The paper explained how routing between different domains in the internet happens. It tackled how the Internet Service Providers (ISPs) cooperate and exchange routing information in order to provide global connectivity and generate money from their customers. Since the internet service is provided by a large number of commercial enterprises who are in competition with each other, the internet routing infrastructure operates in an environment of “competitive cooperation”.
The routing architecture is divided into autonomous systems (ASes) that exchange reachability information. It was defined as owned and administered by a single commercial entity and implements some set of policies in deciding how to route its packets to the rest of the internet. There are two prevalent forms of ASes mentioned: Provider-customer(Transit) and Peering. The transit relationships generate revenue while peering usually don’t. It also explained how ISPs decide on what routes to export (using route filters)and import (by ranking routes). Their main consideration for their routing policies basically boils down to what can help them earn or save money.
These routing policies are realized through Border Gateway Protocol (BGP). It is designed for scalability, enforce different policies and handle cooperation under competitive circumstances. The paper explained how the protocol works, its two types of sessions (eBGP and iBGP) , the key BGP attributes (NEXT HOP, ASPATH, Local Preference and Multi-Exit Discriminator (MED)) and the fragility of the system that can lead to anomalies and disruption of connectivity. These are usually caused by misconfigurations, malice and slow convergence. The authors cited some interesting examples of highjacking routes by mistake or for profit and spam from hijacked prefixes which can be avoided or solved by logging BGP announcements so one can trace where hijacked routes are.
The paper is easy to follow especially on their explanation of the concept of BGP. However, the actual operation is extremely complex because it has to cater to different types of policies and sizes of Internet providers. As the main consideration for routing centers on individual ISPs interests, I think its configurations has to be really flexible to handle the exchanged in routes announcement.
Reference:
Hari Balakrishnan, Interdomain Internet Routing, 2001-2009
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