Chapter 1: Introduction to WAN Architectures

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Almost all the VMWare and IBM or Microsoft cluster architectures call for LAN connectivity as a baseline requirement. Hence, emulating LAN service while still connected via a WAN poses a lot of challenges for convergence (ideally within a few seconds).

The solution requirements in Table 1-7 call for an infrastructure that has the features outlined in Table 1-8.

Table 1-7  DCI Feature Requirements

The solution requirements in Table 1-7 call for an infrastructure that has the features outlined in Table 1-8.

Table 1-8  Router/Switch Feature Requirements Needed to Meet the DCI Solution Requirements

~Large Branch WAN

As universally understood, not all branches are equal. This is not only true for the size of branch (as in number of users or perhaps application servers residing at the branch) but also for how critical the branch is to the overall business function. Consider bank branches, for example. Not all branches provide the entire portfolio of services. In the real world, some provide only basic banking services, whereas others provide full-blown services, including home mortgage, small business loans, and investment services to commercial customers.

Large branches (those that provide more services or services that are critical to the business, or in most cases both) tend to have slightly different requirements for a WAN infrastructure that connects them to the corporate backbone. Table 1-9 outlines the large branch WAN requirements.

Table 1-9  Large Branch Office Deployment Requirements

Table 1-10 maps the requirements onto the infrastructure needed to support such requirements.

Table 1-10  Large Branch Office Requirements/Traits

Summary

This opening chapter covered the basic building blocks of WAN architectures:

• Branch aggregation

• Internet edge

• Data center interconnect

• Large branch office

Although the basic requirements are common across the various roles, they differ significantly enough that you need to understand how they are architected, deployed, and troubleshot. If there were one word to describe the hardware required to meet these needs, that word would beflexibility. Infrastructure needs to be very flexible in terms of feeds and speeds, scale and performance, service richness, and interface diversity (to name a few).

The next chapter covers the various business drivers, and the underlying technical requirements that they are generating. It concludes with an analysis of how these are driving requirements for next-generation WAN infrastructure.

Review Questions

1. What are the four usual WAN architectures?

2. What does optimized WAN mean?

3. What are the few fundamental requirements for WAN aggregation?

4. Why is service richness so important to enterprises?

5. Why would an enterprise connect directly to a service provider or be multihomed?

6. What are the core business drivers for DCI?

Answers

1. Usual WAN architectures typical in today’s networks include the following:

   Branch and private WAN aggregation

   Internet edge

   Data center interconnect

   Large branch WAN

2. 优化指的是在这里capability of the network infrastructure to provide the voice, video, and data traffic optimization before it goes over the WAN links. This helps reduce the need for more bandwidth every time a new application is added to the network. Cisco WAAS and IOS provide such services.

3. WAN aggregation requires, at a minimum, infrastructure to support the following:

   Flexible routing/switching architecture that can evolve with the changing business requirements

   Capability to combine various types and speeds of interfaces into one common infrastructure

   Modular and highly available carrier-class design with the separation of control, data, and I/O planes

   Capability to add basic services without requiring new hardware

4. Service richness refers to an in structure (hardware and software) that can introduce a basic service and some of the advanced services into baseline hardware with simple software upgrades. Enterprises and their businesses thrive on applications, and that in turn requires network-based services for them to work on common physical infrastructure and with the ability for virtualization for today’s typical multitenant requirements.

5. Enterprises connect to multiple Internet providers (or what is generally known as multihoming) for a few key reasons, including the following:

   Fault tolerance and resiliency to failure in one provider’s network

   Granular routing control

   Path selection based on features such as performance-based routing or PfR

6. Core business drivers behind DCI include the following:

   Layer 2 extensions

   Data center consolidation

   Data center disaster recovery site

   Virtualization and clustering applications such as VMWare’s VMotion

Further Reading

Introduction to WAN, document:http://tinyurl.com/6g8cym

Cisco Validated Designs, document:http://tinyurl.com/lnnyjt

Unified WAN Services, document:http://www.cisco.com/en/US/netsol/index.html

DC Interconnect, document:http://tinyurl.com/rclv2f

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