
AWS Certified Advanced Networking – Specialty (ANS-C01) Certification Guide
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Before launching into an explanation of the requirements and limitations of routing over Direct Connect, it would be helpful to give a short recap on BGP in the context of how Direct Connect utilizes the protocol. BGP is a route exchange application that allows network devices to advertise and consume route prefixes known as Network Layer Reachability Information (NLRI), which build a map of the networks that are owned and can reach other networks for the purpose of communication. Network devices require an understanding of where to send traffic, and that means having a route table of destinations. It would be tedious to have to manually maintain such a list, especially as new networks are added and old ones are removed, so BGP does this dynamically.
The most important concepts to understand with BGP and Direct Connect are the ASN, the NLRI, the best path selection, and, to a lesser extent, BGP communities. NLRI was just explained, and Appendix 1, Networking...