Being a transit operator comes with an inherent responsibility to not break your customers routing. Most often transit networks operate in the DFZ (Default-free-zone), although there are often exceptions to this in the research & education industry.
List of things to be written about
- customer prefix filtering
- using communities to control BGP advertisements
- customer AS-path filtering
- using route-maps to control prefix filtering, communities, and as-path filtering
- peering in multiple locations