The BGP-4 Explicit AS Override simplifies the use of the same ASN across multiple RFC 2547 VPRN sites.
The Explicit AS Override feature can be used in VPRN scenarios where a customer is running BGP as the PE-CE protocol and some or all of the CE locations are in the same Autonomous System (AS). With normal BGP, two sites in the same AS would not be able to reach each other directly because there is an apparent loop in the ASPATH.
With AS Override enabled on an egress eBGP session, the Service Provider network can rewrite the customer ASN in the ASPATH with its own ASN as the route is advertised to the other sites within the same VPRN.