| RFC 9326 | IOAM Direct Exporting | October 2022 |
| Song, et al. | Standards Track | [Page] |
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.¶
This is an Internet Standards Track document.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9326.¶
Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
IOAM [RFC9197] 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 [RFC9197]: 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.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Abbreviations used in this document:¶
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 Figure 1. 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 [RFC9197].¶
^
|Exported IOAM data
|
|
|
+--------------+------+-------+--------------+
| | | |
| | | |
User +---+----+ +---+----+ +---+----+ +---+----+
packets |Encapsu-| | Transit| | Transit| |Decapsu-|
--------->|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:¶
As in [RFC9197], 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 Section 3.1.1. 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 Section 3.1.2.¶
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 [RFC7014] and [RFC5475]. 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.¶
The DEX Option-Type specifies which IOAM-Data-Fields should be exported and/or collected, as specified in Section 3.2. 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 [IOAM-RAWEXPORT].¶
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 [RFC9197]); specifically, nodes that do not support the DEX Option-Type ignore it. As per [RFC9197], 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 [IOAM-IPV6-OPTIONS], 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 format of the DEX Option-Type is depicted in Figure 2. 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 Section 4.2.¶
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Namespace-ID | Flags |Extension-Flags|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IOAM-Trace-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
The "IOAM Option-Type" registry is defined in Section 7.1 of [RFC9197]. IANA has allocated the following code point from the "IOAM Option-Type" registry as follows:¶
IANA has created the "IOAM DEX Flags" registry. This registry includes 8 flag bits. Allocation is based on the "IETF Review" procedure defined in [RFC8126].¶
New registration requests MUST use the following template:¶
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 Section 3.2. Allocation of the other bits should be performed based on the "IETF Review" procedure defined in [RFC8126].¶
New registration requests MUST use the following template:¶
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 (Section 3.1.1) and at the transit nodes by limiting exporting rate (Section 3.1.2). 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.¶
The security considerations of IOAM in general are discussed in [RFC9197]. 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 (Section 3) have been defined:¶
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 [IOAM-DATA-INTEGRITY] 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 [IOAM-DATA-INTEGRITY], 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 [RFC9197].¶
This document evolved from combining some of the concepts of PBT-I from [POSTCARD-BASED-TELEMETRY] with immediate exporting from early versions of [RFC9322].¶
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 [RFC9197] 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.¶
The authors thank Martin Duke, Tommy Pauly, Meral Shirazipour, Colin Perkins, Stephen Farrell, Linda Dunbar, Justin Iurman, Greg Mirsky, and other members of the IPPM working group for many helpful comments.¶
The Editors would like to recognize the contributions of the following individuals to this document.¶