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Enterprise Internet Multi-Homing Design – Business Driven Approach
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Enterprise Internet Multi-Homing Design – Business Driven Approach

This topic is one of the most common design topics. If you do a quick google search you will find a lot of blogs and vendors’ papers discussing how to configure BGP and how to steer the traffic over the different paths.

Technically, configuring BGP is not a complex task, what is more critical is when and why we should consider such a connectivity model?

Note: Refer to the new CiscoPress book “Designing for Cisco Network Service Architectures (ARCH) Foundation Learning Guide: CCDP ARCH 300-320, 4th Edition” for more technical design details.

In other words, configuring BGP policies is not the most critical part that you need to worry about in your design. Instead, the drivers to select certain BGP policy model to steer the traffic over a single or different paths is the vital part.

Consequently, as a network architect you need to provide a business driven design that takes into consideration business and applications’ needs. Part -1 of this blog series will focus on the business and application drivers and how these drivers can influence the technical design decisions.

Let’s break the design decision into two primary layers to simplify the design approach

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  • Business drivers

As a designer or architect, first you need to think of “why would the business needs or approve such a connectivity model?”

  • To achieve optimized resiliency? e.g. active/standby Internet paths

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  • Cost control and optimized return on investment (ROI) of the existing links (by considering traffic load-sharing techniques e.g. expensive links can be used for critical type of traffic only)

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  • Flexibility e.g. to serve different entities in multi-tenant environments where different business units or tenants can use different Internet links.

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  • Applications’ requirements

The design “policy wise”, must be derived by the requirements of the traffic flows. Therefore, the following points are key to identify these requirements.mh-6

  • Provide access to locally hosted applications to external users
  • Provide access to externally hosted applications for the internal users
  • Provide service differentiation e.g. critical applications accessed over high speed link/pathmh-7

Practically, you need to consider both “business drivers and applications requirements” to come up with an optimal design.

For example, lets assume an enterprise has a multi-homed Internet edge dual-homed to two different ISP. Currently this enterprise uses one of the links as the active/primary Internet path and the second link is idle (used as back up). The cost model of both links is based on a fixed monthly billing, regardless if the link is fully utilized or not. In addition, this enterprise has subscribed with Microsoft office 365 to provide Online versions of Office with email and video conferencing.

The CIO of this enterprise asked the Infrastructure manger to revise their internet connectivity model to see if there is a possibility to provide an optimized ROI as well as to support their new applications’ requirements.

The simple solution to these requirements is to distribute the traffic across the available links. However, There are few technical aspects that you need to take into consideration to achieve this connectivity model reliably. Part-2 of this blog will discuss some of these considerations

Marwan Al-shawi – CCDE No. 20130066 – is a Cisco Press author (author of the Top Cisco Certifications’ Design Books “CCDE Study Guide & the upcoming CCDP Arch 4th Edition”). He is Experienced Technical Architect. Marwan has been in the networking industry for more than 12 years and has been involved in architecting, designing, and implementing various large-scale networks, some of which are global service provider-grade networks. Marwan holds a Master of Science degree in internetworking from the University of Technology, Sydney. Marwan enjoys helping and assessing others, Therefore, he was selected as a Cisco Designated VIP by the Cisco Support Community (CSC) (official Cisco Systems forums) in 2012, and by the Solutions and Architectures subcommunity in 2014. In addition, Marwan was selected as a member of the Cisco Champions program in 2015 and 2016.

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