I have a follow up question, regarding my impression that "it sounds broken (to me)" if more then one AS announces the same prefix as origin: /* I knew I have read it somewhere... Maybe it's just old and dusted and did not survive the turn of the millennium */ https://tools.ietf.org/html/rfc1930#page-8 from 1996
7. One prefix, one origin AS
Generally, a prefix can should belong to only one AS. This is a direct consequence of the fact that at each point in the Internet there can be exactly one routing policy for traffic destined to each prefix. In the case of an prefix which is used in neighbor peering between two ASes, a conscious decision should be made as to which AS this prefix actually resides in. With the introduction of aggregation it should be noted that a prefix may be represented as residing in more than one AS, however, this is very much the exception rather than the rule. This happens when aggregating using the AS_SET attribute in BGP, wherein the concept of origin is lost. In some cases the origin AS is lost altogether if there is a less specific aggregate announcement setting the ATOMIC_AGGREGATE attribute. So in the second paragraph: "this is very much the exception rather than the rule" -- does it just turned around over time? So today/in modern times: The same prefix, or the same specific network/subnet can be originated from more then one AS and things do not break? In this thread it was mentioned that even valid signed ROA can be created for this scenario. But I'm still puzzled if it is only me that validates it, or do both (the ISP and myself) do validate it? Thanks again for your time and help! Bernd