Change, the one constant in life


Today I introduce the new blog series “Design Use Cases”. I often times say that in life there are a few constants: death, taxes, and change! Not much to say about the first two   “Change”, however, has unique considerations that influence network design. The subject of this blog is how to design for “change” as in Add and Replace technology, service or application.

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Add technology, service or application

The network is running and you are tasked to add to it a new technology, service or application, such as collaboration, multicast, IPv6, etc. Common drivers are to drive innovation and business transformation, increase productivity and agility, enable new or augment current revenue streams, and ensure compliance.


Replace technology, service or application

The network is running, and you are tasked to replace an existing technology (legacy or not), service or application, such as data center, WAN, Layer 2 or Layer 3 protocol, etc. Common drivers are technology consolidation and optimization, cost reduction, risk management, and investment protection.


Network design considerations

How does change affect network design? There are technical and non-technical considerations, as follows.


  • New technology, service or application needs: You should consider what the requirements are for the new “thing” to work smoothly, such as latency, packet drops and jitter, minimum speed, maximum convergence time, potential over-subscription, or traffic patterns. Your design should include QoS and eventually additional bandwidth that can be achieved through faster interfaces, link aggregation, or buying additional bandwidth.
  • Conflict with the remaining technologies, services and applications in the network: Are the remaining technologies, services and applications going to be impacted, such as a modified traffic pattern, conflicting use of a common network resource, a STP or routing loop, or a caveat? The change management process involved should include an assessment of the current state of the network (baseline), piloting the addition on a small scale before full deployment, the research of known vulnerabilities, caveats and required upgrades, careful multicast planning (placement of source(s) and receiver(s)), traffic engineering, and laying out a comprehensive migration plan to avoid disruption of the existing services running on the network.
  • Technology footprint: Is the new technology available across all geographies with adequate support? Your design should account for more than one solution or a phased deployment approach.
  • Application hosting: Where will the new application reside? Is the design part of a bigger overhaul? Your design should consider where the application will be hosted (in a data center / cloud (private, public, and hybrid)), its availability, and scalability.
  • The consumers of the new application: How will the users access the new application? From their own devices (BYOD), or from Windows, Mac and Linux machines? Will they be local, remote, or commuting? Your design should consider compatibility, mobility and security.
  • Serviceability: This often times forgotten topic starts with making sure the staff is able to operate the new technology, and keeping a detailed documentation readily available if troubleshooting is necessary.
  • Future-looking: Finally, is the change focused on consolidation and virtualization? How do your customers react to risk? Your design should consider the use of more mature and tested technologies to deploy if they are risk averse, or you may take on some risk and be an earlier adopter if they are risk adept. Is the technology standard or proprietary?


Adding or replacing technologies, services or applications are common design use cases, and careful identification of the requirements and solid design associated with following a comprehensive change management plan will guarantee a smooth deployment.


Do you consider the implications of change on your network designs? Is there a topic you want to hear about on my upcoming blogs? Add it to the comments below!

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Elaine Lopes is the CCDE and CCAr Certifications Program Manager and Team Lead for the CCIE program team, and she’s passionate about how lives can change for the better through education and certification.




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