The syntax of above command is: crypto isakmp key enc-type-digit keystring {address peer-address [mask] | ipv6 ipv6-address/ ipv6-prefix | hostname hostname} [no-xauth] The peer-address argument specifies the IP or IPv6 address of the remote peer. The syntax of above command is: crypto isakmp key enc-type-digit keystring {address peer-address [mask] | ipv6 ipv6-address/ ipv6-prefix | hostname hostname} [no-xauth] The peer-address argument specifies the IP or IPv6 address of the remote peer. Reference: The syntax of above command is: crypto isakmp key enc-type-digit keystring {address peer-address [mask] | ipv6 ipv6-address/ ipv6-prefix | hostname hostname} [no-xauth] The peer-address argument specifies the IP or IPv6 address of the remote peer.