For devices that use Border Gateway Protocol (BGP), you can also provide
the device's BGP Autonomous System Number (ASN). You can use an
existing ASN assigned to your network. If you don't have an ASN
already, you can use a private ASN (in the 64512 - 65534 range).
Amazon EC2 supports all 2-byte ASN numbers in the range of 1 - 65534,
with the exception of 7224, which is reserved in the us-east-1
region,
and 9059, which is reserved in the eu-west-1
region.
For more information, see AWS Site-to-Site VPN in the
AWS Site-to-Site VPN User Guide.
You cannot create more than one customer gateway with the same VPN type,
IP address, and BGP ASN parameter values. If you run an identical
request more than one time, the first request creates the customer
gateway, and subsequent requests return information about the existing
customer gateway. The subsequent requests do not create new customer
gateway resources.