Cisco Systems

danvoyerwork@gmail.com

Cisco Systems

India sriragop@cisco.com

Swisscom

thomas.graf@swisscom.com

Juniper Networks

vyasraj@juniper.net

Bell Canada

cristian.staicu@bell.ca

Operations and Management Operations This document introduces IP Flow Information Export (IPFIX) Information Elements to report information contained in the Generic Packet Radio Service Tunneling Protocol(GTP) User Plane header such as Tunnel Endpoint Identifier, and data contained in its session container extension header.

A dedicated header, called GPRS Tunneling Protocol (GTP) Header, is defined by the 3GPP for use of user Plane (GTP User (GTP-U)) (latest reference being Release 19) traffic of mobile subscribers. This document specifies six IPFIX Information Elements (IEs) 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.

This document makes use of the terms defined in IPFIX IPFIX Information Element Template Template Record Options Template Options Template Record Data Record Data Set This document makes use of following terms from : 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 QFI: QoS Flow Identifier

This section defines IPFIX IEs corresponding to various fields in the GTP-U header. 8-bit flags field indicating the version of GTP-U header, protocol type, and presence of extension header, sequence number and N-PDU number defined in Section 5.1 of the 3GPP specification . The bits are exported as observed. 8-bit field which indicates the type of the GTP-U message as mentioned in section 6.1 of 3GPP specification . 32-bit tunnel endpoint identifier field unambiguously identifies a tunnel endpoint in the receiving GTP-U protocol entity for a given UDP/IP endpoint. 16-bit sequence number field defined in the GTP-U. This field is interpreted based on the sequence number flag value from gtpuFlags. 6-bit QoS flow identifier field defined in PDU Session Container extension header of GTP-U. This may be used to determine the QoS flow and QoS profile which are associated with the received packet. The presence of this extension header is interpreted based on the extension header flag value from gtpuFlags. 4-bit PDU type field defined in PDU Session Container extension header of GTP-U. This field indicates the structure of the PDU session user plane frame. The presence of this extension header is interpreted based on the extension header flag value from gtpuFlags. 8-bit field indicating the total length of the GTP-U header which includes mandatory fields and all the optional headers as defined in Section 5 of the 3GPP specification . This Information Element carries a series of n octets from the GTP-U header mandatory fields and all the following optional headers if any, defined in Section 5 of the 3GPP specification as a series of octets in IPFIX.

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 ) 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 for a single PDU session there might be multiple IP flows with different GTP-U QFI but with same GTP-U TEID. 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 Uplink Classifier (refer to section 3.1 of ) 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. The use of the IPFIX GTP-U IEs is to identify either a particular PDU Session on a particular slice (using GTP-U TEID in combination with the gNodeB and the UPF IP addresses) or all the IP traffic flows for a 3GPP QoS flow on a slice (using GTP-U QFI in combination with the gNodeB and the UPF IP addresses) or a 3GPP QoS flow for a particular PDU Session on a slice (using both GTP-U TEID and GTP-U QFI in combination with the gNodeB and UPF IP addresses). Additionally, exporting GTP-U IEs together with transportChecksum IE would help detect misbehaving nodes particularly when using GTP-U over IPv6.

IANA has registered the following IEs in the "IPFIX Information Elements" registry available at . Table 1 lists the GTP-U IEs:

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

Name:

gtpuFlags

ElementID:

505

Description:

8-bit flags field indicating the version of GTP-U header, protocol type, and presence of extension header, sequence number and N-PDU number defined in Section 5.1 of the 3GPP specification . The bits are exported as observed. The basic encoding is 8 bits. The layout of basic encoding is as follows:

Examples: value : 0x34 binary: 00110100 decode: 00110100 - Flags value value : 0x30 binary: 00110000 decode: 00110000 - Flags value

Abstract Data Type:

unsigned8

Data Type Semantics:

flags

Additional Information:

Refer to Section 5.1 of .

Reference:

[RFC-to-be]

Name:

gtpuMsgType

ElementID:

506

Description:

8-bit field which indicates the type of the GTP-U message as mentioned in section 6.1 of 3GPP specification .

Abstract Data Type:

unsigned8

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5.1 of the 3GPP specification .

Reference:

[RFC-to-be]

Name:

gtpuTEid

ElementID:

507

Description:

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

Abstract Data Type:

unsigned32

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5.1 of the 3GPP specification .

Reference:

[RFC-to-be]

Name:

gtpuSequenceNum

ElementID:

508

Description:

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

Abstract Data Type:

unsigned16

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5.1 of the 3GPP specification .

Reference:

[RFC-to-be]

Name:

gtpuQFI

ElementID:

509

Description:

6-bit QoS flow identifier field defined in PDU Session Container extension header of GTP-U. This may be used to determine the QoS flow and QoS profile which are associated with the received packet. The presence of this extension header is interpreted based on the extension header flag value from gtpuFlags. The basic encoding is 8 bits. The layout of basic encoding is as follows:

Examples: value : 0x08 binary: 00001000 decode: 001000 - QFI value value : 0x3e binary: 00111110 decode: 111110 - QFI value

Abstract Data Type:

unsigned8

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5.5.3.3 of the 3GPP specification and Section 5.7.1.1 of the 3GPP specification .

Reference:

[RFC-to-be]

Name:

gtpuPduType

ElementID:

510

Description:

4-bit PDU type field defined in PDU Session Container extension header of GTP-U. This field indicates the structure of the PDU session user plane frame. The presence of this extension header is interpreted based on the extension header flag value from gtpuFlags. The basic encoding is 8 bits. The layout of basic encoding is as follows:

Examples: value : 0x01 binary: 00000001 decode: 0001 - PDU Type value

Abstract Data Type:

unsigned8

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5.5.3 of the 3GPP specification .

Reference:

[RFC-to-be]

Name:

gtpuHeaderLength

ElementID:

TBD1

Description:

8-bit field indicating the total header length of the GTP-U which includes mandatory fields and all the optional headers as defined in Section 5 of the 3GPP specification .

Abstract Data Type:

unsigned8

Data Type Semantics:

identifier

Additional Information:

Refer to Section 5 of .

Reference:

[RFC-to-be]

Name:

gtpuHeaderSection

ElementID:

TBD2

Description:

This Information Element carries a series of n octets from the GTP-U header mandatory fields and all the following optional headers if any, defined in Section 5 of the 3GPP specification as a series of octets in IPFIX

Abstract Data Type:

octetArray

Data Type Semantics:

default

Additional Information:

Refer to Section 5 of .

Reference:

[RFC-to-be]

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

Bell Canada

kandhla.chandi@bell.ca

Cisco

rjohny@cisco.com

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

Cisco implemented the following IEs as part of a test implementation in the IOS XR platform: gtpuFlags gtpuMsgType gtpuTEid gtpuSequenceNum gtpuQFI gtpuPduType

There exist no extra security considerations regarding allocation of these IPFIX IEs compared to . 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 as appropriate.

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 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 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.

3GPP Version 17.4.0 3GPP Version 17.1.0 3GPP Version 17.11.0 Juniper Networks Juniper Networks Juniper Networks Orange Telefonica

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.

Sample template consisting of the GTP-U IEs:

In this example, the Template ID is 256, which will be used in the Data Record. The data set is represented as follows: