Hello Vanilson
There are several things you can do to make your Telnet connection even more secure. Other than the access list, you can apply the following:
- Password protection and password policies - Use a password in the console and vty lines and set up your password policy so it only allows three failed attempts before blocking you out for a period of time.
- Use Management Plane Protection (MPP) (take a look at the lesson for more info) to restrict the interfaces via which the device permits packets from protocols such as Telnet.
- Use Control Plane Policing (CoPP) (see lesson) to ensure that the control plane of a device will not get so overwhelmed in a potential attack that Telnet traffic (and any management traffic) will not get processed correctly.
In addition to all of this, if you want to protect your communication session so that intercepted packets cannot be deciphered, it is preferable to use SSH as your management protocol.
I hope this has been helpful!
Laz