In Situ Operations, Administration, and Maintenance (IOAM) Direct Exporting

In Situ Operations, Administration, and Maintenance (IOAM) Direct Exporting Futurewei

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Nvidia

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Cisco Systems, Inc.

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Thoughtspot

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Huawei

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tsv ippm IOAM Telemetry In situ Operations, Administration, and Maintenance (IOAM) is used for recording and collecting operational and telemetry information. Specifically, IOAM allows telemetry data to be pushed into data packets while they traverse the network. This document introduces a new IOAM option type (denoted IOAM-Option-Type) called the "IOAM Direct Export (DEX) Option-Type". This Option-Type is used as a trigger for IOAM data to be directly exported or locally aggregated without being pushed into in-flight data packets. The exporting method and format are outside the scope of this document.

Introduction IOAM is used for monitoring traffic in the network and for incorporating IOAM data fields (denoted IOAM-Data-Fields) into in-flight data packets. IOAM makes use of four possible IOAM-Option-Types, defined in : Pre-allocated Trace, Incremental Trace, Proof of Transit (POT), and Edge-to-Edge. This document defines a new IOAM-Option-Type called the "IOAM Direct Export (DEX) Option-Type". This Option-Type is used as a trigger for IOAM nodes to locally aggregate and process IOAM data and/or to export it to a receiving entity (or entities). Throughout the document, this functionality is referred to as "collection" and/or "exporting". In this context, a "receiving entity" is an entity that resides within the IOAM domain such as a collector, analyzer, controller, decapsulating node, or software module in one of the IOAM nodes. Note that even though the IOAM-Option-Type is called "Direct Export", it depends on the deployment whether the receipt of a packet with a DEX Option-Type leads to the creation of another packet. Some deployments might simply use the packet with the DEX Option-Type to trigger local processing of Operations, Administration, and Maintenance (OAM) data. The functionality of this local processing is not within the scope of this document.

Conventions

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology Abbreviations used in this document:

IOAM:: In situ Operations, Administration, and Maintenance
OAM:: Operations, Administration, and Maintenance
DEX:: Direct Exporting

The Direct Exporting (DEX) IOAM-Option-Type

Overview The DEX Option-Type is used as a trigger for collecting IOAM data locally or exporting it to a receiving entity (or entities). Specifically, the DEX Option-Type can be used as a trigger for collecting IOAM data by an IOAM node and locally aggregating it; thus, this aggregated data can be periodically pushed to a receiving entity or pulled by a receiving entity on-demand. This Option-Type is incorporated into data packets by an IOAM encapsulating node and removed by an IOAM decapsulating node, as illustrated in . The Option-Type can be read, but not modified, by transit nodes. Note that the terms "IOAM encapsulating node", "IOAM decapsulating node", and "IOAM transit node" are as defined in .

DEX Architecture |lating |====>| Node |====>| Node |====>|lating |----> |Node | | A | | B | |Node | +--------+ +--------+ +--------+ +--------+ Insert DEX Export Export Remove DEX option and IOAM data IOAM data option and export data export data]]> The DEX Option-Type is used as a trigger to collect and/or export IOAM data. The trigger applies to transit nodes, the decapsulating node, and the encapsulating node:

An IOAM encapsulating node configured to incorporate the DEX Option-Type encapsulates the packets (or possibly a subset of the packets) it forwards with the DEX Option-Type and MAY export and/or collect the requested IOAM data immediately. Only IOAM encapsulating nodes are allowed to add the DEX Option-Type to a packet. An IOAM encapsulating node can generate probe packets that incorporate the DEX Option-Type. These probe packets can be generated periodically or on-demand (for example, triggered by the management plane). The specification of such probe packets is outside the scope of this document.
A transit node that processes a packet with the DEX Option-Type MAY export and/or collect the requested IOAM data.
An IOAM decapsulating node that processes a packet with the DEX Option-Type MAY export and/or collect the requested IOAM data and MUST decapsulate the IOAM header.

As in , the DEX Option-Type can be incorporated into all or a subset of the traffic that is forwarded by the encapsulating node, as further discussed in . Moreover, IOAM nodes respond to the DEX trigger by exporting and/or collecting IOAM data either for all traversing packets that carry the DEX Option-Type or selectively only for a subset of these packets, as further discussed in .

DEX Packet Selection If an IOAM encapsulating node incorporates the DEX Option-Type into all the traffic it forwards, it may lead to an excessive amount of exported data, which may overload the network and the receiving entity. Therefore, an IOAM encapsulating node that supports the DEX Option-Type MUST support the ability to incorporate the DEX Option-Type selectively into a subset of the packets that are forwarded by the IOAM encapsulating node. Various methods of packet selection and sampling have been previously defined, such as and . Similar techniques can be applied by an IOAM encapsulating node to apply DEX to a subset of the forwarded traffic. The subset of traffic that is forwarded or transmitted with a DEX Option-Type SHOULD NOT exceed 1/N of the interface capacity on any of the IOAM encapsulating node's interfaces. It is noted that this requirement applies to the total traffic that incorporates a DEX Option-Type, including traffic that is forwarded by the IOAM encapsulating node and probe packets that are generated by the IOAM encapsulating node. In this context, N is a parameter that can be configurable by network operators. If there is an upper bound, M, on the number of IOAM transit nodes in any path in the network, then it is RECOMMENDED to use an N such that N >> M (i.e., N is much greater than M). The rationale is that a packet that includes a DEX Option-Type may trigger an exported packet from each IOAM transit node along the path for a total of M exported packets. Thus, if N >> M, then the number of exported packets is significantly lower than the number of data packets forwarded by the IOAM encapsulating node. If there is no prior knowledge about the network topology or size, it is RECOMMENDED to use N>100.

Responding to the DEX Trigger The DEX Option-Type specifies which IOAM-Data-Fields should be exported and/or collected, as specified in . As mentioned above, the data can be locally collected, aggregated, and/or exported to a receiving entity proactively or on-demand. If IOAM data is exported, the format and encapsulation of the packet that contains the exported data is not within the scope of the current document. For example, the export format can be based on . An IOAM node that performs DEX-triggered exporting MUST support the ability to limit the rate of the exported packets. The rate of exported packets SHOULD be limited so that the number of exported packets is significantly lower than the number of packets that are forwarded by the device. The exported data rate SHOULD NOT exceed 1/N of the interface capacity on any of the IOAM node's interfaces. It is RECOMMENDED to use N>100. Depending on the IOAM node's architecture considerations, the export rate may be limited to a lower number in order to avoid loading the IOAM node. An IOAM node MAY maintain a counter or a set of counters that count the events in which the IOAM node receives a packet with the DEX Option-Type and does not collect and/or export data due to the rate limits. IOAM nodes SHOULD NOT be configured to export packets over a path or a tunnel that is subject to IOAM direct exporting. Furthermore, IOAM encapsulating nodes that can identify a packet as an IOAM exported packet MUST NOT push a DEX Option-Type into such a packet. This requirement is intended to prevent nested exporting and/or exporting loops. A transit or decapsulating IOAM node that receives an unknown IOAM-Option-Type ignores it (as defined in ); specifically, nodes that do not support the DEX Option-Type ignore it. As per , note that a decapsulating node removes the IOAM encapsulation and all its IOAM-Option-Types. Specifically, this applies to the case where one of these options is a (possibly unknown) DEX Option-Type. The ability to skip over a (possibly unknown) DEX Option-Type in the parsing or in the decapsulation procedure is dependent on the specific encapsulation, which is outside the scope of this document. For example, when IOAM is encapsulated in IPv6 , the DEX Option-Type is incorporated either in a Hop-by-Hop options header or in a Destination options header; thus, it can be skipped using the length field in the options header.

The DEX Option-Type Format The format of the DEX Option-Type is depicted in . The length of the DEX Option-Type is at least 8 octets. The DEX Option-Type MAY include one or more optional fields. The existence of the optional fields is indicated by the corresponding flags in the Extension-Flags field. Two optional fields are defined in this document: the Flow ID and Sequence Number fields. Every optional field MUST be exactly 4 octets long. Thus, the Extension-Flags field explicitly indicates the length of the DEX Option-Type. Defining a new optional field requires an allocation of a corresponding flag in the Extension-Flags field, as specified in .

DEX Option-Type Format

Namespace-ID:

A 16-bit identifier of the IOAM namespace, as defined in .

Flags:

An 8-bit field, comprised of 8 1-bit subfields. Flags are allocated by IANA, as defined in .

Extension-Flags:

An 8-bit field, comprised of 8 1-bit subfields. Extension-Flags are allocated by IANA, as defined in . Every bit in the Extension-Flag field that is set to 1 indicates the existence of a corresponding optional 4-octet field. An IOAM node that receives a DEX Option-Type with an unknown flag set to 1 MUST ignore the corresponding optional field.

IOAM-Trace-Type:

A 24-bit identifier that specifies which IOAM-Data-Fields should be exported. The format of this field is as defined in . Specifically, the bit that corresponds to the Checksum Complement IOAM-Data-Field SHOULD be assigned to be zero by the IOAM encapsulating node and ignored by transit and decapsulating nodes. The reason for this is that the Checksum Complement is intended for in-flight packet modifications and is not relevant for direct exporting.

Reserved:

This field MUST be ignored by the receiver.

Optional fields:

The optional fields, if present, reside after the Reserved field. The order of the optional fields is according to the order of the respective bits, starting from the most significant bit, that are enabled in the Extension-Flags field. Each optional field is 4 octets long.

Flow ID:: An optional 32-bit field representing the flow identifier. If the actual Flow ID is shorter than 32 bits, it is zero padded in its most significant bits. The field is set at the encapsulating node. The Flow ID can be used to correlate the exported data of the same flow from multiple nodes and from multiple packets. Flow ID values are expected to be allocated in a way that avoids collisions. For example, random assignment of Flow ID values can be subject to collisions, while centralized allocation can avoid this problem. The specification of the Flow ID allocation method is not within the scope of this document.
Sequence Number:: An optional 32-bit sequence number starting from 0 and incremented by 1 for each packet from the same flow at the encapsulating node that includes the DEX option. The Sequence Number, when combined with the Flow ID, provides a convenient approach to correlate the exported data from the same user packet.

IANA Considerations

IOAM Type The "IOAM Option-Type" registry is defined in . IANA has allocated the following code point from the "IOAM Option-Type" registry as follows:

Code Point:: 4
Name: IOAM Direct Export (DEX) Option-Type
Description:: Direct exporting
Reference:: This document

IOAM DEX Flags IANA has created the "IOAM DEX Flags" registry. This registry includes 8 flag bits. Allocation is based on the "IETF Review" procedure defined in . New registration requests MUST use the following template:

Bit:: Desired bit to be allocated in the 8-bit Flags field of the DEX Option-Type.
Description:: Brief description of the newly registered bit.
Reference:: Reference to the document that defines the new bit.

IOAM DEX Extension-Flags IANA has created the "IOAM DEX Extension-Flags" registry. This registry includes 8 flag bits. Bit 0 (the most significant bit) and bit 1 in the registry are allocated by this document and described in . Allocation of the other bits should be performed based on the "IETF Review" procedure defined in .

Bit 0:: "Flow ID [RFC9326]"
Bit 1:: "Sequence Number [RFC9326]"

New registration requests MUST use the following template:

Bit:: Desired bit to be allocated in the 8-bit Extension-Flags field of the DEX Option-Type.
Description:: Brief description of the newly registered bit.
Reference:: Reference to the document that defines the new bit.

Performance Considerations The DEX Option-Type triggers IOAM data to be collected and/or exported packets to be exported to a receiving entity (or entities). In some cases, this may impact the receiving entity's performance or the performance along the paths leading to it. Therefore, the performance impact of these exported packets is limited by taking two measures: at the encapsulating nodes by selective DEX encapsulation () and at the transit nodes by limiting exporting rate (). These two measures ensure that direct exporting is used at a rate that does not significantly affect the network bandwidth and does not overload the receiving entity. Moreover, it is possible to load balance the exported data among multiple receiving entities, although the exporting method is not within the scope of this document. It should be noted that, in some networks, DEX data may be exported over an out-of-band network in which a large volume of exported traffic does not compromise user traffic. In this case, an operator may choose to disable the exporting rate limiting.

Security Considerations The security considerations of IOAM in general are discussed in . Specifically, an attacker may try to use the functionality that is defined in this document to attack the network. An attacker may attempt to overload network devices by injecting synthetic packets that include the DEX Option-Type. Similarly, an on-path attacker may maliciously incorporate the DEX Option-Type into transit packets or maliciously remove it from packets in which it is incorporated. Forcing DEX, either in synthetic packets or in transit packets, may overload the IOAM nodes and/or the receiving entity (or entities). Since this mechanism affects multiple devices along the network path, it potentially amplifies the effect on the network bandwidth, the storage of the devices that collect the data, and the receiving entity's load. The amplification effect of DEX may be worse in wide area networks in which there are multiple IOAM-Domains. For example, if DEX is used in IOAM-Domain 1 for exporting IOAM data to a receiving entity, then the exported packets of IOAM-Domain 1 can be forwarded through IOAM-Domain 2, in which they are subject to DEX. In turn, the exported packets of IOAM-Domain 2 may be forwarded through another IOAM domain (or through IOAM-Domain 1); theoretically, this recursive amplification may continue infinitely. In order to mitigate the attacks described above, the following requirements () have been defined:

Selective DEX () is applied by IOAM encapsulating nodes in order to limit the potential impact of DEX attacks to a small fraction of the traffic.
Rate limiting of exported traffic () is applied by IOAM nodes in order to prevent overloading attacks and to significantly limit the scale of amplification attacks.
IOAM encapsulating nodes are required to avoid pushing the DEX Option-Type into IOAM exported packets (), thus preventing some of the amplification and export loop scenarios.

Although the exporting method is not within the scope of this document, any exporting method MUST secure the exported data from the IOAM node to the receiving entity in order to protect the confidentiality and guarantee the integrity of the exported data. Specifically, an IOAM node that performs DEX exporting MUST send the exported data to a pre-configured trusted receiving entity that is in the same IOAM-Domain as the exporting IOAM node. Furthermore, an IOAM node MUST gain explicit consent to export data to a receiving entity before starting to send exported data. An attacker may keep track of the information sent in DEX headers as a means of reconnaissance. This form of recon can be mitigated to some extent by careful allocation of the Flow ID and Sequence Number space in a way that does not compromise privacy aspects, such as customer identities. The integrity of the DEX Option-Type can be protected through a mechanism of the encapsulating protocol. While introduces an integrity protection mechanism that protects the integrity of IOAM-Data-Fields, the DEX Option-Type does not include IOAM-Data-Fields; therefore, these integrity protection mechanisms are not applicable to the DEX Option-Type. As discussed in the threat analysis of , injection or modification of IOAM-Option-Type headers are threats that are not addressed in IOAM. IOAM is assumed to be deployed in a restricted administrative domain, thus limiting the scope of the threats above and their effect. This is a fundamental assumption with respect to the security aspects of IOAM, as further discussed in .

References Normative References Informative References In Situ Operations, Administration, and Maintanence (IOAM) Loopback and Active Flags

Notes about the History of This Document This document evolved from combining some of the concepts of PBT-I from with immediate exporting from early versions of . In order to help correlate and order the exported packets, it is possible to include the Hop_Lim/Node_ID IOAM-Data-Field in exported packets. If the IOAM-Trace-Type has the Hop_Lim/Node_ID bit set, then exported packets include the Hop_Lim/Node_ID IOAM-Data-Field, which contains the TTL/Hop Limit value from a lower layer protocol. An alternative approach was considered during the design of this document, according to which a 1-octet Hop Count field would be included in the DEX header (presumably by claiming some space from the Flags field). The Hop Limit would start from 0 at the encapsulating node and be incremented by each IOAM transit node that supports the DEX Option-Type. In this approach, the Hop Count field value would also be included in the exported packet.

Acknowledgments The authors thank , , , s, , , , , and other members of the IPPM working group for many helpful comments.

Contributors The Editors would like to recognize the contributions of the following individuals to this document. Huawei

156 Beiqing Rd. Beijing 100095 China zhoutianran@huawei.com

Huawei

156 Beiqing Rd. Beijing 100095 China lizhenbin@huawei.com

Cisco Systems, Inc.

170 West Tasman Dr. San Jose CA95134 United States of America sramesh@cisco.com