Dynamic ACL are very interesting. They provide temporary access at certain times for certain users. Basically, the user will telnet to the router. If the authentication passes, then router permits that IP to to access the internal parts of the network.
First, we need to create access-list, lets make the access
access-list 101 dynamic Mydyn permit ip any any
access-list 101 permit ip host x.x.x.x host x.x.x.x eq telnet
After that, we need to configure the vty lines to accept
line vty 0
autocommand access-enable host
lets not forget to configure the username and password.
username xxxx password xxxxx
lasty, apply the access list into the physical interface.
ip access-group 101
with that, the dynamic access list is created. As long as the session is open. when the session times out. the ACL entry will be deleted and a new authentication would be required access the protected networks by the router.