Network Service Chaining Problem Statement
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|Authors||Jim Guichard , Surendra Kumar , Paul Quinn , Michael Smith , Navindra Yadav|
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|RFC Editor Note||(None)|
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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 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 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 December 15, 2013. 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 Guichard, et al. Expires December 15, 2013 [Page 1] Internet-Draft NSC Problem Statement June 2013 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 Guichard, et al. Expires December 15, 2013 [Page 2] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 3] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 4] Internet-Draft NSC Problem Statement June 2013 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 Guichard, et al. Expires December 15, 2013 [Page 5] Internet-Draft NSC Problem Statement June 2013 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 Guichard, et al. Expires December 15, 2013 [Page 6] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 7] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 8] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 9] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 10] Internet-Draft NSC Problem Statement June 2013 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. Guichard, et al. Expires December 15, 2013 [Page 11] Internet-Draft NSC Problem Statement June 2013 7. Acknowledgments The authors would like to thank David Ward and Rex Fernando for their contributions. Guichard, et al. Expires December 15, 2013 [Page 12] Internet-Draft NSC Problem Statement June 2013 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)", <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/>. Guichard, et al. Expires December 15, 2013 [Page 13] Internet-Draft NSC Problem Statement June 2013 Authors' Addresses Jim Guichard Cisco Systems, Inc. Email: email@example.com Surendra Kumar Cisco Systems, Inc. Email: firstname.lastname@example.org Paul Quinn Cisco Systems, Inc. Email: email@example.com Michael Smith Insieme Networks Email: firstname.lastname@example.org Navindra Yadav Insieme Networks Email: email@example.com Guichard, et al. Expires December 15, 2013 [Page 14]