From the output exhibit, we notice that the key-string of R1 is -Cisco123! (letter -C is in capital) while that of R2 is -cisco123!. This causes a mismatch in the authentication so we have to fix their key-strings. key-string [encryption-type] text-string: Configures the text string for the key. The text-string argument is alphanumeric, case-sensitive, and supports special characters.