There are a few things rattling in my head that I have never truly understood, I am hoping this list might be able to help.
A multi-homed AS consists of an AS number registration (from ARIN), a routing policy (i.e. BGP4), and an IP range assingment (from ARIN).
The AS is registered with your name, address, etc.,.
The IP assignment is registered to an OrgID, with POCs, etc.,.
However, there is nothing that explicitly associates a given IP block with an ASN. Most of the time, the AS is run by the same people who have that IP assignment, aka ISPs, and so on. But it is possible, and occurs every day, where an end-user runs their own AS, and is advertising an IP range that is not assigned to them, rather it is assigned to one of their upstream providers.
To really find out which AS is advertising a given IP range, you have to query a variety of live BGP and route server resources, and there are plenty of them out on the internet.
Here's my question. Lets say Joe Schmoe registers an AS. He connects it to the internet via some provider using BGP.
- Joe "steals" an IP range from somebody else, that is currently not being advertised anywhere by any AS - and starts advertising it from his newly formed AS.
- Joe "steals" an IP range from somebody else, that IS currently being used and advertised by another AS, but Joe advertises it anyway from his AS,
For those two cases, what happens? What prevents it? What is the fallout from #2 to the real owner of that IP assignment? Does this ever occur, or is it so rare its not an issue.
These questions came about because I am in the process of migrating a datacenter. We are setting up a new AS in the new datacenter, it wont advertise any IPs right now. But the night we cutover, it will start advertising the IPs that previously have been running on our original AS - after we shutdown the original AS/router.