RFC6374 Synonymous Flow Labels
draft-bryant-mpls-rfc6374-sfl-01

Abstract

This document describes a method of providing flow identification information when making RFC6374 performance measurements. This allows RFC6374 measurements to be made on multi-point to point LSPs and allows the measurement of flows within an MPLS construct using RFC6374.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Requirements Language
• 3. RFC6374 Packet Loss Measurement with SFL
• 3.1. RFC6374 SFL TLV
• 4. The Application of SFL to other PM Types
• 5. Privacy Considerations
• 6. Security Considerations
• 7. IANA Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

[I-D.ietf-mpls-flow-ident] describes the requirement for introducing flow identities when using RFC6374 [RFC6374] packet Loss Measurements (LM). In summary RFC6374 uses the LM packet as the packet accounting demarcation point. Unfortunately this gives rise to a number of problems that may lead to significant packet accounting errors in certain situations. For example:

1. Where a flow is subjected to Equal Cost Multi-Path (ECMP) treatment packets can arrive out of order with respect to the LM packet.
2. Where a flow is subjected to ECMP treatment, packets can arrive at different hardware interfaces, thus requiring reception of an LM packet on one interface to trigger a packet accounting action on a different interface which may not be co-located with it. This is a difficult technical problem to address with the required degree of accuracy.
3. Even where there is no ECMP (for example on RSVP-TE, MPLS-TP LSPs and PWs) local processing may be distributed over a number of processor cores, leading to synchronization problems.
4. Link aggregation techniques may also lead to synchronization issues.
5. Some forwarder implementations have a long pipeline between processing a packet and incrementing the associated counter again leading to synchronization difficulties.

An approach to mitigating these synchronization issue is described in [I-D.tempia-ippm-p3m] and [I-D.chen-ippm-coloring-based-ipfpm-framework] in which packets are batched by the sender and each batch is marked in some way such that adjacent batches can be easily recognized by the receiver.

An additional problem arises where the LSP is a multi-point to point LSP, since MPLS does not include a source address in the packet. Network management operations require the measurement of packet loss between a source and destination. It is thus necessary to introduce some source specific information into the packet to identify packet batches from a specific source.

{{I-D.ietf-mpls-sfl-framework specifies a method of encoding per flow instructions in an MPLS label stack using a technique called Synonymous Flow Labels (SFL) in which labels which mimic the behaviour of other labels provide the packet batch identifiers and enable the per batch packet accounting. This memo specifies how SFLs are used to perform RFC6374 performance measurements.

2. Requirements Language

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

3. RFC6374 Packet Loss Measurement with SFL

The packet format of an RFC6374 Query message using SFLs is shown in Figure 1.

+-------------------------------+
|                               |
|             LSP               |
|            Label              |
+-------------------------------+
|                               |
|        Synonymous Flow        |
|            Label              |
+-------------------------------+
|                               |
|                               |
|  RFC6374 Measurement Message  |
|                               |
|  +-------------------------+  |
|  |                         |  |
|  |     RFC6374 Fixed       |  |
|  |     Header              |  |
|  |                         |  |
|  +-------------------------+  |
|  |                         |  |
|  |      Optional SFL TLV   |  |
|  |                         |  |
|  +-------------------------+  |
|  |                         |  |
|  |      Optional Return    |  |
|  |      Information        |  |
|  |                         |  |
|  +-------------------------+  |
|                               |
+-------------------------------+

 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     |MBZ| SFL Batch |    SFL Index  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 SFL                   |        Reserved       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 FEC                                           |
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type      Type is set to Synonymous Flow Label (SFL-TLV).

Length    The length of the TLV as specified in RFC6374.

MBZ       MUST be sent as zero and ignored on receive. 

SFL Batch The SFL batch that this SFL was allocated as part 
          of see [I-D.bryant-mpls-sfl-control]            

SPL Index The index into the list of SFLs that were assigned  
          against the FEC that corresponds to the SFL.         

SFL       The SFL used to deliver this packet.  This is an MPLS
          label which is a component of a label stack entry as 
          defined in Section 2.1 of RFC3032.               

Reserved  MUST be sent as zero and ignored on receive.         

FEC       The Forwarding Equivalence Class that was used to    
          request this SFL.  This is encoded as per            
          Section 3.4.1 of TBD                                 

      Type Description                       Reference
      ---- --------------------------------- ---------
      TBD  Synonymous Flow Label             This