Network Working Group M. Boucadair
Internet-Draft C. Jacquenet
Intended status: Standards Track France Telecom
Expires: February 22, 2014 R. Parker
Affirmed Networks
D. Lopez
Telefonica I+D
P. Yegani
Juniper Networks
J. Guichard
P. Quinn
Cisco Systems, Inc.
August 21, 2013
Differentiated Service Function Chaining Framework
draft-boucadair-network-function-chaining-03
Abstract
IP networks rely more and more on the combination of advanced
functions (besides the basic routing and forwarding functions). This
document defines a solution to enforce Service Function Chaining
(SFC) with minimum requirements on the underlying network.
The proposed solution allows for Differentiated Forwarding
(DiffForward): packets are classified and marked at the entry point
of an SFC-enabled network, and are then forwarded on a per SFC map
basis.
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 RFC 2119 [RFC2119].
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 22, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. On the Proliferation of Service Functions . . . . . . . . 3
1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Objectives . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Functional Elements . . . . . . . . . . . . . . . . . . . . . 7
4. SFC Provisioning . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Assign Service Function Identifiers . . . . . . . . . . . 7
4.2. Service Function Locator . . . . . . . . . . . . . . . . 7
4.3. Building Service Function Chaining (SFC) Maps . . . . . . 8
4.4. Building Service Function Chaining (SFC) Policy Tables . 8
5. Theory Of Operation . . . . . . . . . . . . . . . . . . . . . 10
5.1. SFC Boundary Node . . . . . . . . . . . . . . . . . . . . 10
5.2. SFC Classifier . . . . . . . . . . . . . . . . . . . . . 10
5.3. SFC Ingress Node . . . . . . . . . . . . . . . . . . . . 11
5.4. SFC Egress Node . . . . . . . . . . . . . . . . . . . . . 11
5.5. SF Node . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.6. Intermediate Nodes . . . . . . . . . . . . . . . . . . . 12
6. Fragmentation Considerations . . . . . . . . . . . . . . . . 12
7. Differentiated Services . . . . . . . . . . . . . . . . . . . 12
8. Design Considerations . . . . . . . . . . . . . . . . . . . . 13
8.1. Transmit A SFC Map Index In A Packet . . . . . . . . . . 13
8.1.1. SFC Map Index . . . . . . . . . . . . . . . . . . . . 13
8.1.2. Why Not Loose Or Strict Source Routing (SSR)? . . . . 13
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8.1.3. Where To Store SFC Map Indexes In A Packet? . . . . . 13
8.2. Steer Paths To Cross Specific SF Nodes . . . . . . . . . 14
9. Deployment Considerations . . . . . . . . . . . . . . . . . . 14
9.1. Generic Requirements . . . . . . . . . . . . . . . . . . 14
9.2. Deployment Models . . . . . . . . . . . . . . . . . . . . 14
9.3. On Service Function Profiles (a.k.a., Contexts) . . . . . 15
9.4. SF Node is also a Classifier . . . . . . . . . . . . . . 16
9.5. Direct Adjacency . . . . . . . . . . . . . . . . . . . . 16
9.6. Service Function Loops . . . . . . . . . . . . . . . . . 17
9.7. Lightweight SFC Policy Table . . . . . . . . . . . . . . 17
9.8. Liveness Detection Of SFs By The PDP . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
13.1. Normative References . . . . . . . . . . . . . . . . . . 19
13.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
1.1. On the Proliferation of Service Functions
IP networks rely more and more on the combination of advanced
functions (besides the basic routing and forwarding functions).
Typical examples of such functions include firewall (e.g.,
[RFC6092]), DPI (Deep Packet Inspection), LI (Lawful Intercept)
module, NAT44 [RFC3022], NAT64 [RFC6146], DS-Lite AFTR [RFC6333],
NPTv6 [RFC6296], HOST_ID injection, HTTP Header Enrichment function,
TCP tweaking and optimization functions, transparent caching,
charging function, load-balancer, etc.
Such advanced functions are denoted SF (Service Function) in this
document.
The dynamic enforcement of a SF-derived, adequate forwarding policy
for packets entering a network that supports such advanced Service
Functions has become a key challenge for operators and service
providers. SF-inferred differentiated forwarding is ensured by
tweaking the set of Service Functions to be invoked. How to bind a
flow of packets that share at least one common characteristic to a
forwarding plane is policy-based, and subject to the set of SF
functions that need to be solicited for the processing of this
specific flow.
The overall problem space is described in
[I-D.quinn-nsc-problem-statement]. A list of requirements is
available at [I-D.boucadair-chaining-requirements].
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1.2. Scope
This document defines a framework to enforce Service Function
Chaining (SFC) with minimum requirements on the underlying network.
The proposed solution allows for Differentiated Forwarding
(DiffForward): packets are classified at the entry point of an SFC-
enabled network, and are then forwarded according to the ordered set
of SF functions that need to be activated to process these packets in
the SFC-enabled network.
This document does not make any assumption on the deployment context.
The proposed framework covers both fixed and mobile networks (e.g.,
to rationalize the proliferation of advanced features at the Gi
Interface [RFC6459]).
1.3. Objectives
The main objectives of the proposed framework are listed below:
o Efficiently master the chained activation of Service functions,
regardless of the underlying network topology and routing
policies.
o Allow for differentiated packet forwarding by selecting the set of
Service functions to be invoked.
o Allow to easily change the chronology of the activation of Service
functions to be invoked.
o Allow to easily change the set of Service functions to be invoked.
o Ease management (including withdrawal) of Service functions and
minimize any subsequent topology upgrade.
o Automate the overall process of generating and enforcing policies
to accommodate a set of network connectivity service objectives.
1.4. Assumptions
The following assumptions are made:
o Not all SFs can be characterized with a standard definition in
terms of technical description, detailed specification,
configuration, etc.
o There is no global nor standard list of SFs enabled in a given
administrative domain. The set of SFs varies as a function of the
service to be provided and according to the networking
environment.
o There is no global nor standard SF chaining logic. The ordered
set of SFs that need to be activated to deliver a given
connectivity service is specific to each administrative entity.
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o The chaining of SFs and the criteria to invoke some of them are
specific to each administrative entity that operates the SF-
enabled network (also called administrative domain).
o SF chaining logic and related policies should not be exposed
outside a given administrative domain.
o Several SF chaining logics can be simultaneously enforced within
an administrative domain to meet various business requirements.
o No assumption is made on how FIBs and RIBs of involved nodes are
populated.
o How to bind the traffic to a given SF chaining is policy-based.
1.5. Rationale
Given the assumptions listed in Section 1.4, the rationale of the
framework is as follows:
o The framework separates the dynamic provisioning of required SF
functions from packet handling operations (e.g., forwarding
decisions).
o SFs are handled as black boxes; the technical characterization of
each SF is not required.
o No IANA registry is required to store the list of SFs.
o No IANA registry is required to store the SF chaining candidates.
o No specific SF chaining is assumed. The description of SF chains
is an information that will be processed by the nodes that
participate to the delivery of a network service. The set of
listed/chained SF functions is generated by each administrative
entity operating the network.
o SF handling is policy-based: SF chains can be updated or deleted,
new SFs can be added without any impact on existing SFs, etc. In
particular, this design is compliant with the global framework
discussed in [I-D.sin-sdnrg-sdn-approach].
o For the sake of efficiency, policy enforcement is automated (but
policies can be statically enforced, for example).
o To minimize fragmentation, a minimal set of information needs to
be signaled (possibly in data packets).
o Advanced features (e.g., load balancing) are also described and
configured according to policies that can be service-specific.
Policy decisions are made by a Policy Decision Point [RFC2753] and
the solicited enforcement points are responsible for applying
these decisions, whatever the objective to achieve.
o SFs can be embedded in nodes that intervene in the transport
service or supported by dedicated nodes (e.g., dedicated servers).
The decision to implement one of these two models (or a
combination thereof) is deployment-specific and it is orthogonal
to the overall procedure.
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o Multiple SFC-enabled domains can be deployed within the same
administrative domain. Nodes are provisioned with the policy
table of the SFC-enabled domain they belong to.
o The overall consistency of the differentiated forwarding policy is
ensured by the PDP.
o The PDP can be responsible to enforce other policies than those
described in the SFC Policy Tables.
2. Terminology
This document makes use of the following terms:
o DiffForward: refers to the differentiated forwarding procedure as
specified in this document.
o SF (Service Function): refers to a function which is enabled in
the network operated by an administrative entity. One or many
Service Functions can be involved in the delivery of added-value
services. A non-exhaustive list of Service Functions include:
firewall (e.g., [RFC6092]), DPI (Deep Packet Inspection), LI
(Lawful Intercept) module, NAT44 [RFC3022], NAT64 [RFC6146], DS-
Lite AFTR [RFC6333], NPTv6 [RFC6296], HOST_ID injection, HTTP
Header Enrichment function, TCP optimizer, load-balancer, etc.
This document does not make any assumption in the OSI Layer on
which the Service Function acts on; the exact definition of each
Service Function is deployment-specific.
o SFC-enabled domain: denotes a network (or a region thereof) that
implements DiffForward.
o SF Identifier: is a unique identifier that unambiguously
identifies a SF within a SFC-enabled domain. SF Identifiers are
assigned, configured and managed by the administrative entity that
operates the SFC-enabled domain. SF identifiers can be structured
as strings; other formats can be used. SF Identifiers are not
required to be globally unique nor be exposed to or used by
another SF-enabled domain.
o SFC Map: refers to an ordered list of SF identifiers. Each SFC
Map is identified with a unique identifier called SFC Map Index.
o SFC Policy Table: is a table containing a list of SFC Maps, SFC
classification rules and Locators for all SF Nodes. A SFC Policy
Table may contain a default SFC Map.
o SF Locator: A SF Node identifier used to reach the said SF node.
A locator is typically an IP address or a FQDN.
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o Legacy Node (Node for short): refers to any node that is not a SF
Node nor a SFC Boundary Node. This node can be located within a
SFC-enabled domain or outside a SFC-enabled domain.
3. Functional Elements
The following functional elements are defined in this document:
o SFC Boundary Node (or Boundary Node): denotes a node that connects
one SFC-enabled domain to a node either located in another SFC-
enabled domain or in a domain that is SFC-unaware.
o SFC Egress Node (or Egress Node): denotes a SFC Boundary Node that
handles traffic which leaves the SFC-enabled domain the Egress
Node belongs to.
o SFC Ingress Node (or Ingress Node): denotes a SFC Boundary Node
that handles traffic which enters the SFC-enabled domain the
ingress Node belongs to.
o SF Node: denotes any node within an SFC-enabled domain that embeds
one or multiple SFs.
o SFC Classifier (or Classifier): an entity which classifies packets
based on the packet header contents according to classification
rules defined in a SFC Policy Table. Packets are then marked with
the corresponding SFC Map Index. SFC Classifier is embedded in a
SFC Boundary Node. A SFC Classifier may be identified by a
dedicated SF Identifier.
4. SFC Provisioning
4.1. Assign Service Function Identifiers
The administrative entity that operates a SFC-enabled domain
maintains a local repository that lists the enabled SFs. This
administrative entity assigns a unique SF identifier for each SF.
SF identifiers can be structured as strings or any other format. The
main constraint on the format is that two SFs MUST be assigned with
different identifiers. SF identifiers are case-sensitive.
4.2. Service Function Locator
A SF may be embedded in one or several SF Nodes. The SF locator is
typically the IP address or the FQDN to reach a given SF Node.
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The use of an IP address is RECOMMENDED to avoid any extra complexity
related to the support of name resolution capabilities in SF Nodes.
Resolution capabilities are supported by the PDP (Policy Decision
Point). In the rest of the document, we assume a SF locator is
structured as an IP address (IPv4 or IPv6).
A SF Node can be reached by one or more locators, which may therefore
be bound to the same SF.
4.3. Building Service Function Chaining (SFC) Maps
Added-value services delivered to the end-user rely on the invocation
of several SFs. For each of these services, the administrative
entity that operates an SFC-enabled domain builds one or several SFC
Maps. Each of these maps characterizes the list of SFs to be invoked
with their exact invocation order.
Each SFC Map is unambiguously identified with a unique identifier
called the SFC Map Index. The SFC Map Index MUST be described as an
unsigned integer.
Distinct chains can be applied for inbound and outbound traffic. The
directionality of traffic is not included as an attribute of the SFC
Map, but it may be implicitly described by using two SFC Maps
installed and maintained in the SFC Policy Table. In such case,
incoming packets would be marked with Index_1 for example, while
outgoing packets would be forwarded according to a distinct SFC Map
identified with Index_2.
An example of SFC Map to handle IPv6 traffic destined to an IPv4
remote server is defined as follows:
{15, {IPv6_Firewall, HOST_ID_Inject, NAT64}}.
To handle incoming packets destined to the same IPv6 host, the
following SFC Map can be defined:
{10, {IPv4_Firewall, NAT64}}.
4.4. Building Service Function Chaining (SFC) Policy Tables
A PDP (Policy Decision Point, [RFC2753]) is the central entity which
is responsible for maintaining SFC Policy Tables (Figure 1), and
enforcing appropriate policies in SF Nodes and SFC Boundary Nodes
(Figure 1). PDP-made decisions can be forwarded to the participating
nodes by using a variety of protocols (e.g., NETCONF [RFC6241]).
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One or multiple SFC-enabled domains may be under the responsibility
of the same PDP. Delimiting the scope of each SFC-enabled domain is
under the responsibility of the administrative entity that operates
the SF-enabled network.
o . . . . . . . . . . . . . . . . . . . . . . . o
. SFC Policy Enforcement .
. +-------+ .
. | |-----------------+ .
. +-------| PDP | | .
. | | |-------+ | .
. | +-------+ | | .
o . . | . . . . . | . . . . . | . . . . | . . . o
o . . | . . . . . | . . . . . | . . . . | . . . o
. | | | | .
. v v v v .
. +---------+ +---------+ +-------+ +-------+ .
. |SFC_BN_1 | |SFC_BN_n | | SF_1 | | SF_m | .
. +---------+ +---------+ +-------+ +-------+ .
. SFC-enabled Domain .
o . . . . . . . . . . . . . . . . . . . . . . . o
Figure 1: SFC Policy Enforcement Scheme.
The SF Node MUST be provisioned with the following information:
o Local SF Identifier(s): This information is required for an SF to
identify itself within an SFC Map.
o List of SFC Maps: The PDP may configure the full list (default
mode) or only as subset of SFC Maps in which a SF supported by the
local SF node is involved (see Section 9.7).
o List of SF Locators: The PDP may configure the full list of
locators (default mode) or only the locators of next hop SFs of
SFC Maps in which a SF supported by the local SF node is involved
(see Section 9.7).
Likewise, the SFC Boundary Node MUST be provisioned with the
following information:
o List of SFC Maps
o List of SF Locators
o List of SFC Map Classification Rules (see Section Section 5.2).
In addition to the SFC Policy Table, other SF-specific policies can
be installed by the PDP (e.g., configure distinct user profiles,
activate specific traffic filters, configure traffic conditioners,
etc.).
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Policies managed by the PDP may be statically instantiated or
dynamically triggered by external means (e.g., a AAA server).
In the event of any update (e.g., define a new SFC Map, delete an SFC
Map, add a new SF Locator, update classification policy), the PDP
MUST forward the updated policy configuration information in all
relevant SF Nodes and SFC Boundary Nodes.
Load-balancing among several SF Nodes supporting the same SF can be
driven by the PDP. Indeed, the PDP can generate multiple
classification rules and SFC Maps to meet load-balancing objectives.
The processing of packets by the nodes that belong to a SFC-enabled
domain does not necessarily require any interaction with the PDP,
depending on the nature of the SF supported by the nodes and the
corresponding policies to be enforced. For example, traffic
conditioning capabilities [RFC2475] are typical SF functions that may
require additional solicitation of the PDP for the SF node to decide
what to do with some out-of-profile traffic.
5. Theory Of Operation
The behavior of each node of a SFC-enabled domain is specified in the
following sections. We assume that the provisioning operations
discussed in Section 4 have been successful (i.e., SF functions have
been adequately configured according to the (service-specific) policy
to be enforced).
5.1. SFC Boundary Node
SFC Boundary Nodes act both as a SFC Ingress Node and as a SFC Egress
Node for the respective directions of the traffic.
Traffic enters a SFC-enabled domain at a SFC Ingress Node
(Section 5.3) and exits the domain at a SFC Egress Node
(Section 5.4).
5.2. SFC Classifier
The SFC Classifier classifies packets based on (some of) the contents
of the packet header. Concretely, it classifies packets based on the
possible combination of one or more header fields, such as source
address, destination address, DS field, protocol ID, source port and
destination port numbers, and any other information.
Each SFC Map Classification Rule MUST be bound to one single SFC Map
(i.e., the classification rule must include only one SFC Map Index).
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5.3. SFC Ingress Node
When a packet is received through an interface of the SFC Ingress
Node that connects to the outside of the SFC domain, the Ingress Node
MUST:
o Inspect the received packet and strip any existing SFC Map Index.
o Check whether the received packet matches an existing
classification rule (see Section 5.2).
o If no rule matches, forward the packet to the next hop according
to legacy forwarding behavior (e.g., based upon the IP address
conveyed in the DA field of the header).
o If a rule matches, proceed with the following operations:
* Retrieve the locator of the first SF as indicated in the SFC
Map entry the rule matches.
* Check whether the corresponding SF node is an immediate
neighbor.
+ If so, update the packet with the SFC Map Index of SFC Map
entry it matches and then forward the packet to the
corresponding SF Node.
+ If not, (1) encapsulate the original packet into a new one
that will be forwarded to the corresponding SF node, (2)
update the encapsulated packet with the SFC Map Index of SFC
Map entry it matches, and (3) forward the packet to the next
hop to reach the first SF node.
As a result of this process, the packet will be sent to an SF Node or
an Intermediate Node.
5.4. SFC Egress Node
When a packet is received through an interface that connects the SFC
Egress Node to its SFC domain, the Egress Node MUST:
o Strip any existing SFC Map Index.
o Forward the packet according to legacy forwarding policies.
5.5. SF Node
This section assumes the default behavior is each SF Node does not
embed a Classifier as discussed in Section 9.4.
When a packet is received by a SF Node, the SF Node MUST:
o Check whether the packet conveys a SFC Map Index.
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o If no SFC Map Index is included, forward the packet according to
legacy forwarding policies.
o If the packet conveys a SFC Map Index,
* Retrieve the corresponding SFC Map from the SFC Policy Table.
* Check whether the local SF Identifier is present in the SFC
Map:
+ If not, forward the packet according to legacy forwarding
policies.
+ If so, the packet is decapsulated (if needed) and then
presented as an input to the local SF. In case several SFs
are co-located in the same node, the packet is processed by
all SFs indicated in the SFC Map. Once the packet is
successfully handled by local SF(s), the packet is forwarded
to the next SF Node in the list or to an intermediate node
(if the local SFC Node is the last element in the SFC Map).
If the local SF node is not the last one in the SFC Map, it
retrieves the next SF Node from the list, retrieve its
locator for the SFC Policy Table, and forwards the packet to
the next hop. If the local SF Node is the last element in
the SFC Map, it forwards the packet to the next hop
according to legacy forwarding policies.
5.6. Intermediate Nodes
An Intermediate Node is any node that does not support any Service
Function and which is located within a SFC-enabled domain.
No modification is required to intermediate nodes to handle incoming
packets. In particular, routing and forwarding are achieved using
legacy procedures.
6. Fragmentation Considerations
If adding the Service Chaining Header would result in a fragmented
packet, the classifier should include a Service Chaining Header in
each fragment.
Other fragmentation considerations will be added in a future version
of the document.
7. Differentiated Services
When encapsulating an IP packet, the Ingress Node and each SF Node
SHOULD use its Diffserv Codepoint (DSCP, [RFC2474]) to derive the
DSCP (or MPLS Traffic-Class Field) of the encapsulated packet.
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Generic considerations related to Differentiated Services and tunnels
are further detailed in [RFC2983].
8. Design Considerations
This section discusses two main protocol issues to be handled in
order to deploy DiffForward.
A detailed design analysis is documented in [I-D.boucadair-chaining-
design-analysis].
8.1. Transmit A SFC Map Index In A Packet
8.1.1. SFC Map Index
A SFC Map Index is an integer that points to a SFC Map.
In order to avoid all nodes of a SFC-enabled domain to be SF-aware,
this specification recommends to undertake classifiers at boundary
nodes while intermediate nodes forward the packets according to the
SFC Map Index conveyed in the packet (SF Node) or according to
typical forwarding policies (any SF-unaware node).
An 8-bit field would be sufficient to accommodate deployment contexts
that assume a reasonable set of SFC Maps. A 16-bit (or 32-bit) field
would be more flexible (e.g., to accommodate the requirement
discussed in Section 9.3).
8.1.2. Why Not Loose Or Strict Source Routing (SSR)?
Instead of injecting a Map Index, an alternate solution would be to
use the SSRR/LSRR IPv4 option or any similar solution to indicate a
loose or strict explicit route. This alternative was not considered
because of the likely dramatic impact on the processing and potential
fragmentation issues that may jeopardize the overall performance of
the DiffForward operation.
Injecting an 8-bit or a 16-bit field would minimize fragmentation
issues.
8.1.3. Where To Store SFC Map Indexes In A Packet?
SFC Map Indexes can be conveyed in various locations of a packet:
o At L2 level
o Define a new IP option or a new IPv6 extension header
o Use IPv6 Flow Label
o Re-use an existing field (e.g., DS field)
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o TCP option
o GRE Key
o Define a new shim
o Etc.
8.2. Steer Paths To Cross Specific SF Nodes
A SFC Ingress Node or a SF Node MUST be able to forward a packet that
matches an existing SFC Map to the relevant next hop SF Node. The
locator of the next SF is retrieved from the SFC Policy Table. In
case the next SF Node in the list is not an immediate neighbor, a
solution to force the packet to cross that SF Node MUST be supported.
This document suggests the use of the IP-in-IP encapsulation scheme.
Other tunneling solutions can be considered in the future.
9. Deployment Considerations
9.1. Generic Requirements
The following deployment considerations should be taken into account:
o Avoid inducing severe path stretch compared to the path followed
if no SF is involved.
o Minimize path computation delays: due to the enforcement of
classification rules in all participating nodes, misconception of
Service function chaining, inappropriate choice of nodes elected
to embed Service functions, etc., must be avoided.
o Avoid SF invocation loops: the design of SF chainings should
minimize as much as possible SF invocation loops. Note that means
to prevent SF loops may be enabled in each SF Node (see
Section 9.6).
9.2. Deployment Models
Below are listed some deployment model examples:
1. A full marking mechanism: Ingress nodes perform the
classification and marking functions. Then, involved SF Nodes
process received packets according to their marking.
2. SF node mechanism, in which every SF Node embeds also a
classifier, and the ingress node only decides the first node to
forward to. Packets are forwarded at each node according to
local policies. No marking is required when all SFs are co-
located with a classifier. This model suffers from some
limitations (see Section 9.4).
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3. A router-based mechanism: All SF Nodes forward packets once
processed to their default router. This default routes is
responsible for deciding how the packet should be progressed at
each step in the chain. One or multiple routers can be involved
in the same Service Function Chain.
4. A combination thereof.
9.3. On Service Function Profiles (a.k.a., Contexts)
Service Functions may often enforce multiple differentiated policy
sets. These policy sets may be coarsely-grained or fine-grained. An
example of coarsely-grained policy sets would be an entity that
performs HTTP content filtering where one policy set may be
appropriate for child users whereas another is appropriate for adult
users. An example of finely-grained policy sets would be PCEF (3GPP
Policy Control Enforcement Function) that has a large number of
differentiated QoS and charging profiles that are mapped on a per-
subscriber basis.
The Service Function Chaining mechanism directly support coarsely-
grained differentiated policy sets and indirectly support finely-
grained differentiated policy sets.
From a Service Function Chaining perspective, each coarsely-grained
policy set for a Service Function will be considered as a distinct
logical instance of that Service Function. Consider the HTTP content
filtering example where one physical or virtual entity provides both
child and adult content filtering. The single entity is represented
as two distinct logical Service Functions, each with their own
Service Function Identifier from a chaining perspective. The two
(logical) Service Functions may share the same IP address or may have
distinct IP addresses.
Finely-grained policy sets, on the other hand, would unacceptably
explode the number of distinct Service Chains that were required with
an administrative domain. For this reason, Service Functions that
utilize finely-grained policy sets are represented as a single
Service Function that has its own internal classification mechanism
in order to determine which of its differentiated policy sets to
apply. Doing so avoids from increasing the size of the SFC Policy
Table.
The threshold, in terms of number of policies, between choosing the
coarsely-grained policy or finely-grained policy technique is left to
the administrative entity managing a given domain.
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9.4. SF Node is also a Classifier
If SF Nodes are also configured to behave as Classifiers, the SFC Map
Index is not required to be explicitly signalled in each packet.
Concretely, the SFC Policy Table maintained by the SF Node includes
classification rules. These classification rules are enforced to
determine whether the local SF must be involved. If an incoming
packet matches at least one classification rule pointing to an SFC
Map in which the SF Identifier is listed, the SF Node retrieves the
next hop SF from the SF Map indicated in the classification rule.
The packet is then handled by the local SF, and the SF Node
subsequently forwards the packet to the next hop SF. If not, the
packet is forwarded to the next hop according to a typical IP
forwarding policy.
Let us consider the example shown in Figure 2. The local SF Node
embeds SFa. Once classification rules and the SFC Maps are checked,
the SF Node concludes SFa must be invoked only when a packet matches
Rules 1 and 3. If a packet matches Rule 1, the next SF is SFC. If a
packet matches Rule 3, the next SF is SFh.
+-----------------------------------------------+
| SFC Policy Table |
+-----------------------------------------------+
|Local SF Identifier: SFa |
+-----------------------------------------------+
|Classification Rules |
| Rule 1: If DEST=IP1; then SFC_MAP_INDEX1 |
| Rule 2: If DEST=IP2; then SFC_MAP_INDEX2 |
| Rule 3: IF DEST=IP3; then SFC_MAP_INDEX3 |
+-----------------------------------------------+
|SFC Maps |
| {SFC_MAP_INDEX1, {SFa, SFC} |
| {SFC_MAP_INDEX2, {SFd, SFb} |
| {SFC_MAP_INDEX3, {SFa, SFh} |
+-----------------------------------------------+
Figure 2: SFC Policy Table Example.
9.5. Direct Adjacency
SF Nodes may be enabled in a SFC-enabled domain so that each of them
has a direct adjacency with other SF Nodes. In such configuration,
no specific encapsulation scheme is required to exchange traffic
between these nodes.
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9.6. Service Function Loops
SF Nodes use the SFC Policy Table to detect whether the local SF was
already applied to the received packet (i.e., detect SF Loop). The
SF Node MUST invoke the local SF only if the packet is received from
a SFC Boundary Node or a SF Node having an identifier listed before
the local SF in the SF Map matched by the packet. SF Loop detection
SHOULD be a configurable feature.
Figure 3 shows an example of a SFC Policy Table of a SF Node
embedding SFa. Assume a packet received from Locb that matches Rule
2. SFa must not be invoked because SFb is listed after SFa (see the
SFC Map list). That packet will be forwarded without invoking SFa.
+-----------------------------------------------+
| SFC Policy Table |
+-----------------------------------------------+
|Local SF Identifier: SFa |
+-----------------------------------------------+
|SFC Maps |
| {SFC_MAP_INDEX1, {SFa, SFC} |
| {SFC_MAP_INDEX2, {SFd, SFa, SFb, SFh} |
+-----------------------------------------------+
|SFC Locators |
| Locator_SFb: Locb |
| Locator_SFC: Locc |
| Locator_SFd: Locd |
| Locator_SFh: Loch |
+-----------------------------------------------+
Figure 3: Dealing With SF Loops.
The support of this feature is OPTIONAL.
9.7. Lightweight SFC Policy Table
If SF loop detection is not activated in an SFC-enabled domain, the
PDP may provision SF nodes with a "lightweight" SFC Policy Table. A
lightweight SFC Policy Table is a subset of the full SFC Policy Table
that includes:
o Only the SFC Maps in which the local SF is involved.
o Only the next hop SF instead of the full SF chain.
An example of a lightweight SFC Policy Table is shown in Figure 4.
+-----------------------------------------------+
| SFC Policy Table |
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+-----------------------------------------------+
|Local SF Identifier: SFa |
+-----------------------------------------------+
|Lite SFC Maps |
| SFC_MAP_INDEX1, Next_Hop_SF = SFC |
| SFC_MAP_INDEX2, Next_Hop_SF = SFb |
+-----------------------------------------------+
|SFC Locators |
| Locator_SFb: Locb |
| Locator_SFC: Locc |
+-----------------------------------------------+
Figure 4: Lightweight SFC Policy Table.
9.8. Liveness Detection Of SFs By The PDP
The ability of the PDP to check the liveness of each SF invoked in a
service chain has several advantages, including:
o Enhanced status reporting by the PDP (i.e., an operational status
for any given service chain derived from liveness state of its
SFs).
o Ability to support various resiliency policies (i.e., bypass SF
Node, use alternate SF Node, use alternate chain, drop traffic,
etc.) .
o Ability to support load balancing capabilities to solicit multiple
SF instances that provide equivalent functions.
In order to determine the liveness of any particular SF Node,
standard protocols such as ICMP or BFD (both single-hop [RFC5881] and
multi-hop [RFC5883]) may be utilized between the PDP and the SF
Nodes.
For more sophisticated load-balancing support, protocols that allow
for both liveness determination and the transfer of application-
specific data, such as SNMP and NETCONF may be utilized between the
PDP and the SF Nodes.
The support of this feature is OPTIONAL.
10. IANA Considerations
Required IANA actions will be discussed in future versions of the
document.
11. Security Considerations
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Means to protect SFC Boundary Nodes and SF Nodes against various
forms of DDoS attacks MUST be supported. For example, mutual PDP and
SF node authentication should be supported. Means to protect SF
nodes against malformed, poorly configured (deliberately or not) SFC
Policy Tables should be supported.
SFC Boundary Nodes MUST strip any existing SFC Map Index when
handling an incoming packet. A list of authorized SFC Map Indexes
are configured in the SFC elements.
NETCONF-related security considerations are discussed in [RFC6146].
Means to prevent SF loops should be supported.
Nodes involved in the same SFC-enabled domain MUST be provisioned
with the same SFC Policy Table. Possible table inconsistencies may
result in forwarding errors.
12. Acknowledgments
Many thanks to D. Abgrall, D. Minodier, Y. Le Goff, and D. Cheng for
their review and comments.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)", RFC
6241, June 2011.
13.2. Informative References
[I-D.boucadair-chaining-requirements]
Boucadair, M., Jacquenet, C., and R. Parker, "Requirements
for Network Function Chaining", draft-boucadair-chaining-
requirements-00 (work in progress), August 2013.
[I-D.quinn-nsc-problem-statement]
Quinn, P., Guichard, J., Surendra, S., Agarwal, P., Manur,
R., Chauhan, A., Leymann, N., Boucadair, M., Jacquenet,
C., Smith, M., Yadav, N., Nadeau, T., Gray, K., and B.
McConnell, "Network Service Chaining Problem Statement",
draft-quinn-nsc-problem-statement-02 (work in progress),
July 2013.
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[I-D.sin-sdnrg-sdn-approach]
Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Service Provider's Perspective", draft-sin-
sdnrg-sdn-approach-03 (work in progress), June 2013.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2753] Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
for Policy-based Admission Control", RFC 2753, January
2000.
[RFC2983] Black, D., "Differentiated Services and Tunnels", RFC
2983, October 2000.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
2010.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, June 2010.
[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092, January
2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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[RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Christian Jacquenet
France Telecom
Rennes 35000
France
Email: christian.jacquenet@orange.com
Ron Parker
Affirmed Networks
Acton, MA
USA
Email: Ron_Parker@affirmednetworks.com
Diego R. Lopez
Telefonica I+D
Don Ramon de la Cruz, 82
Madrid 28006
Spain
Phone: +34 913 129 041
Email: diego@tid.es
Parviz Yegani
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: pyegani@juniper.net
Boucadair, et al. Expires February 22, 2014 [Page 21]
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Jim Guichard
Cisco Systems, Inc.
USA
Email: jguichar@cisco.com
Paul Quinn
Cisco Systems, Inc.
USA
Email: paulq@cisco.com
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