I'm trying to understand the principles of routing in the internet, especially regarding (E)BGP.
So far, I understand the situation of a "typical" ISP (e.g. with the ASN 2) that has its own backbone, and peering/transit/customer interconnections at various points.
Since all of the border routers are connected over some internal routing protocol and backbone, if some AS with ASN 1 has a route to ASN 3 via ASN 2, there is a path (1, 2, 3), and ASN 2 will forward the traffic over its internal backbone.
However, I'm wondering if it's possible to have an ASN present at multiple locations without a backbone to connect those locations internally. Let's say another ISP, with ASN 4, is connected to both ASN 1 and 3, but not 2; also, let's assume that ASN 1 and 3 have no connectivity other than over 2. Will that work (e.g. ASN 4 has connectivity to ASNs 1, 2 and 3)? If so, how?
So far, I've found a pretty good explanation that specifically mentions that situation, and says that it can be resolved by statically configuring routes for the "split" ASN 4, but also mentions that everything has to be configured statically.
Is such a configuration common, or are such situations handled differently? Are there other ways to enable such "edge" networks? I'm thinking especially about content delivery networks with a lot of caches at various locations - do they all have a backbone, or is it done differently?