A Design Challenge – Part 1 with Mohamed Sobair

Network Design Methodology In Action: Challenge


In this blog, I am doing a methodology walk-through based on requirements and constraints to select and justify the correct design option for the fictitious company called Vision. The ultimate objective of this methodology is to be in the mindset of a network designer by going through the elicited business and technical requirements and selecting one design option over all other options. This is the first of a two-part series, so here I will present a design challenge with options for you to evaluate. Read through the challenge details below, and stay tuned for my next installment where you’ll learn how I approached this challenge and chose a design option. This methodology walk-through should be very helpful for candidates preparing for the CCDE exam as well as for real life design experience.


Following are the steps to be taken for solving this design challenge:

  1. Ensure you have technical knowledge of BGP and MPLS in order to help you select and justify one option over another to solve this design challenge.
  2. List and compare all business and technical requirement to choose the best design given the options provided
  3. List and compare all constraints.
  4. Select the best design option and justify it (why it’s correct).
  5. Justify the design options not selected (why they’re incorrect).


The challenge:

  • Vision is a national Tier-2 ISP that has POPs spread out across three cities dispersed within the country.
  • Vision ISP has fiber links connecting its core MPLS network across the cities.
  • Vision ISP requires business continuity.
  • Vision ISP provides data, Internet, Layer 2 VPN, Layer 3 VPN, IPTV, multicast VPN and voice services to its customers: including business, home users and local ISPs.
  • Vision ISP utilizes MPLS to cost-effectively classify data and VoIP traffic.
  • City “2” is a transit city connecting the other two cities.
  • Each city contains 8 POPs and 4 P routers, with each POP’s PE router dual-homed to 2 P routers. Each POP consists of 1 PE router.
  • The P routers are deployed in-line to perform control and data plane functionalities on high-end routers with STM-64 10 GE line cards.



Figure 1: Vision’s main topology


MP-BGP is mandatory to be implemented within the MPLS backbone, and management is also looking for a design solution that provides scalability, simplicity, resiliency of the physical and core layers, increased policy control granularity, and both intra-city (intra-POP) and inter-city (inter-POP) connectivity.


There are 6 proposed design options shown below.


Figure 2 – Proposed design option 1 – Hierarchical RR design with 2 horizontal RRs in a BGP cluster



Figure 3 - Proposed design option 2 - Hierarchical RR design with 2 vertical RRs in a BGP cluster



Figure 4 - Proposed design option 3 - Hierarchical RR design with all city RRs in a single BGP cluster



Figure 5 - Proposed design option 4 - BGP Confederation with each city RRs in a single BGP cluster



Figure 6 - Proposed design option 5 - BGP Confederation with 2 horizontal city RRs, each in a different BGP cluster



Figure 7 - Proposed design option 6 - BGP Confederation with 2 vertical city RRs, each in a different BGP cluster



Select and justify the option which best meets the stated requirements, and on the next blog I’ll go through the steps I took for the design option selection.


About the Author

Blog16-17- Mohamed Sobair pic.png


Mohamed Sobair, CCIE# 29645, MSc, ITiLv3, JNCIS & PMP has over 10 years of professional experience in the IT Industry providing solutions and consultation services for various Enterprise, Telecom and ISP customers. He is currently volunteering as a Subject Matter Expert for Cisco’s Expert-level program. Mohamed is passionate about design and architecture, usually participating in discussions and making contributions related to Cisco technologies on CLN and Cisco Support Community.



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