Black Holes

When you "advertise" routes to other entities (ASs), one way of thinking of those route "advertisements" is as "promises" to carry data to the IP space represented in the route being advertised.  The cardinal sin of BGP routing is advertising routes that you don't know how to get to. This is called "black-holing" someone – and all of the data on the Internet destined for the black-holed IP space will flow to your border router.

Needless to say, this makes that address space "disconnected from the 'net" for the provider that owns the space, and makes many people unhappy.  They in turn will “black-hole you”, and will cease to listen to your updates, and cease to route to you.  This is a temporary penalty.

The second most heinous sin of BGP routing is not having strict enough filters on the routes you advertise.