O'Reilly logo
  • Eiji Tanioka thinks this is interesting:

One problem with the alternate ASN being prepended when receiving the routes is that other iBGP peers will drop the network prefixes as part of a routing loop detection

From

Cover of IP Routing on Cisco IOS, IOS XE, and IOS XR: An Essential Guide to Understanding and Implementing IP Routing Protocols

Note

only use "neighbor local-as" causes routing-loop to iBGP peer in Real-ASN.