Diving into Cloud Router
Cloud Router is a Google Cloud service that emulates the standard behavior of a real physical IP router. It is not a physical device (and so it cannot cause bottlenecks), but indeed it is a service, fully managed and distributed (it can work whether regionally or globally to the entire GCP suite). Being a fully managed service, it is also automatically scalable to satisfy the dynamic needs of your VPC network.
When used in cooperation with an interconnect option, between your on-prem network and your VPCs, it uses the BGP protocol to dynamically exchange routes between your networks.
BGP
BGP is one of the most important (or maybe the most important) routing protocols used on the entire internet nowadays. It is responsible for exchange routing information among different ASes.
ASes are connected groups of one or more IP prefixes run by one or more network operators that have a single and clearly defined routing policy (see IETF RFC 1930, March 1996...