To restrict access to the router to only administrators from the subnet 10.10.10.0/24 and ensure that a secure protocol is used, the configuration should include an access control list (ACL) that specifies the allowed subnet and applies it to the vty lines. Additionally, it should specify the use of a secure protocol like SSH for remote access. Here's an example configuration:
access-list 10 permit 10.10.10.0 0.0.0.255
line vty 0 4
login local
transport input ssh
access-class 10 in
This configuration creates an ACL that permits only the 10.10.10.0/24 subnet and applies it to the vty lines, which are used for remote access to the router. It also specifies that only SSH is allowed as the input transport protocol for these lines, ensuring secure communication.