Data Fields for In-situ OAM

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. IOAM-Data-Fields can be encapsulated into a variety of protocols, such as NSH, Geneve, IPv6, etc. The definition of how IOAM-Data-Fields are encapsulated into other protocols is outside the scope of this document. 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

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 the "IOAM encapsulating node", whereas a device which removes an IOAM-Option-Type is referred to as the "IOAM decapsulating node". Nodes within the domain which are aware of IOAM data and read and/or write or process the 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" 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. A transit node MUST NOT add new IOAM-Option-Types to 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. 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.

A subset or all of the IOAM-Option-Types and their corresponding IOAM-Data-Fields can be associated to an IOAM-Namespace. IOAM-Namespaces add further context to IOAM-Option-Types and associated IOAM-Data-Fields. Any IOAM-Namespace MUST interpret the IOAM-Option-Types and associated IOAM-Data-Fields per the definition in this document. IOAM-Namespaces group nodes to support different deployment approaches of IOAM (see a few example use-cases below) as well as resolve 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. An IOAM-Namespace is identified by a 16-bit namespace identifier (Namespace-ID). IOAM-Namespace identifiers MUST be present and populated in all 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 default and known to all the nodes implementing IOAM. 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) should 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 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 (node_id, see below) 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 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 at 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 are IOAM capable, IOAM tracing information (i.e., node data, see below) will only be collected on those nodes which are IOAM capable. Nodes which 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 is assumed to be known. To optimize hardware and software implementations IOAM tracing is defined as two separate options. Any deployment MAY 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 should be collected and how large the node data list can grow. IOAM transit nodes push their node data to the node data list, decrease the remaining length available to subsequent nodes and adjust the lengths and possibly checksums in outer headers. A particular implementation of IOAM MAY choose to support only one of the two trace option types. In the event that both options are utilized at the same time, the Incremental Trace-Option MUST be placed before the Pre-allocated Trace-Option. Deployments which mix devices which 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, 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 should 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.

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":

16-bit identifier of an IOAM-Namespace. The Namespace-ID value of 0x0000 is defined as the default value 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 + Opaque Data Length). For example, if 3 IOAM-Trace-Type bits are set and none of them are wide, 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 may rely on the NodeLen value, or it may ignore the NodeLen value and calculate the node length from the IOAM-Trace-Type bits (see below). 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). This bit is set by the network element if there are not enough octets left to record node data, no field is added and the overflow "O-bit" must be set 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. When RemainingLen reaches 0, nodes are no longer allowed to add node data. Given that the sender knows the minimum path MTU, the sender MAY set the initial value of RemainingLen according to the number of node data bytes allowed before exceeding the MTU. 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, RemainingLength 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. 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 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 subseconds 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. An IOAM encapsulating node MUST set the value of each of these bits 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. 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. Must be zero. Variable-length field. The type of which is determined by the IOAM-Trace-Type bit representing the n-th node data in the node data list. The node data list is encoded starting from the last node data of the path. The first element of the node data list (node data list [0]) contains the last node of the path while the last node data of the node data list (node data list[n]) contains the first node data of the path traced. 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". Their use is not 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 field and associated data type for each of the IOAM-Data-Fields is shown below: 4-octet field defined as follows:

1-octet unsigned integer. It is set to the Hop Limit value in the packet at 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 over, and therefore its specific semantics are outside the scope of this memo. 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. 4-octet field 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. 4-octet unsigned integer. 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 , 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 should correlate several packets or compare the timestamp value to its own time-of-day in order to detect the error indication. 4-octet unsigned integer. Absolute timestamp in subseconds that specifies the time at which the packet was received by the node. This field has three possible formats; based on either PTP , NTP , or POSIX . The three timestamp formats are specified in . In all three cases, the Timestamp Subseconds 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 should correlate several packets in order to detect the error indication. 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.

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.

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 number of memory buffers used by the queue (a packet may consume one or more memory buffers, depending on its size).

8-octet field defined as follows:

1-octet unsigned integer. It is set to the Hop Limit value in the packet at 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 for e.g. TTL value in IPv4 header or hop limit field from IPv6 header of the packet. The semantics of the Hop_Lim field depend on the lower layer protocol that IOAM is encapsulated over, and therefore its specific semantics are outside the scope of this memo. 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. 8-octet field 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. 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.

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 depend on the equipment type and deployment and has to be interpreted within the context of an IOAM-Namespace and/or node-id if used.

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 must update the UDP Checksum field. 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 .

Opaque State Snapshot is a variable length field and immediately 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 should 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.

An entry in the "node data list" array can have different formats, following the needs of the deployment. Some deployments might only be interested in recording the node identifiers, whereas others might be interested in recording node identifier and timestamp. The 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 to support path or service function chain verification use cases. Proof-of-transit uses methods like nested hashing or nested encryption of the IOAM data or mechanisms such as Shamir's Secret Sharing Schema (SSSS). 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: Random: Unique identifier for the packet (e.g., 64-bits allow for the unique identification of 2^64 packets). 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":

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":