Lab 15.1 on centos
the solution for lab 15.1 does not work on centos, seems like systemd is not linked against libwrap:
# systemctl --version systemd 219 +PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN
so when you start the telnet socket, telnet will be accessible despite denying all access via hosts.deny.
nevertheless xinetd uses libwrap, so starting in.telnetd via xinetd and denying all access works as expected.
just to be sure here is the content of my hosts.deny file:
all : all
sshd : ALL