Which reserved AS number or range of numbers is used for backward compatibility between old BGP
peers using 16-bit AS number and new BGP peers using 32-bit AS number?
A.
AS 65001 to 65535
B.
AS 65512 to 65535
C.
AS 12345
D.
AS 23456
E.
AS 64001
Explanation:
http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/4byte_asnios.pdf
New Reserved AS#
AS_TRANS = AS #23456
2-byte placeholder for a 4-byte AS number
Used for backward compatibility between OLD and NEW BGP speakers