SFC dynamic instantiation
draft-lee-sfc-dynamic-instantiation-01

Abstract

This document describes a control plane architecture for dynamic instantiation of service function chains which dynamically creates and adapts service function paths to optimize performance of the service function paths. This document further defines basic operations for the dynamic instantiations; and performance metrics of service function path components, i.e., service function instances and forwarding links among service function forwarders for evaluation of the service function path.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. SFC dynamic instantiation
• 4. Control plane architecture
• 5. Operational procedures
• 6. Security Considerations
• 7. IANA Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

The current service delivery model is bound to static topologies and manually configured resources. This has motivated a more flexible deployment model which orchestrates the service delivery separated from the network. Service function chaining [I-D.ietf-sfc-problem-statement] provides a new service deployment model that delivers the traffic along the predefined logical paths of service functions (SFs), called service function chains (SFCs) with no regard of network topologies or transport mechanisms.

A SFC is determined by classification of target traffic based on operator's policy. Since it is described with logical SFs, the service function chain needs to be instantiated by selecting instances of the SFs, which results in a service function path (SFP). Performance of a SFP depends on the current state or attributes (e.g., availability, topological location, and latency) of SFP components (i.e., SF instances (SFIs) and forwarding links among SFFs (SFLs)). Thus, the SFP performance may vary according to which SFIs are selected at SFC instantiation; and it may also vary in time with the state or attributes of the SFP components.

This document describes a control plane architecture for dynamic instantiation of SFCs which dynamically creates and adapts SFPs to optimize the SFP performance considering the current state and attributes of SFIs and SFLs. This document further defines basic operations for the dynamic instantiations and performance metrics of SFP components for SFP evaluation.

2. Terminology

This document uses the following terms and most of them were reproduced from [I-D.ietf-sfc-problem-statement] and [I-D.ietf-sfc-architecture].

• Classification: Locally instantiated policy and customer/network/service profile matching of traffic flows for identification of appropriate outbound forwarding actions.
• Service Function Chain (SFC): A service function chain defines a set of abstract service functions and ordering constraints that must be applied to packets and/or frames selected as a result of classification. The implied order may not be a linear progression as the architecture allows for SFCs that copy to more than one branch, and also allows for ere there is flexibility in the order in which service functions need to be applied. The term service chain is often used as shorthand for service function chain.
• Service Function (SF): A function that is responsible for specific treatment of received packets. A Service Function can act at various layers of a protocol stack (e.g., at the network layer or other OSI layers). As a logical component, a Service Function can be realized as a virtual element or be embedded in a physical network element. One or multiple Service Functions can be embedded in the same network element. Multiple occurrences of the Service Function can exist in the same administrative domain.
• Service Function Instance (SFI): The instantiation of Service Function that can be a virtual instance or be embedded in a physical network element. One of multiple Service Functions can be embedded in the same network element. Multiple instances of the Service Function can be enabled in the same administrative domain.
• Service Function Forwarder (SFF): A service function forwarder is responsible for delivering traffic received from the network to one or more connected service functions according to information carried in the SFC encapsulation, as well as handling traffic coming back from the SF. Additionally, a service function forwarder is responsible for delivering traffic to a classifier when needed and supported, mapping out traffic to another SFF (in the same or different type of overlay), and terminating the SFP.
• Service Function Path (SFP): The SFP provides a level of indirection between the fully abstract notion of service chain as a sequence of abstract service functions to be delivered, and the fully specified notion of exactly which SFF/SFs the packet will visit when it actually traverses the network. By allowing the control components to specify this level of indirection, the operator may control the degree of SFF/SF selection authority that is delegated to the network.
• Service Forwarding Link (SFL): An overlay link between two SFFs over which the packet will visit SF along the SFP.

3. SFC dynamic instantiation

A service function chain is composed of one or more logical service functions and it can be further instantiated with a SFP which contains physical instances of the logical SFs. Since multiple instances of a SF may be available, different sets of SFI (i.e., SFPs) can be built per SFC.

For example in Figure 1, a SFC {SF1 -> SF2 -> SF3} selected for a traffic flow can be further instantiated with two different SFPs: SFP#1 {SF1_a -> SF2_a -> SF3_a} and SFP#2 {SF1_b -> SF2_b -> SF3_b} by selecting one of multiple instances of the service functions.

       +------+           +------+           +------+
SFC    | SF1  |-----------| SF2  |-----------| SF3  |
       +------+           +------+           +------+

                                                     
       +------+           +------+           +------+
       |SF1_a |           |SF2_a |           |SF3_a |
       +------+           +------+           +------+
SFP#1     |                   |                  |   
       ********           ********           ********
       * SFF  *-----------* SFF  *-----------* SFF  *
       ********    SFL    ********    SFL    ********
SFP#2     |                   |                  |
       +------+           +------+           +------+
       |SF1_b |           |SF2_b |           |SF3_b |
       +------+           +------+           +------+

#=================================================#
#                                                 #
#       +---------------+      +---------------+  #
#   ____|      SFC      |______| SFP component |  #
#   |   | instantiation |      |   management  |  #
#   |   +---------------+      +---------------+  #
#   |             |                 ^     ^       #
#===|=============|=================|=====|=======#
    |             |                 |     | 
    |(a)          |(b)              |(c)  |(d) 
    |             |                 |     |    
    |             |  +------+       |  +------+ 
    |             |  | SFI  |       |  | SFI  | 
    |             |  +------+       |  +------+ 
    V             V   |             |    |      
 ********       ********           ********
-* CLSF *-------* SFF  *-----------* SFF  *--------
 ********       ********           ********