Commercial Considerations in Routing

As stated in "Interdomain Internet Routing" [1], wide-area routing today occurs between "...autonomous systems (ASes) that exchange reachability information." Using Border Gateway Protocol (BGP), they send this information through two prevalent AS-AS relationships--"transit" and "peering." Transit involves a "provider" that provides access to most, if not all, of the destinations in its routing tables to its "customers." Peering, on the other hand, involves ASes that provide access only to a subset of these destinations.

These two relationships suggest roles that ASes play--that of a provider and of a customer, as already described in the case of transit, and that of a peer in peering. A provider has to allow its customers access to whatever it needs access to, because, as also stated in the paper, they pay for this access. Peers, meanwhile, limit the access they provide as they do not want other peers to use their resources for free. BGP is able to handle these roles with eBGP for routers in different ASes and iBGP for routers in the same AS.

This author wonders whether this routing architecture counteracts the Internet design's goal of survivability.

If one considers it closely, the relationships mentioned above imply a somewhat hierarchical structure, with peering disrupting what might otherwise be a perfect star topology of ASes. Removing one "provider" AS from the star removes its "customers" as well, since customers are--and this is an assumption by this author--generally connected to only one provider at a time. An answer might be to connect a customer to multiple providers--but this means that the customer now has to pay two providers to ensure constant connectivity.

It is very interesting to see how strongly routing on the Internet today is influenced by commercial considerations.

Reference:
[1] Hari Balakrishnan and Nick Feamster, "Interdomain Internet Routing."