Definitely there is AS number being used within our backbone but not advertised to public network. So the AS number should be allowed to be registered but not advertised the same way as IP address is treated.
Isn't that the definition of private AS?
Not exactly.
There are some cases where there is a valid reason for a public AS number to be issued, despite of the fact that it has semi-private nature. Same thing applies with IP addresses - take, for example, 147.204.0.0/16 ...
"Some cases" and "semi-private" doesn't sound to convincing to me :) I think that this is up to the definition of "publicly visible". If I have one upstream and several peers, that is to me "public". I see few (no?) other real reasons for assigning an AS that is not seen through two or more paths in the global routing table. Best regards, - kurtis -