Jacques,
Note also that in the case of a multi-homed customer not using BGP, the route would indeed appear in multiple ASes, and would require the other ISP to announce its whole PA block _and_ the more specific for load-sharing to occur...
Indeed. I missed that point since we (before becoming a LIR) got an own AS-Number before having any own PA networks except the prefixes from our upstream. The difference there, of course, is the own AS-number. Since there ain't very much AS-numbers (as 2-byte counter, am I right?), no ISP should ever consider getting an own ASN for their to-be multihomed customers. Sure...
It looks to me like it should be prohibited to announce parts of a PA block. If the customer needs to announce addresses via multiple providers, he should switch to PI, shouldn't he?
Sounds good for me. As long the customer doesn't have an own ASN. Imagine the setup of ISP1, Customer and ISP2. ISP1 has a /19. Customer has a /24 out of the /19. ISP2 is the new upstream to give redundancy / multihoming to Customer. ISP1 announces the /24 as addition to the /19 to their upstreams AND announces the /24 to ISP2. Most companies wouldn't do that because their customer is "Customer" and not ISP1. Anyway, this should work. What do you think? With that setup you wouldn't have inconsistent-ASes. Ok. Redundancy is a little bit complicated, that way. The BGP-speaking router of ISP1 should be physically located at "Customer". GNgh... that is getting too far.
Jacques.
Sascha