Internet DRAFT - draft-quinn-nsc-problem-statement
draft-quinn-nsc-problem-statement
Network Working Group P. Quinn
Internet-Draft J. Guichard
Intended status: Informational S. Kumar
Expires: February 27, 2014 Cisco Systems, Inc.
P. Agarwal
R. Manur
Broadcom
A. Chauhan
Citrix
N. Leymann
Deutsche Telekom
M. Boucadair
C. Jacquenet
France Telecom
M. Smith
N. Yadav
Insieme Networks
T. Nadeau
K. Gray
Juniper Networks
B. McConnell
Rackspace
K. Glavin
Riverbed
August 26, 2013
Network Service Chaining Problem Statement
draft-quinn-nsc-problem-statement-03.txt
Abstract
This document provides an overview of the issues associated with the
deployment of services functions (such as firewalls, load balancers)
in large-scale environments. The term service function chaining is
used to describe the deployment of such service functions, and the
ability of a network operator to specify an ordered list of service
functions that should be applied to a deterministic set of traffic
flows. Such service function chains require integration of service
policy alongside the deployment of applications, while allowing for
the optimal utilization of network resources.
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
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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
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 27, 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
(http://trustee.ietf.org/license-info) in effect on the date of
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 4
2. Problem Areas . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Service Function Chaining . . . . . . . . . . . . . . . . . . 9
4. Service Function Chaining Use Cases . . . . . . . . . . . . . 11
4.1. Enterprise Data Center Service Chaining . . . . . . . . . 11
4.2. Mobility Service Chaining . . . . . . . . . . . . . . . . 11
5. Related IETF Work . . . . . . . . . . . . . . . . . . . . . . 12
6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
Services that are composed of service functions require more flexible
service function deployment models than those typically available in
networks today. Such services may utilize traditional network
service functions (for example firewalls and server load balancers),
as well as higher layer applications and features. Services may be
delivered within a specific context so that isolated user groups
attached to a common network may be formed. Such user groups may
require unique capabilities with the ability to tailor service
characteristics on a per-tenant/per-subscriber/per-VPN basis that
must not affect other user groups
Current service function deployment models are relatively static in
that they are bound to fixed network topologies and resources. At
present, these deployments are not easily manipulated (i.e.: moved,
created or destroyed) even when virtualized elements are deployed.
This poses a problem in highly elastic service environments that
require relatively rapid creation, destruction or movement of real or
virtual service functions or network elements. Additionally, the
transition to virtual platforms requires an agile service insertion
model that supports elastic and very granular service delivery, and
post-facto modification; supports the movement of service functions
and application workloads in the existing network, all the while
retaining the network and service policies and the ability to easily
bind service policy to granular information such as per-subscriber
state.
This document outlines the problems encountered with existing service
deployment models for service function chaining (often referred to
simply as service chaining; in this document the terms will be used
interchangeably), as well as the problems of service chain creation/
deletion, policy integration with service chains, and policy
enforcement within the network infrastructure.
1.1. Definition of Terms
Classification: Locally instantiated policy and customer/network/
service profile matching of traffic flows for identification of
appropriate outbound forwarding actions.
Network Overlay: Logical network built on top of existing network
(the underlay). Packets are encapsulated or tunneled to create
the overlay network topology.
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Service Chain: A service chain defines the required functions and
associated order (service-function1 --> service-function 2) that
must be applied to packets and/or frames. A service chain does
not specify the network location or specific instance of service
functions (e.g. firewall1 vs. firewall2).
Service Function: A network or application based packet treatment,
application, compute or storage resource, used singularly or in
concert with other service functions within a service chain to
enable a service offered by a network operator.
A non-exhaustive list of Service Functions includes: firewalls,
WAN and application acceleration, Deep Packet Inspection (DPI),
server load balancers, NAT44 [RFC3022], NAT64 [RFC6146], HOST_ID
injection, HTTP Header Enrichment functions, TCP optimizer, etc.
The generic term "L4-L7 services" is often used to describe many
service functions.
Service Node: Physical or virtual element providing one or more
service functions.
Network Service: An externally visible service offered by a network
operator; a service may consist of a single service function or a
composite built from several service functions executed in one or
more pre-determined sequences and delivered by one or more service
nodes.
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2. Problem Areas
The following points describe aspects of existing service deployment
that are problematic, and are being addressed by the network service
chaining effort.
1. Topological Dependencies: Network service deployments are often
coupled to the physical network topology creating constraints on
service delivery and potentially inhibiting the network operator
from optimally utilizing service resources. This limits scale,
capacity, and redundancy across network resources.
These topologies serve only to "insert" the service function
(i.e. ensure that traffic traverse a service function); they are
not required from a native packet delivery perspective. For
example, firewalls often require an "in" and "out" layer-2
segment and adding a new firewall requires changing the topology
(i.e. adding new L2 segments).
As more service functions are required - often with strict
ordering - topology changes are needed before and after each
service function resulting in complex network changes and device
configuration. In such topologies, all traffic, whether a
service function needs to be applied or not, often passes
through the same strict order.
A common example is web servers using a server load balancer as
the default gateway. When the web service responds to non-load
balanced traffic (e.g. administrative or backup operations) all
traffic from the server must traverse the load balancer forcing
network administrators to create complex routing schemes or
create additional interfaces to provide an alternate topology.
2. Configuration complexity: A direct consequence of topological
dependencies is the complexity of the entire configuration,
specifically in deploying service chains. Simple actions such
as changing the order of the service functions in a service
chain require changes to the topology. Changes to the topology
are avoided by the network operator once installed, configured
and deployed in production environments fearing misconfiguration
and downtime. All of this leads to very static service delivery
models. Furthermore, the speed at which these topological
changes can be made is not rapid or dynamic enough as it often
requires manual intervention, or use of slow provisioning
systems.
The service itself can contribute to complexity: it may require
an intricate combination of very different capabilities,
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regardless of the underlying topology. QoS-based, resilient VPN
service offerings are a typical example of such complexity.
3. Constrained High Availability: An effect of topological
dependency is constrained service function high availability.
Worse, when modified, inadvertent non-high availability can
result.
Since traffic reaches service functions based on network
topology, alternate, or redundant service functions must be
placed in the same topology as the primary service.
4. Consistent Ordering of Service Functions: Service functions are
typically independent; service function_1 (SF1)...service
function_n (SFn) are unrelated and there is no notion at the
service layer that SF1 occurs before SF2. However, to an
administrator many service functions have a strict ordering that
must be in place, yet the administrator has no consistent way to
impose and verify the ordering of the functions that used to
deliver a given service.
5. Service Chain Construction: Service chains today are most
typically built through manual configuration processes. These
are slow and error prone. With the advent of newer service
deployment models the control / management planes will provide
not only connectivity state, but will also be increasingly
utilized for the formation of services. Such a control /
management plane could be centrally controlled and managed, or
be distributed between a subset of end-systems.
6. Application of Service Policy: Service functions rely on
topology information such as VLANs or packet (re) classification
to determine service policy selection, i.e. the service function
specific action taken. Topology information is increasingly
less viable due to scaling, tenancy and complexity reasons. The
topological information is often stale, providing the operator
with inaccurate placement that can result in suboptimal resource
utilization. Per-service function packet classification is
inefficient and prone to errors, duplicating functionality
across service functions. Furthermore packet classification is
often too coarse lacking the ability to determine class of
traffic with enough detail.
7. Transport Dependence: Service functions can and will be deployed
in networks with a range of transports, including under and
overlays. The coupling of service functions to topology
requires service functions to support many transports or for a
transport gateway function to be present.
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8. Elastic Service Delivery: Given the current state of the art for
adding/removing service functions largely centers around VLANs
and routing changes, rapid changes to the service layer can be
hard to realize due to the risk and complexity of such changes.
9. Traffic Selection Criteria: Traffic selection is coarse, that
is, all traffic on a particular segment traverse service
functions whether the traffic requires service enforcement or
not. This lack of traffic selection is largely due to the
topological nature of service deployment since the forwarding
topology dictates how (and what) data traverses service
function(s). In some deployments, more granular traffic
selection is achieved using policy routing or access control
filtering. This results in operationally complex configurations
and is still relatively inflexible.
10. Limited End-to-End Service Visibility: Troubleshooting service
related issues is a complex process that involve network and
service expertise. This is especially the case when service
chains span multiple DCs, or across administrative boundaries
such as externally consumable service chain components.
Furthermore, the physical and virtual environments (network and
service), can be highly divergent in terms of topology and that
topological variance adds to these challenges.
11. Per-Service (re)Classification: Classification occurs at each
service, independent from previously applied service functions.
These unrelated classification events consume resources per
service. More importantly, the classification functionality
often differs per service function and service function cannot
leverage the results from other deployed network or service.
12. Symmetric Traffic Flows: Service chains may be unidirectional or
bidirectional; unidirectional is one where traffic is passed
through a set of service functions in one forwarding direction
only. Bidirectional is one where traffic is passed through a
set of service functions in both forwarding directions.
Existing service deployment models provide a static approach to
realizing forward and reverse service chain association most
often requiring complex configuration of each network device
throughout the forwarding path.
13. Multi-vendor Service Functions: Deploying service functions from
multiple vendors often requires per-vendor expertise: insertion
models differ, there are limited common attributes and inter-
vendor service functions do not share information.
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3. Service Function Chaining
Service chaining provides a framework to address the aforementioned
problems associated with service deployments:
1. Service Overlay: Service chaining utilizes a service specific
overlay that creates the service topology: the overlay creates a
path between service nodes. The service overlay is independent
of the network topology and allows operators to use whatever
overlay or underlay they prefer and to locate service functions
in the network as needed.
Within the service topology, service functions can be viewed as
resources for consumption and an arbitrary topology constructed
to connect those resources in a required order. Adding new
service functions to the topology is easily accomplished, and no
underlying network changes are required. Furthermore, additional
service instances, for redundancy or load distribution, can be
added or removed to the service topology as required.
Lastly, the service overlay can provide service specific
information needed for troubleshooting service-related issues.
2. Generic Service Control Plane (GSCP): GSCP provides information
about the available service functions on a network. The
information provided by the control plane includes service
network location (for topology creation), service type (e.g.
firewall, load balancer, etc.) and, optionally, administrative
information about the service functions such as load, capacity
and operating status. GSCP allows for the formulation of service
chains and disseminates the service chains to the network.
3. Service Classification: Classification is used to select which
traffic enters a service overlay. The granularity of the
classification varies based on device capabilities, customer
requirements, and service functionality. Initial classification
is used to start the service chain. Subsequent classification
can be used within a given service chain to alter the sequence of
service functions applied. Symmetric classification ensures that
forward and reverse chains are in place.
4. Dataplane Metadata: Dataplane metadata provides the ability to
exchange information between the network and service functions,
service functions and service functions and service functions and
the network. Metadata can include the result of antecedent
classification, information from external sources or forwarding
related data. For example, service functions utilize metadata,
as required, for localized policy decision. A common approach to
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service metadata creates a common foundation for interoperability
between service functions, regardless of vendor.
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4. Service Function Chaining Use Cases
The following sections provide high level overviews of several common
service chaining deployments.
4.1. Enterprise Data Center Service Chaining
TBD
4.2. Mobility Service Chaining
TBD
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5. Related IETF Work
The following subsections discuss related IETF work and are provided
for reference. This section is not exhaustive, rather it provides an
overview of the various initiatives and how they relate to network
service chaining.
1. L3VPN[L3VPN]: The L3VPN working group is responsible for
defining, specifying and extending BGP/MPLS IP VPNs solutions.
Although BGP/MPLS IP VPNs can be used as transport for service
chaining deployments, the service chaining WG focuses on the
service specific protocols, not the general case of VPNs.
Furthermore, BGP/MPLS IP VPNs do not address the requirements for
service chaining.
2. LISP[LISP]: LISP provides locator and ID separation. LISP can be
used as an L3 overlay to transport service chaining data but does
not address the specific service chaining problems highlighted in
this document.
3. NVO3[NVO3]: The NVO3 working group is chartered with creation of
problem statement and requirements documents for multi-tenant
network overlays. NVO3 WG does not address service chaining
protocols.
4. ALTO[ALTO]: The Application Layer Traffic Optimization Working
Group is chartered to provide topological information at a higher
abstraction layer, which can be based upon network policy, and
with application-relevant service functions located in it. The
mechanism for ALTO obtaining the topology can vary and policy can
apply to what is provided or abstracted. This work could be
leveraged and extended to address the need for services
discovery.
5. I2RS[I2RS]: The Interface to the Routing System Working Group is
chartered to investigate the rapid programming of a device's
routing system, as well as the service of a generalized, multi-
layered network topology. This work could be leveraged and
extended to address some of the needs for service chaining in the
topology and device programming areas.
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6. Summary
This document highlights problems associated with network service
deployment today and identifies several key areas that will be
addressed by the service chaining working group. Furthermore, this
document identifies four components that are the basis for serice
chaining. These components will form the areas of focus for the
working group.
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7. Security Considerations
Security considerations are not addressed in this problem statement
only document. Given the scope of service chaining, and the
implications on data and control planes, security considerations are
clearly important and will be addressed in the specific protocol and
deployment documents created by the service chaining working group.
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8. Acknowledgments
The authors would like to thank David Ward, Rex Fernando and Jim
French for their contributions.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[ALTO] "Application-Layer Traffic Optimization (alto)",
<http://datatracker.ietf.org/wg/alto/>.
[I2RS] "Interface to the Routing System (i2rs)",
<http://datatracker.ietf.org/wg/i2rs/>.
[L3VPN] "Layer 3 Virtual Private Networks (l3vpn)",
<http://datatracker.ietf.org/wg/l3vpn/>.
[LISP] "Locator/ID Separation Protocol (lisp)",
<http://datatracker.ietf.org/wg/lisp/>.
[NVO3] "Network Virtualization Overlays (nvo3)",
<http://datatracker.ietf.org/wg/nvo3/>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 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, April 2011.
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Authors' Addresses
Paul Quinn
Cisco Systems, Inc.
Email: paulq@cisco.com
Jim Guichard
Cisco Systems, Inc.
Email: jguichar@cisco.com
Surendra Kumar
Cisco Systems, Inc.
Email: smkumar@cisco.com
Puneet Agarwal
Broadcom
Email: pagarwal@broadcom.com
Rajeev Manur
Broadcom
Email: rmanur@broadcom.com
Abhishek Chauhan
Citrix
Email: Abhishek.Chauhan@citrix.com
Nic Leymann
Deutsche Telekom
Email: n.leymann@telekom.de
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Mohamed Boucadair
France Telecom
Email: mohamed.boucadair@orange.com
Christian Jacquenet
France Telecom
Email: christian.jacquenet@orange.com
Michael Smith
Insieme Networks
Email: michsmit@insiemenetworks.com
Navindra Yadav
Insieme Networks
Email: nyadav@insiemenetworks.com
Thomas Nadeau
Juniper Networks
Email: tnadeau@juniper.net
Ken Gray
Juniper Networks
Email: kgray@juniper.net
Brad McConnell
Rackspace
Email: bmcconne@rackspace.com
Kevin Glavin
Riverbed
Email: Kevin.Glavin@riverbed.com
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