Before attempting this configuration, please ensure that your networking devices meet the following prerequisites:
Router Requirements - The AES feature was introduced in Cisco IOS Software Release 12.2(13)T. To enable AES, your router must support IPSec and run an IOS image with "k9" long keys (the "k9" subsystem).
Hardware support for AES is also available on Cisco 2600XM, 2691, 3725, and 3745 AES acceleration VPN modules. This feature has no configuration implications and the hardware module is automatically selected if both are available.
VPN Concentrator Requirements - The software support for the AES feature was introduced in release 3.6. Hardware support is provided by the new enhanced, scalable encryption processor (SEP-E). This feature has no configuration implications.