Export of GTP-U Information in IP Flow Information Export (IPFIX)

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Table of Contents

1. Introduction

A dedicated header, called GPRS Tunneling Protocol Header (GTP), is defined by the 3GPP for use of user Plane (GTP User (GTP-U)) [TS.29281] traffic of mobile subscribers.¶

This document specifies six IPFIX Information Elements (IEs) [RFC7012] to export GTP-U information.¶

Specifically, these IEs are used to export the GTP-U Tunnel Endpoint Identifier (TEID), QoS Flow Identifier (QFI), and PDU Type from the PDU Session Container extension header.¶

Some examples are provided in Appendix A.¶

2. Terminology

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 makes use of the terms defined in [RFC7011]¶

• IPFIX¶

• IPFIX Information Element¶

• Template¶

• Template Record¶

• Options Template¶

• Options Template Record¶

• Data Record¶

• Data Set¶

This document makes use of following terms from [RFC6459]:¶

• User Plane¶

The document uses the following abbreviations:¶

• IE: Information Element¶

• GTP: GPRS Tunneling Protocol¶

• GTP-U: GTP User¶

• GTP-C: GTP Control¶

• PDU: Protocol Data Unit¶

• TEID: Tunnel Endpoint Identifier¶

• UPF: User Plane Function¶

3. IPFIX GTP-U Information Elements

This section defines IPFIX IEs corresponding to various fields in the GTP-U header.¶

gtpuFlags

8-bit flags field defined in the GTP-U.¶

gtpuMsgType

8-bit message type field defined in the GTP-U.¶

gtpuTEid

32-bit tunnel endpoint identifier field defined in GTP-U which unambiguously identifies a tunnel endpoint in the receiving GTP-U protocol entity for a given UDP/IP endpoint.¶

gtpuSequenceNum

16-bit sequence number field defined in the GTP-U. This field is interpreted based on the sequence number flag value from gtpuFlags.¶

gtpuQFI

6-bit QoS flow identifier field defined in PDU Session Container extension header of GTP-U. The presense of this extension header is interpreted based on the extension header flag value from gtpuFlags.¶

gtpuPduType

4-bit PDU Type field defined in PDU Session Container extension header of GTP-U. The presense of this extension header is interpreted based on the extension header flag value from gtpuFlags.¶

4. Sample Use Cases

The GTP-U related IPFIX IEs are helpful in order to identify the transport performance of PDU Sessions, e.g., with specific QoS class within a network slice (refer to [I-D.ietf-teas-5g-ns-ip-mpls]) or within a group of network slices hosted on the same User Plane Function (UPF).¶

For example, when a set of UPFs are deployed per 5G slice, the slice is identified first using a list of gNodeB IP addresses composing the slice and a list of IP addresses of UPFs dedicated for the slice. The gNodeB and the UPF form the tunnel endpoints. The traffic for each individual PDU Session per direction is identified using the GTP-U TEID, GTP-U PDU Type together with the above mentioned IP tunnel endpoints. Furthermore, the traffic for a specific QoS class within a PDU Session per traffic direction is identified using the combination of GTP-U TEID, GTP-U PDU Type, and GTP-U QFI attributes. It is possible that within the same PDU session there might be multiple IP flows having the same attributes.¶

In another scenario when multiple 5G slices share the same UPF, each slice is identified using a separated list of gNodeB IPv4 or IPv6 addresses per slice. If an intermediate UPF or Uplink Classifier is deployed there is an addition of a GTP-U tunnel between the Intermediate/Uplink-Classifier UPF and the final UPF. This brings a challenge for identifying the end-to-end path for a certain PDU Session - the GTP-U PDU Type and GTP-U QFI attributes from the gNodeB and Intermediate/Uplink-Classifier UPF tunnel will be the same on the Intermediate/Uplink-Classifier and final UPF tunnels, however the GTP-U TEIDs will be different since on each tunnel.¶

5. IANA Considerations

IANA has registered the following IEs in the "IPFIX Information Elements" registry available at [IANA-IPFIX].¶

Table 1 lists the GTP-U IEs:¶

     +-------+-----------------+
     |Element| Name            |
     |       |                 |
     |   ID  |                 |
     |       |                 |
     +-------+-----------------+
     | 505   | gtpuFlags       |
     |       |                 |
     +-------+-----------------+
     | 506   | gtpuMsgType     |
     |       |                 |
     +-------+-----------------+
     | 507   | gtpuTEid        |
     |       |                 |
     |       |                 |
     +-------+-----------------+
     | 508   | gtpuSequenceNum |
     |       |                 |
     +-------+-----------------+
     | 509   | gtpuQFI         |
     |       |                 |
     |       |                 |
     |       |                 |
     |       |                 |
     +-------+-----------------+
     | 510   | gtpuPduType     |
     |       |                 |
     |       |                 |
     |       |                 |
     +-------+-----------------+

  Table 1: GTP-U IEs in the "IPFIX Information Elements" Registry

IANA is requested to update these entries as indicated in the following subsections.¶

6. Acknowledgements

The authors would like to thank Ketan Talaulikar, Dhananjay Patki, Paul Aitken and Shraddha Hegde for their reviews and valuable comments.¶

7. Contributors

8. Implementation Status

Note to the RFC-Editor: Please remove this section before publishing.¶

9. Security Considerations

There exist no extra security considerations regarding allocation of these IPFIX IEs compared to [RFC7012].¶

The IEs described in this document export GTP user plane data information on how packets are being forwarded in a 3GPP network. Applications and operators using the IEs described in this document must evaluate the sensitivity of this information in their implementation context, and apply the data-at-rest storage guidance in Section 11.8 of [RFC7011] as appropriate.¶

10. Operational Considerations

The IPFIX IEs defined in this document require extraction of fields from packets. There may exist older devices in the network that do not support extensions defined in this document. For those devices [RFC7133] defines dataLinkFrameSection which is a useful mechanism to export the packet header as a fallback scenario. However, when dataLinkFrameSection is used, Flow aggregation as per [RFC7015] can't be applied. This document will serve as a guideline to extract the necessary fields from the GTP-U header for the above scenarios.¶

Appendix A. IPFIX Encoding Examples

In this section, an example is provided to show IPFIX encoding format for the GTP-U introduced IEs. Template definition and data set corresponding to an observed GTP-U header is illustrated below.¶

          Observed GTP-U Header:
          Flags = 0x36, Message Type = 0xff, TEID = 0x1,
          Sequence number = 0x0000,
          Next extension header type = 0x85 (PDU Session container),
          PDU Type = 0, QFI = 8

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          SET ID = 2           |       Length = 32             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Template ID = 256        |      Field Count = 6          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuFlags = 505            |      Field Length = 1         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuMsgType = 506          |      Field Length = 1         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuTEid = 507             |      Field Length = 4         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuSequenceNum = 508      |      Field Length = 2         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuQFI = 509              |      Field Length = 1         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|  gtpuPduType = 510          |      Field Length = 1         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1: Sample Template Record

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         SET ID = 256          |           Length = 14         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | gtpuFlags     |  gtpuMsgType  |      gtpuTEid = 0x1           |
   | = 0x36        |  = 0xff       |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |   gtpuSequenceNum = 0x0000    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | gtpuQFI = 8   | gtpuPduType   |
   |               | = 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



           Figure 2: Data Set Encoding Format

Authors' Addresses