One document matched: draft-boucadair-sfc-requirements-06.xml
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<rfc category="info" docName="draft-boucadair-sfc-requirements-06"
ipr="trust200902">
<front>
<title abbrev="SFC Requirements">Requirements for Service Function
Chaining (SFC)</title>
<author fullname="Mohamed Boucadair" initials="M." surname="Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author fullname="Christian Jacquenet" initials="C." surname="Jacquenet">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>christian.jacquenet@orange.com</email>
</address>
</author>
<author fullname="Yuanlong Jiang" initials="Y." surname="Jiang">
<organization>Huawei Technologies Co., Ltd.</organization>
<address>
<postal>
<street>Bantian, Longgang district</street>
<city>Shenzhen 518129,</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<email>jiangyuanlong@huawei.com</email>
</address>
</author>
<author fullname="Ron Parker" initials="R." surname="Parker">
<organization>Affirmed Networks</organization>
<address>
<postal>
<street></street>
<city>Acton,</city>
<region></region>
<code>MA</code>
<country>USA</country>
</postal>
<email>Ron_Parker@affirmednetworks.com</email>
</address>
</author>
<author fullname="Kengo Naito" initials="K." surname="Naito">
<organization>NTT</organization>
<address>
<postal>
<street>Midori-Cho 3-9-11</street>
<city>Musashino-shi, Tokyo 180-8585</city>
<region></region>
<country>Japan</country>
</postal>
<email>naito.kengo@lab.ntt.co.jp</email>
</address>
</author>
<date day="" month="" year="2015" />
<workgroup>SFC</workgroup>
<abstract>
<t>This document identifies the requirements for the Service Function
Chaining (SFC).</t>
</abstract>
<note title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>This document identifies the requirements for the Service Function
Chaining (SFC).</t>
<t>The overall problem space is described in <xref
target="I-D.ietf-sfc-problem-statement"></xref>.<!--[[Service Function Discovery has been removed as per as comment from J. Halper. The issue can be revived in the future to have more feedback
REQ#29: Means to dynamically discover Service Functions SHOULD be
supported.
]]--></t>
</section>
<section title="Terminology">
<t>The reader should be familiar with the terms defined in <xref
target="I-D.ietf-sfc-problem-statement"></xref>.</t>
<t>The document makes use of the following terms:</t>
<t><list style="symbols">
<t>SFC-enabled domain: denotes a network (or a region thereof) that
implements SFC.</t>
<t>Service Function Loop: If a Service Function Chain is structured
to not invoke Service Functions multiple times, a loop is the error
that occurs when the same Service Function is invoked several times
when handling data bound to that Service Function Chain. In other
words, a loop denotes an error that occurs when a packet handled by
a Service Function, forwarded onwards, and arrives once again at
that Service Function while this is not allowed by the Service
Function Chain it is bound to.</t>
<t>Service Function Spiral: denotes a Service Function Chain in
which data is handled by a Service Function, forwarded onwards, and
arrives once again at that Service Function. <list style="symbols">
<t>Note that some Service Functions support built-in functions
to accommodate spirals; these service-specific functions may
require that the data received in a spiral should differ in a
way that will result in a different processing decision than the
original data. This document does not make such assumption.</t>
<t>A Service Function Chain may involve one or more Service
Function Spirals.</t>
<t>Unlike Service Function loop, spirals are not considered as
errors.</t>
</list></t>
</list></t>
</section>
<section anchor="gen" title="Detailed Requirements List">
<t>The following set of functional requirements should be considered for
the design of the Service Function Chaining solution.</t>
<section anchor="sf"
title="Instantiating and Invoking Service Functions">
<t><?rfc subcompact="no" ?><list hangIndent="11"
style="format SF_REQ#%d:">
<t>The solution MUST NOT make any assumption on whether Service
Functions (SF) are deployed directly on physical hardware, as one
or more Virtual Machines, or any combination thereof.</t>
<t>The solution MUST NOT make any assumption on whether Service
Functions each reside on a separate addressable Network Element,
or as a horizontal scaling of Service Functions, or are
co-resident in a single addressable Network Element, or any
combination thereof. <list hangIndent="11" style="empty">
<t>Note: Communications between Service Functions having the
same locator are considered implementation-specific. These
considerations are therefore out of scope of the SFC
specification effort.</t>
</list></t>
<t>The solution MUST NOT require any IANA registry for Service
Functions.</t>
<t>The solution MUST allow multiple instances of a given Service
Function ( i.e., instances of a Service Function can be embedded
in or attached to multiple Network Elements). <list
hangIndent="11" style="letters">
<t>This is used for load-balancing, load-sharing, to minimize
the impact of failures (e.g., by means of a hot or cold
standby protection design), to accommodate planned maintenance
operations, etc.</t>
<t>How these multiple devices are involved in the service
delivery is deployment-specific.</t>
</list></t>
<t>The solution MUST separate SF-specific policy
provisioning-related aspects from the actual handling of packets
(including forwarding decisions).</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="sfc" title="Chaining Service Functions">
<t><?rfc subcompact="no" ?><list hangIndent="12"
style="format SFC_REQ#%d:">
<t>The solution MUST NOT assume any predefined order of Service
Functions. In particular, the solution MUST NOT require any IANA
registry to store typical Service Function Chains.</t>
<t>The identification of instantiated Service Function Chains is
local to each administrative domain; it is policy-based and
deployment-specific.</t>
<t>The solution MUST allow for multiple Service Chains to be
simultaneously enforced within an administrative domain.</t>
<t>The solution MUST allow the same Service Function to belong to
multiple Service Function Chains.</t>
<t>The solution MUST support the ability to deploy multiple
SFC-enabled domains within the same administrative domain.</t>
<t>The solution MUST be able to associate the same or distinct
Service Function Chains for each direction (inbound/outbound) of
the traffic pertaining to a specific service. In particular,
unidirectional Service Function Chains, bi-directional Service
Function Chains, or any combination thereof MUST be
supported.<list style="empty">
<t>Note, the solution must allow to involve distinct SFC
Boundary Nodes for upstream and downstream. Multiple SFC
Boundary Nodes may be deployed within an administrative
domain.</t>
</list></t>
<t>The solution MUST be able to dynamically enforce Service
Function Chains. In particular, the solution MUST allow the update
or the withdrawal of existing Service Function Chains, the
definition of a new Service Function Chain, the addition of new
Service Functions without having any impact on other existing
Service Functions or other Service Function Chains.</t>
<t>The solution MUST provide means to control the SF-inferred
information to be leaked outside an SFC-enabled domain. In
particular, an administrative entity MUST be able to prevent the
exposure of the Service Function Chaining logic and its related
policies outside the administrative domain.</t>
<t>The solution MUST prevent infinite Service Function Loops.<list
hangIndent="11" style="letters">
<t>Service Functions MAY be invoked multiple times in the same
Service Function Chain (denoted as SF Spiral), but the
solution MUST prevent infinite forwarding loops.</t>
</list></t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="mtu" title="MTU Requirements">
<t>Packet fragmentation can be very expensive in SFC environment where
fragmented packets have to be reassembled before sending to each SF on
the chain. It is also worth noting that IPv6 traffic can only be
fragmented by the end systems.</t>
<t><?rfc subcompact="no" ?><list hangIndent="12"
style="format MTU_REQ#%d:">
<t>The solution SHOULD minimize fragmentation; in particular, a
minimal set of SFC-specific information should be conveyed in the
data packet.</t>
<t>Traffic forwarding on a SFC basis MUST be undertaken without
relying on dedicated resources to treat fragments. In particular,
Out of order fragments MUST be forwarded on a per-SFC basis
without relying on any state.</t>
<t>Some SFs (e.g., NAT) may require dedicated resources (e.g.,
resources to store fragmented packets) or they may adopt a
specific behavior (e.g, limit the time interval to accept
fragments). The solution MUST NOT interfere with such
practices.</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="un"
title="Independence from the Underlying Transport Infrastructure Requirements">
<t><?rfc subcompact="no" ?><list hangIndent="11"
style="format UN_REQ#%d:">
<t>The solution MUST NOT make any assumption on how RIBs (Routing
Information Bases) and FIBs (Forwarding Information Bases) are
populated. Particularly, the solution does not make any assumption
on protocols and mechanisms used to build these tables.</t>
<t>The solution MUST be transport independent.<list
hangIndent="11" style="letters">
<t>The Service Function Chaining should operate regardless of
the network transport used by the administrative entity. In
particular, the solution can be used whatever the switching
technologies deployed in the underlying transport
infrastructure.</t>
<t>Techniques such as MPLS are neither required nor
excluded.</t>
</list></t>
<t>The solution MUST allow for chaining logics where involved
Service Functions are not within the same layer 3 subnet.</t>
<t>The solution MUST NOT exclude Service Functions to be within
the same IP subnet (because this is deployment-specific).</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="class" title="Traffic Classification Requirements">
<t><?rfc subcompact="no" ?><list hangIndent="11"
style="format TC_REQ#%d:">
<t>The solution MUST NOT make any assumption on how the traffic is
to be bound to a given chaining policy. In other words,
classification rules are deployment-specific and policy-based. 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. <list style="empty">
<t>Because a large number (e.g., 1000s) of classification
policy entries may be configured, means .Means to reduce
classification look-up time such as optimizing the size of the
classification table (e.g., aggregation) should be supported
by the Classifier.</t>
</list></t>
<t>The solution MUST NOT require every Service Function to be
co-located with a SFC Classifier; this is a deployment-specific
decision.</t>
<t>The solution MAY allow traffic re-classification at the level
of Service Functions (i.e., a Service Function can also be
co-located with a Classifier). The configuration of classification
rules in such context are the responsibility of the administrative
entity that operates the SFC-enabled domain.</t>
<t>The solution MUST allow Service Function Nodes to be configured
(or pushed) with the detailed policies on which local Service
Functions to invoke for packets associated with some Service
Function Chains. The solution MUST allow those steering policies
to be updated based on demand.</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="dp" title="Data Plane Requirements">
<t><?rfc subcompact="no" ?><list hangIndent="11"
style="format DP_REQ#%d:">
<t>The solution MUST be able to forward traffic between two
Service Functions (involved in the same Service Function Chain)
without relying upon the destination address field of the a data
packet.</t>
<t>The solution MUST allow for the association of a context with
the data packets. In particular:<list hangIndent="11"
style="letters">
<t>The solution MUST support the ability to invoke
differentiated sets of policies for a Service Function (such
sets of policies are called Profiles). A profile denotes a set
of policies configured to a local Service Function (e.g.,
content-filter-child, content-filter-adult).<list
hangIndent="11" style="letters">
<t>Few profiles should be assumed per Service Function to
accommodate the need for scalable solutions.</t>
<t>A finer granularity of profiles may be configured
directly to each Service Function; there is indeed no need
to overload the design of Service Function Chains with
policies of low-level granularity.</t>
</list></t>
</list></t>
<t>Service Functions may be reachable using IPv4 and/or IPv6. The
administrative domain entity MUST be able to define and enforce
policies with regards to the address family to be used when
invoking a Service Function. <list hangIndent="11" style="letters">
<t>A Service Function Chain may be composed of IPv4 addresses,
IPv6 addresses, or a mix of both IPv4 and IPv6 addresses.</t>
<t>Multiple Service Functions can be reachable using the same
IP address. Each of these Service Functions is unambiguously
identified with a Service Function Identifier.</t>
</list></t>
<t></t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="oam" title="OAM Requirements">
<t><?rfc subcompact="no" ?><list hangIndent="12"
style="format OAM_REQ#%d:">
<t>The solution MUST allow for Operations, Administration, and
Maintenance (OAM) features <xref target="RFC6291"></xref>. In
particular, the solution MUST:<list hangIndent="11"
style="letters">
<t>Support means to verify the completion of the forwarding
actions until the SFC Border Node is reached (see Section
3.4.1 of <xref target="RFC5706"></xref>).</t>
<t>Support means to ensure coherent classification rules are
installed in and enforced by all the Classifiers of the SFC
domain.</t>
<t>Support means to correlate classification policies with
observed forwarding actions.</t>
<t>Support in-band liveliness and functionality checking
mechanisms for the instantiated Service Function Chains and
the Service Functions that belong to these chains.</t>
</list></t>
<t>The solution MUST support means to detect the liveliness of
Service Functions of an SFC-enabled domain. In particular, the
solution MUST support means to (dynamically) detect that a Service
Function instance is out of service and notify the relevant
elements accordingly (PDP and Classifiers, for one).</t>
<t>Detailed diagnosis requirements are listed below:<list
hangIndent="11" style="letters">
<t>The solution MUST allow to assess the status of the
serviceability of a Service Function (i.e., the Service
Function provides the service(s) it is configured for).</t>
<t>The solution MUST NOT rely only on IP reachability to
assess whether a Service Function is up and running.</t>
<t>The solution MUST allow to diagnose the availability of a
Service Function Chain (including the availability of a
particular Service Function Path bound to a given Service
Function Chain).</t>
<t>The solution MUST allow to retrieve the set of Service
Function Chains that are enabled within a domain.</t>
<t>The solution MUST allow to retrieve the set of s Service
Function Chains in which a given Service Function is
involved.</t>
<t>The solution MUST allow to assess whether an SFC-enabled
domain is appropriately configured (including the configured
chains are matching what should be configured in that
domain).</t>
<t>The solution MUST allow to assess the output of the
classification rule applied on a packet presented to a
Classifier of an SFC-enabled domain.</t>
<t>The solution MUST support the correlation between a Service
Function Chain and the actual forwarding path followed by a
packet matching that SFC.</t>
<t>The solution MUST allow to diagnose the availability of a
segment of a Service Function Chain, i.e., a subset of Service
Functions that belong to the said chain.</t>
<t>The solution MUST support means to notify the PDPs whenever
some events occur (for example, a malfunctioning Service
Function instance).</t>
<t>The solution MUST allow for local diagnostic procedures
specific to each Service Function (i.e., SF built-in
diagnostic procedures).</t>
<t>The solution MUST allow for customized service
diagnostic.</t>
</list></t>
<t>Liveness status records for all Service Functions (including
Service Function instances), Service Function Nodes, Service
Function Chains (including the Service Function Paths bound to a
given chain) MUST be maintained.</t>
<t>SFC-specific counters and statistics MUST be provided. These
data include (but not limited to): <list style="symbols">
<t>Number of flows ever and currently assigned to a given
Service Function Chain and a given Service Function Path.</t>
<t>Number of flows, packets, bytes dropped due to policy.</t>
<t>Number of packets and bytes in/out per Service Function
Chain and per Service Function Path.</t>
<t>Number of flows, packets, bytes dropped due to unknown
Service Function Chain or Service Function Path (this is valid
in particular for a Service Function Node).</t>
</list></t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="lb" title="Recovery and Load Balancing Requirements ">
<t><?rfc subcompact="no" ?><list hangIndent="11"
style="format LB_REQ#%d:">
<t>The solution MUST allow for load-balancing among multiple
instances of the same Service Function.<list hangIndent="11"
style="letters">
<t>Load-balancing may be provided by legacy technologies or
protocols (e.g., make use of load-balancers)</t>
<t>Load-balancing may be part of the Service Function
itself.</t>
<t>Load-balancer may be considered as a Service Function
element.</t>
<t>Because of the possible complications, load balancing
SHOULD NOT be driven by the SFC Classifier.</t>
</list></t>
<t>The solution MUST separate SF-specific policy
provisioning-related aspects from the actual handling of packets
(including forwarding decisions).</t>
<t>The solution SHOULD support protection of the failed or
over-utilized Service Function instances. The protection mechanism
can rely on local decisions among the nodes that are connected to
both active/standby Service Function instances.</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="bw"
title="Compatibility with Legacy Service Functions Requirements">
<t><?rfc subcompact="no" ?><list hangIndent="12"
style="format LEG_REQ#%d:">
<t>The solution MUST allow for gradual deployment in legacy
infrastructures, and therefore coexist with legacy technologies
that cannot support SFC-specific capabilities, such as Service
Function Chain interpretation and processing. The solution MUST be
able to work in a domain that may be partly composed of opaque
elements, i.e., elements that do not support SFC-specific
capabilities.</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="qos" title="QoS Requirements ">
<t><?rfc subcompact="no" ?><list hangIndent="12"
style="format QoS_REQ#%d:">
<t>The solution MUST be able to provide different SLAs (Service
Level Agreements, <xref target="RFC7297"></xref>). In
particular,<list style="letters">
<t>The solution MUST allow for different levels of service to
be provided for different traffic streams (e.g., configure
Classes of Service (CoSes)).</t>
<t>The solution MUST be able to work properly within a
Diffserv domain <xref target="RFC2475"></xref>.</t>
<t>The solution SHOULD support the two modes defined in <xref
target="RFC2983"></xref>.</t>
</list></t>
<t>ECN re-marking, when required, MUST be performed according to
<xref target="RFC6040"></xref>.</t>
</list><?rfc subcompact="no" ?></t>
</section>
<section anchor="sec" title="Security Requirements">
<t><?rfc subcompact="yes" ?><list hangIndent="12"
style="format SEC_REQ#%d:">
<t>The solution MUST provide means to prevent any information
leaking that would be used as a hint to guess internal engineering
practices (e.g., network topology, service infrastructure
topology, hints on the enabled mechanisms to protect internal
service infrastructures, etc.).<list style="empty">
<t>The solution MUST support means to protect the SFC domain
as a whole against attacks that would lead to the discovery of
Service Functions enabled in a SFC domain.</t>
<t>In particular, topology hiding means MUST be supported to
avoid the exposure of the SFC-enabled domain topology
(including the set of the service function chains supported
within the domain and the corresponding Service Functions that
belong to these chains).</t>
</list></t>
<t>The solution MUST support means to protect the SFC-enabled
domain against any kind of denial-of-service and theft of service
(e.g., illegitimate access to the service) attack. <list
style="empty">
<t>For example, a user should not be granted access to
connectivity services he/she didn't subscribe to (including
direct access to some SFs), at the risk of providing
illegitimate access to network resources.</t>
</list></t>
<t>The solution MUST NOT interfere with IPsec <xref
target="RFC4301"></xref> (in particular IPsec integrity
checks).<?rfc subcompact="no" ?></t>
</list></t>
</section>
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document does not require any action from IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>Some security-related requirements to be taken into account when
designing the Service Function Chaining solution are listed in <xref
target="sec"></xref>. These requirements do not cover the provisioning
interface used to enforce policies into the Classifier, Service
Functions, and Service Function Nodes.</t>
</section>
<section title="Contributors">
<t>The following individuals contributed text to the document:<figure>
<artwork><![CDATA[ Hongyu Li
Huawei Technologies Co., Ltd.
Bantian, Longgang district
Shenzhen 518129,
China
EMail: hongyu.lihongyu@huawei.com
Jim Guichard
Cisco Systems, Inc.
USA
EMail: jguichar@cisco.com
Paul Quinn
Cisco Systems, Inc.
USA
Email: paulq@cisco.com
Linda Dunbar
Huawei Technologies
5430 Legacy Drive, Suite #175
Plano TX
USA
EMail: linda.dunbar@huawei.com]]></artwork>
</figure></t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Many thanks to K. Gray, N. Takaya, H. Kitada, H. Kojima, D. Dolson,
B. Wright, and J. Halpern for their comments.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.6291'?>
<?rfc include='reference.RFC.6040'?>
<?rfc include='reference.RFC.2475'?>
<?rfc include='reference.RFC.4301'?>
<?rfc include='reference.RFC.2983'?>
<?rfc include="reference.I-D.ietf-sfc-problem-statement"?>
<?rfc include='reference.RFC.5706'?>
<reference anchor="RFC7297">
<front>
<title>IP Connectivity Provisioning Profile (CPP)</title>
<author fullname="Mohamed Boucadair" initials="M."
surname="Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author fullname="Christian Jacquenet" initials="C."
surname="Jacquenet">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region></region>
<code>35000</code>
<country>France</country>
</postal>
<email>christian.jacquenet@orange.com</email>
</address>
</author>
<author fullname="Ning Wang" initials="N." surname="Wang">
<organization>University of Surrey</organization>
<address>
<postal>
<street></street>
<city>Guildford</city>
<region></region>
<code></code>
<country>UK</country>
</postal>
<email>n.wang@surrey.ac.uk</email>
</address>
</author>
<date month="July" year="2014" />
</front>
</reference>
</references>
</back>
</rfc>
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