Data Fields for In-situ OAM

This section defines IOAM data types and data fields and associated data types required for IOAM. The different uses of IOAM require the definition of different types of data. The IOAM data fields for the data being carried corresponds to the three main categories of IOAM data defined in , which are: edge-to-edge, per node, and for selected nodes only. Transport options for IOAM data are outside the scope of this memo, and are discussed in . IOAM data fields are fixed length data fields. A bit field determines the set of OAM data fields embedded in a packet. Depending on the type of the encapsulation, a counter field indicates how many data fields are included in a particular packet. IOAM is expected to be deployed in a specific domain rather than on the overall Internet. The part of the network which employs IOAM is referred to as the "IOAM-domain". IOAM data is added to a packet upon entering the IOAM-domain and is removed from the packet when exiting the domain. Within the IOAM-domain, the IOAM data may be updated by network nodes that the packet traverses. The device which adds an IOAM data container to the packet to capture IOAM data is called the "IOAM encapsulating node", whereas the device which removes the IOAM data container 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 container can also update the IOAM data fields at the same time. Or in other words, IOAM encapsulation 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 Segment Routing deployment might require the segment routing path to be verified. In that case, only the SR nodes would also be IOAM transit nodes rather than all nodes.

"IOAM tracing data" is expected to be collected at every 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 in-situ OAM-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 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 tracing is defined as two separate options. Any deployment MAY choose to configure and support one or both of the following options. An implementation of the transport protocol that carries these in-situ OAM data MAY choose to support only one of the options. 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. 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 enabled for a particular domain. 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 software implementations where it is efficient to allocate the space once and index into the array to populate the data during transit. The IOAM encapsulating node allocates the option header and sets the fields in the option header. The in situ OAM 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. A pointer which is part of the IOAM trace data points to the next empty slot in the array, which is where the next IOAM transit node fills in its data. 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. The maximum length of the node data list is written into the option header. This type of trace recording is useful for some of the hardware implementations as this 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 in-situ OAM encapsulating node allocates the option header. The in-situ OAM encapsulating node based on operational state and configuration sets the fields in the header to control how large the node data list can grow. IOAM transit nodes push their node data to the node data list and increment the number of node data fields in the header. Every node data entry is to hold information for a particular IOAM transit node that is traversed by a packet. The in-situ OAM decapsulating node removes the IOAM data and processes and/or exports the metadata. IOAM data uses its own name-space for information such as node identifier or interface identifier. This allows for a domain-specific definition and interpretation. For example: In one case an interface-id could 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). The following IOAM data is defined for IOAM tracing: 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. 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 deployment, 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. A mechanism to detect whether IOAM trace data was added at every hop or whether certain hops in the domain weren't in-situ OAM transit nodes. The "node data list" array 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.

A 16-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 bit fields are defined in this document, with details on each field 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 nanoseconds in the node data. When set indicates presence of transit delay in the node data. When set indicates presence of app_data (short format) in the node data. When set indicates presence of queue depth in the node data. When set indicates presence of variable length Opaque State Snapshot field. 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 app_data wide in the node data. When set indicates presence of the Checksum Complement node data. Undefined in this draft. describes the IOAM data types and their formats. Within an in-situ OAM domain possible combinations of these bits making the IOAM-Trace-Type can be restricted by configuration knobs. 4-bit unsigned integer. This field specifies the length of data added by each node in multiples of 4-octets. For example, if 3 IOAM-Trace-Type bits are set and none of them is wide, then the Node Data Length would be 3. If 3 IOAM-Trace-Type bits are set and 2 of them are wide, then the Node Data Length would be 5. 5-bit field. Following flags are defined: "Overflow" (O-bit) (most significant bit). This bit is set by the network element if there is not enough number of octets left to record node data, no field is added and the overflow "O-bit" must be set to "1" in the header. This is useful for transit nodes to ignore further processing of the option. "Loopback" (L-bit). Loopback mode is used to send a copy of a packet back towards the source. Loopback mode assumes that a return path from transit nodes and destination nodes towards the source exists. The encapsulating node decides (e.g. using a filter) which packets loopback mode is enabled for by setting the loopback bit. The encapsulating node also needs to ensure that sufficient space is available in the IOAM header for loopback operation. The loopback bit when set indicates to the transit nodes processing this option to create a copy of the packet received and send this copy of the packet back to the source of the packet while it continues to forward the original packet towards the destination. The source address of the original packet is used as destination address in the copied packet. The address of the node performing the copy operation is used as the source address. The L-bit MUST be cleared in the copy of the packet a nodes sends it back towards the source. On its way back towards the source, the packet is processed like a regular packet with IOAM information. Once the return packet reaches the IOAM domain boundary IOAM decapsulation occurs as with any other packet containing IOAM information. Reserved: Must be zero. 7-bit unsigned integer. It is the data space in multiples of 4-octets remaining for recording the node data. This is used as an offset in data space to record the node data element. Variable-length field. The type of which is determined by the IOAM-Trace-Type 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. The index contained in "Octets-left" identifies the offset for current active node data to be populated.

A 16-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 bit fields are defined in this document, with details on each field 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 nanoseconds in the node data. When set indicates presence of transit delay in the node data. When set indicates presence of app_data in the node data. When set indicates presence of queue depth in the node data. When set indicates presence of variable length Opaque State Snapshot field. When set indicates presence of Hop_Lim and node_id wide 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 app_data wide in the node data. When set indicates presence of the Checksum Complement node data. Undefined in this draft. describes the IOAM data types and their formats. 4-bit unsigned integer. This field specifies the length of data added by each node in multiples of 4-octets. For example, if 3 IOAM-Trace-Type bits are set and none of them is wide, then the Node Data Length would be 3. If 3 IOAM-Trace-Type bits are set and 2 of them are wide, then the Node Data Length would be 5. 5-bit field. Following flags are defined: "Overflow" (O-bit) (least significant bit). This bit is set by the network element if there is not enough number of octets left to record node data, no field is added and the overflow "O-bit" must be set to "1" in the header. This is useful for transit nodes to ignore further processing of the option. "Loopback" (L-bit). This bit when set indicates to the transit nodes processing this option to send a copy of the packet back to the source of the packet while it continues to forward the original packet towards the destination. The L-bit MUST be cleared in the copy of the packet before sending it. Reserved. Must be zero. 7-bit unsigned integer. This field specifies the maximum length of the node data list in multiples of 4-octets. Given that the sender knows the minimum path MTU, the sender can set the maximum length according to the number of node data bytes allowed before exceeding the MTU. Thus, a simple comparison between "Opt data Len" and "Max Length" allows to decide whether or not data could be added. Variable-length field. The type of which is determined by the OAM Type 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.

All the data fields MUST be 4-octet aligned. The IOAM encapsulating node MUST initialize data fields that it adds to the packet to zero. 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 left unaltered except when explicitly specified in the field description below. In the description of data below if zero is valid value then a non-zero value to mean not populated is specified. Data field and associated data type for each of the data field 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 in-situ OAM domain. The procedure to allocate, manage and map the node_ids is beyond the scope of this document. 4-octet field defined as follows: When this field is part of the data field but a node populating the field is not able to fill it, the position in the field must be filled with value 0xFFFFFFFF to mean not populated.

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. 4-octet unsigned integer. Absolute timestamp in seconds that specifies the time at which the packet was received by the node. The structure of this field is identical to the most significant 32 bits of the 64 least significant bits of the timestamp. This truncated field consists of a 32-bit seconds field. As defined in , the timestamp specifies the number of seconds elapsed since 1 January 1970 00:00:00 according to the International Atomic Time (TAI).

4-octet unsigned integer in the range 0 to 10^9-1. This timestamp specifies the fractional part of the wall clock time at which the packet was received by the node in units of nanoseconds. This field is identical to the 32 least significant bits of the timestamp. This fields allows for delay computation between any two nodes in the network when the nodes are time synchronized. 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 unsigned integer in the range 0 to 2^30-1. 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 2^30-1 nanoseconds then the top bit 'O' is set to indicate overflow. 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 placeholder which can be used by the node to add application specific data. App_data represents a "free-format" 4-octet bit field with its semantics defined by a specific deployment.

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). 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.

Variable length field. It allows the network element to store an arbitrary state in the node data field , without a pre-defined schema. 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. The 24-bit "Schema Id" field in the field 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 octets of the Opaque data field that follows Schema Id. It MUST always be a multiple of 4. 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. 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 in-situ OAM domain. The procedure to allocate, manage and map the node_ids is beyond the scope of this document. 8-octet field defined as follows: 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 0xFFFFFFFFFFFFFFFF to mean not populated.

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 placeholder which can be used by the node to add application specific data. App data represents a "free-format" 8-octed bit field with its semantics defined by a specific deployment.

4-octet node data which contains a two-octet Checksum Complement field, and a 2-octet reserved field. The Checksum Complement can be used when IOAM is transported over encapsulations that make use of a UDP transport, such as VXLAN-GPE or Geneve. In this case, incorporating the IOAM node data requires the UDP Checksum field to be updated. Rather than to recompute the Chekcsum field, a node can 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. Checksum Complement fields are used in a similar manner in and .

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 defines different types that an entry in "node data list" can take. IOAM-Trace-Type is 0x2B then the format of node data is:

IOAM-Trace-Type is 0x0003 then the format is:

IOAM-Trace-Type is 0x0009 then the format is:

IOAM-Trace-Type is 0x0021 then the format is:

IOAM-Trace-Type is 0x0029 then the format is:

IOAM-Trace-Type is 0x104D then the format is:

IOAM Proof of Transit data is to support the 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 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.

7-bit identifier of a particular POT variant that dictates the POT data that is included. This document defines POT Type 0: POT data is a 16 Octet field as described below. 1-bit. Indicates which POT-profile is used to generate the Cumulative. Any node participating in POT will have a maximum of 2 profiles configured that drive the computation of cumulative. The two profiles are numbered 0, 1. This bit conveys whether profile 0 or profile 1 is used to compute the Cumulative. 64-bit Per packet Random number. 64-bit Cumulative that is updated at specific nodes by processing per packet Random number field and configured parameters. Note: Larger or smaller sizes of "Random" and "Cumulative" data are feasible and could be required for certain deployments (e.g. in case of space constraints in the transport protocol used). Future versions of this document will address different sizes of data for "proof of transit".

The IOAM edge-to-edge option 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 without modifying it. Currently only sequence numbers use the IOAM edge-to-edge option. In order to detect packet loss, packet reordering, or packet duplication in an in-situ OAM-domain, sequence numbers can be added to packets of a particular tube (see ). Each tube leverages a dedicated namespace for its sequence numbers.

8-bit identifier of a particular in situ OAM E2E variant. 0: E2E option data is a 64-bit sequence number added to a specific tube which is used to identify packet loss and reordering for that tube.