There’s also a 2017 book from O’Reilly, BGP in the data center for anyone interested.
Am I mistaken for having heard that ECMP is better for large scale data centers? Post makes no mention of alternatives and considerations for pursuing BGP as the chosen standard besides “it’s popular”
BGP distributes routes and sets next hop. ECMP allows multiple routes to a single destination to exist and the router can forward packets across all outgoing interfaces usually in a load balanced way (using a l4 hash usually).
BGP is just one protocol to distributes routes. Equal Cost Multi Pathing does not distribute routes.
The longer paper linked in the post seems to mention ECMP, and the positives & negatives of BGMP. Link to the paper: https://research.fb.com/wp-content/uploads/2021/03/Running-BGP-in-Data-Centers-at-Scale_final.pdf