Export of UDP Options Information in IP Flow Information Export (IPFIX)

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Table of Contents

1. Introduction

IP Flow Information Export (IPFIX) [RFC7011] is a protocol that is widely deployed in operators networks for traffic management purposes (Section 2 of [RFC6632]). The protocol specifies the encoding of a set of basic data types and how the various Information Elements (IEs) are transmitted. In order to support the export of new flow-related measurement data, new IEs can be defined and registered in a dedicated IANA registry [IANA-IPFIX] for interoperability.¶

This document specifies new IPFIX Information Elements for UDP options (Section 4). A brief overview of UDP options is provided in Section 3.¶

The IE specified in Section 4.1 uses the new abstract data type defined in Section 8.2.¶

Examples to illustrate the use of the new IPFIX Information Elements are provided in Section 6.¶

2. Conventions and Definitions

This document uses the IPFIX-specific terminology (e.g., Flow) defined in Section 2 of [RFC7011]. As in [RFC7011], these IPFIX-specific terms have the first letter of a word capitalized.¶

The document adheres to the naming conventions for Information Elements per Section 2.3 of [RFC7012].¶

Also, this document uses the terms defined in Section 3 of [I-D.ietf-tsvwg-udp-options], especially "datagram" and "surplus area".¶

3. UDP Options at a Glance

UDP [RFC0768] does not support an extension mechanism similar to the options supported by other transport protocols, such as TCP [RFC9293], SCTP [RFC9260], or DCCP [RFC4340]. Such a mechanism can be useful for various applications, e.g., to discover a path MTU or share timestamps. To fill that void, [I-D.ietf-tsvwg-udp-options] extends UDP with a mechanism to insert extensions in datagrams. To do so, and unlike the conventional approach that relies upon transport headers, [I-D.ietf-tsvwg-udp-options] uses trailers. Concretely, UDP options are placed in the surplus area (that is, the area of an IP payload that follows a UDP packet). See Figure 1. An example of the use of UDP options is described in [I-D.ietf-tsvwg-udp-options-dplpmtud].¶

                       IP transport payload
          <------------------------------------------------->
+--------+---------+----------------------+------------------+
| IP Hdr | UDP Hdr |     UDP user data    |   surplus area   |
+--------+---------+----------------------+------------------+
          <------------------------------>
                     UDP Length

Sections 4.1 and 4.2 introduce new IEs to export the observed UDP options.¶

Options indicated by Kind values in the range 0-191 are called SAFE options. Such options can be silently ignored by legacy receivers because they do not alter the UDP user data (Section 11 of [I-D.ietf-tsvwg-udp-options]). Safe options are exported using the IE defined in Section 4.1.¶

Options indicated by Kind values in the range 192-255 are called UNSAFE options. Such options are not safe for legacy receivers to ignore because they alter the UDP user data (Section 12 of [I-D.ietf-tsvwg-udp-options]). Unsafe options are exported using the IE defined in Section 4.2.¶

UDP options occur per-packet within a Flow and can be inserted at any time in the Flow.¶

[I-D.ietf-tsvwg-udp-options] reserves two options for experiments: the Experimental option (EXP, Kind=127) for SAFE options and the UNSAFE Experimental option (UEXP, Kind=254). For both options, Experimental ID (ExIDs) are used to differentiate concurrent use of these options. Known ExIDs are expected to be registered within IANA. Section 4.3 specifies a new IPFIX IE to export observed ExIDs in the EXP options. Also, Section 4.4 specifies a new IPFIX IE to export observed ExIDs in the UEXP options. Only 16-bit ExIDs are supported in [I-D.ietf-tsvwg-udp-options].¶

This document does not intend to elaborate operational guidance/implications of UDP options. The document focuses exclusively on exporting observed UDP options in datagrams.¶

4. New UDP IPFIX Information Elements

• RFC Editor Note: Please update "URL_IANA_UDP_OPTIONS" reference with the URL of the "UDP Option Kind Numbers" registry group and "URL_IANA_UDP_ExIDs" with the URL of the "UDP Experimental Option Experiment Identifiers (UDP ExIDs)" registry that will be created by IANA as per Section 25 of [I-D.ietf-tsvwg-udp-options].¶

5. Operational Considerations

The reduced-size encoding specified in Section 6.2 of [RFC7011] is followed whenever fewer octets are needed to report observed safe and unsafe UDP options. For example, if only option Kinds <= 32 are observed, then the value of the udpSafeOptions IE can be encoded as unsigned32, or if only option Kinds <= 63 are observed, then the value of the udpSafeOptions IE can be encoded as unsigned64.¶

The presence of udpSafeExperimentalOptionExID (or udpUnsafeExperimentalOptionExID) is an indication that the SAFE (or UNSAFE) Experimental option is observed in a Flow. The presence of udpSafeExperimentalOptionExID (or udpUnsafeExperimentalOptionExID) takes precedence over setting the correspoding bit in the udpSafeOptions (or udpUnsafeOptions) IE for the same Flow. In order to make use of the reduced-size encoding in the presence of udpSafeExperimentalOptionExID (or udpUnsafeExperimentalOptionExID) IE, the Exporter SHOULD NOT set to 1 the EXP (or UEXP) flags of the the udpSafeOptions (or udpUnsafeOptions) IE that is reported for the same Flow.¶

Transport (including MTU) considerations are discussed in Section 10 of [RFC7011].¶

6. Examples

Given UDP Kind allocation in Section 10 of [I-D.ietf-tsvwg-udp-options] and the option mapping defined in Section 4.1 of this document, fewer octets are likely to be used for Flows with mandatory UDP options.¶

Figure 2 shows an example of reported values in a udpSafeOptions IE for a Flow in which End of Options List (EOL, Kind=0) and Alternate payload checksum (APC, Kind=2) options are observed. One octet is sufficient to report these observed options because the leading zeros are dropped per the reduced-size encoding guidance in Section 5. Concretely, the reported udpSafeOptions IE will be set to 0x05.¶

MSB                                                       LSB
                     1                                  19
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 ... 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|   |0|0|0|0|0|1|0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-++-+-+-+-+...+-+-+-+-+-+-+-+-+

Let us now consider a UDP Flow in which SAFE Experimental options are observed. If a udpSafeOptions IE is exported for this Flow, then that IE will have the EXP bit set to 1 (Figure 3). This example does not make any assumption about the presence of other UDP options.¶

MSB                                                     LSB
                  12                                  19
 0 1 2 3 ... 7 8 9 0 1 2 3 4 5 6 7 8 9 ... 4 5 6 7 8 9 0 1
+-+-+-+-+...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+-+-+
|X|X|X|X|   |X|X|X|X|X|X|X|X|X|X|X|1|X|X|   |X|X|X|X|X|X|X|
+-+-+-+-+...+-+-+-+-+-+-+-+-++-++-+-+-+-+...+-+-+-+-+-+-+-+

Now assume that EOL, APC, EXP, and UEXP options are observed in a Flow. Let us also consider that the observed SAFE Experimental options have ExIDs set to 0x9858 and 0xE2D4, and UNSAFE Experimental options have ExIDs set to 0xC3D9 and 0x1234. As shown in Figure 4, the following IEs are used to report observed ExIDs:¶

1. udpSafeExperimentalOptionExID IE set to 0x9858E2D4 to report observed ExIDs of SAFE Experimental options.¶

2. udpUnsafeExperimentalOptionExID IE set to 0xC3D91234 to report the ExIDs of the observed UNSAFE Experimental options.¶

udpSafeExperimentalOptionExID IE:

MSB                                                          LSB
                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              0x9858           |             0xE2D4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

udpUnsafeExperimentalOptionExID IE:

                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              0xC3D9           |             0x1234            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7. Security Considerations

This document does not introduce new security considerations other than those already discussed in Section 11 of [RFC7011] and Section 8 of [RFC7012].¶

The reader may refer to Section 24 of [I-D.ietf-tsvwg-udp-options] for the security considerations related to UDP options.¶

8. IANA Considerations

Acknowledgments

Thanks to Benoît Claise for the discussion on the ordering of IPFIX IEs. Thanks to Paul Aitken for the review and comments.¶

Thanks to Tommy Pauly for the tsvart review, Joe Touch for the intdir review, Robert Sparks for the genart review, and Watson Ladd for the secdir review.¶

Thanks to Thomas Graf for the Shepherd review.¶

Thanks to Mahesh Jethanandani for the AD review.¶

Authors' Addresses