Network Working Group J. Guichard
Internet-Draft S. Kumar
Intended status: Informational P. Quinn
Expires: December 15, 2013 Cisco Systems, Inc.
M. Smith
N. Yadav
Insieme Networks
June 13, 2013
Network Service Chaining Problem Statement
draft-quinn-nsc-problem-statement-00.txt
Abstract
This document provides an overview of the issues associated with the
deployment of network services (such as firewalls, load balancers) in
large-scale environments. The term service chaining is used to
describe the deployment of such services, and the ability of a
network operator to specify an ordered list of services that should
be applied to a deterministic set of traffic flows. Such service
chains require integration of service policy alongside the deployment
of applications, while maintaining optimal use of available network
capacity and resources.
Status of this Memo
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This Internet-Draft will expire on December 15, 2013.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 3
2. Problem Areas . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Service Chaining for Adding Network Services . . . . . . . . . 8
4. Related IETF Work . . . . . . . . . . . . . . . . . . . . . . 9
5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
New data center (DC) network and Internet cloud architectures require
more flexible deployment models that are able to support many
different forms of applications and related network services.
Network services include traditional services such as firewalls and
server load balancer, as well as applications and features that
operate on network data. Additionally, these services must be
delivered in the context of multi-tenancy where each individual
tenant is an isolated client organization attached to the data
center, and may require unique capabilities with the ability to
tailor service characteristics on a per-tenant basis.
The current network service deployment models are relatively static,
and bound to topology for insertion and policy selection.
Furthermore, they do not adapt well to elastic service environments
enabled by virtualization. Additionally, the transition to virtual
platforms requires an agile service insertion model that supports
elastic service delivery; supports the movement of service functions
and application workloads in the network 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 chaining, as well as the problems of
service chain creation/deletion, policy selection 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.
Service Chain: A service chain defines the services required
(e.g.FW), and their order (service1 --> service2) that must be
applied to packets and/or frames.
Service Function: A L4-L7 service function (NAT, FW, DPI, IDS,
application based packet treatment), application, compute
resource, storage, or content used singularly or in collaboration
with other service functions to enable a service offered by a
network operator.
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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.
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2. Problem Areas
The following points describe aspects of existing service deployment
techniques 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 artificial
constraints on delivery and inhibiting the network operator from
sharing service resources and scale capacity/redundancy across
multiple network devices. These topologies serve only to
"insert" the 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 services are required - often with strict
ordering - topology changes are needed before and after each
service resulting in complex network changes and device
configuration. In such topologies, all traffic, whether a
service 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
is 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.
3. Constrained High Availability: An effect of topological
dependency is constrained service high availability. Since
traffic reaches services 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
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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 deployed service ordering.
5. Service Chain Construction: Service chains today are most
typically built through manual configuration processes. With
the advent of newer service deployment models the control plane
will provide not only connectivity state and membership
distribution across tenants, but will also be increasingly
utilized for the formation of services. Such a control plane
could be centrally controlled and managed, or be distributed
between a subset of end-systems. Formation of closed user
groups that are able to maintain separation of forwarding and
connectivity state, while at the same time be independently
identified and directed through appropriate services, requires
the ability to create "zones" of awareness and "chained"
services.
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 action
taken. Topology information is increasingly less viable due to
scaling, tenancy and complexity reasons. Per-service function
packet classification is inefficient and prone to errors,
duplicating functionality across services. Furthermore packet
classification is often too coarse lacking the ability to
determine class of traffic with enough detail.
7. Transport Dependence: Services can and will be deployed in
networks with a range of transports, including under and
overlays. The coupling of services to topology requires
services to support many transports or for a transport gateway
function to be present.
8. Elastic Service Delivery: Given the current state of the art for
adding/removing services 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 is sent to a service
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 the service(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
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inflexible.
10. Limited End-to-End Service Visibility: Troubleshooting service
related issues is a complex process that involve network and
service expertise.
11. Per-Service (re)Classification: Classification occurs at each
service, independently from previous service functions. These
unrelated classification events consume resources per service.
More importantly, the classification functionality often differs
per service and services 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.
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3. Service Chaining for Adding Network Services
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 place services in the
network as needed. Within the service topology, services can be
viewed as resources for consumption and an arbitrary topology
constructed to connect those resources in a required order.
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 services on a network. The information
provided by the control plane includes service network location
(for topology creation), service type (e.g. firewall vs. load
balancer) and, optionally, administrative information about the
services 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
services 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 services, services
and services and services and the network. Metadata can include
the result of antecedent classification, information from
external sources or forwarding related data. For example,
services utilize metadata, as required, for localized policy
decision.
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4. 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: 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 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: 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.
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5. 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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6. 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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7. Acknowledgments
The authors would like to thank David Ward and Rex Fernando for their
contributions.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[L3VPN] "Layer 3 Virtual Private Networks (l3vpn)",
.
[LISP] "Locator/ID Separation Protocol (lisp)",
.
[NVO3] "Network Virtualization Overlays (nvo3)",
.
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Authors' Addresses
Jim Guichard
Cisco Systems, Inc.
Email: jguichar@cisco.com
Surendra Kumar
Cisco Systems, Inc.
Email: smkumar@cisco.com
Paul Quinn
Cisco Systems, Inc.
Email: paulq@cisco.com
Michael Smith
Insieme Networks
Email: michsmit@insiemenetworks.com
Navindra Yadav
Insieme Networks
Email: nyadav@insiemenetworks.com
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