============
TCP WRAPPERS  [man] tcpd(8) hosts_access(5) [man]
============

/etc/hosts.allow
in.telnetd: .midominio.com

/etc/hosts.deny
in.telnetd: ALL EXCEPT LOCAL

[man] xinetd(8) xinetd.conf(5) xinetd.log(5) [man]
/etc/xinetd.conf
/etc/xinetd.d/telnet