Export of Segment Routing IPv6 Information in IP Flow Information Export (IPFIX)

A new type of Routing Extension Header called Segment Routing Header (SRH) is defined by which is used for applying Segment Routing (SR) on the IPv6 data plane. Three routing protocol extensions, OSPFv3 Extensions, IS-IS Extensions, BGP Prefix Segment Identifiers (Prefix-SIDs) and one Path Computation Element Communication Protocol (PCEP) Extension have been defined to propagate Segment Identifiers (SIDs) for the IPv6 data plane. SRv6 segment endpoint behaviors have been defined in and describe how packets should be processed. This document defines eleven new IPFIX Information Elements (IEs) and three new subregistries within the "IPFIX Information Elements" registry , respectively for the new SRH dimensions, SRv6 endpoint behaviors and routing protocol and PCEP extensions.

This section defines and describes the new IPFIX IEs. 8-bit flags defined in the SRH. 16-bit tag field defined in the SRH that marks a packet as part of a class or group of packets sharing the same set of properties. 128-bit IPv6 address that represents an SRv6 segment. 128-bit IPv6 address that represents the active SRv6 segment. Ordered basicList of zero or more 128-bit IPv6 addresses in the SRH that represents the SRv6 segment list. The Segment List is encoded starting from the last segment of the SR Policy. That is, the first element of the Segment List (Segment List[0]) contains the last segment of the SR Policy, the second element contains the penultimate segment of the SR Policy, and so on. Exposes the SRH Segment List as defined in section 2 of as series of n octets. 8-bit unsigned integer defining the number of route segments remaining to reach the end of the segment list. Exposes the SRH and its TLV's as defined in section 2 of as series of n octets. Name of the routing protocol or PCEP extension from where the active SRv6 segment has been learned from. The number of significant bits. Together with srhSegmentIPv6 it enables the calculation of the SRv6 Locator. 16-bit unsigned integer that represents a SRv6 Endpoint behavior. Note that the srhSegmentIPv6, srhSegmentLocatorLength, and srhSegmentEndpointBehavior IPFIX IEs are generic fields, to be used in the context of IPFIX Options Templates or IPFIX Structured Data .

By using srhSegmentIPv6BasicList(TBD5) or the srhSegmentIPv6ListSection (TBD6), srhActiveSegmentIPv6 (TBD4), srhSegmentIPv6sLeft (TBD7), srhActiveSegmentIPv6Type(TBD9), the forwardingStatus(89), and some counters information, it is possible to answer the following questions (amongst others): how many packets are forwarded or dropped if dropped, for which reasons, identify the active segment and its control plane protocol, the SRv6 segment list, the next SRv6 node and its type, and how many SRv6 segments are left.

This document requests IANA to create new IEs (see table 1) and three new subregistries called "IPFIX IPv6 SRH Flags" (table 2), "IPFIX IPv6 SRH Segment type" (table 3) and "IPFIX SRV6 Endpoint Behavior" (table 4) under the "IPFIX Information Elements" registry available at and assign the following initial code points.

Note to the RFC-Editor: Please replace TBD1 - TBD16 with the values allocated by IANA Please replace the [RFC-to-be] with the RFC number assigned to this document

Name: srhFlagsIPv6 ElementID: TBD1 Description: This Information Element identifies the 8-bit flags defined in the SRH. Values for this Information Element are listed in the "IPFIX IPv6 SRH Flags" registry, see . srhFlagsIPv6 values must not be directly added to this "IPFIX IPv6 SRH Flags" registry. They must instead be added to the "Segment Routing Header Flags" registry. Both the "IPFIX IPv6 SRH Flags" and the "Segment Routing Header Flags" registries must be kept in synch. Initial values in the registry are defined by the table below.

Abstract Data Type: unsigned8 Data Type Semantics: flags Reference: [RFC-to-be], RFC8754

Name: srhTagIPv6 ElementID: TBD2 Description: This Information Element identifies the 16-bit tag field defined in the SRH that marks a packet as part of a class or group of packets sharing the same set of properties. Abstract Data Type: unsigned16 Data Type Semantics: identifier Reference: [RFC-to-be], RFC8754

Name: srhSegmentIPv6 ElementID: TBD3 Description: This Information Element identifies the 128-bit IPv6 address that represents an SRv6 segment. Abstract Data Type: ipv6address Data Type Semantics: default Reference: [RFC-to-be], RFC8754

Name: srhActiveSegmentIPv6 ElementID: TBD4 Description: This Information Element identifies the 128-bit IPv6 address that represents the active SRv6 segment. Abstract Data Type: ipv6address Data Type Semantics: default Reference: [RFC-to-be], RFC8754

Name: srhSegmentIPv6BasicList ElementID: TBD5 Description: This Information Element identifies the Ordered basicList [RFC6313] of zero or more 128-bit IPv6 addresses in the SRH that represents the SRv6 segment list. The Segment List is encoded starting from the last segment of the SR Policy. That is, the first element of the Segment List (Segment List[0]) contains the last segment of the SR Policy, the second element contains the penultimate segment of the SR Policy, and so on. Abstract Data Type: basicList Data Type Semantics: list Reference: [RFC-to-be], RFC8754

Name: srhSegmentIPv6ListSection ElementID: TBD6 Description: Exposes the SRH Segment List as defined in section 2 of as series of n octets. Abstract Data Type: octetArray Data Type Semantics: default Reference: [RFC-to-be], RFC8754

Name: srhSegmentIPv6sLeft ElementID: TBD7 Description: This Information Element identifies the 8-bit unsigned integer defining the number of route segments remaining to reach the end of the segment list. Abstract Data Type: unsigned8 Data Type Semantics: quantity Reference: [RFC-to-be], RFC8754

Name: srhSectionIPv6 ElementID: TBD8 Description: This Information Element exposes the SRH and its TLV's as defined in section 2 of as series of n octets. Abstract Data Type: octetArray Data Type Semantics: default Reference: [RFC-to-be], RFC8754

Name: srhActiveSegmentIPv6Type ElementID: TBD9 Description: This Information Element identifies the name of the routing protocol or PCEP extension from where the active SRv6 segment has been learned from. Values for this Information Element are listed in the "IPFIX IPv6 SRH Segment type" registry, see . Initial values in the registry are defined by the table below. New assignments of values will be administered by IANA and are subject to Expert Review . Experts need to check definitions of new values for completeness, accuracy, and redundancy.

Abstract Data Type: unsigned8 Data Type Semantics: identifier Reference: [RFC-to-be]

Name: srhSegmentLocatorLength ElementID: TBD10 Description: This Information Element identifies the number of significant bits and together with srhSegmentIPv6 enables the calculation of the SRv6 Locator. Abstract Data Type: unsigned8 Data Type Semantics: default Reference: [RFC-to-be], RFC8986 Section 3.1

Name: srhSegmentEndpointBehavior ElementID: TBD11 Description: This Information Element identifies the 16-bit SRv6 Endpoint behavior. Values for this Information Element are listed in the "IPFIX SRV6 Endpoint Behavior" registry, see . srhSegmentEndpointBehavior values must not be directly added to this "IPFIX SRV6 Endpoint Behavior" registry. They must instead be added to the "Segment Routing SRv6 Endpoint Behaviors" registry. Both the "IPFIX SRV6 Endpoint Behavior" and the "Segment Routing SRv6 Endpoint Behaviors" registries must be kept in synch.

Abstract Data Type: unsigned16 Data Type Semantics: identifier Reference: [RFC-to-be], RFC8986 Section 4

The zero or more 128-bit IPv6 addresses in the SRH [RFC8754] can be exported in two different ways, with two different IPFIX IEs: srhSegmentIPv6BasicList srhSegmentIPv6ListSection The srhSegmentIPv6BasicList encodes the SID list of IPv6 addresses with a basicList, specified in the IPFIX Structured Data . This encoding offers the advantage to the data collection that the different IPv6 addresses are already structured as a list, without the need of post processing. However, this method requires some extra processing on the exporter, to realize the BasicList data mapping. The srhSegmentIPv6ListSection, on the other hand, encodes the list of IPv6 addresses as an octetArray. This doesn't impose any data flow manipulation on the exporter, facilitating the immediate export. However, the data collection must be able to decode the IPv6 addresses according the SR specifications. Compared to the srhSegmentIPv6BasicList, the srhSegmentIPv6ListSection flow records length is slightly reduced. It is not expected that an exporter would support both srhSegmentIPv6BasicList and srhSegmentIPv6ListSection at the same time.

The SRv6 segment list in the IPFIX IEs srhSegmentIPv6BasicList and srhSegmentIPv6ListSection could contain compressed-SID containers as described in . The SID endpoint behaviors described in section 4 of determine wherever the segment list is compressed or not. The SID Locator as described in section 3.1 , determines the common most significant bits.

There exists no significant extra security considerations regarding the allocation of these new IPFIX IEs compared to .

The authors would like to thank Yao Liu, Paolo Lucente, Eduard Vasilenko, Alex Huang Feng and Bruno Decraene for their review and valuable comments.

IANA, "IP Flow Information Export (IPFIX) Entities"

This appendix represents three different encodings for the newly introduced IEs, for the example values in the table 5. The three different encodings uses the following IEs, respectively: srhSegmentIPv6BasicList, srhSegmentIPv6ListSection, and srhSectionIPv6.

With this encoding, the examples in Table 5 are represented with the following IEs: SR Flags => srhFlagsIPv6 SR Tag => srhTagIPv6 Active Segment Type => srhActiveSegmentIPv6Type Segment List => srhSegmentIPv6BasicList

In this example, the Template ID is 256, which will be used in the Data Record. The field length for srhSegmentIPv6BasicList is 0xFFFF, which means the length of this IE is variable, and the actual length of this IE is indicated by the List Length field in the basicList format as per . The data set is represented as follows:

In this example, the Template ID is 257, which will be used in the Data Record. The field length for srhSegmentIPv6ListSection is 0xFFFF, which means the length of this IE is variable. The data set is represented as follows:

With this encoding, the examples in Table 5 are represented with the following IEs: SR Flags + SR Tag + Segment List => srhSectionIPv6 Active Segment Type => srhActiveSegmentIPv6Type

In this example, the Template ID is 258, which will be used in the Data Record. The field length for srhSectionIPv6 is 0xFFFF, which means the length of this IE is variable. The data set is represented as follows:

(*) The Length must be calculated to include the optional Type Length Value objects.

This appendix provides an SRv6 EndPoint Bevahior Options Template example, for the values presented in Table 12. In the Options Template case, the srhEndPointIPv6 Information Element is a Scope field

In this example, the Template ID is 259, which will be used in the Data Record. The data set is represented as follows:

(*) The Length must be calculated to include the optional Type Length Value objects.