These devices only allow one active telnet connection at a time. Make sure that you log out when finished. Also, if the unit is exposed to the Internet, limit management access to trusted hosts. Configuration screen, list the trusted hosts on option 11, then enable security on option 10.
Once I preform protection switch to gain access back into the MX2800’s - (sometimes I can login/log out – for minutes, days or week before telnet locks back up). Though I have been logging out properly the system is set to log out after 15 minutes of inactivity.
The system is not exposed to the internet “Only Network within AEP”,