A private Autonomous System Number (ASN) for the Amazon side of a BGP session. The range is 64512 to 65534 for 16-bit ASNs and 4200000000 to 4294967294 for 32-bit ASNs.
The modify ASN operation is not allowed on a transit gateway with active BGP sessions. You must first delete all transit gateway attachments that have BGP configured prior to modifying the ASN on the transit gateway.
