Service Function Chaining (sfc) H. Li
Internet-Draft Q. Wu
Intended status: Informational O. Huang
Expires: May 28, 2016 Huawei
M. Boucadair, Ed.
C. Jacquenet
France Telecom
W. Haeffner
S. Lee
R. Parker
Affirmed Networks
L. Dunbar
A. Malis
Huawei Technologies
J. Halpern
T. Reddy
P. Patil
November 25, 2015

Service Function Chaining (SFC) Control Plane Components & Requirements


This document describes requirements for conveying information between Service Function Chaining (SFC) control elements and SFC functional elements. Also, this document identifies a set of control interfaces to interact with SFC-aware elements to establish, maintain or recover service function chains. This document does not specify protocols nor extensions to existing protocols.

This document exclusively focuses on SFC deployments that are under the responsibility of a single administrative entity. Inter-domain considerations are out of scope.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

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This Internet-Draft will expire on May 28, 2016.

Copyright Notice

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Table of Contents

1. Introduction

The dynamic enforcement of a service-derived forwarding policy for packets entering a network that supports advanced Service Functions (SFs) has become a key challenge for operators. Typically, many advanced Service Functions (e.g., Performance Enhancement Proxies ([RFC3135]), NATs [RFC3022][RFC6333][RFC6146], firewalls [I-D.ietf-opsawg-firewalls], etc.) are solicited for the delivery of value-added services, particularly to meet various service objectives such as IP address sharing, avoiding covert channels, detecting and protecting against ever increasing Denial-of-Service (DoS) attacks, etc.

Because of the proliferation of such advanced service functions together with complex service deployment constraints that demand more agile service delivery procedures, operators need to rationalize their service delivery logics and master their complexity while optimising service activation time cycles. The overall problem space is described in [RFC7498]. A more in-depth discussion on use cases can be found in [I-D.ietf-sfc-use-case-mobility] and [I-D.ietf-sfc-dc-use-cases].

[RFC7665] presents a model addressing the problematic aspects of existing service deployments, including topological dependence and configuration complexity. It also describes an architecture for the specification, creation, and ongoing maintenance of Service Function Chains (SFC) within a network. That is, how to define an ordered set of Service Functions and ordering constraints that must be applied to packets and/or frames and/or flows selected as a result of classification.

1.1. Scope

While [RFC7665] focuses on data plane considerations, this document describes requirements for conveying information between SFC control elements and SFC data plane functional elements. Also, this document identifies a set of control interfaces to interact with SFC-aware elements to establish, maintain or recover service function chains.

Both distributed and centralized control plane schemes to install SFC-related state and influence forwarding policies are discussed.

This document does not make any assumption on the deployment use cases. In particular, the document implicitly covers fixed, mobile, data center networks and any combination thereof.

This document does not make any assumption about which control protocol to use, whether one or multiple control protocols are required, or whether the same or distinct control protocols will be invoked for each of the control interfaces. It is out of scope of this document to specify a profile for an existing protocol, to define protocol extensions, or to select a protocol.

Considerations related to the chaining of Service Functions (SFs) that span domains owned by multiple administrative entities are out of scope.

It is out of scope of this document to discuss SF-specific control and policy enforcement schemes; only SFC considerations are elaborated, regardless of the various connectivity services that may be supported in the SFC-enabled domain. Likewise, only the control of SFC-aware elements is discussed.

Service catalogue (including guidelines for deriving service function chains) is out of scope.

1.2. Terminology

The reader should be familiar with the terms defined in [RFC7498] and [RFC7665].

The document makes use of the following terms:

1.3. Assumptions

This document adheres to the assumptions listed in Section 1.2 of [RFC7665].

As a reminder, a Service Function Path (SFP) designates a subset of the collection designated by the SFC. For some SFPs, in some deployments, that will be a set of 1. For other SFPs (in the same or other deployments) it may be a larger set. For some SFPs in some deployments the SFP may designate the same set of choices as the SFC. This document accommodates all those deployments.

This document does not make any assumptions about the co-location of SFC data plane functional elements; this is deployment-specific. This document can accommodate a variety of deployment contexts such as (but not limited to):

Furthermore, the following assumptions are made:

2. Generic Considerations

2.1. Generic Requirements

For deployments that would require so, forwarding within an SFC-enabled domain must be allowed even if no control protocols are enabled. Static configuration must be allowed.

A permanent association between an SFC data plane element with a Control Element must not be required; specifically, the SFC-enabled domain must keep on processing incoming packets according to the SFC instructions even during temporary unavailability events of control plane components. SFC implementations that do not meet this requirement will suffer from another flavor of the constrained high availability issue, discussed in Section 2.3 of [RFC7498], supposed to be solved by SFC designs.

2.2. SFC Control Plane Bootstrapping

The interface that is used to feed the SFC control plane with service objectives and guidelines is not part of the SFC control plane itself. Therefore, this document assumes the SFC control plane is provided with a set of information that is required for proper SFC operation with no specific assumption about how this information is collected/provisioned, nor about the structure of such information. The following information that is likely to be provided to the SFC control plane at bootstrapping includes (non-exhaustive list):

Also, the SFC control plane may gather the following information from an SFC-enabled domain at bootstrapping (non-exhaustive list). How this information is collected is left unspecified in this document:

During the bootstrapping phase, a Control Element may detect a conflict between the running configuration in an SFC data plane element and the information maintained by the control plane. Consequently, the control plane undertakes appropriate actions to fix those conflicts. This is typically achieved by invoking one of the interfaces defined in Section 3.3.

2.3. Coherent Setup of an SFC-enabled Domain

Various transport encapsulation schemes and/or variations of SFC header implementations may be supported by one or several nodes of an SFC-enabled domain. For the sake of coherent configuration, the SFC control plane is responsible for instructing all the involved SFC data plane functional elements about the behavior to adopt to select the transport encapsulation scheme(s), the version of the SFC header to enable, etc.

3. SFC Control Plane: Reference Architecture & Interfaces

3.1. Reference Architecture

The SFC control plane is responsible for the following:

Figure 1 shows the overall SFC control plane architecture, including interface reference points.

This document does not elaborate on the internal decomposition of the SFC control plane functional blocks. The components within the SFC control plane and their interactions are out of scope.

As discussed in Section 3.2, the SFC control plane can be implemented in a (logically) centralized or distributed fashion.

               |                                              |
               |               SFC  Control Plane             |
       +-------|                                              |
       |       |                                              |
       C1      +------^-----------^-------------^-------------+
|      |            +----+        |             |             |
|      |            | SF |        |C2           |C2           |
|      |            +----+        |             |             |
| +----V--- --+       |           |             |             |
| |   SFC     |     +----+      +-|--+        +----+          |
| |Classifier |---->|SFF |----->|SFF |------->|SFF |          |
| |   Node    |<----|    |<-----|    |<-------|    |          |
| +-----------+     +----+      +----+        +----+          |
|                     |           |              |            |
|                     |C2      -------           |            |
|                     |       |       |     +-----------+ C4  |
|                     V     +----+ +----+   | SFC Proxy |-->  |
|                           | SF | |SF  |   +-----------+     |
|                           +----+ +----+                     |
|                             |C3    |C3                      |
|  SFC Data Plane Components  V      V                        |

Figure 1: SFC Control Plane: Overview

Note, the SFC control plane must be able to invoke SFC OAM mechanisms, and to determine the results of OAM operations.

3.2. Centralized vs. Distributed

The SFC control plane can be (logically) centralized, distributed or a combination thereof. Whether one or multiple SFC Control Elements are enabled is deployment-specific. Nevertheless, the following comments can be made:

SFC management (including SFC monitoring and supervision):
is likely to be centralized.
SFC Mapping Rules:
i.e., service instructions to bind a flow to a service function chain are likely to be managed by a central SFC Control Element, but the resulting policies can be shared among several Control Elements. Note, these policies can be complemented with local information (e.g., an IPv4 address/IPv6 prefix assigned to a customer) because such information may not be available to the central entity but known only during network attachment phase.
Path computation:
can be either distributed or centralized. Distributed path computation means that the selection of the exact sequence of SF functions that a packet needs to invoke (along with instances and/or SFF locator information) is a result of a distributed path selection algorithm executed by involved nodes. For some traffic engineering proposes, the SFP may be constrained by the control plane; as such, some SFPs can be fully specified (i.e., list all the SFF/SFs that need to be solicited) or partially specified (e.g., exclude some nodes, explicitly select which instance of a given SF needs to be invoked, etc.).
SFP Resiliency (including restoration)
refers to mechanisms to ensure high available service function chains. It includes means to detect node/link/path failures. Both centralized and distributed mechanism to ensure SFP resiliency can be envisaged.

Implementing a (logically) centralized path computation engine requires information to be dynamically communicated to the central SFC Control Element, such as the list of available SF instances, SFF locators, load status, SFP availability, etc.

3.3. Interface Reference Points

The following sub-sections describe the interfaces between the SFC control plane, as well as various SFC data plane elements.

3.3.1. C1: Interface between SFC Control Plane & SFC Classifier

As a reminder, a classifier is a function that is responsible for classifying traffic based on (pre-defined) rules.

This interface is used to install SFC classification rules in classifiers. Once classification rules are populated, classifiers are responsible for binding incoming traffic to service function chains according to these classification rules. Note, the SFC control plane must not make any assumption on how the traffic is to be bound to a given service function chain. In other words, classification rules are deployment-specific. For instance, classification can rely on a subset of the information carried in a received packet such as 5-tuple classification, be subscriber-aware, be driven by traffic engineering considerations, or any combination thereof.

The SFC control plane should be responsible for removing invalid (and stale) mappings from the classification tables maintained by the classifiers. Also, local sanity checks mechanisms may be supported locally by the classifiers, but those are out of scope.

The classifier may be notified by the control plane about the available SFs (including their locators) or be part of the service function discovery procedure.

Classification rules may be updated, deleted or disabled by the control plane. Criteria that would trigger those operations are deployment-specific.

Given that service function chaining solutions may be applied to very large sets of traffic, any control solution should take scaling issues into consideration as part of the design.

Below are listed some functional objectives for this interface:

The control plane must instruct the classifier whether it can trust an existing SFC information of an incoming packet or whether it must be ignored.

For bidirectional packet processing purposes (e.g., full or partial path symmetry), the control plane invokes this interface to configure the appropriate classification entries.

A classifier can send unsolicited messages through this interface to notify the SFC control plane about specific events. Triggers for sending unsolicited messages is a configurable parameter.

When re-classification is allowed in an SFC-enabled domain, this interface can be used to control classifiers co-resident with SFC-aware SFs, SFC proxies, or SFFs to manage re-classification rules.

When an incoming packet matches more than one classification entry, tie-breaking criteria should be followed (e.g., priority). Such tie-breaking criteria should be instructed by the control plane.

The identification of instantiated SFCs/SFPs is local to each administrative domain; it is policy-based and deployment-specific.

3.3.2. C2: Interface between SFC Control Plane & SFF

SFFs make traffic forwarding decisions according to the entries maintained in their SFP Forwarding Policy Table. Such table is populated by the SFC control plane through the C2 interface. In particular, this interface is used to instruct the SFF about the set of information to use for lookup purposes (e.g., SFP-id, 5-tuple transport coordinates).

This interface is used to instruct a SFF about the SFC-aware SFs that it can service. This interface is also used by the SFF to report the connectivity to their attached (including embedded) SFs. Local means may be enabled between the SFC-aware SFs and SFFs to allow for the dynamic attachment of SFs to a SFF and/or discovery of SFs by a SFF but those means are unspecified in this document.

The C2 interface is also used for collecting states of attributes (e.g., availability, workload, latency), for example, to dynamically adjust Service Function Paths.

3.3.3. C3: Interface between SFC Control Plane & SFC-aware SFs

The SFC control plane uses this interface to interact with SFC-aware SFs.

SFs may need to output some processing results of packets to the SFC control plane. This information can be used by the SFC control plane to update the SFC classification rules and the SFP Forwarding Policy Table entries.

This Interface is used to collect such kind of feedback information from SFs. For example, the following information can be exchanged between a SF and the SFC control plane:

The SFC control needs the above status information for various tasks it undertakes, but this information may be acquired directly from SFs or indirectly from other management and control systems in the operational environment.

This interface is also used to instruct an SFC-aware SF about any context information it needs to supply in the context of a given SFC.

Also, this interface informs the SFC-aware SF about the semantics of a context information, which would otherwise have opaque meaning. Several attributes may be associated with a context information such as (but not limited to) the "scope" (e.g., per-packet, per-flow or per host), whether it is "mandatory" or "optional" to process flows bound to a given chain, etc. Note that a context may be mandatory for "chain 1", but optional for "chain 2".

The control plane may indicate, for a given service function chain, an order for consuming a set of contexts supplied in a packet.

A SFC-aware SF can also be instructed about the behavior is should adopt after consuming a context information that was supplied in the SFC header. For example, the context can be maintained or stripped. The SFC-aware SF can be instructed to inject a new context header into the SFC header.

Multiple SFs may be located within the same physical node, and no SFF is enabled in that same node, means to unambiguously forward the traffic to the appropriate SF must be supported.

An SF can be instructed to strip the SFC information for the chains it terminates.

3.3.4. C4: Interface between SFC Control Plane & SFC Proxy

The SFC control plane uses this interface to interact with an SFC proxy.

The SFC proxy can be instructed about authorized SFC-unaware SFs it can service. A SFC proxy can be instructed about the behavior it should adopt to process the context information that was supplied in the SFC header on behalf of a SFC-unaware SF, e.g., the context can be maintained or stripped.

The SFC proxy is also instructed about the semantics of a context information, which would otherwise have opaque meaning. Several attributes may be associated with a context information such as (but not limited to) the "scope" (e.g., per-packet, per-flow or per host), whether it is "mandatory" or "optional" to process flows bound to a given chain, etc.

The SFC proxy can also be instructed to add some new context information into the SFC header on behalf of a SFC-unaware SF.

The C4 interface is also used for collecting attribute states (e.g., availability, workload, latency), for example, to dynamically adjust Service Function Paths.

4. Additional Considerations

4.1. Discovery of the SFC Control Element

SFC data plane functional elements need to be provisioned with the locators of the Control Elements. This can be achieved using a variety if mechanisms such as static configuration or the activation of a service discovery mechanism. The exact specification of how this provisioning is achieved is out of scope.

4.2. SF Symmetry

Some SFs require both directions of a flow to traverse. Some service function chains require full symmetry. If a SF (e.g., stateful firewall or NAT) needs both direction of a flow, it is the SF instantiation that needs both direction of a flow to traverse, not the abstract SF (which can have many instantiations spread across the network).

4.3. Pre-deploying SFCs

Enabling service function chains should preserve some deployment practices adopted by Operators. Particularly, installing a service function chain (and its associated SFPs) should allow for pre-deployment testing and validation purposes (that is a restricted and controlled usage of such service function chain (and associated SFPs)).

4.4. Withraw a Service Function (SF)

During the lifetime of a SFC, a given SF can be decommissioned. To accommodate such context and any other case where a SF is to be withdrawn, the control plane should instruct the SFC data plane functional element about the behavior to adopt. Particularly:

  1. a first approach would be to update the service function chains (and associated SFPs) where that SF is present by removing any reference to that SF. Doing so avoids to induce service failures for end users.
  2. a second approach would be to delete/deactivate any service function chain (and its associated SFPs) that involves that SF but install new service function chains.

4.5. SFC/SFP Operations

Various actions can be executed on a service function chain (and associated SFPs) that is structured by the SFC control plane. Indeed, a service function chain (and associated SFPs) can be enabled, disabled, its structure modified by adding a new SF hop or remove an SF from the sequence of SFs to be invoked, its classification rules modified, etc.

A modification of a service function chain can trigger control messages with the appropriate SFC-aware nodes accordingly.

4.6. Unsolicited (Notification) Messages

Involved SFC data plane functional element must be instructed to send unsolicited notifications when loops are detected, a problem in the structure of a service function chain is encountered, a long unavailable forwarding path time is observed, etc.

Specific criteria to send unsolicited notifications to a Control Element should be fine tuned by the control plane using the interface defined in Section 3.3.

4.7. SF Liveness Detection

The control plane must allow to detect the liveliness of SFs of an SFC-enabled domain. In particular, it must allow to dynamically detect that a SF instance is out of service and notify the relevant Control Element elements accordingly. The liveness information may be acquired directly from SFs or indirectly from other management and control systems in the operational environment.

Liveness status records for all SF instances, and service function chains (including the SFPs bound to a given chain) are maintained by the SFC Control.

The classifier may be notified by the control plane or be part of the liveness detection procedure.

The ability of a SFC Control Element to check the liveness of each SF present in service function chain has several advantages, including:

Local failure detect and repair mechanisms may be enabled by SFC-aware nodes. Control Elements may be fed directly or indirectly with inputs from these mechanisms.

Because a node embedding a SF can be responsive from a reachability standpoint (e.g., IP level) while the function its provides may be broken (e.g., a NAT module may be down), additional means to assess whether an SF is up and running are required. These means may be service-specific.

4.8. Monitoring & Counters

SFC-specific counters and statistics must be provided using the interfaces defined in Section 3.3. These data include (but not limited to):

4.9. Validity Lifetime

SFC instructions communicated via the various interfaces introduced in Section 3.3 may be associated with validity lifetimes, in which case classification entries will be automatically removed upon the expiry of the validity lifetime without requiring an explicit action from a Control Element.

Lifetimes are used in particular by an SFC data plane element to clear invalid control entries that would be maintained in the system if, for some reason, no appropriate action was undertaken by the control plane to clear such entries.

Both short and long lifetimes may be assigned.

4.10. Considerations Specific to the Centralized Path Computation Model

This section focuses on issues that are specific to the centralized deployment model (Section 3.2).

4.10.1. Service Function Path Adjustment

A SFP is determined by composing SF instances and overlay links among SFFs. Thus, the status of a SFP depends on the states or attributes (e.g., availability, topological location, latency, workload, etc.) of its components. For example, failure of a single SF instance results in failure of the whole SFP. Since these states or attributes of SFP components may vary in time, their changes should monitored and SFPs should be dynamically adjusted.

Examples of use cases for SFP adjustment are listed below:

SFP fail-over:
re-construct a SFP with replacing the failed SF instance with another instance of the same SF or withdraw the failed SF from being invoked. Note that withdrawing an SF may be envisaged if the resulting connectivity service is not broken (that is, packets bound to the updated SFP can be successfully delivered to their ultimate destinations). Rerouting the traffic to another SF instance or withdrawing the failed SF is deployment-specific.
SFP with better latency experience:
re-construct a SFP with a low path stretch considering the changes in topological locations of SF instances and the latency induced by the (overlay) connectivity among SFFs.
Traffic engineered SFP:
re-construct SFPs to localize the traffic in the network considering various TE goals such as bypass a node, bypass a link, etc. These techniques may be used for planned maintenance operations on a SFC-enabled domain.
SF/SFP Load balancing:
re-construct SFPs to distribute the workload among various SF instances. Particularly, load distribution policies can be taken into account by the Control Element to re-compute an SFP or be provisioned as attributes to SFPs that will be installed using the control interfaces.

For more details about the use cases, refer to [I-D.lee-nfvrg-resource-management-service-chain].

The procedures for SFP adjustment may be handled by the SFC control plane as follows:

4.10.2. Head End Initiated SFP Establishment

In some scenarios where a SFC Control Element is not connected to all SFFs in a SFC-enabled domain, the SFC control plane can send the explicit SFF/SF sequence or SF sequence to the SFC head-end, e.g., the classifier via the C1 interface (Section 3.3.1). SFC head-end can use a signaling protocol to establish the SFF/SF sequence based on the SF sequence.

4.10.3. (Regional) Restoration of Service Functions

There are situations that it might not be feasible for the classifier to be notified of the changes of SFF-sequence or SFF/SF Sequence for a given SFP because of the time taken for the notification and the limited capability of the classifiers.

If a SF has a large number of instantiations, it scales better if the classifier doesn't need to be notified with status of visible instantiations of SFs on a SFP.

It might not be always feasible for the classifier to be aware of the exact SF instances selected for a given SFP due to too many instances for each SF, notifications not being promptly sent to the classifier, or other reasons. This is about multiple instances of the same SF attached to one SFF node; those instances can be handled by the SFF via local load balancing schemes.

Regional restoration can take the similar approach as the global restoration: choosing a regional ingress node that can take over the responsibility of installing the new steering policies to the involved SFFs or network nodes. Typically, the regional ingress node should be:

4.10.4. Encoding the Exact SFF/SF Sequence in Data Packets

Encoding the exact Rendered Service Path (RSP) in every packet has the benefit and the issues associated with source routing. This approach may not be optimal when the SFP doesn't change very frequently, as in minutes or hours.

There are contexts that it might not be feasible for the head end classifier to be notified of the changes of SFF sequence or SFF/SF sequence for a given SFP because of the time taken for the notification and the limited capability of the classifier nodes.

4.10.5. Fully Controlled SFF/SF Sequence for a SFP

This section discusses some information that can be exchanged over C2 interface (Section 3.3.2) when the SFC Control Element explicitly passes the steering policies to all SFFs for the SFF/SF sequence of a given SFC. In this model, each SFF doesn't need to signal other SFFs for the SFP.

Suppose the SFP-id is id#1, an example of policy to sff-a is depicted in Figure 2 (for illustration proposes).

           Match Condition            |       Action
SFP-id = "id#1" & ingress = sffx-port | next-hop: "sf2" & VLAN-ID
SFP-id = "id#2" & ingress = sf2-port  | next-hop: "sf3" & VLAN-ID
SFP-id = "id#3" & ingress = sf3-port  | next-hop: sff-b 

Figure 2: Example of Traffic Steering Policy to a SFF node

The SFF nodes may not be directly adjacent to each other. They can be interconnected by tunnels, such as GRE, VxLAN, etc. SFs are attached to a SFF node or SFC proxy node via Ethernet link or other link types. Therefore, the steering policies to a SFF node for service function chain depends on if the packet comes from previous SFF or comes from a specific SF, i.e., the SFP Forwarding Policy Table entries have to be ingress port specific. There are multiple different steering policies for one flow within one SFF and each set of steering policies is specific for an ingress port.

For example, the semantics of traffic steering rules can be a match condition and an action, similar to the route described in Section 2.3 of [I-D.ietf-i2rs-rib-info-model]. The match conditions and action for distinct ports can be different.

The matching criteria for SFF can be more sophisticated. For example, the matching criteria could be any fields in the data packets, such as:

  • Ingress port
  • Destination MAC address
  • Source MAC address
  • VLAN-ID,
  • Destination IP address
  • Source IP address
  • Source port number
  • Destination port number
  • DSCP
  • Packet size, etc., or any combination thereof.

The actions to SFC proxy may include a method to map the SFP Identifier carried in the packet header to a locally significant link identifier, e.g., VLAN-ID, and a method to construct and encapsulate the SFC header back to the packets when they come back from the attached SFs.

This approach does not require using an end-to-end signaling protocol among Classier nodes and SFF nodes. However, there may be problems encountered if SFF nodes are not updated in the proper order or not at the same time. For example, if the SFF "A" and SFF "C" get flow steering policies at slightly different times, some packets might not be directed to some service functions on a chain.

5. Security Considerations

5.1. Secure Communications

The SFC Control Elements and the participating SFC data plane elements must mutually authenticate. SFC data plane elements must ignore instructions received from unauthenticated SFC Control Elements. The credentials details used during authentication can be used by the SFC control plane to decide whether specific authorization may be granted to a Service Function with regards to some specific operations (e.g., authorize a given SF to access specific context information).

In case multiple SFC data plane elements are embedded in the same node, the authentication mechanism may be executed as a whole; not for each instance.

A SFC data plane element must be able to send authenticated unsolicited notifications to a SFC Control Element.

The communication between a Control Element and SFC data plane elements must provide integrity and replay protection.

An SFC Control Element may instruct a Service Function to include specific security token(s) that may be used to decrypt traffic upstream. The security token may be supplied by the SFC control plane or by an authorized Service Function (e.g., TLS proxy). The exact details on how authorization is granted to a specific SF, including via a control plane interface, should be specified.

A Service Function must by default discard any action from a SFC Control Element that requires specific right privileges (e.g., access to a legal intercept log, mirror the traffic, etc.).

5.2. Pervasive Monitoring

The authentication mechanism should be immune to pervasive monitoring [RFC7258]. An attacker can intercept traffic by installing classification rules that would lead to redirect all or part of the traffic to an illegitimate network node. Means to protect against attacks that would lead to install, remove, or modify classification rules must be supported.

5.3. Privacy

The SFC control plane must be able to instruct SFC data plane elements about the information to be leaked outside an SFC-enabled domain. Particularly, the SFC control plane must support means to preserve privacy [RFC6973]. Context headers may indeed reveal privacy information (e.g., IMSI, user name, user profile, location, etc.). Those headers must not be exposed outside the operator's domain.

5.4. Denial-of-Service (DoS)

In order to protect against denial of service that would be caused by a misbehaving trusted SFC Control Element, SFC data plane elements should rate limit the messages received from an SFC Control Element.

5.5. Illegitimate Discovery of SFs and SFC Control Elements

Means to defend against soliciting illegitimate SFs/SFFs that do not belong to the SFC-enabled domain must be enabled. Such means must be defined in service function discovery and SFC Control Element discovery specification documents.

6. IANA Considerations

This document does not require any IANA actions.

7. References

7.1. Normative References

[RFC7665] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015.

7.2. Informative References

[I-D.ietf-i2rs-rib-info-model] Bahadur, N., Kini, S. and J. Medved, "Routing Information Base Info Model", Internet-Draft draft-ietf-i2rs-rib-info-model-08, October 2015.
[I-D.ietf-opsawg-firewalls] Baker, F. and P. Hoffman, "On Firewalls in Internet Security", Internet-Draft draft-ietf-opsawg-firewalls-01, October 2012.
[I-D.ietf-sfc-dc-use-cases] Surendra, S., Tufail, M., Majee, S., Captari, C. and S. Homma, "Service Function Chaining Use Cases In Data Centers", Internet-Draft draft-ietf-sfc-dc-use-cases-03, July 2015.
[I-D.ietf-sfc-use-case-mobility] Haeffner, W., Napper, J., Stiemerling, M., Lopez, D. and J. Uttaro, "Service Function Chaining Use Cases in Mobile Networks", Internet-Draft draft-ietf-sfc-use-case-mobility-05, October 2015.
[I-D.lee-nfvrg-resource-management-service-chain] Lee, S., Pack, S., Shin, M. and E. Paik, "Resource Management in Service Chaining", Internet-Draft draft-lee-nfvrg-resource-management-service-chain-01, March 2015.
[I-D.lee-sfc-dynamic-instantiation] Lee, S., Pack, S., Shin, M. and E. Paik, "SFC dynamic instantiation", Internet-Draft draft-lee-sfc-dynamic-instantiation-01, October 2014.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z. Shelby, "Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations", RFC 3135, DOI 10.17487/RFC3135, June 2001.
[RFC6146] Bagnulo, M., Matthews, P. and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J. and Y. Lee, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M. and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014.
[RFC7498] Quinn, P. and T. Nadeau, "Problem Statement for Service Function Chaining", RFC 7498, DOI 10.17487/RFC7498, April 2015.


This document is the result of merging with [I-D.lee-sfc-dynamic-instantiation].

Many thanks to Shibi Huang, Lac Chidung, Taeho Kang, Sumandra Majee, Dave Dolson, Paul Bottorff, Reinaldo Penno, Jim Guichard, Paul Quinn, Shunsuke Homma, and Ken Gray for the feedback and discussion on the mailing list.

The text about the semantic of a context information is provided by Dave Dolson.

Authors' Addresses

Hongyu Li Huawei Huawei Industrial Base,Bantian,Longgang Shenzhen China EMail:
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail:
Yong(Oliver) Huang Huawei Huawei Industrial Base,Bantian,Longgang Shenzhen China EMail:
Mohamed Boucadair (editor) France Telecom Rennes 35000 France EMail:
Christian Jacquenet France Telecom Rennes 35000 France EMail:
Walter Haeffner Vodafone D2 GmbH Ferdinand-Braun-Platz 1 Duesseldorf 40549 DE EMail:
Seungik Lee ETRI 218 Gajeong-ro Yuseung-Gu Daejeon, 305-700 Korea Phone: +82 42 860 1483 EMail:
Ron Parker Affirmed Networks Acton MA 01720 USA EMail:
Linda Dunbar Huawei Technologies USA EMail:
Andrew Malis Huawei Technologies USA EMail:
Joel M. Halpern Ericsson EMail:
Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India EMail:
Prashanth Patil Cisco Systems, Inc. Bangalore, India EMail: