Chapter 2. The Scope of Service Types

This chapter discusses the breadth and depth of services available to the service provider and the enterprise customer. It provides an overview of Layer 2; Layer 3; remote access; and value-added services, such as managed VPN, web hosting, and managed shared services, as well as their applicability in the current environment. Subsequent chapters cover more detailed service descriptions; for example, Chapter 4, "Layer 2 VPNs," covers Layer 2; Chapter 5, "Layer 3 VPNS," examines Layer 3 MPLS VPN; and Chapter 6, "Remote Access and IPSec/MPLS VPN Integration," discusses remote access and IPSec integration.

Although enterprise IT managers must continually manage costs and maintain reliable wide area network (WAN) infrastructures to meet their business goals, success in today's business climate also depends on the ability to overcome a more complex set of challenges to their corporate-wide area networks. Enterprise IT managers are faced with:

• Geographically dispersed sites and teams that must share information across the network and have secure access to networked corporate resources.

• Mission-critical, distributed applications that must be deployed and managed on a network-wide basis. Most IT managers additionally must confront a combination of centralized hosted applications and distributed applications that further complicate the management and operations tasks.

• Security requirements for networked resources and information that must be reliably available but protected from unauthorized access.

• Business-to-business communication needs, both to users within the company as well as extending to partners and customers.

Layer 3 MPLS VPNs provide enterprise IT managers with a variety of opportunities for meeting these challenges, including:

• Enhanced ability to deliver a wide range of connectivity options to geographically dispersed branch offices, remote users, and teleworkers (who are viewed somewhat differently from remote users). Remote users are generally considered to be in a fixed location for at least some period of time. Traveling users or teleworkers are usually in a variety of locations and often cross several geographical borders in a day. Layer 3 MPLS VPNs also serve as foundations for extranets, such as business partners, subsidiaries, and Internet access, which are Q-quality of service (QoS) features that ensure end-to-end application performance.

• Support for the convergence of previously disparate data, voice, and video networks resulting in cost savings for the enterprise.

• Security and privacy equivalent to Frame Relay and ATM.

• Easier deployment of productivity-enhancing applications, such as enterprise resource planning (ERP), e-learning, and streaming video. (These productivity-enhancing applications are IP based, and Layer 2 VPNs do not provide the basis to support these applications.)

• Pay-as-you-go scalability as companies expand, merge, or consolidate.

• Flexibility to support thousands of sites and tens of thousands of users.

New challenges arise when extending a network footprint globally. Large enterprises with a global reach have a few options for handling these issues when working with service providers that supply global services. The preferred option is to work with a service provider that already has a global presence. Alternatively, enterprises might choose to work with multiple service providers to achieve the same global network presence. When working with multiple service providers, enterprises can choose to self-manage the interconnection between the two networks or require the service providers to manage the interconnection. In the case of self-managing the interconnection, the enterprise purchases and installs the appropriate network devices, provides the necessary support and management, and determines how to handle the routing policies between the two networks.

In the second casewhen service providers manage the interconnectionthe two service providers might cooperate and work out the interoperability and interconnect service issues without active participation from the enterprise. The two service providers might even implement mechanisms to maintain service quality consistently across the two networks.

Building such VPNs requires the use of Inter-Autonomous Systems (Inter-AS) VPNs. Providing seamless Layer 3 MPLS VPNs requires Inter-AS; however, networks can also be connected using other methods for which VRFs are not exchanged. Some examples of non-Layer 3 MPLS VPNs constructs are at Layer 2for example, peering at Layer 2. Additionally, there is emerging work in the industry: Some customers are implementing Inter-AS traffic at Layer 3. IETF RFC2547bis describes alternatives for Inter-AS Layer 3 connectivity options. Additionally, Chapter 5 provides an overview of the three Layer 3 Inter-as options along with their benefits and limitations. Finally, we examine Inter-as traffic in Chapter 8, "Traffic Engineering."

Whichever situation arises, the enterprise IT managers must address interconnect issues with the service providers and be prepared to address future issues as the networks and services scale and as new services are introduced onto the MPLS-based VPNs. We explore the migration scenarios and alternatives in the Chapter 14 case study "MPLS Case Studies."

This chapter examines Layer 2, Layer 3, remote access, and value-added services as input for an IT manager and a service provider business development manager.