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I've recently been looking for the IP prefixes originating from a specific AS. And there are a few questions I'd like to get confirmed.

  1. We can register IP addresses and ASN from RIR. But where can we get the accurate mapping between ASN and the IP prefix? Is there an official information distribution agency?

  2. As far as I know, one IP address is owned by one AS. However, I find 8.8.8 belongs to different ASes from bgp.he.net. I also don't know why different ASes have overlapping prefixes. (8.0.0.0/12 - 8.8.8.0/24) Is this a data platform problem or the result of route aggregation?

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  • The AS concept is really decoupled from the IP addressing concept. You could certainly set up a transit AS between two other ASes and use only private addresses, or one or two public addresses without advertising any of your addressing because only the two ASes for which you are providing transit services need to know only your directly connected addresses and not advertise them.
    – Ron Maupin
    Feb 11, 2023 at 6:34

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You're mixing up two things here: ownership of the IP-range and the right to advertise IP addresses. Ownership of IP addresses has nothing to do with ASN's. The owner of an IP range may allow one or more ASNs to advertise their IP's. That can be done by registering route objects in one of the internet routing registries (IRRs). All regional internet registries (RIRs, like RIPE, ARIN, etc) operate one, but there are also others like RADB. Another way to let others know that a specific ASN is allowed to advertise an IP range is by creating RPKI route origin attestations (ROAs). Both route objects and ROAs link an IP range to an ASN.

Your example of the 8.0.0.0 space shows that Level3 is authorized to advertise the /9, but Google's AS15169 is alllowed to advertise the 8.8.8.0/24 from that /9. It has nothing to do with ownership of the IP range.

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  • Got it! Then how can we get all IP prefixes owned by a specific AS through official public information on BGP?
    – wyb
    Feb 11, 2023 at 11:23
  • Like I said: prefixes aren’t owned by an ASN, they’re owned by an organization and can be announced by one or more ASNs.
    – Teun Vink
    Feb 11, 2023 at 12:49
  • Perhaps I was not very clear. If an ISP registers some IP prefixes and an AS number to provide service, can we say these IP prefixes form the AS? I thought "the prefixes owned by an AS" refer to the network devices' ip addresses in that AS. @TeunVink
    – wyb
    Feb 11, 2023 at 13:28
  • @wyb, "can we say these IP prefixes form the AS?" No. You are confusing two different concepts. AS (Autonomous System) only means that the entity with the AS is autonomously managed; it can do what it likes within its own network. An AS can, or not, advertise prefixes to other ASes, and that really has nothing to do with the IP prefixes that may be assigned to an entity that has an AS. The DoD has several very large prefixes assigned to it, but does not advertise some, so other ASes may use those internally, and the DoD has authorized outside ASes to advertise some of them.
    – Ron Maupin
    Feb 11, 2023 at 19:14
  • In addition to what Ron said, an ASN can also announce prefixes belonging to another (downstream) ASN.
    – Teun Vink
    Feb 11, 2023 at 19:25

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