Data Fields for In-situ OAM

This document defines data fields for "in-situ" Operations, Administration, and Maintenance (IOAM). In-situ OAM records 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 is to complement mechanisms such as Ping or Traceroute. In terms of "active" or "passive" OAM, "in-situ" OAM 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 , 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, such as proving that a certain traffic flow takes a pre-defined path, SLA verification for the data traffic, detailed statistics on traffic distribution paths in networks that distribute traffic across multiple paths, or scenarios in which probe traffic is potentially handled differently from regular data traffic by the network devices. The term "in situ OAM" was originally motivated by the use of OAM related mechanisms that add information into a packet. This document uses IOAM as a term defining the IOAM technology. IOAM includes "in-situ" mechanisms, but also mechanisms that could trigger the creation of additional packets dedicated to OAM.

This document was the collective effort of several authors. The text and content were contributed by the editors and the co-authors listed below. The contact information of the co-authors appears at the end of this document. Carlos Pignataro Mickey Spiegel Barak Gafni Jennifer Lemon Hannes Gredler John Leddy Stephen Youell David Mozes Petr Lapukhov Remy Chang Daniel Bernier

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. Abbreviations and definitions used in this document: Edge to Edge Generic Network Virtualization Encapsulation In-situ Operations, Administration, and Maintenance Maximum Transmit Unit Network Service Header Operations, Administration, and Maintenance Path MTU Proof of Transit Service Function Chain "Short format" refers to an IOAM-Data-Field which comprises 4 octets. Segment Identifier Segment Routing Virtual eXtensible Local Area Network, Generic Protocol Extension "Wide format" refers to an IOAM-Data-Field which comprises 8 octets.

IOAM assumes a set of constraints as well as guiding principles and concepts that go hand in hand with the definition of the IOAM data fields. These constraints, guiding principles, and concepts are described in this section. A discussion of how IOAM data fields and the associated concepts are applied to an IOAM deployment are out of scope for this document. Please refer to for IOAM deployment considerations. Scope: This document defines the data fields and associated data types for in-situ OAM. The in-situ OAM data fields can be encapsulated in a variety of protocols, including NSH, Segment Routing, Geneve, and IPv6. Specification details for these different protocols are outside the scope of this document. It is expected that each such encapsulation would be specified by an RFC, jointly designed by the working group that develops or maintains the encapsulation protocol and the IETF IPPM working group. Deployment domain (or scope) of in-situ OAM deployment: IOAM is focused on "limited domains" as defined in . For IOAM, a limited domain could for example be an enterprise campus using physical connections between devices or an overlay network using virtual connections / tunnels for connectivity between said devices. A limited domain which uses IOAM is called an "IOAM domain". An IOAM domain is bounded by its perimeter or edge. Designers of protocol encapsulations for IOAM specify mechanisms to ensure that IOAM data stays within an IOAM domain. In addition, the operator of such a domain is expected to put provisions in place to ensure that IOAM data does not leak beyond the edge of an IOAM domain using, for example, packet filtering methods. The operator has to consider the potential operational impact of IOAM to mechanisms such as ECMP processing (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 to support the increased packet size due to IOAM) and ICMP message handling (i.e., in case of IPv6, IOAM support for ICMPv6 Echo Request/Reply is desired which would translate into ICMPv6 extensions to enable IOAM-Data-Fields to be copied from an Echo Request message to an Echo Reply message). IOAM control points: IOAM-Data-Fields are added to or removed from the user traffic by the devices which form the edge of a domain. Devices which form an IOAM-Domain can add, update or remove IOAM-Data-Fields. Edge devices of an IOAM-Domain can be hosts or network devices. Traffic-sets that IOAM is applied to: IOAM can be deployed on all or only on subsets of the user traffic. Using IOAM on a selected set of traffic (e.g., per interface, based on an access control list or flow specification defining a specific set of traffic, etc.) could be useful in deployments where the cost of processing IOAM-Data-Fields by encapsulating, transit, or decapsulating node(s) might be a concern from a performance or operational perspective. Thus limiting the amount of traffic IOAM is applied to could be beneficial in some deployments. Encapsulation independence: The definition of IOAM-Data-Fields is independent from the protocols the IOAM-Data-Fields are encapsulated into. IOAM-Data-Fields can be encapsulated into several encapsulating protocols. Layering: If several encapsulation protocols (e.g., in case of tunneling) are stacked on top of each other, IOAM-Data-Fields could be present at multiple layers. The behavior follows the ships-in-the-night model, i.e., IOAM-Data-Fields in one layer are independent from IOAM-Data-Fields in another layer. Layering allows operators to instrument the protocol layer they want to measure. The different layers could, but do not have to, share the same IOAM encapsulation mechanisms. IOAM implementation: The definition of the IOAM-Data-Fields take the specifics of devices with hardware data planes and software data planes into account.

This section details IOAM-related nomenclature and describes data types such as IOAM-Data-Fields, IOAM-Types, IOAM-Namespaces as well as the different types of IOAM nodes.

An IOAM-Data-Field is a set of bits with a defined format and meaning, which can be stored at a certain place in a packet for the purpose of IOAM. To accommodate the different uses of IOAM, IOAM-Data-Fields fall into different categories. In IOAM, these categories are referred to as IOAM-Option-Types. A common registry is maintained for IOAM-Option-Types, see for details. Corresponding to these IOAM-Option-Types, different IOAM-Data-Fields are defined. This document defines four IOAM-Option-Types: Pre-allocated Trace Option-Type Incremental Trace Option-Type Proof of Transit (POT) Option-Type Edge-to-Edge (E2E) Option-Type Future IOAM-Option-Types can be allocated by IANA, as described in .

IOAM is expected to be deployed in a specific domain. The part of the network which employs IOAM is referred to as the "IOAM-Domain". One or more IOAM-Option-Types are added to a packet upon entering the IOAM-Domain and are removed from the packet when exiting the domain. Within the IOAM-Domain, the IOAM-Data-Fields MAY be updated by network nodes that the packet traverses. 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. A device which adds at least one IOAM-Option-Type to the packet is called an "IOAM encapsulating node", whereas a device which removes an IOAM-Option-Type is referred to as an "IOAM decapsulating node". Nodes within the domain which are aware of IOAM data and read and/or write and/or process IOAM data are called "IOAM transit nodes". IOAM nodes which 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 which support IOAM. In that case, only the set of firewall nodes would be IOAM transit nodes rather than all nodes. An "IOAM encapsulating node" incorporates one or more IOAM-Option-Types (from the list of IOAM-Types, see ) 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" read and/or write and/or process 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 based on configuration and available implementation of IOAM populates IOAM trace data in either Pre-allocated or Incremental Trace Option-Type but not both. A transit node MUST ignore IOAM-Option-Types that it does not understand. A transit node MUST NOT add new IOAM-Option-Types to a packet, MUST NOT remove IOAM-Option-Types from a packet, and MUST NOT change the IOAM-Data-Fields of an IOAM Edge-to-Edge Option-Type. An "IOAM decapsulating node" removes IOAM-Option-Type(s) 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 which 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. Note that this applies even for IOAM-Option-Types that the node does not understand, for example an IOAM-Option-Type other than the four described above, that is added in a future revision. An IOAM decapsulating node situated at the edge of an IOAM domain MUST remove 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. 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 it could refer to a logical interface (e.g., in case of tunnels). Please refer to for details on IOAM-Namespaces.

An IOAM-Namespace can be associated to a subset or all of the the IOAM-Option-Types and their corresponding IOAM-Data-Fields. IOAM-Namespaces add further context to IOAM-Option-Types and associated IOAM-Data-Fields. The IOAM-Option-Types and associated IOAM-Data-Fields are interpreted as defined in this document, regardless of the value of the IOAM-Namespace. However, IOAM-Namespaces provide a way to group nodes to support different deployment approaches of IOAM (see a few example use-cases below). IOAM-Namespaces also help to resolve potential issues which can occur due to IOAM-Data-Fields not being globally unique (e.g., IOAM node identifiers do not have to be globally unique). IOAM-Data-Fields significance is always within a particular IOAM-Namespace. Given that IOAM-Data-Fields are always interpreted the context of a specific namespace, the namespace-id field always needs to be carried along with the IOAM data-fields themselves. An IOAM-Namespace is identified by a 16-bit namespace identifier (Namespace-ID). The IOAM-Namespace field is included in all the IOAM-Option-Types defined in this document, and MUST be included in all future IOAM-Option-Types. The Namespace-ID value is divided into two sub-ranges: An operator-assigned range from 0x0001 to 0x7FFF An IANA-assigned range from 0x8000 to 0xFFFF The IANA-assigned range is intended to allow future extensions to have new and interoperable IOAM functionality, while the operator-assigned range is intended to be domain-specific, and managed by the network operator. The Namespace-ID value of 0x0000 is the "Default-Namespace-ID". The Default-Namespace-ID indicates that no specific namespace is associated with the IOAM data fields in the packet. The Default-Namespace-ID MUST be supported by all nodes implementing IOAM. A use-case for the Default-Namespace-ID are deployments which do not leverage specific namespaces for some or all of their packets that carry IOAM data fields. Namespace identifiers allow devices which are IOAM capable to determine: whether IOAM-Option-Type(s) need to be processed by a device: If the Namespace-ID contained in a packet does not match any Namespace-ID the node is configured to operate on, then the node MUST NOT change the contents of the IOAM-Data-Fields. which IOAM-Option-Type needs to be processed/updated in case there are multiple IOAM-Option-Types present in the packet. Multiple IOAM-Option-Types can be present in a packet in case of overlapping IOAM-Domains or in case of a layered IOAM deployment. whether IOAM-Option-Type(s) have to be removed from the packet, e.g., at a domain edge or domain boundary. IOAM-Namespaces support several different uses: IOAM-Namespaces can be used by an operator to distinguish 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 and thus can be used to ensure that IOAM-Data-Fields are unique and are interpreted properly by management stations or network controllers. For example, the node identifier field (node_id, see below) does not need to be unique in a deployment (e.g., if an operator wishes 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 Namespace-ID can be used as a context identifier, such that the combination of node_id and Namespace-ID will 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) which do not have a unit associated are to be interpreted within the context of a IOAM-Namespace. 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. 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. 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 a IOAM-Namespace to which it doesn't belong. To retrieve a full view of the deployment, the captured IOAM-Data-Fields of the two IOAM-Namespaces need to be correlated.

"IOAM tracing data" is expected to be collected at every IOAM transit node that a packet traverses to ensure visibility into the entire path a packet takes within an IOAM-Domain. I.e., in a typical deployment, all nodes in an IOAM-Domain would participate in IOAM and thus be IOAM transit nodes, IOAM encapsulating or IOAM decapsulating nodes. If not all nodes within a domain support IOAM functionality as defined in this document, IOAM tracing information (i.e., node data, see below) will only be collected on those nodes which support IOAM functionality as defined in this document. Nodes which do not support IOAM functionality as defined in this document 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 is assumed to be known. An overflow indicator (O-bit) is defined as one of the ways to deal with situations where the PMTU was underestimated, i.e., where the number of hops which are IOAM capable exceeds the available space in the packet. To optimize hardware and software implementations, IOAM tracing is defined as two separate options. A deployment can choose to configure and support one or both of the following options. This trace option is defined as a container of node data fields (see below) 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). The IOAM encapsulating node allocates space for Pre-allocated Trace Option-Type in the packet and sets corresponding fields in this IOAM-Option-Type. The IOAM encapsulating node allocates an array which is used to store operational data retrieved from every node while the packet traverses the domain. IOAM transit nodes update the content of the array, and possibly update the checksums of outer headers. A pointer which is part of the IOAM trace data, points to the next empty slot in the array. An IOAM transit node that updates the content of the pre-allocated option also updates the value of the pointer, which specifies where the next IOAM transit node fills in its data. The "node data list" array (see below) in the packet is populated iteratively as the packet traverses the network, starting with the last entry of the array, i.e., "node data list [n]" is the first entry to be populated, "node data list [n-1]" is the second one, etc. 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. This type of trace recording is useful for some of the hardware implementations as it eliminates the need for the transit network elements to read the full array in the option and allows for arbitrarily long packets as the MTU allows. The IOAM encapsulating node allocates space for the Incremental Trace Option-Type. Based on operational state and configuration, the IOAM encapsulating node sets the fields in the Option-Type that control what IOAM-Data-Fields have to be collected and how large the node data list can grow. IOAM transit nodes push their node data to the node data list subject to any protocol constraints of the encapsulating layer. They then decrease the remaining length available to subsequent nodes and adjust the lengths and possibly checksums in outer headers. IOAM encapsulating nodes and IOAM decapsulating nodes which support tracing MUST support both Trace-Option-Types. For IOAM transit nodes it is sufficient to support one of the Trace-Option-Types. In the event that both options are utilized in a deployment at the same time, the Incremental Trace-Option MUST be placed before the Pre-allocated Trace-Option. Deployments which mix devices with either the Incremental Trace-Option or the Pre-allocated Trace-Option could result in both Option-Types being present in a packet. Given that the operator knows which equipment is deployed in a particular IOAM domain, the operator will decide by means of configuration which type(s) of trace options will be used for a particular domain. Every node data entry holds information for a particular IOAM transit node that is traversed by a packet. The IOAM decapsulating node removes the IOAM-Option-Type(s) and processes and/or exports the associated data. Like all IOAM-Data-Fields, the IOAM-Data-Fields of the IOAM-Trace-Option-Types are defined in the context of an IOAM-Namespace. IOAM tracing can 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 in-situ OAM domain follow the same definition. Generic data: Format-free information where syntax and semantic of the information is defined by the operator in a specific deployment. For a specific IOAM-Namespace, all IOAM nodes have to interpret the generic data the same way. Examples for generic IOAM data include geo-location 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. It should be noted that the semantics of some of the node data fields that are defined below, such as the queue depth and buffer occupancy, are implementation specific. This approach is intended to allow IOAM nodes with various different architectures.

The IOAM Pre-allocated Trace-Option and the IOAM Incremental Trace-Option have similar formats. Except where noted below, the internal formats and fields of the two trace options are identical. Both Trace-Options consist of a fixed size "trace option header" and a variable data space to store gathered data, the "node data list". An IOAM transit node (that is not an IOAM encapsulating node or IOAM decapsulating node) MUST NOT modify any of the fields in the fixed size “trace option header”, other than “flags” and “RemainingLen”, i.e., an IOAM transit node MUST NOT modify the Namespace-ID, NodeLen, IOAM-Trace-Type, or Reserved fields.

16-bit identifier of an IOAM-Namespace. The Namespace-ID value of 0x0000 is defined as the "Default-Namespace-ID" (see ) and MUST be known to all the nodes implementing IOAM. For any other Namespace-ID value that does not match any Namespace-ID the node is configured to operate on, the node MUST NOT change the contents of the IOAM-Data-Fields. 5-bit unsigned integer. This field specifies the length of data added by each node in multiples of 4-octets, excluding the length of the "Opaque State Snapshot" field. If IOAM-Trace-Type bit 22 is not set, then NodeLen specifies the actual length added by each node. If IOAM-Trace-Type bit 22 is set, then the actual length added by a node would be (NodeLen + length of the "Opaque State Snapshot" field) in 4 octet units. For example, if 3 IOAM-Trace-Type bits are set and none of them are in wide format, then NodeLen would be 3. If 3 IOAM-Trace-Type bits are set and 2 of them are wide, then NodeLen would be 5. An IOAM encapsulating node MUST set NodeLen. A node receiving an IOAM Pre-allocated or Incremental Trace-Option relies on the NodeLen value. 4-bit field. Flags are allocated by IANA, as specified in . This document allocates a single flag as follows: "Overflow" (O-bit) (most significant bit). In case a network element is supposed to add node data to a packet, but detects that there are not enough octets left to record the node data, the network element MUST NOT add any fields and MUST set the overflow "O-bit" to "1" in the IOAM-Trace-Option header. This is useful for transit nodes to ignore further processing of the option. 7-bit unsigned integer. This field specifies the data space in multiples of 4-octets remaining for recording the node data, before the node data list is considered to have overflowed. The sender MUST assign the initial value of the RemainingLen field. The sender MAY calculate the value of the RemainingLen field by computing the number of node data bytes allowed before exceeding the path MTU (PMTU), given that the PMTU is known to the sender. Subsequent nodes can carry out a simple comparison between RemainingLen and NodeLen, along with the length of the "Opaque State Snapshot" if applicable, to determine whether or not data can be added by this node. When node data is added, the node MUST decrease RemainingLen by the amount of data added. In the pre-allocated trace option, RemainingLen is used to derive the offset in data space to record the node data element. Specifically, the recording of the node data element would start from RemainingLen - NodeLen - sizeof(opaque snapshot) in 4 octet units. If RemainingLen in a pre-allocated trace option exceeds the length of the option, as specified in the lower layer header (which is not within the scope of this document), then the node MUST NOT add any fields. A 24-bit identifier which specifies which data types are used in this node data list. The IOAM-Trace-Type value is a bit field. The following bits are defined in this document, with details on each bit described in the . The order of packing the data fields in each node data element follows the bit order of the IOAM-Trace-Type field, as follows: (Most significant bit) When set, indicates presence of Hop_Lim and node_id (short format) in the node data. When set, indicates presence of ingress_if_id and egress_if_id (short format) in the node data. When set, indicates presence of timestamp seconds in the node data. When set, indicates presence of timestamp fraction in the node data. When set, indicates presence of transit delay in the node data. When set, indicates presence of IOAM-Namespace specific data (short format) in the node data. When set, indicates presence of queue depth in the node data. When set, indicates presence of the Checksum Complement node data. When set, indicates presence of Hop_Lim and node_id in wide format in the node data. When set, indicates presence of ingress_if_id and egress_if_id in wide format in the node data. When set, indicates presence of IOAM-Namespace specific data in wide format in the node data. When set, indicates presence of buffer occupancy in the node data. Undefined. These values are available for future assignment in the IOAM Trace-Type Registry (). Every future node data field corresponding to one of these bits MUST be 4-octets long. An IOAM encapsulating node MUST set the value of each undefined bit to 0. If an IOAM transit node receives a packet with one or more of these bits set to 1, it MUST either: Add corresponding node data filled with the reserved value 0xFFFFFFFF, after the node data fields for the IOAM-Trace-Type bits defined above, such that the total node data added by this node in units of 4-octets is equal to NodeLen, or Not add any node data fields to the packet, even for the IOAM-Trace-Type bits defined above. When set, indicates presence of variable length Opaque State Snapshot field. Reserved: MUST be set to zero upon transmission and ignored upon receipt. This bit is reserved to allow for future extensions of the IOAM-Trace-Type bit field. describes the IOAM-Data-Types and their formats. Within an IOAM-Domain possible combinations of these bits making the IOAM-Trace-Type can be restricted by configuration knobs. 8-bits. An IOAM encapsulating node MUST set the value to zero upon transmission. IOAM transit nodes MUST ignore the received value. Variable-length field. This is a list of node data elements where the content of each node data element is determined by the IOAM-Trace-Type. The order of packing the data fields in each node data element follows the bit order of the IOAM-Trace-Type field. Each node MUST prepend its node data element in front of the node data elements that it received, such that the transmitted node data list begins with this node's data element as the first populated element in the list. The last node data element in this list is the node data of the first IOAM capable node in the path. Populating the node data list in this way ensures that the order of node data list is the same for incremental and pre-allocated trace options. In the pre-allocated trace option, the index contained in RemainingLen identifies the offset for current active node data to be populated.

All the IOAM-Data-Fields MUST be 4-octet aligned. If a node which is supposed to update an IOAM-Data-Field is not capable of populating the value of a field set in the IOAM-Trace-Type, the field value MUST be set to 0xFFFFFFFF for 4-octet fields or 0xFFFFFFFFFFFFFFFF for 8-octet fields, indicating that the value is not populated, except when explicitly specified in the field description below. Some IOAM-Data-Fields defined below, such as interface identifiers or IOAM-Namespace specific data, are defined in both "short format" as well as "wide format". "Short format" refers to an IOAM-Data-Field which comprises 4 octets. "Wide format" refers to an IOAM-Data-Field which comprises 8 octets. The use of "short format" or "wide format" is not mutually exclusive. A deployment could choose to leverage both. For example, ingress_if_id_(short format) could be an identifier for the physical interface, whereas ingress_if_id_(wide format) could be an identifier for a logical sub-interface of that physical interface. Data fields and associated data types for each of the IOAM-Data-Fields are specified in the following sections. The definition of IOAM-Data-Fields focuses on the syntax of the data-fields and avoids specifying the semantics where feasible. This is why no units are defined for data-fields like e.g., "buffer occupancy" or "queue depth". With this approach, nodes can supply the information in their native format and are not required to perform unit or format conversions. Systems that further process IOAM information, like e.g., a network management system are assumed to also handle unit conversions as part of their IOAM data-fields processing. The combination of a particular data-field and the namespace-id provides for the context to interpret the provided data appropriately.

The "Hop_Lim and node_id short format" field is a 4-octet field that is defined as follows:

1-octet unsigned integer. It is set to the Hop Limit value in the packet at egress from the node that records this data. Hop Limit information is used to identify the location of the node in the communication path. This is copied from the lower layer, e.g., TTL value in IPv4 header or hop limit field from IPv6 header of the packet when the packet is ready for transmission. The semantics of the Hop_Lim field depend on the lower layer protocol that IOAM is encapsulated into, and therefore its specific semantics are outside the scope of this memo. The value of this field MUST be set to 0xff when the lower level does not have a TTL/Hop limit equivalent field. 3-octet unsigned integer. Node identifier field to uniquely identify a node within the IOAM-Namespace and associated IOAM-Domain. The procedure to allocate, manage and map the node_ids is beyond the scope of this document. See for a discussion of deployment related aspects of the node_id.

The "ingress_if_id and egress_if_id" field is a 4-octet field that is defined as follows:

2-octet unsigned integer. Interface identifier to record the ingress interface the packet was received on. 2-octet unsigned integer. Interface identifier to record the egress interface the packet is forwarded out of. Note that due to the fact that IOAM uses its own IOAM-Namespaces for IOAM-Data-Fields, data fields like interface identifiers can be used in a flexible way to represent system resources that are associated with ingressing or egressing packets, i.e., ingress_if_id could represent a physical interface, a virtual or logical interface, or even a queue.

The "timestamp seconds" field is a 4-octet unsigned integer field. It contains the absolute timestamp in seconds that specifies the time at which the packet was received by the node. This field has three possible formats; based on either PTP (see e.g., ), NTP , or POSIX . The three timestamp formats are specified in . In all three cases, the Timestamp Seconds field contains the 32 most significant bits of the timestamp format that is specified in . If a node is not capable of populating this field, it assigns the value 0xFFFFFFFF. Note that this is a legitimate value that is valid for 1 second in approximately 136 years; the analyzer has to correlate several packets or compare the timestamp value to its own time-of-day in order to detect the error indication.

The "timestamp fraction" field is a 4-octet unsigned integer field. Fraction specifies the fractional portion of the number of seconds since the NTP epoch . The field specifies the time at which the packet was received by the node. This field has three possible formats; based on either PTP (see e.g., ), NTP , or POSIX . The three timestamp formats are specified in . In all three cases, the Timestamp fraction field contains the 32 least significant bits of the timestamp format that is specified in . If a node is not capable of populating this field, it assigns the value 0xFFFFFFFF. Note that this is a legitimate value in the NTP format, valid for approximately 233 picoseconds in every second. If the NTP format is used the analyzer has to correlate several packets in order to detect the error indication.

The "transit delay" field is a 4-octet unsigned integer in the range 0 to 2^31-1. It is the time in nanoseconds the packet spent in the transit node. This can serve as an indication of the queuing delay at the node. If the transit delay exceeds 2^31-1 nanoseconds then the top bit 'O' is set to indicate overflow and value set to 0x80000000. When this field is part of the data field but a node populating the field is not able to fill it, the field position in the field MUST be filled with value 0xFFFFFFFF to mean not populated.

The "namespace specific data" field is a 4-octet field which can be used by the node to add IOAM-Namespace specific data. This represents a "free-format" 4-octet bit field with its semantics defined in the context of a specific IOAM-Namespace.

The "queue depth" field is a 4-octet unsigned integer field. This field indicates the current length of the egress interface queue of the interface from where the packet is forwarded out. The queue depth is expressed as the current amount of memory buffers used by the queue (a packet could consume one or more memory buffers, depending on its size).

The "Checksum Complement" field is a 4-octet node data which contains a 4-octet Checksum Complement field. The Checksum Complement is useful when IOAM is transported over encapsulations that make use of a UDP transport, such as VXLAN-GPE or Geneve. Without the Checksum Complement, nodes adding IOAM node data update the UDP Checksum field following the recommendation of the encapsulation protocols. When the Checksum Complement is present, an IOAM encapsulating node or IOAM transit node adding node data MUST carry out one of the following two alternatives in order to maintain the correctness of the UDP Checksum value: Recompute the UDP Checksum field. Use the Checksum Complement to make a checksum-neutral update in the UDP payload; the Checksum Complement is assigned a value that complements the rest of the node data fields that were added by the current node, causing the existing UDP Checksum field to remain correct. IOAM decapsulating nodes MUST recompute the UDP Checksum field, since they do not know whether previous hops modified the UDP Checksum field or the Checksum Complement field. Checksum Complement fields are used in a similar manner in and .

The "Hop_Lim and node_id wide" field is an 8-octet field defined as follows:

1-octet unsigned integer. See for the definition of the field. 7-octet unsigned integer. Node identifier field to uniquely identify a node within the IOAM-Namespace and associated IOAM-Domain. The procedure to allocate, manage and map the node_ids is beyond the scope of this document.

The "ingress_if_id and egress_if_id wide" field is an 8-octet field which is defined as follows:

4-octet unsigned integer. Interface identifier to record the ingress interface the packet was received on. 4-octet unsigned integer. Interface identifier to record the egress interface the packet is forwarded out of.

The "namespace specific data wide" field is an 8-octet field which can be used by the node to add IOAM-Namespace specific data. This represents a "free-format" 8-octet bit field with its semantics defined in the context of a specific IOAM-Namespace.

The "buffer occupancy" field is a 4-octet unsigned integer field. This field indicates the current status of the occupancy of the common buffer pool used by a set of queues. The units of this field are implementation specific. Hence, the units are interpreted within the context of an IOAM-Namespace and/or node-id if used. The authors acknowledge that in some operational cases there is a need for the units to be consistent across a packet path through the network, hence it is recommended for implementations to use standard units such as Bytes.

The "Opaque State Snapshot" is a variable length field and follows the fixed length IOAM-Data-Fields defined above. It allows the network element to store an arbitrary state in the node data field, without a pre-defined schema. The schema is to be defined within the context of an IOAM-Namespace. The schema needs to be made known to the analyzer by some out-of-band mechanism. The specification of this mechanism is beyond the scope of this document. A 24-bit "Schema Id" field, interpreted within the context of an IOAM-Namespace, indicates which particular schema is used, and has to be configured on the network element by the operator.

1-octet unsigned integer. It is the length in multiples of 4-octets of the Opaque data field that follows Schema Id. 3-octet unsigned integer identifying the schema of Opaque data. Variable length field. This field is interpreted as specified by the schema identified by the Schema ID. When this field is part of the data field but a node populating the field has no opaque state data to report, the Length MUST be set to 0 and the Schema ID MUST be set to 0xFFFFFF to mean no schema.

The format used for the entries in a packet's "node data list" array can vary from packet to packet and deployment to deployment". Some deployments might only be interested in recording the node identifiers, whereas others might be interested in recording node identifiers and timestamps. This section provides example entries of the "node data list". IOAM-Trace-Type is 0xD40000 (0b110101000000000000000000) then the format of node data is:

IOAM-Trace-Type is 0xC00000 (0b110000000000000000000000) then the format is:

IOAM-Trace-Type is 0x900000 (0b100100000000000000000000) then the format is:

IOAM-Trace-Type is 0x840000 (0b100001000000000000000000) then the format is:

IOAM-Trace-Type is 0x940000 (0b100101000000000000000000) then the format is:

IOAM-Trace-Type is 0x308002 (0b001100001000000000000010) then the format is:

IOAM Proof of Transit Option-Type is used to support path or service function chain verification use cases. Proof-of-transit leverages mechanisms like Shamir's Secret Sharing Schema (SSSS) . For further information on Proof-of-transit, please refer to . While details on how the IOAM data for the Proof-of-transit option is processed at IOAM encapsulating, decapsulating and transit nodes are outside the scope of the document, all of these approaches share the need to uniquely identify a packet as well as iteratively operate on a set of information that is handed from node to node. Correspondingly, two pieces of information are added as IOAM-Data-Fields to the packet: PktID: Unique identifier for the packet. Cumulative: Information which is handed from node to node and updated by every node according to a verification algorithm. The IOAM Proof-of-Transit Option-Type consist of a fixed size "IOAM proof of transit option header" and "IOAM proof of transit option data fields":

16-bit identifier of an IOAM-Namespace (see above). 8-bit identifier of a particular POT variant that specifies the POT data that is included (see above). For this case here, IOAM POT Type is set to the value 0. 1-bit. "Profile-to-use" (P-bit) (most significant bit), see above. Undefined (see above). 64-bit packet identifier. 64-bit Cumulative that is updated at specific nodes by processing per packet PktID field and configured parameters. Note: Larger or smaller sizes of "PktID" and "Cumulative" data are feasible and could be required for certain deployments, e.g., in case of space constraints in the encapsulation protocols used. Future documents could introduce different sizes of data for "proof of transit".

The IOAM Edge-to-Edge Option-Type is to carry 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 Edge-to-Edge Option-Type consist of a fixed size "IOAM Edge-to-Edge Option-Type header" and "IOAM Edge-to-Edge Option-Type data fields":

The IOAM-Data-Fields include a timestamp field which is represented in one of three possible timestamp formats. It is assumed that the management plane is responsible for determining which timestamp format is used.

The Precision Time Protocol (PTP) uses an 80-bit timestamp format. The truncated timestamp format is a 64-bit field, which is the 64 least significant bits of the 80-bit PTP timestamp. The PTP truncated format is specified in Section 4.3 of , and the details are presented below for the sake of completeness.

Timestamp field format: Seconds: specifies the integer portion of the number of seconds since the PTP epoch. + Size: 32 bits. + Units: seconds. Nanoseconds: specifies the fractional portion of the number of seconds since the PTP epoch. + Size: 32 bits. + Units: nanoseconds. The value of this field is in the range 0 to (10^9)-1. Epoch: PTP epoch. For details see e.g., . Resolution: The resolution is 1 nanosecond. Wraparound: This time format wraps around every 2^32 seconds, which is roughly 136 years. The next wraparound will occur in the year 2106. Synchronization Aspects: It is assumed that nodes that run this protocol are synchronized among themselves. Nodes MAY be synchronized to a global reference time. Note that if PTP is used for synchronization, the timestamp MAY be derived from the PTP-synchronized clock, allowing the timestamp to be measured with respect to the clock of an PTP Grandmaster clock. The PTP truncated timestamp format is not affected by leap seconds.

The Network Time Protocol (NTP) timestamp format is 64 bits long. This format is specified in Section 4.2.1 of , and the details are presented below for the sake of completeness.

Timestamp field format: Seconds: specifies the integer portion of the number of seconds since the NTP epoch. + Size: 32 bits. + Units: seconds. Fraction: specifies the fractional portion of the number of seconds since the NTP epoch. + Size: 32 bits. + Units: the unit is 2^(-32) seconds, which is roughly equal to 233 picoseconds. Epoch: NTP Epoch. For details see . Resolution: The resolution is 2^(-32) seconds. Wraparound: This time format wraps around every 2^32 seconds, which is roughly 136 years. The next wraparound will occur in the year 2036. Synchronization Aspects: Nodes that use this timestamp format will typically be synchronized to UTC using NTP . Thus, the timestamp MAY be derived from the NTP-synchronized clock, allowing the timestamp to be measured with respect to the clock of an NTP server. The NTP timestamp format is affected by leap seconds; it represents the number of seconds since the epoch minus the number of leap seconds that have occurred since the epoch. The value of a timestamp during or slightly after a leap second could be temporarily inaccurate.

This timestamp format is based on the POSIX time format . The detailed specification of the timestamp format used in this document is presented below.

Timestamp field format: Seconds: specifies the integer portion of the number of seconds since the POSIX epoch. + Size: 32 bits. + Units: seconds. Microseconds: specifies the fractional portion of the number of seconds since the POSIX epoch. + Size: 32 bits. + Units: the unit is microseconds. The value of this field is in the range 0 to (10^6)-1. Epoch: POSIX epoch. For details, see , appendix A.4.16. Resolution: The resolution is 1 microsecond. Wraparound: This time format wraps around every 2^32 seconds, which is roughly 136 years. The next wraparound will occur in the year 2106. Synchronization Aspects: It is assumed that nodes that use this timestamp format run the Linux operating system, and hence use the POSIX time. In some cases nodes MAY be synchronized to UTC using a synchronization mechanism that is outside the scope of this document, such as NTP . Thus, the timestamp MAY be derived from the NTP-synchronized clock, allowing the timestamp to be measured with respect to the clock of an NTP server.

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., IPFIX. The mechanisms and associated data formats for exporting IOAM data is outside the scope of this document. Raw data export of IOAM data using IPFIX is discussed in .

This document requests the following IANA Actions. IANA is requested to define a registry group named "In-Situ OAM (IOAM) Protocol Parameters". This group will include the following registries: IOAM Option-Type IOAM Trace-Type IOAM Trace-Flags IOAM POT-Type IOAM POT-Flags IOAM E2E-Type IOAM Namespace-ID New registries in this group can be created via RFC Required process as per . The subsequent sub-sections detail the registries herein contained.

This registry defines 128 code points for the IOAM Option-Type field for identifying IOAM Option-Types as explained in . The following code points are defined in this draft: IOAM Pre-allocated Trace Option-Type IOAM Incremental Trace Option-Type IOAM POT Option-Type IOAM E2E Option-Type 4 - 127 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Name of the newly registered Option-Type. Desired value of the requested code point. Brief description of the newly registered Option-Type. Reference to the document that defines the new Option-Type.

This registry defines code point for each bit in the 24-bit IOAM-Trace-Type field for Pre-allocated Trace-Option-Type and Incremental Trace-Option-Type defined in . The meaning of Bits 0 - 11 is defined in this document in of : hop_Lim and node_id in short format ingress_if_id and egress_if_id in short format timestamp seconds timestamp fraction transit delay namespace specific data in short format queue depth checksum complement hop_Lim and node_id in wide format ingress_if_id and egress_if_id in wide format namespace specific data in wide format buffer occupancy variable length Opaque State Snapshot reserved The meaning for Bits 12 - 21 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Desired bit to be allocated in the 24-bit IOAM Trace-Option-Type field for Pre-allocated Trace-Option-Type and Incremental Trace-Option-Type. Brief description of the newly registered bit. Reference to the document that defines the new bit.

This registry defines code points for each bit in the 4 bit flags for the Pre-allocated trace option and for the Incremental trace option defined in . The meaning of Bit 0 (the most significant bit) for trace flags is defined in this document in of : "Overflow" (O-bit) Bit 1 - 3 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Desired bit to be allocated in the 8 bit flags field of the Pre-allocated Trace-Option-Type and for the Incremental Trace-Option-Type. Brief description of the newly registered bit. Reference to the document that defines the new bit.

This registry defines 256 code points to define IOAM POT Type for IOAM proof of transit option . The code point value 0 is defined in this document: 16 Octet POT data 1 - 255 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Name of the newly registered POT-Type. Desired value of the requested code point. Brief description of the newly registered POT-Type. Reference to the document that defines the new POT-Type.

This registry defines code points for each bit in the 8 bit flags for IOAM POT Option-Type defined in . The meaning of Bit 0 for IOAM POT flags is defined in this document in : "Profile-to-use" (P-bit) The meaning for Bits 1 - 7 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Desired bit to be allocated in the 8 bit flags field of the IOAM POT Option-Type. Brief description of the newly registered bit. Reference to the document that defines the new bit.

This registry defines code points for each bit in the 16 bit IOAM-E2E-Type field for IOAM E2E option . The meaning of Bit 0 - 3 are defined in this document: 64-bit sequence number 32-bit sequence number timestamp seconds timestamp fraction The meaning of Bits 4 - 15 are available for assignment via "IETF Review" process as per . New registration requests MUST use the following template: Desired bit to be allocated in the 16 bit IOAM-E2E-Type field. Brief description of the newly registered bit. Reference to the document that defines the new bit.

IANA is requested to set up an "IOAM Namespace-ID Registry", containing 16-bit values and following the template for requests shown below. The meaning of 0x0000 is defined in this document. IANA is requested to reserve the values 0x0001 to 0x7FFF for private use (managed by operators), as specified in of the current document. Registry entries for the values 0x8000 to 0xFFFF are to be assigned via the "Expert Review" policy defined in . Upon receiving a new allocation request, a designated expert will perform the following: Review whether the request is complete, i.e., the registration template has been filled in. The expert will send incomplete requests back to the requestor. Check whether the request is neither a duplicate of nor conflicting with either an already existing allocation or a pending allocation. In case of duplicates or conflicts, the expert will ask the requestor to update the allocation request accordingly. Solicit feedback from relevant working groups and communities to ensure that the new allocation request has been properly reviewed and that rough consensus on the request exists. At a minumum, the expert will solicit feedback from the IPPM working group in the IETF by posting the request to the ippm@ietf.org mailing list. If the feedback received from the relevant working groups and communities indicates rough consensus on the request, the expert will approve the request and ask IANA for allocating the new Namespace-ID. In case the expert senses a lack of consensus from the feedback received, the expert will ask the requestor to engage with the corresponding working groups and communities to further review and refine the request. It is intended that any allocation will be accompanied by a published RFC. In order to allow for the allocation of code points prior to the RFC being approved for publication, the designated expert can approve allocations once it seems clear that an RFC will be published. default namespace (known to all IOAM nodes) reserved for private use unassigned New registration requests MUST use the following template: Name of the newly registered Namespace-ID. Desired value of the requested Namespace-ID. Brief description of the newly registered Namespace-ID. Reference to the document that defines the new Namespace-ID. Status can be either "permanent" or "provisional". Namespace-ID registrations following a successful expert review will have the status "provisional". Once the RFC, which defines the new Namespace-ID is published, the status is changed to "permanent".

This document defines the structure and use of IOAM data fields. This document does not define the encapsulation of IOAM data fields into different protocols. Management and deployment aspects for IOAM have to be considered within the context of the protocol IOAM data fields are encapsulated into and as such, are out of scope for this document. For a discussion of IOAM deployment, please also refer to , which outlines a framework for IOAM deployment and provides best current practices.

As discussed in , a successful attack on an OAM protocol in general, and specifically on IOAM, can prevent the detection of failures or anomalies, or create a false illusion of nonexistent ones. In particular, these threats are applicable by compromising the integrity of IOAM data, either by maliciously modifying IOAM options in transit, or by injecting packets with maliciously generated IOAM options. All nodes in the path of a IOAM carrying packet can perform such an attack. The Proof of Transit Option-Type (see ) is used for verifying the path of data packets. The security considerations of POT are further discussed in . In case an attacker gains access to several nodes in a network and would be able to change the system software of these nodes, IOAM data fields could be misused and repurposed for a use different from what is specified in this document. One type of misuse is the implementation of a covert channel between network nodes. From a confidentiality perspective, although IOAM options are not expected to contain user data, they can be used for network reconnaissance, allowing attackers to collect information about network paths, performance, queue states, buffer occupancy and other information. Moreover, if IOAM data leaks from the IOAM domain it could enable reconnaissance beyond the scope of the IOAM domain. IOAM can be used as a means for implementing Denial of Service (DoS) attacks, or for amplifying them. For example, a malicious attacker can add an IOAM header to packets in order to consume the resources of network devices that take part in IOAM or entities that receive, collect or 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. In case POT is used, an attacker could corrupt the POT data fields in the packet, resulting in a verification failure of the POT data, even if the packet followed the correct path. Since IOAM options can include timestamps, if network devices use synchronization protocols then any attack on the time protocol can compromise the integrity of the timestamp-related data fields. At the management plane, attacks can be set up by misconfiguring or by maliciously configuring IOAM-enabled nodes in a way that enables other attacks. IOAM configuration should only managed by authorized processes or users. Solutions to ensure the integrity of IOAM data fields are outside the scope of this document. discusses several methods to ensure the integrity of IOAM data fields for those deployments that have a need to protect the integrity of IOAM data fields. The current document does not define a specific IOAM encapsulation. It has to be noted that some IOAM encapsulation types can introduce specific security considerations. A specification that defines an IOAM encapsulation is expected to address the respective encapsulation-specific security considerations. Notably, IOAM is expected to be deployed in limited domains, thus confining the potential attack vectors to within the limited domain. A limited administrative domain provides the operator with the means to select, monitor, and control the access of all the network devices, making these devices trusted by the operator. Indeed, in order to limit the scope of threats mentioned above to within the current limited domain the network operator is expected to enforce policies that prevent IOAM traffic from leaking outside of the IOAM domain, and prevent IOAM data from outside the domain to be processed and used within the domain. The security considerations of a system that deploys IOAM, much like any system, has to be reviewed on a per-deployment-scenario basis, based on a systems-specific threat analysis, which can lead to specific security solutions that are beyond the scope of the current document. Specifically, in an IOAM deployment that is not confined to a single LAN, but spans multiple inter-connected sites (for example, using an overlay network), the inter-site links can be secured (e.g., by IPsec) in order to avoid external threats. IOAM deployment considerations, including approaches to mitigate the above discussed threads and potential attacks are outside the scope of this document. IOAM deployment considerations are discussed in .

The authors would like to thank Eric Vyncke, Nalini Elkins, Srihari Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya Nadahalli, LJ Wobker, Erik Nordmark, Vengada Prasad Govindan, Andrew Yourtchenko, Aviv Kfir, Tianran Zhou, Zhenbin (Robin) and Greg Mirsky for the comments and advice. This document leverages and builds on top of several concepts described in . The authors would like to acknowledge the work done by the author Hiroshi Kitamura and people involved in writing it. The authors would like to gracefully acknowledge useful review and insightful comments received from Joe Clarke, Al Morton, Tom Herbert, Haoyu Song, Mickey Spiegel, Roman Danyliw, Benjamin Kaduk, Ian Swett, Martin Duke, Francesca Palombini, Lars Eggert, Dan Romascanu and Barak Gafni.