IETF-96 Proceedings

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Service Function Chaining (sfc) (WG)

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Routing Area Area Director(s):

Assigned Area Director


Meeting Slides:

Blue Sheets:


Request for Comments:

Charter (as of 2015-10-14):

Network operators frequently utilize service functions such as packet
filtering at firewalls, load-balancing and transactional proxies (for
example spam filters) in the delivery of services to end users. Delivery
of these types of services is undergoing significant change with the
introduction of virtualization, network overlays, and orchestration.

Deploying service functions to support service delivery is currently both
a technical and an organizational challenge that involves significant
modification to the network configuration, impacting the speed at which
services can be deployed and increasing operational costs. Such
services are typically implemented by the ordered combination of a
number of service functions that are deployed at different points within
a network.

Today, common deployment models have service functions inserted on
the data-forwarding path between communicating peers. Going forward,
however, there is a need to move to a different model, where service
functions, whether physical or virtualized, are not required to reside on
the direct data path and traffic is instead steered through required
service functions, wherever they are deployed.

For a given service, the abstracted view of the required service
functions and the order in which they are to be applied is called a
Service Function Chain (SFC). An SFC is instantiated through selection
of specific service function instances on specific network nodes to form
a service graph: this is called a Service Function Path (SFP). The
service functions may be applied at any layer within the network
protocol stack (network layer, transport layer, application layer, etc.).

The SFC working group will document a new approach to service delivery
and operation. It will produce an architecture for service function
chaining that includes the necessary protocols or protocol extensions to
convey the Service Function Chain and Service Function Path information
to nodes that are involved in the implementation of service functions
and Service Function Chains, as well as mechanisms for steering traffic
through service functions. The WG will examine existing identifier schemes,
if there is a need for such identifiers in the context of the Generic SFC
encapsulation, before defining any new identifier scheme.

The working group will examine what information needs to be gathered
from the network and service functions in support of Service Function
Chaining and how that information may be made available to the
components of the Service Function Chaining architecture. The SFC
WG will closely consider and address the management and security
implications when documenting these deliverables.

Specifically, the SFC WG is chartered to deliver the following:

1. Problem Statement: This document will provide a summary of the
problem space to be addressed by the SFC working group including
example high-level use cases. Additionally, the working group will
normalize nomenclature and definitions for service function chaining.

2. Architecture: This document will provide a description of the SFC
architectural building blocks and their relationships including
interconnection, placement of SFC specific capabilities, management,
diagnostics, design analysis, and security models, as well as
requirements on the protocol mechanisms. The initial scope is
restricted to a single administrative domain, keeping in mind that
architectural decisions made for the intra-domain case may have
implications for the inter-domain case.

3. Generic SFC Encapsulation: This document will describe a single
service-level data plane encapsulation format that:
- indicates the sequence of service functions that make up the
Service Function Chain
- specifies the Service Function Path,
- communicates context information between nodes that implement
service functions and Service Function Chains.
It is intended that the encapsulation format be agnostic to the
layer at which it is applied and the service that is being
constructed. That is, the same encapsulation may be used on a
service function chain applied at the network layer or at any other
layer, and the same encapsulation format will apply for the
construction of Service Function Paths regardless of the actual
service. The working group will consider using an existing
encapsulation (with extensions as appropriate) if a suitable
candidate is found.

4. Control Plane Mechanisms: A document will be developed to describe
requirements for conveying information between control or management
elements and SFC implementation points. All protocol extension work
resulting from these requirements should be carried out in the
working group responsible for the protocol being modified in
coordination with this working group, but may be done in this working
group under a revised charter after agreement with all the relevant
WG chairs and responsible ADs.

5. Manageability: Work on the management and configuration of SFC
components related to the support of Service Function Chaining will
certainly be needed, but first needs to be better understood and