SRH Extension for Redundancy Protection
draft-geng-spring-redundancy-protection-srh-00

Abstract

Redundancy protection is a method of service protection by sending copies of the same packets of one flow over multiple paths, which includes packet replicaiton, elimination and ordering. This document defines SRv6 header(SRH) extensions to support redundancy protection.

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 .

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Terminology and Conventions
• 3. Redundancy Protection Requirement Analysis
• 4. SRH Extensions for Redundancy Protection
• 4.1. Option 1: seperated TLVs for flow identification and sequence number
• 4.2. Option 2 unified TLV for flow identification and sequence number
• 5. IANA Considerations
• 6. Security Considerations
• 7. Acknowledgements
• 8. Normative References
• Authors' Addresses

1. Introduction

Redundancy protection is a method of providing 1+1 protection by sending copies of the same packets of one flow over multiple paths, which includes packet replicaiton, elimination and ordering. This document defines SRv6 header(SRH) extensions to support redundancy protection.

2. Terminology and 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].

Redundancy Node: the start point of redudancy protection, which is a network device that could implement packet replication.

Merging Node: the end point of redudancy protection, which is a network node that could implement packet elimination and ordering(optionally).

Editor's Note: Similar mechanism is defined as "Service Protection" in the [RFC8655]. In this document, we define a new term "Redundancy Protection" to distinguish with other service protection method. Some of the terms are the similar as [RFC8655].

3. Redundancy Protection Requirement Analysis

The figure shows how to provide redundancy protection over SRv6.

             |                                         |
 ----IPv6--->|<---------------SRv6 Domain------------->|<----IPv6---
             |                                         |
             |             +------+T2+----+            |
   +---+    +---+        +-+-+          +-+-+        +---+    +---+
   | E1+----| In|--+T1+--+Red|          |Mer|--+T4+--| Eg+----+ E2|
   +---+    +---+        +-+-+          +-+-+        +---+    +---+
                           +-----+T3+-----+

The process of redundancy protection is as follows: 1) The flow is replicated in Rep(Redundancy Node); 2) Tow replicated flows go through different paths till Mer (Merging Node); When there is any failures happened in one the path, the service continues to deliver through the other path without break; 3) The first received packet of the flow is transmitted from Mer (Merging Node) to Eg(Egress), and the redundant packets are eliminated. 4) Sometimes, the packet will arrive out of order because of redundancy protection, the function of reordering may be necessary in the Merging Node.

This document defines Flow Identification and Sequence Number in Segment Routing Header(SRH) as an extension of the current draft[I-D.ietf-6man-segment-routing-header] to support redundancy protection.

Flow Identification is used to distinguish flows and Sequence Number is used to distinguish packets in the same flow when doing packet merging and ordering.

4. SRH Extensions for Redundancy Protection

Flow Identification and Sequence Number could be defined in SRH optional TLV.

4.1. Option 1: seperated TLVs for flow identification and sequence number

  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            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        RESERVED       |           Flow Identification         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Type: 8bits, to be assigned by IONA.
• Length: 8 octets.
• RESERVED: 28 bits, MUST be 0 on transmission and ignored on receipt.
• Flow Identification: 20 bits, which is used for identifying redundant protection flow.

  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            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |RESERVED|                    Sequence Number                   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Type: 8 bits, to be assigned by IONA.
• Length: 8.
• RESERVED: 20 bits. MUST be 0 on transmission and ignored on receipt.
• Sequence Number: 28 bits, which is used for indicating sequence number of the redundant protection flow.

4.2. Option 2 unified TLV for flow identification and sequence number

  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     |    Flow Identification        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       |                    Sequence Number                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             RESERVED                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Type: 8bits, to be assigned by IANA.
• Length: 8 octets.
• Flow Identification: 20 bits, which is used for identifying the redundant protection flow.
• Sequence Number: 28 bits, which is used for indicating sequence number of the redundant protection flow.
• Reserved: 32 bits. MUST be 0 on transmission and ignored on receipt.

5. IANA Considerations

TBD

6. Security Considerations

TBD

7. Acknowledgements

Thank you for valuable comments from James Guichard and Andrew Mail

8. Normative References

Authors' Addresses