Part-2 -Advanced- BGP Policies & Path Selection – Visualized Case Study – Design Foundations Series

Disclaimer: This blog series aims to use a visualized approach, a new way to describe designs in over simplified manner, where diagrams and figures are mainly used to explain this topic. (there is nothing better than diagrams and figures to explain designs)!

The previous blog “BGP Path Selection – Visualized Case Study-” covered some foundational BGP path selection options , this blog will take it a step further to cover more complicated BGP polices and path selection considerations. keep in mind this is not a best practice or only way of achieving the case study requirements, as the selection of the policy and BGP attributes always influenced by the actual scenario and intended goal. that being said, you should always keep it simple and avoid complex polices where applicable.

Structuring the BGP policy model and application

ISP/AS 500 establish a mapping between customer configurable community values and the corresponding local preference values within the provider network.


Practically, what are the limitations/implications of using AS_Prepending toward the Internet/ISPs?

In case of node F(AS 300) failure:

BGP community value 600:603 is an example of tagging certain prefixes with a BGP community value to control its propagation across BGP domains.

as mentioned earlier, always consider the simplest solution and ensure it offers enough flexibility to add and change prefixes in the future with minimal configurations.

Marwan Al-shawi – CCDE No. 20130066, Google Cloud Certified Architect, AWS Certified Solutions Architect, Cisco Press author (author of the Top Cisco Certifications’ Design Books “CCDE Study Guide and 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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