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. 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 option is provided in Section 3.¶

2. Conventions and Definitions

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.¶

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.¶

Also, this document uses the terms defined in Section 3 of [I-D.ietf-tsvwg-udp-options].¶

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., 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

Section 4.1 introduces a new IE to export the observed UDP options.¶

Options indicated by Kind values in the range 0-191 are called SAFE options because they do not alter the UDP data payload. Such options can be silently ignored by legacy receivers because they do not alter the UDP user data (Section 9 of [I-D.ietf-tsvwg-udp-options]).¶

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 10 of [I-D.ietf-tsvwg-udp-options]).¶

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 experiements: 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 4.2 specifies a new IPFIX IE to export observed ExIDs in the EXP options. Also, Section 4.3 specifies a new IPFIX to export observed ExIDs in the UEXP options. Only 16-bits ExIDs are supported.¶

This document does not intend to elaborate operational guidance/implications of UDP options. The document focuses exclusively on exporting observed UDP options in datagrams. The motivation for exporting such data is similar to the one for exporting TCP options (tcpOptions) or IPv6 Extension Headers (ipv6ExtensionHeaders).¶

4. New UDP IPFIX Information Elements

• Note: "URL_IANA_UDP_OPTIONS" is the URL of the "UDP Option Kind Numbers" registry group while "URL_IANA_UDP_ExIDs" is the URL of the "UDP Experimental Option Experiment Identifiers (UDP ExIDs)" registry that will be created by IANA as per Section 23 of [I-D.ietf-tsvwg-udp-options].¶

5. An Example

Given UDP kind allocation in Section 8 of [I-D.ietf-tsvwg-udp-options] and the option mapping defined in Section 4.1, fewer octers are likely to be used for Flows with mandatory UDP options.¶

Figure 2 shows an example of reported values in a udpOptions IE for a Flow in which End of Options List (EOL) and Alternate payload checksum (APC) options are observed. One octet is sufficient to report these observed options. Concretely, the udpOptions IE will be set to 5.¶

MSB                                                       LSB
                     1                   2     …  25
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 … 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+…+-+-+-+-+-+-+
|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|0|1|0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+…+-+-+-+-+-+-+

6. Security Considerations

This document does not introduce new security considerations other than those already discussed in [RFC7012].¶

The reader may refer to Section 22 of [I-D.ietf-tsvwg-udp-options] for the security considerations related to UDP options.¶

7. IANA Considerations

This document requests IANA to add the following new IEs to the IANA registry entitled "IP Flow Information Export (IPFIX) Entities" [IANA-IPFIX]:¶

Acknowledgments

Thanks to Benoît Claise for the discussion on the ordering of IPFIX IEs.¶

Thanks to Tommy Pauly for the tsvart review and Joe Touch for the intdir review.¶

Authors' Addresses