Router(config-isakmp)#authentication ? pre-share Pre-Shared Key rsa-encr Rivest-Shamir-Adleman Encryption rsa-sig Rivest-Shamir-Adleman Signature
Router(config-isakmp)#encryption ? 3des Three key triple DES aes AES - Advanced Encryption Standard. des DES - Data Encryption Standard (56 bit keys).
Router(config-isakmp)#group ? 1 Diffie-Hellman group 1 2 Diffie-Hellman group 2 5 Diffie-Hellman group 5
Router(config-isakmp)#hash ? md5 Message Digest 5 sha Secure Hash Standard
Router(config-isakmp)#lifetime ? <60-86400> lifetime in seconds