At the most basic level, there are only three BGP policies: pushing traffic through a specific exit point; pulling traffic through a specific entry point; preventing a remote AS (more than one AS hop away) from transiting your AS to reach a specific destination. In this series I'm going to discuss different reasons for these kinds of policies, and different ways to implement them in interdomain BGP.

In this post, I'll cover the first of a few ways to give surrounding autonomous systems a hint about where traffic should enter a network. Note this is one of the most vexing problems in BGP policy, so there will be a lot of notes across the next several posts about why some solutions don't work all that well, or when they will and won't work.

There are at least three reasons an operator may want to control the point at which traffic enters their network, including:

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