IPv6 Encapsulation for SFC and IFIT
draft-li-6man-ipv6-sfc-ifit-02

Abstract

Service Function Chaining (SFC) and In-situ Flow Information Telemetry (IFIT) are important path services along with the packets. In order to support these services, several encapsulations have been defined. The document analyzes the problems of these encapsulations in the IPv6 scenario and proposes the possible optimized encapsulation for IPv6.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on March 13, 2020.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Problem Statement
• 4. Design Consideration
• 4.1. Service Options
• 4.2. IPv6 Service Metadata Options
• 4.2.1. SFC Service Metadata Option
• 4.2.2. IOAM Service Metadata Option
• 4.2.3. IFA Service Metadata Option
• 5. IANA Considerations
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

Service Function Chaining (SFC) [RFC7665] and In-situ Flow Information Telemetry (IFIT) [I-D.song-opsawg-ifit-framework] are important path services along with the packets. In order to support these services, several encapsulations have been defined. Network Service Header (NSH) is defined in [RFC8300] as the encapsulation for SFC. For IFIT encapsulations, In-situ OAM (iOAM) Header is defined in [I-D.ietf-ippm-ioam-data] and Postcard-Based Telemetry (PBT) Header is defined in [I-D.song-ippm-postcard-based-telemetry]. Inband Flow Analyzer (IFA) is also defined in [I-D.kumar-ippm-ifa] to record flow specific information from an end station and/or switches across a network. In the application scenario of IPv6, these encapsulations propose challenges for the data plane. The document analyzes the problems and proposes the possible optimized encapsulation for IPv6.

2. Terminology

SFC: Service Function Chaining

IFIT: In-situ Flow Information Telemetry

IOAM: In-situ OAM

PBT: Postcard-Based Telemetry

IFA: Inband Flow Analyzer

SRH: Segment Routing Header

3. Problem Statement

The problems posed by the current encapsulations for SFC and IFIT in the application scenarios of IPv6 and SRv6 include:

1. According to the encapsulation order recommended in [RFC8200], if the IOAM is encapsulated in the IPv6 Hop-by-Hop options header, in the incremental trace mode of IOAM as the number of nodes traversed by the IPv6 packets increases, the recorded IOAM information will increase accordingly. This will increase the length of the Hop-by-Hop options header and cause increasing difficulties in reading the subsequent Segment Routing Extension Header (SRH) [I-D.ietf-6man-segment-routing-header] and thereby reduce the forwarding performance of the data plane greatly.

2. With the introduction of SRv6 network programming [I-D.ietf-spring-srv6-network-programming], the path services along with the IPv6 packets can be processed at all the IPv6 network nodes or only at the SRv6 enabled network nodes along the path. It is necessary to distinguish the encapsulations for the specific path service which should be processed by the IPv6 path or the SRv6 path.

3. Both NSH and IOAM need the Metadata field to record metadata information. However currently these metadata has to be recorded separately which may generate redundant metadata information or increase the cost of process.

4. There is unnecessary inconsistency in the current encapsulations for IOAM, IFA and PBT in the IPv6 scenario. Especially it seems unnecessary to define a new specific IPv6 header for IFA, i.e. IFA header.

4. Design Consideration

To solve the problems stated above, in the application scenarios of IPv6 and SRv6, the encapsulations of SFC and IFIT can be optimized with the following design considerations:

• To separate the SFC/IFIT path service into two parts, i.e. instruction and recording parts. The instruction part (normally with fixed length) can be placed in the front IPv6 extension headers including Hop-by-Hop options header, Destination options header, Routing header, etc. while the recording part can be placed in the back IPv6 extension headers such as being placed after IPv6 Routing Header. In this way the path service instruction in the IPv6 extension headers can be fixed as much as possible to facilitate hardware process to keep forwarding performance while the SFC/IFIT metadata recording part is placed afterwards which enables to stop recording when too much recording information has to be carried to reach the limitation of hardware process.
• To define SFC/IFIT path service instructions as IPv6 options uniformly whichs can be placed either in the Hop-by-hop options which indicates the path service processed by all IPv6 enabled nodes along the path or in the SRH option TLVs which indicates the path service processed only by the SRv6 nodes along the SRv6 path indicated by the Segment List in the SRH.
• To define a unified IPv6 metadata header which can be used as a container to record the service metadata of SFC, IFIT and other possible path services.

According to the above design optimization consideration, in the application scenarios of IPv6 and SRv6 the encapsulations for SFC and IFIT can be defined as below.

4.1. Service Options

1. NSH Service Option

 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
                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                |  Option Type  |  Opt Data Len | 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Service Path Identifier              | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1. IPv6 Options with NSH instructions

Option Type: TBD_0

Opt Data Len: 8 octets.

Other fields: refer to [RFC8300].

2. IOAM Service Option

 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
                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                |  Option Type  |  Opt Data Len | 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Namespace-ID           |NodeLen  | Flags | RemainingLen|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               IOAM-Trace-Type                 |  Reserved     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 2. IPv6 Options with IOAM instructions

Option Type: TBD_1

Opt Data Len: 8 octets.

Other fields: refer to [I-D.ietf-ippm-ioam-data].

3. PBT Service Option

 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
                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                |  Option Type  |  Opt Data Len | 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header   |  TIH Length   |   Reserved    |   Hop Count   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Flow ID                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Flow ID                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Sequence Number                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Data Set ID                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 3. IPv6 Options with PBT instructions

Option Type: TBD_2

Opt Data Len: 20 octets.

Other fields: refer to [I-D.song-ippm-postcard-based-telemetry].

4. IFA Service Option

 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
                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                |  Option Type  |  Opt Data Len | 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver=2.0|  GNS  |NextHdr = IP_xx|R|R|R|M|T|I|T|C|   Max Length  |
|       |       |               | | | |F|S| |A| |               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 4. IPv6 Options with IFA instructions

Option Type: TBD_3

Opt Data Len: 4 octets.

Other fields: refer to [I-D.kumar-ippm-ifa].

These options can be put in the IPv6 Hop-by-Hop Options Header or SRH TLV.

4.2. IPv6 Service Metadata Options

As introduced in [I-D.li-6man-enhanced-extension-header], IPv6 Metadata Header is defined as a new type of IPv6 extension header. The metadata is the information recorded by each hop for specific path services, and carried in corresponding service metadata options. The length of the metadata is variable.

4.2.1. SFC Service Metadata Option

For the SFC service, the corresponding SFC service metadata option is defined as shown in Figure 5.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   SFC Type    |     Length    |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      SFC Metadata Class       |      Type     |U|    Length   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Variable-Length Metadata                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     
                   Figure 5. SFC Service Metadata

      SFC Type            8-bit identifier of the service type, i.e. SFC.
                          The value is TBD-4.  

      Length              8-bit unsigned integer. Length of the
                          Service Metadata field, in octets.

      Metadata Class      Defines the scope of the Type field to
                          provide a hierarchical namespace.  IANA has 
                          set up the "NSH MD Class" registry, which 
                          contains 16-bit values [RFC8300].

      Type                Indicates the explicit type of metadata 
                          being carried.  The definition of the Type is 
                          the responsibility of the MD Class owner.

      Unassigned bit      One unassigned bit is available for future use.
                          This bit MUST NOT be set, and it MUST be 
                          ignored on receipt.

      Length              Indicates the length of the variable-length 
                          metadata, in bytes. Detailed specification 
                          in [RFC8300].

4.2.2. IOAM Service Metadata Option

For the IOAM service, the corresponding IOAM service metadata option is defined as shown in Figure 6.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   IOAM Type   |     Length    |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                                               ~
|            IOAM Service Metadata Options (variable)           |
~                                                               ~ 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     
                 Figure 6. IOAM Service Metadata

      IOAM Type           8-bit identifier of the IOAM Service Metadata 
                          type. The value is TBD-5.

      Length              8-bit unsigned integer. Length of the
                          IOAM Service Metadata field, in octets.

      RESERVED            8-bit reserved field MUST be set to zero upon 
                          transmission and ignored upon receipt.

      IOAM Service        IOAM option data is present as specified by the 
      Metadata Options    IOAM Type field, and is defined in Section 4 of 
                          [I-D.ietf-ippm-ioam-data].

All the IOAM IPv6 options require 4n alignment. This ensures that 4 octet fields specified in [I-D.ietf-ippm-ioam-data] such as transit delay are aligned at a multiple-of-4 offset from the start of the IPv6 Metadata header.

In addition, to maintain IPv6 extension header 8-octet alignment and avoid the need to add or remove padding at every hop, the Trace-Type for Incremental Tracing Option in IPv6 MUST be selected such that the IOAM node data length is a multiple of 8-octets.

4.2.3. IFA Service Metadata Option

For the IOAM service, the corresponding IOAM service metadata option is defined as shown in Figure 6.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   IFA Type   |     Length    |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                                                               ~
|             IFA Service Metadata Options (variable)           |
~                                                               ~ 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     
                 Figure 6. IFA Service Metadata

      IFA Type            8-bit identifier of the IFA Service Metadata 
                          type. The value is TBD-6. 

      Length              8-bit unsigned integer. Length of the
                          IOAM Service Metadata field, in octets.

      RESERVED            8-bit reserved field MUST be set to zero upon 
                          transmission and ignored upon receipt.

      IFA Service         IFA option data is present as specified by the 
      Metadata Options    IFA Type field.

5. IANA Considerations

Value            Description                          Reference
---------------------------------------------------------------------
TBD_0            NSH Service Option                  [This draft]
TBD_1            IOAM Service Option                 [This draft]
TBD_2            PBT Service Option                  [This draft]
TBD_3            IFA Service Option                  [This draft]
TBD_4            SFC Service Metadata Type           [This draft] 
TBD_5            IOAM Service Metadata Type          [This draft]   
TBD_6            IFA Service Metadata Type           [This draft]                                
           

6. Security Considerations

TBD.

7. References

7.1. Normative References

7.2. Informative References

Authors' Addresses