace Option-Types are present in a packet, it is up to the IOAM data processing systems (see Section 6) to integrate the data from the two Trace Option-Types to form a view of the entire journey of the packet. A transit node does not add new IOAM Option-Types to a packet and does not change the IOAM-Data-Fields of an IOAM Edge-to-Edge (E2E) Option-Type.¶

An IOAM decapsulating node removes any IOAM Option-Types from packets.¶

The role of an IOAM encapsulating, IOAM transit, or IOAM decapsulating node is always performed within a specific IOAM-Namespace. This means that an IOAM node that is, e.g., an IOAM decapsulating node for IOAM-Namespace "A" but not for IOAM-Namespace "B" will only remove the IOAM Option-Types for IOAM-Namespace "A" from the packet. An IOAM decapsulating node situated at the edge of an IOAM-Domain removes all IOAM Option-Types and associated encapsulation headers for all IOAM-Namespaces from the packet.¶

IOAM-Namespaces allow for a namespace-specific definition and interpretation of IOAM-Data-Fields. Please refer to Section 7.1 for a discussion of IOAM-Namespaces.¶

             Export of      Export of      Export of     Export of
             IOAM data      IOAM data      IOAM data     IOAM data
             (optional)     (optional)     (optional)     (optional)
                 ^              ^              ^              ^
                 |              |              |              |
                 |              |              |              |
    User     +---+----+     +---+----+     +---+----+     +---+----+
    packets  |Encapsu-|     | Transit|     | Transit|     |Decapsu-|
    -------->|lating  |====>| Node   |====>| Node   |====>|lating  |-->
             |Node    |     | A      |     | B      |     |Node    |
             +--------+     +--------+     +--------+     +--------+

Figure 1: Roles of IOAM Nodes

IOAM nodes that add or remove the IOAM-Data-Fields can also update the IOAM-Data-Fields at the same time. Or, in other words, IOAM encapsulating or decapsulating nodes can also serve as IOAM transit nodes at the same time. Note that not every node in an IOAM-Domain needs to be an IOAM transit node. For example, a deployment might require that packets traverse a set of firewalls that support IOAM. In that case, only the set of firewall nodes would be IOAM transit nodes rather than all nodes.¶

## 4. Types of IOAM

IOAM supports different modes of operation. These modes are differentiated by the type of IOAM data fields that are being carried in the packet, the data being collected, the type of nodes that collect or update data, and if and how nodes export IOAM information.¶

Per-hop tracing:

  OAM information about each IOAM node a packet traverses is collected and stored within the user data packet as the packet progresses through the IOAM-Domain. Potential uses of IOAM per-hop tracing include:¶

  - Understanding the different paths that different packets traverse between an IOAM encapsulating node and an IOAM decapsulating node in a network that uses load balancing, such as Equal Cost Multi-Path (ECMP). This information could be used to tune the algorithm for ECMP for optimized network resource usage.¶
  - With regard to operations and troubleshooting, understanding which path a particular packet or set of packets take as well as what amount of jitter and delay different IOAM nodes in the path contribute to the overall delay and jitter between the IOAM encapsulating node and the IOAM decapsulating node.¶
Proof of Transit:
  Information that a verifier node can use to verify whether a packet has traversed all nodes that it is supposed to traverse is stored within the user data packet. For example, Proof of Transit could be used to verify that a packet indeed passes through all services of a service function chain (e.g., verify whether a packet indeed traversed the set of firewalls that it is expected to traverse) or whether a packet indeed took the expected path.¶
Edge-to-Edge (E2E):
  OAM information that is specific to the edges of an IOAM-Domain is collected and stored within the user data packet. E2E OAM could be used to gather operational information about a particular network domain, such as the delay and jitter incurred by that network domain or the traffic matrix of the network domain.¶
Direct Export:
  OAM information about each IOAM node a packet traverses is collected and immediately exported to a collector. Direct Export could be used in situations where per-hop tracing information is desired, but gathering the information within the packet -- as with per-hop tracing -- is not feasible. Rather than automatically correlating the per-hop tracing information, as done with per-hop tracing, Direct Export requires a collector to correlate the information from the individual nodes. In addition, all nodes enabled for Direct Export need to be capable of exporting the IOAM information to the collector.¶

### 4.1. Per-Hop Tracing IOAM

"IOAM tracing data" is expected to be collected at every IOAM transit node that a packet traverses to ensure visibility into the entire path that a packet takes within an IOAM-Domain. In other words, in a typical deployment, all nodes in an IOAM-Domain would participate in IOAM and, thus, be IOAM transit nodes, IOAM encapsulating nodes, or IOAM decapsulating nodes. If not all nodes within a domain are IOAM capable, IOAM tracing information (i.e., node data, see below) will only be collected on those nodes that are IOAM capable. Nodes that are not IOAM capable will forward the packet without any changes to the IOAM-Data-Fields. The maximum number of hops and the minimum path MTU of the IOAM-Domain are assumed to be known.¶

IOAM offers two different Trace Option-Types: the "Incremental" Trace Option-Type and the "Pre-allocated" Trace Option-Type. For a discussion about which of the two option types is the most suitable for an implementation and/or deployment, see Section 7.3.¶

Every node data entry holds information for a particular IOAM transit node that is traversed by a packet. The IOAM decapsulating node removes any IOAM Option-Types and processes and/or exports the associated data. All IOAM-Data-Fields are defined in the context of an IOAM-Namespace.¶

IOAM tracing can, for example, collect the following types of information:¶

- Identification of the IOAM node. An IOAM node identifier can match to a device identifier or a particular control point or subsystem within a device.¶
- Identification of the interface that a packet was received on, i.e., ingress interface.¶
- Identification of the interface that a packet was sent out on, i.e., egress interface.¶
- Time of day when the packet was processed by the node as well as the transit delay. Different definitions of processing time are feasible and expected, though it is important that all devices of an IOAM-Domain follow the same definition.¶
- Generic data, which is format-free information, where the syntax and semantics of the information are defined by the operator in a specific deployment. For a specific IOAM-Namespace, all IOAM nodes should interpret the generic data the same way. Examples for generic IOAM data include geolocation information (location of the node at the time the packet was processed), buffer queue fill level or cache fill level at the time the packet was processed, or even a battery charge level.¶
- Information to detect whether IOAM trace data was added at every hop or whether certain hops in the domain weren't IOAM transit nodes.¶
- Data that relates to how the packet traversed a node (transit delay, buffer occupancy in case the packet was buffered, and queue depth in case the packet was queued).¶

The Incremental Trace Option-Type and Pre-allocated Trace Option-Type are defined in [RFC9197].¶

### 4.2. Proof of Transit IOAM

The IOAM Proof of Transit Option-Type is to support path or service function chain [RFC7665] verification use cases. Proof of transit could use methods like nested hashing or nested encryption of the IOAM data.¶

The IOAM Proof of Transit Option-Type consists of a fixed-size "IOAM Proof of Transit Option header" and "IOAM Proof of Transit Option data fields". For details, see [RFC9197].¶

### 4.3. E2E IOAM

The IOAM E2E Option-Type is to carry the data that is added by the IOAM encapsulating node and interpreted by IOAM decapsulating node. The IOAM transit nodes may process the data but must not modify it.¶

The IOAM E2E Option-Type consists of a fixed-size "IOAM Edge-to-Edge Option-Type header" and "IOAM Edge-to-Edge Option-Type data fields". For details, see [RFC9197].¶

### 4.4. Direct Export IOAM

Direct Export is an IOAM mode of operation within which IOAM data are to be directly exported to a collector rather than be collected within the data packets. The IOAM Direct Export Option-Type consists of a fixed-size "IOAM direct export option header". Direct Export for IOAM is defined in [RFC9326].¶

## 5. IOAM Encapsulations

IOAM data fields and associated data types for IOAM are defined in [RFC9197]. The IOAM data field can be transported by a variety of transport protocols, including NSH, Segment Routing, Geneve, BIER, IPv6, etc.¶

### 5.1. IPv6

IOAM encapsulation for IPv6 is defined in [IOAM-IPV6-OPTIONS], which also discusses IOAM deployment considerations for IPv6 networks.¶

### 5.2. NSH

IOAM encapsulation for NSH is defined in [IOAM-NSH].¶

### 5.3. BIER

IOAM encapsulation for BIER is defined in [BIER-IOAM].¶

### 5.4. GRE

IOAM encapsulation for GRE is outlined as part of the "EtherType Protocol Identification of In-situ OAM Data" in [IOAM-ETH].¶

### 5.5. Geneve

IOAM encapsulation for Geneve is defined in [IOAM-GENEVE].¶

### 5.6. Segment Routing

IOAM encapsulation for Segment Routing is defined in [MPLS-IOAM].¶

### 5.7. Segment Routing for IPv6

IOAM encapsulation for Segment Routing over IPv6 is defined in [IOAM-SRV6].¶

### 5.8. VXLAN-GPE

IOAM encapsulation for VXLAN-GPE is defined in [IOAM-VXLAN-GPE].¶

## 6. IOAM Data Export

IOAM nodes collect information for packets traversing a domain that supports IOAM. IOAM decapsulating nodes, as well as IOAM transit nodes, can choose to retrieve IOAM information from the packet, process the information further, and export the information using, e.g., IP Flow Information Export (IPFIX).¶

Raw data export of IOAM data using IPFIX is discussed in [IOAM-RAWEXPORT]. "Raw export of IOAM data" refers to a mode of operation where a node exports the IOAM data as it is received in the packet. The exporting node does not interpret, aggregate, or reformat the IOAM data before it is exported. Raw export of IOAM data is to support an operational model where the processing and interpretation of IOAM data is decoupled from the operation of encapsulating/updating/decapsulating IOAM data, which is also referred to as "IOAM data-plane operation". Figure 2 shows the separation of concerns for IOAM export. Exporting IOAM data is performed by the "IOAM node", which performs IOAM data-plane operation, whereas the interpretation of IOAM data is performed by one or several IOAM data processing systems. The separation of concerns is to offload interpretation, aggregation, and formatting of IOAM data from the node that performs data-plane operations. In other words, a node that is focused on data-plane operations, i.e., forwarding of packets and handling IOAM data, will not be tasked to also interpret the IOAM data. Instead, that node can leave this task to another system or a set of systems. For scalability reasons, a single IOAM node could choose to export IOAM data to several systems that process IOAM data. Similarly, several monitoring systems or analytics systems can be used to further process the data received from the IOAM preprocessing systems. Figure 2 shows an overview of IOAM export, including IOAM data processing systems and monitoring and analytics systems.¶

                                  +--------------+
                                 +-------------+ |
                                 | Monitoring/ | |
                                 | Analytics   | |
                                 | system(s)   |-+
                                 +-------------+
                                        ^
                                        |  Processed/interpreted/
                                        |  aggregated IOAM data
                                        |
                                  +--------------+
                                 +-------------+ |
                                 | IOAM data   | |
                                 | processing  | |
                                 | system(s)   |-+
                                 +-------------+
                                        ^
                                        |  Raw export of
                                        |  IOAM data
                                        |
                 +--------------+-------+------+--------------+
                 |              |              |              |
                 |              |              |              |
    User     +---+----+     +---+----+     +---+----+     +---+----+
    packets  |Encapsu-|     | Transit|     | Transit|     |Decapsu-|
    -------->|lating  |====>| Node   |====>| Node   |====>|lating  |-->
             |Node    |     | A      |     | B      |     |Node    |
             +--------+     +--------+     +--------+     +--------+

Figure 2: IOAM Framework with Data Export

## 7. IOAM Deployment Considerations

This section describes several concepts of IOAM and provides considerations that need to be taken into account when implementing IOAM in a network domain. This includes concepts like IOAM-Namespaces, IOAM Layering, traffic-sets that IOAM is applied to, and IOAM Loopback. For a definition of IOAM-Namespaces and IOAM Layering, please refer to [RFC9197]. IOAM Loopback is defined in [RFC9322].¶

### 7.1. IOAM-Namespaces

IOAM-Namespaces add further context to IOAM Option-Types and associated IOAM-Data-Fields. IOAM-Namespaces are defined in Section 4.3 of [RFC9197]. The Namespace-ID is part of the IOAM Option-Type definition. See Section 4.4 of [RFC9197] for IOAM Trace Option-Types or Section 4.6 of [RFC9197] for the IOAM E2E Option-Type. IOAM-Namespaces support several uses:¶

- IOAM-Namespaces can be used by an operator to distinguish between different operational domains. Devices at domain edges can filter on Namespace-IDs to provide for proper IOAM-Domain isolation.¶
- IOAM-Namespaces provide additional context for IOAM-Data-Fields; thus, they ensure that IOAM-Data-Fields are unique and can be interpreted properly by management stations or network controllers. While, for example, the node identifier field does not need to be unique in a deployment (e.g., an operator may wish to use different node identifiers for different IOAM layers, even within the same device; or node identifiers might not be unique for other organizational reasons, such as after a merger of two formerly separated organizations), the combination of node_id and Namespace-ID should always be unique. Similarly, IOAM-Namespaces can be used to define how certain IOAM-Data-Fields are interpreted. IOAM offers three different timestamp format options. The Namespace-ID can be used to determine the timestamp format. IOAM-Data-Fields (e.g., buffer occupancy) that do not have a unit associated are to be interpreted within the context of an IOAM-Namespace. The Namespace-ID could also be used to distinguish between different types of interfaces. An interface-id could, for example, point to a physical interface (e.g., to understand which physical interface of an aggregated link is used when receiving or transmitting a packet). Whereas, in another case, an interface-id could refer to a logical interface (e.g., in case of tunnels). Namespace-IDs could be used to distinguish between the different types of interfaces.¶

- IOAM-Namespaces can be used to identify different sets of devices (e.g., different types of devices) in a deployment. If an operator desires to insert different IOAM-Data-Fields based on the device, the devices could be grouped into multiple IOAM-Namespaces. This could be due to the fact that the IOAM feature set differs between different sets of devices, or it could be for reasons of optimized space usage in the packet header. It could also stem from hardware or operational limitations on the size of the trace data that can be added and processed, preventing collection of a full trace for a flow.¶

  - Assigning different IOAM Namespace-IDs to different sets of nodes or network partitions and using the Namespace-ID as a selector at the IOAM encapsulating node, a full trace for a flow could be collected and constructed via partial traces in different packets of the same flow. For example, an operator could choose to group the devices of a domain into two IOAM-Namespaces in a way that, on average, only every second hop would be recorded by any device. To retrieve a full view of the deployment, the captured IOAM-Data-Fields of the two IOAM-Namespaces need to be correlated.¶
  - Assigning different IOAM Namespace-IDs to different sets of nodes or network partitions and using a separate instance of an IOAM Option-Type for each Namespace-ID, a full trace for a flow could be collected and constructed via partial traces from each IOAM Option-Type in each of the packets in the flow. For example, an operator could choose to group the devices of a domain into two IOAM-Namespaces in a way that each IOAM-Namespace is represented by one of two IOAM Option-Types in the packet. Each node would record data only for the IOAM-Namespace that it belongs to, ignoring the other IOAM Option-Type with an IOAM-Namespace it doesn't belong to. To retrieve a full view of the deployment, the captured IOAM-Data-Fields of the two IOAM-Namespaces need to be correlated.¶

### 7.2. IOAM Layering

If several encapsulation protocols (e.g., in case of tunneling) are stacked on top of each other, IOAM-Data-Fields could be present in different protocol fields at different layers. Layering allows operators to instrument the protocol layer they want to measure. The behavior follows the ships-in-the-night model, i.e., IOAM-Data-Fields in one layer are independent of IOAM-Data-Fields in another layer. Or in other words, even though the term "layering" often implies there is some form of hierarchy and relationship, in IOAM, layers are independent of each other and don't assume any relationship among them. The different layers could, but do not have to, share the same IOAM encapsulation mechanisms. Similarly, the semantics of the IOAM-Data-Fields can, but do not have to, be associated to cross different layers. For example, a node that inserts node-id information into two different layers could use "node-id=10" for one layer and "node-id=1000" for the second layer.¶

Figure 3 shows an example of IOAM Layering. The figure shows a Geneve tunnel carried over IPv6, which starts at node A and ends at node D. IOAM information is encapsulated in IPv6 as well as in Geneve. At the IPv6 layer, node A is the IOAM encapsulating node (into IPv6), node D is the IOAM decapsulating node, and nodes B and C are IOAM transit nodes. At the Geneve layer, node A is the IOAM encapsulating node (into Geneve), and node D is the IOAM decapsulating node (from Geneve). The use of IOAM at both layers, as shown in the example here, could be used to reveal which nodes of an underlay (here the IPv6 network) are traversed by a tunneled packet in an overlay (here the Geneve network) -- which assumes that the IOAM information encapsulated by nodes A and D into Geneve and IPv6 is associated to each other.¶

             +---+----+                                   +---+----+
    User     |Geneve  |                                   |Geneve  |
    packets  |Encapsu-|                                   |Decapsu-|
    -------->|lating  |==================================>|lating  |-->
             |  Node  |                                   |  Node  |
             |   A    |                                   |   D    |
             +--------+                                   +--------+
                 ^                                            ^
                 |                                            |
                 v                                            v
             +--------+     +--------+     +--------+     +--------+
             |IPv6    |     | IPv6   |     | IPv6   |     |IPv6    |
             |Encapsu-|     | Transit|     | Transit|     |Decapsu-|
             |lating  |====>|  Node  |====>|  Node  |====>|lating  |
             |  Node  |     |        |     |        |     |  Node  |
             |   A    |     |   B    |     |   C    |     |   D    |
             +--------+     +--------+     +--------+     +--------+

Figure 3: IOAM Layering Example

### 7.3. IOAM Trace Option-Types

IOAM offers two different IOAM Option-Types for tracing: "Incremental" Trace Option-Type and "Pre-allocated" Trace Option-Type. "Incremental" refers to a mode of operation where the packet is expanded at every IOAM node that adds IOAM-Data-Fields. "Pre-allocated" describes a mode of operation where the IOAM encapsulating node allocates room for all IOAM-Data-Fields in the entire IOAM-Domain. More specifically:¶

Pre-allocated Trace Option:
  This trace option is defined as a container of node data fields with pre-allocated space for each node to populate its information. This option is useful for implementations where it is efficient to allocate the space once and index into the array to populate the data during transit (e.g., software forwarders often fall into this class).¶
Incremental Trace Option:
  This trace option is defined as a container of node data fields where each node allocates and pushes its node data immediately following the option header.¶

Which IOAM Trace Option-Types can be supported is not only a function of operator-defined configuration but may also be limited by protocol constraints unique to a given encapsulating protocol. For encapsulating protocols that support both IOAM Trace Option-Types, the operator decides, by means of configuration, which Trace Option-Type(s) will be used for a particular domain. In this case, deployments can mix devices that include either the Incremental Trace Option-Type or the Pre-allocated Trace Option-Type. For example, if different types of packet forwarders and associated different types of IOAM implementations exist in a deployment and the encapsulating protocol supports both IOAM Trace Option-Types, a deployment can mix devices that include either the Incremental Trace Option-Type or the Pre-allocated Trace Option-Type. As a result, both Option-Types can be present in a packet. IOAM decapsulating nodes remove both types of Trace Option-Types from the packet.¶

The two different Option-Types cater to different packet-forwarding infrastructures and allow an optimized implementation of IOAM tracing:¶

Pre-allocated Trace Option:
  For some implementations of packet forwarders, it is efficient to allocate the space for the maximum number of nodes that IOAM Trace Data-Fields should be collected from and insert/update information in the packet at flexible locations based on a pointer retrieved from a field in the packet. The IOAM encapsulating node allocates an array of the size of the maximum number of nodes that IOAM Trace Data-Fields should be collected from. IOAM transit nodes index into the array to populate the data during transit. Software forwarders often fall into this class of packet-forwarder implementations. The maximum number of nodes that IOAM information could be collected from is configured by the operator on the IOAM encapsulating node. The operator has to ensure that the packet with the pre-allocated array that carries the IOAM Data-Fields does not exceed the MTU of any of the links in the IOAM-Domain.¶
Incremental Trace Option:
  Looking up a pointer contained in the packet and inserting/updating information at a flexible location in the packet as a result of the pointer lookup is costly for some forwarding infrastructures. Hardware-based packet-forwarding infrastructures often fall into this category. Consequently, hardware-based packet forwarders could choose to support the IOAM Incremental Trace Option-Type. The IOAM Incremental Trace Option-Type eliminates the need for the IOAM transit nodes to read the full array in the Trace Option-Type and allows packets to grow to the size of the MTU of the IOAM-Domain. IOAM transit nodes will expand the packet and insert the IOAM-Data-Fields as long as there is space available in the packet, i.e., as long as the size of the packet stays within the bounds of the MTU of the links in the IOAM-Domain. There is no need for the operator to configure the IOAM encapsulation node with the maximum number of nodes that IOAM information could be collected from. The operator has to ensure that the minimum MTU of the links in the IOAM-Domain is known to all IOAM transit nodes.¶

### 7.4. Traffic-Sets That IOAM Is Applied To

IOAM can be deployed on all or only on subsets of the live user traffic, e.g., per interface, based on an access control list or flow specification defining a specific set of traffic, etc.¶

### 7.5. Loopback Flag

IOAM Loopback is used to trigger each transit device along the path of a packet to send a copy of the data packet back to the source. Loopback allows an IOAM encapsulating node to trace the path to a given destination and to receive per-hop data about both the forward and the return path. Loopback is enabled by the encapsulating node setting the Loopback flag. Looped-back packets use the source address of the original packet as a destination address and the address of the node that performs the Loopback operation as source address. Nodes that loop back a packet clear the Loopback flag before sending the copy back towards the source. Loopack applies to IOAM deployments where the encapsulating node is either a host or the start of a tunnel. For details on IOAM Loopback, please refer to [RFC9322].¶

### 7.6. Active Flag

The Active flag indicates that a packet is an active OAM packet as opposed to regular user data traffic. Active flag is expected to be used for active measurement using IOAM. For details on the Active flag, please refer to [RFC9322].¶

Example use cases for the Active flag include:¶

Endpoint detailed active measurement:
  Synthetic probe packets are sent between the source and destination. These probe packets include a Trace Option-Type (i.e., either incremental or pre-allocated). Since the probe packets are sent between the endpoints, these packets are treated as data packets by the IOAM-Domain and do not require special treatment at the IOAM layer. The source, which is also the IOAM encapsulating node, can choose to set the Active flag, providing an explicit indication that these probe packets are meant for telemetry collection.¶
IOAM active measurement using probe packets:
  Probe packets are generated and transmitted by an IOAM encapsulating node towards a destination that is also the IOAM decapsulating node. Probe packets include a Trace Option-Type (i.e., either incremental or pre-allocated) that has its Active flag set.¶
IOAM active measurement using replicated data packets:
  Probe packets are created by an IOAM encapsulating node by selecting some or all of the en route data packets and replicating them. A selected data packet that is replicated and its (possibly truncated) copy are forwarded with one or more IOAM options, while the original packet is forwarded, normally, without IOAM options. To the extent possible, the original data packet and its replica are forwarded through the same path. The replica includes a Trace Option-Type that has its Active flag set, indicating that the IOAM decapsulating node should terminate it. In this case, the IOAM Active flag ensures that the replicated traffic is not forwarded beyond the IOAM-Domain.¶

### 7.7. Brown Field Deployments: IOAM-Unaware Nodes

A network can consist of a mix of IOAM-aware and IOAM-unaware nodes. The encapsulation of IOAM-Data-Fields into different protocols (see also Section 5) are defined such that data packets that include IOAM-Data-Fields do not get dropped by IOAM-unaware nodes. For example, packets that contain the IOAM Trace Option-Types in IPv6 Hop-by-Hop extension headers are defined with bits to indicate "00 - skip over this option and continue processing the header". This will ensure that when an IOAM-unaware node receives a packet with IOAM-Data-Fields included, it does not drop the packet.¶

Deployments that leverage the IOAM Trace Option-Type(s) could benefit from the ability to detect the presence of IOAM-unaware nodes, i.e., nodes that forward the packet but do not update or add IOAM-Data-Fields in IOAM Trace Option-Types. The node data that is defined as part of the IOAM Trace Option-Type(s) includes a Hop_Lim field associated to the node identifier to detect missed nodes, i.e., "holes" in the trace. Monitoring/Analytics systems could utilize this information to account for the presence of IOAM-unaware nodes in the network.¶

## 8. IOAM Manageability

The YANG model for configuring IOAM in network nodes that support IOAM is defined in [IOAM-YANG].¶

A deployment can leverage IOAM profiles to limit the scope of IOAM features, allowing simpler implementation, verification, and interoperability testing in the context of specific use cases that do not require the full functionality of IOAM. An IOAM profile defines a use case or a set of use cases for IOAM and an associated set of rules that restrict the scope and features of the IOAM specification, thereby limiting it to a subset of the full functionality. IOAM profiles are defined in [IOAM-PROFILES].¶

For deployments where the IOAM capabilities of a node are unknown, [RFC9359] could be used to discover the enabled IOAM capabilities of nodes.¶

## 9. IANA Considerations

This document has no IANA actions.¶

## 10. Security Considerations

As discussed in [RFC7276], a successful attack on an OAM protocol in general and, specifically, on IOAM can prevent the detection of failures or anomalies or can create a false illusion of nonexistent ones.¶

The Proof of Transit Option-Type (Section 4.2) is used for verifying the path of data packets. The security considerations of POT are further discussed in [PROOF-OF-TRANSIT].¶

Security considerations related to the use of IOAM flags, particularly the Loopback flag, are found in [RFC9322].¶

IOAM data can be subject to eavesdropping. Although the confidentiality of the user data is not at risk in this context, the IOAM data elements can be used for network reconnaissance, allowing attackers to collect information about network paths, performance, queue states, buffer occupancy, and other information. Recon is an improbable security threat in an IOAM deployment that is within a confined physical domain. However, in deployments that are not confined to a single LAN but span multiple interconnected sites (for example, using an overlay network), the inter-site links are expected to be secured (e.g., by IPsec) in order to avoid external eavesdropping and introduction of malicious or false data. Another possible mitigation approach is to use "Direct Exporting" [RFC9326]. In this case, the IOAM-related trace information would not be available in the customer data packets but would trigger the exporting of (secured) packet-related IOAM information at every node. IOAM data export and securing IOAM data export is outside the scope of this document.¶

IOAM can be used as a means for implementing or amplifying Denial-of-Service (DoS) attacks. For example, a malicious attacker can add an IOAM header to packets or modify an IOAM header in en route packets in order to consume the resources of network devices that take part in IOAM or collectors that analyze the IOAM data. Another example is a packet-length attack, in which an attacker pushes headers associated with IOAM Option-Types into data packets, causing these packets to be increased beyond the MTU size, resulting in fragmentation or in packet drops. Such DoS attacks can be mitigated by deploying IOAM in confined administrative domains and by limiting the rate and/or the percentage of packets that an IOAM encapsulating node adds IOAM information to as well as limiting rate and/or percentage of packets that an IOAM transit or an IOAM decapsulating node creates to export IOAM information extracted from the data packets that carry IOAM information.¶

Even though IOAM focused on limited domains [RFC8799], there might be deployments for which it is important for IOAM transit nodes and IOAM decapsulating nodes to know that the data received haven't been tampered with. In those cases, the IOAM data should be integrity protected. Integrity protection of IOAM data fields is described in [IOAM-DATA-INTEGRITY]. In addition, since IOAM options may include timestamps, if network devices use synchronization protocols, then any attack on the time protocol [RFC7384] can compromise the integrity of the timestamp-related data fields. Synchronization attacks can be mitigated by combining a secured time distribution scheme, e.g., [RFC8915], and by using redundant clock sources [RFC5905] and/or redundant network paths for the time distribution protocol [RFC8039].¶

At the management plane, attacks may be implemented by misconfiguring or by maliciously configuring IOAM-enabled nodes in a way that enables other attacks. Thus, IOAM configuration should be secured in a way that authenticates authorized users and verifies the integrity of configuration procedures.¶

Notably, IOAM is expected to be deployed in limited network domains [RFC8799], thus, confining the potential attack vectors within the limited domain. Indeed, in order to limit the scope of threats within the current network domain, the network operator is expected to enforce policies that prevent IOAM traffic from leaking outside the IOAM-Domain and prevent an attacker from introducing malicious or false IOAM data to be processed and used within the IOAM-Domain. IOAM data leakage could lead to privacy issues. Consider an IOAM encapsulating node that is a home gateway in an operator's network. A home gateway is often identified with an individual. Revealing IOAM data, such as "IOAM node identifier" or geolocation information outside of the limited domain, could be harmful for that user. Note that Direct Exporting [RFC9326] can mitigate the potential threat of IOAM data leaking through data packets.¶

## 11. Informative References

[BIER-IOAM]
  Min, X., Zhang, Z., Liu, Y., Nainar, N., and C. Pignataro, "BIER Encapsulation for IOAM Data", Work in Progress, Internet-Draft, draft-xzlnp-bier-ioam-05, 27 January 2023, <https://datatracker.ietf.org/doc/html/draft-xzlnp-bier-ioam-05>.
[IOAM-DATA-INTEGRITY]
  Brockners, F., Bhandari, S., Mizrahi, T., and J. Iurman, "Integrity of In-situ OAM Data Fields", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-data-integrity-03, 24 November 2022, <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-ioam-data-integrity-03>.
[IOAM-ETH]
  Weis, B., Ed., Brockners, F., Ed., Hill, C., Bhandari, S., Govindan, V., Pignataro, C., Ed., Nainar, N., Ed., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B., Lapukhov, P., and M. Spiegel, "EtherType Protocol Identification of In-situ OAM Data", Work in Progress, Internet-Draft, draft-weis-ippm-ioam-eth-05, 21 February 2022, <https://datatracker.ietf.org/doc/html/draft-weis-ippm-ioam-eth-05>.
[IOAM-GENEVE]
  Brockners, F., Ed., Bhandari, S., Govindan, V., Pignataro, C., Ed., Nainar, N., Ed., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Lapukhov, P., Gafni, B., Kfir, A., and M. Spiegel, "Geneve encapsulation for In-situ OAM Data", Work in Progress, Internet-Draft, draft-brockners-ippm-ioam-geneve-05, 19 November 2020, <https://datatracker.ietf.org/doc/html/draft-brockners-ippm-ioam-geneve-05>.
[IOAM-IPV6-OPTIONS]
  Bhandari, S., Ed. and F. Brockners, Ed., "In-situ OAM IPv6 Options", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-ipv6-options-10, 28 February 2023, <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-ioam-ipv6-options-10>.
[IOAM-NSH]
  Brockners, F., Ed. and S. Bhandari, Ed., "Network Service Header (NSH) Encapsulation for In-situ OAM (IOAM) Data", Work in Progress, Internet-Draft, draft-ietf-sfc-ioam-nsh-11, 30 September 2022, <https://datatracker.ietf.org/doc/html/draft-ietf-sfc-ioam-nsh-11>.
[IOAM-PROFILES]
  Mizrahi, T., Brockners, F., Bhandari, S., Ed., Sivakolundu, R., Pignataro, C., Kfir, A., Gafni, B., Spiegel, M., and T. Zhou, "In Situ OAM Profiles", Work in Progress, Internet-Draft, draft-mizrahi-ippm-ioam-profile-06, 17 February 2022, <https://datatracker.ietf.org/doc/html/draft-mizrahi-ippm-ioam-profile-06>.
[IOAM-RAWEXPORT]
  Spiegel, M., Brockners, F., Bhandari, S., and R. Sivakolundu, "In-situ OAM raw data export with IPFIX", Work in Progress, Internet-Draft, draft-spiegel-ippm-ioam-rawexport-06, 21 February 2022, <https://datatracker.ietf.org/doc/html/draft-spiegel-ippm-ioam-rawexport-06>.
[IOAM-SRV6]
  Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar, N., Pignataro, C., Li, C., Chen, M., and G. Dawra, "Segment Routing Header encapsulation for In-situ OAM Data", Work in Progress, Internet-Draft, draft-ali-spring-ioam-srv6-06, 10 July 2022, <https://datatracker.ietf.org/doc/html/draft-ali-spring-ioam-srv6-06>.
[IOAM-VXLAN-GPE]
  Brockners, F., Bhandari, S., Govindan, V., Pignataro, C., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B., Lapukhov, P., and M. Spiegel, "VXLAN-GPE Encapsulation for In-situ OAM Data", Work in Progress, Internet-Draft, draft-brockners-ipxpm-ioam-vxlan-gpe-03, 4 November 2019, <https://datatracker.ietf.org/doc/html/draft-brockners-ippm-ioam-vxlan-gpe-03>.
[IOAM-YANG]
  Zhou, T., Ed., Guichard, J., Brockners, F., and S. Raghavan, "A YANG Data Model for In-Situ OAM", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-yang-06, 27 February 2023, <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-ioam-yang-06>.
[MPLS-IOAM]
  Gandhi, R., Ed., Brockners, F., Wen, B., Decraene, B., and H. Song, "MPLS Data Plane Encapsulation for In Situ OAM Data", Work in Progress, Internet-Draft, draft-gandhi-mpls-ioam-10, 10 March 2023, <https://datatracker.ietf.org/doc/html/draft-gandhi-mpls-ioam-10>.
[PROOF-OF-TRANSIT]
  Brockners, F., Ed., Bhandari, S., Ed., Mizrahi, T., Ed., Dara, S., and S. Youell, "Proof of Transit", Work in Progress, Internet-Draft, draft-ietf-sfc-proof-of-transit-08, 31 October 2020, <https://datatracker.ietf.org/doc/html/draft-ietf-sfc-proof-of-transit-08>.
[RFC2784]
  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, DOI 10.17487/RFC2784, March 2000, <https://www.rfc-editor.org/info/rfc2784>.
[RFC5905]
  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, <https://www.rfc-editor.org/info/rfc5905>.
[RFC7276]
  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. Weingarten, "An Overview of Operations, Administration, and Maintenance (OAM) Tools", RFC 7276, DOI 10.17487/RFC7276, June 2014, <https://www.rfc-editor.org/info/rfc7276>.
[RFC7384]
  Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC7665]
  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, <https://www.rfc-editor.org/info/rfc7665>.
[RFC7799]
  Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8039]
  Shpiner, A., Tse, R., Schelp, C., and T. Mizrahi, "Multipath Time Synchronization", RFC 8039, DOI 10.17487/RFC8039, December 2016, <https://www.rfc-editor.org/info/rfc8039>.
[RFC8279]
  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., Przygienda, T., and S. Aldrin, "Multicast Using Bit Index Explicit Replication (BIER)", RFC 8279, DOI 10.17487/RFC8279, November 2017, <https://www.rfc-editor.org/info/rfc8279>.
[RFC8300]
  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, <https://www.rfc-editor.org/info/rfc8300>.
[RFC8799]
  Carpenter, B. and B. Liu, "Limited Domains and Internet Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020, <https://www.rfc-editor.org/info/rfc8799>.
[RFC8915]
  Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R. Sundblad, "Network Time Security for the Network Time Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020, <https://www.rfc-editor.org/info/rfc8915>.
[RFC8926]
  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed., "Geneve: Generic Network Virtualization Encapsulation", RFC 8926, DOI 10.17487/RFC8926, November 2020, <https://www.rfc-editor.org/info/rfc8926>.
[RFC9197]
  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi, Ed., "Data Fields for In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197, May 2022, <https://www.rfc-editor.org/info/rfc9197>.
[RFC9322]
  Mizrahi, T., Brockners, F., Bhandari, S., Gafni, B., and M. Spiegel, "In Situ Operations, Administration, and Maintenance (IOAM) Loopback and Active Flags", RFC 9322, DOI 10.17487/RFC9322, November 2022, <https://www.rfc-editor.org/info/rfc9322>.
[RFC9326]
  Song, H., Gafni, B., Brockners, F., Bhandari, S., and T. Mizrahi, "In Situ Operations, Administration, and Maintenance (IOAM) Direct Exporting", RFC 9326, DOI 10.17487/RFC9326, November 2022, <https://www.rfc-editor.org/info/rfc9326>.
[RFC9359]
  Min, X., Mirsky, G., and L. Bo, "Echo Request/Reply for Enabled In Situ OAM (IOAM) Capabilities", RFC 9359, DOI 10.17487/RFC9359, April 2023, <https://www.rfc-editor.org/info/rfc9359>.
[VXLAN-GPE]
  Maino, F., Ed., Kreeger, L., Ed., and U. Elzur, Ed., "Generic Protocol Extension for VXLAN (VXLAN-GPE)", Work in Progress, Internet-Draft, draft-ietf-nvo3-vxlan-gpe-12, 22 September 2021, <https://datatracker.ietf.org/doc/html/draft-ietf-nvo3-vxlan-gpe-12>.

## Acknowledgements

The authors would like to thank Tal Mizrahi, Eric Vyncke, Nalini Elkins, Srihari Raghavan, Ranganathan T S, Barak Gafni, Karthik Babu Harichandra Babu, Akshaya Nadahalli, LJ Wobker, Erik Nordmark, Vengada Prasad Govindan, Andrew Yourtchenko, Aviv Kfir, Tianran Zhou, Zhenbin (Robin), Joe Clarke, Al Morton, Tom Herbet, Haoyu Song, and Mickey Spiegel for the comments and advice on IOAM.¶

## Authors' Addresses