Encapsulations for In-band OAM Data
draft-brockners-inband-oam-transport-01

Abstract

In-band operation, administration and maintenance (OAM) records operational and telemetry information in the packet while the packet traverses a path between two points in the network. In-band OAM is to complement current out-of-band OAM mechanisms based on ICMP or other types of probe packets. This document outlines how in-band OAM data records can be transported in protocols such as NSH, Segment Routing, VXLAN-GPE, native IPv6 (via extension header), and IPv4. Transport options are currently investigated as part of an implementation study. This document is intended to only serve informational purposes.

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Table of Contents

• 1. Introduction
• 2. Conventions
• 3. In-Band OAM Metadata Transport in IPv6
• 3.1. In-band OAM in IPv6 Hop by Hop Extension Header
• 3.1.1. In-band OAM Hop by Hop Options
• 3.1.2. Procedure at the Ingress Edge to Insert the In-band OAM Header
• 3.1.3. Procedure at Intermediate Nodes
• 3.1.4. Procedure at the Egress Edge to Remove the In-band OAM Header
• 4. In-band OAM Metadata Transport in VXLAN-GPE
• 5. In-band OAM Metadata Transport in NSH
• 6. In-band OAM Metadata Transport in Segment Routing
• 6.1. In-band OAM in SR with IPv6 Transport
• 6.2. In-band OAM in SR with MPLS Transport
• 7. IANA Considerations
• 8. Manageability Considerations
• 9. Security Considerations
• 10. Acknowledgements
• 11. References
• 11.1. Normative References
• 11.2. Informative References
• Authors' Addresses

1. Introduction

This document discusses transport mechanisms for "in-band" operation, administration, and maintenance (OAM) data records. In-band OAM records OAM information within the packet while the packet traverses a particular network domain. The term "in-band" refers to the fact that the OAM data is added to the data packets rather than is being sent within packets specifically dedicated to OAM. A discussion of the motivation and requirements for in-band OAM can be found in [draft-brockners-inband-oam-requirements]. Data types and data formats for in-band OAM are defined in [draft-brockners-inband-oam-data].

This document outlines transport encapsulations for the in-band OAM data defined in [draft-brockners-inband-oam-data]. This document is to serve informational purposes only. As part of an in-band OAM implementation study different protocol encapsulations for in-band OAM data are being explored. Once data formats and encapsulation approaches are settled, protocol specific specifications for in-band OAM data transport will address the standardization aspect.

The data for in-band OAM defined in [draft-brockners-inband-oam-data] can be carried in a variety of protocols based on the deployment needs. This document discusses transport of in-band OAM data for the following protocols:

• IPv6
• VXLAN-GPE
• NSH
• Segment Routing (IPv6 and MPLS)

This list is non-exhaustive, as it is possible to carry the in-band OAM data in several other protocols and transports.

A feasibility study of in-band OAM is currently underway as part of the FD.io project [FD.io]. The in-band OAM implementation study should be considered as a "tool box" to showcase how "in-band" OAM can complement probe-packet based OAM mechanisms for different deployments and packet transport formats. For details, see the open source code in the FD.io [FD.io].

2. Conventions

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 [RFC2119].

Abbreviations used in this document:

MTU:

Maximum Transmit Unit

OAM:

Operations, Administration, and Maintenance

SR:

Segment Routing

SID:

Segment Identifier

NSH:

Network Service Header

POT:

Proof of Transit

SFC:

Service Function Chain

VXLAN-GPE:

Virtual eXtensible Local Area Network, Generic Protocol Extension

3. In-Band OAM Metadata Transport in IPv6

This mechanisms of in-band OAM in IPv6 complement others proposed to enhance diagnostics of IPv6 networks, such as the IPv6 Performance and Diagnostic Metrics Destination Option described in [I-D.ietf-ippm-6man-pdm-option]. The IP Performance and Diagnostic Metrics Destination Option is destination focused and specific to IPv6, whereas in-band OAM is performed between end-points of the network or a network domain where it is enabled and used.

A historical note: The idea of IPv6 route recording was originally introduced by [draft-kitamura-ipv6-record-route] back in year 2000. With IPv6 now being generally deployed and new concepts such as Segment Routing [I-D.ietf-spring-segment-routing] being introduced, it is imperative to further mature the operations, administration, and maintenance mechanisms available to IPv6 networks.

The in-band OAM options translate into options for an IPv6 extension header. The extension header would be inserted by either a host source of the packet, or by a transit/domain-edge node.

3.1. In-band OAM in IPv6 Hop by Hop Extension Header

This section defines in-band OAM for IPv6 transport. In-band OAM data is transported as an IPv6 hop-by-hop extension header.

3.1.1. In-band OAM Hop by Hop Options

Brief recap of the IPv6 hop-by-hop header as well as the options used for carrying in-band OAM data:

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Next Header  |  Hdr Ext Len  |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                                                               |
 .                                                               .
 .                            Options                            .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   |  Option Type  |  Opt Data Len |  Option Data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
      
With 2 highest order bits of Option Type indicating the following:

   00 - skip over this option and continue processing the header.

   01 - discard the packet.

   10 - discard the packet and, regardless of whether or not the
        packet's Destination Address was a multicast address, send an
        ICMP Parameter Problem, Code 2, message to the packet's
        Source Address, pointing to the unrecognized Option Type.

   11 - discard the packet and, only if the packet's Destination
        Address was not a multicast address, send an ICMP Parameter
        Problem, Code 2, message to the packet's Source Address,
        pointing to the unrecognized Option Type.

3rd highest bit:

   0 - Option Data does not change en-route

   1 - Option Data may change en-route

In-band OAM data records are inserted as options in an IPv6 hop-by-hop extension header:

1. Tracing Option: The in-band OAM Tracing option defined in [draft-brockners-inband-oam-data] is represented as a IPv6 option in hop by hop extension header by allocating following type:

   Option Type:

   001xxxxxx 8-bit identifier of the type of option. xxxxxx=TBD_IANA_TRACE_OPTION_IPV6.

2. Proof of Transit Option: The in-band OAM POT option defined in [draft-brockners-inband-oam-data] is represented as a IPv6 option in hop by hop extension header by allocating following type:

   Option Type:

   001xxxxxx 8-bit identifier of the type of option. xxxxxx=TBD_IANA_POT_OPTION_IPV6.

3. Edge to Edge Option: The in-band OAM E2E option defined in [draft-brockners-inband-oam-data] is represented as a IPv6 option in hop by hop extension header by allocating following type:

   Option Type:

   000xxxxxx 8-bit identifier of the type of option. xxxxxx=TBD_IANA_E2E_OPTION_IPV6.

3.1.2. Procedure at the Ingress Edge to Insert the In-band OAM Header

In an administrative domain where in-band OAM is used, insertion of the in-band OAM header is enabled at the required edge nodes by means of configuration.

Such a config SHOULD allow selective enablement of in-band OAM header insertion for a subset of traffic (e.g., one or several "pipes").

Further the ingress edge node should be aware of maximum size of the header that can be inserted. Details on how the maximum size/size of the in-band OAM domain are retrieved are outside the scope of this document.

Let n = max number of nodes to be allocated;
(Based on PMTU advertised in the domain)
                                              
Let k = number of node data that can be allocated by this node
Let node_data_size = size of each node_data based on in-band OAM type
 
if (packet matches traffic for which in-band OAM is enabled) {
    Create in-band OAM hbyh ext header with k node data preallocated
    Increment payload length in IPv6 header :
                      with size of in-band OAM hbyh ext header
    Populate node data at :
        (size of in-band OAM hbyh header = 8) + k * node_data_size
    from the beginning of the header
    Set segments left to : k - 1
    
 }

3.1.3. Procedure at Intermediate Nodes

If a network node receives a packet with an in-band OAM header and it is enabled to process in-band OAM data it performs the following:

k = number of node data that this node can allocate
if (in-band OAM ext hbyh header is present) {
    if (Segments Left > 0)) {
      populate node data at :
         node_data_start[Segments Left]
      Segments Left = Segments Left - 1
    } 
}

3.1.4. Procedure at the Egress Edge to Remove the In-band OAM Header

egress_edge = list of interfaces where in-band OAM hbyh ext 
               header is to be stripped
Before forwarding packet out of interfaces in egress_edge list:
if (in-band OAM hbyh ext header is present) {
   remove the in-band OAM hbyh ext header, 
   possibly store the record along with additional 
   fields for analysis and export
   Decrement Payload Length in IPv6 header
   by size of in-band OAM ext header
}

4. In-band OAM Metadata Transport in VXLAN-GPE

VXLAN-GPE [I-D.ietf-nvo3-vxlan-gpe] encapsulation is somewhat similar to IPv6 extension headers in that a series of headers can be contained in the header as a linked list. The different in-band OAM types are added as options within a new in-band OAM protocol header in VXLAN GPE.

In-band OAM header in VXLAN GPE header:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Outer Ethernet Header                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Outer IP Header                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Outer UDP Header                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
|R|R|Ver|I|P|R|O|          Reserved             | NP = i.b.OAM  |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GPE
|     Virtual Network Identifier (VNI)          | Reserved      |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Type =i.b.OAM | i.b.OAM HDR len |  Reserved     | NP = IP/Eth |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+iOAM
|                     in-band OAM options                       |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
|                                                               |
|                                                               |
|                     Payload + Padding (L2/L3/ESP/...)         |
|                                                               |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
|  Option Type  |  Opt Data Len |  Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

   Option Type          8-bit identifier of the type of option.
 
   Opt Data Len         8-bit unsigned integer.  Length of the Option
                        Data field of this option, in octets.
 
   Option Data          Variable-length field.  Option-Type-specific
                        data.

[I-D.ietf-nvo3-vxlan-gpe]. in-band OAM specific fields and header are defined here:[draft-brockners-inband-oam-data] are encoded with an option type allocated in the new in-band OAM IANA registry - in-band OAM_PROTOCOL_OPTION_REGISTRY_IANA_TBD. In addition the following padding options are defined to be used when necessary to align subsequent options and to pad out the containing header to a multiple of 8 octets in length.

Type:

8-bit unsigned integer defining in-band OAM header type

in-band OAM HDR len:

8-bit unsigned integer. Length of the in-band OAM HDR in 8-octet units

in-band OAM options:

Variable-length field, of length such that the complete in-band OAM header is an integer multiple of 8 octets long. Contains one or more TLV-encoded options of the format:

Pad1 option  (alignment requirement: none)
 
    +-+-+-+-+-+-+-+-+
    |       0       |
    +-+-+-+-+-+-+-+-+
    NOTE: The format of the Pad1 option is a special case -- it does
          not have length and value fields.
 
    The Pad1 option is used to insert one octet of padding into the
    Options area of a header.  If more than one octet of padding is
    required, the PadN option, described next, should be used, rather
    than multiple Pad1 options.
 
PadN option  (alignment requirement: none)
 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
    |       1       |  Opt Data Len |  Option Data
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
    The PadN option is used to insert two or more octets of padding
    into the Options area of a header.  For N octets of padding, the
    Opt Data Len field contains the value N-2, and the Option Data
    consists of N-2 zero-valued octets.

5. In-band OAM Metadata Transport in NSH

In Service Function Chaining (SFC) [RFC7665], the Network Service Header (NSH) [I-D.ietf-sfc-nsh] already includes path tracing capabilities [I-D.penno-sfc-trace], but currently does not offer a solution to securely prove that packets really traversed the service chain. The "Proof of Transit" capabilities (see [draft-brockners-inband-oam-requirements] and [draft-brockners-proof-of-transit]) of in-band OAM can be leveraged within NSH. Proof of transit in-band OAM data is added as NSH Type 2 metadata:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      TLV Class=Cisco (0x0009) |C|    Type=POT |F|R|R| Len=4   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
|                           Random                              |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  S
|                        Random(contd)                          |  C
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  V
|                         Cumulative                            |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                         Cumulative (contd)                    |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

TLV Class:

Describes the scope of the "Type" field. In some cases, the TLV Class will identify a specific vendor, in others, the TLV Class will identify specific standards body allocated types. POT is currently defined using the Cisco (0x0009) TLV class.

Type:

The specific type of information being carried, within the scope of a given TLV Class. Value allocation is the responsibility of the TLV Class owner. Currently a type value of 0x94 is used for proof of transit

Reserved bits:

Two reserved bit are present for future use. The reserved bits MUST be set to 0x0.

F:

One bit. Indicates which POT-profile is active. 0 means the even POT-profile is active, 1 means the odd POT-profile is active.

Length:

Length of the variable metadata, in 4-octet words. Here the length is 4.

Random:

64-bit Per packet Random number.

Cumulative:

64-bit Cumulative that is updated by the Service Functions.

6. In-band OAM Metadata Transport in Segment Routing

6.1. In-band OAM in SR with IPv6 Transport

Similar to NSH, a service chain or path defined using Segment Routing for IPv6 can be verified using the in-band OAM "Proof of Transit" approach. The Segment Routing Header (SRH) for IPv6 offers the ability to transport TLV structured data, similar to what NSH does (see [I-D.ietf-6man-segment-routing-header]). A new "POT TLV" is defined for the SRH which is to carry proof of transit in-band OAM data.

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Type     |    Length     |   RESERVED    |F|   Flags     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+
 |                           Random                              |  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  P
 |                        Random(contd)                          |  O
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  T
 |                         Cumulative                            |  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
 |                         Cumulative (contd)                    |  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+

Type:

To be assigned by IANA.

Length:

18.

RESERVED:

8 bits. SHOULD be unset on transmission and MUST be ignored on receipt.

F:

1 bit. Indicates which POT-profile is active. 0 means the even POT-profile is active, 1 means the odd POT-profile is active.

Flags:

8 bits. No flags are defined in this document.

Random:

64-bit per packet random number.

Cumulative:

64-bit cumulative value that is updated at specific nodes that form the service path to be verified.

6.2. In-band OAM in SR with MPLS Transport

In-band OAM "Proof of Transit" data can also be carried as part of the MPLS label stack. Details will be addressed in a future version of this document.

7. IANA Considerations

IANA considerations will be added in a future version of this document.

8. Manageability Considerations

Manageability considerations will be addressed ín a later version of this document..

9. Security Considerations

Security considerations will be addressed ín a later version of this document. For a discussion of security requirements of in-band OAM, please refer to [draft-brockners-inband-oam-requirements].

10. Acknowledgements

The authors would like to thank Eric Vyncke, Nalini Elkins, Srihari Raghavan, Ranganathan T S, Karthik Babu Harichandra Babu, Akshaya Nadahalli, Stefano Previdi and Andrew Yourtchenko for the comments and advice. For the IPv6 encapsulation, this document leverages and builds on top of several concepts described in [draft-kitamura-ipv6-record-route]. The authors would like to acknowledge the work done by the author Hiroshi Kitamura and people involved in writing it.

11. References

11.1. Normative References

11.2. Informative References

Authors' Addresses