有个单机环境限制ssh登录，有多种方式，这里选择了配置hosts.allow和hosts.deny
root@db \~# more /etc/hosts.allow
hosts.allow This file contains access rules which are used to
allow or deny connections to network services that
either use the tcp_wrappers library or that have been
started through a tcp_wrappers-enabled xinetd.
See 'man 5 hosts_options' and 'man 5 hosts_access'
for information on rule syntax.
See 'man tcpd' for information on tcp_wrappers
sshd:172.100.100.56:allow
sshd:172.100.100.57:allow
sshd:172.100.100.42:allow
sshd:172.100.100.43:allow
sshd:172.100.100.46:allow
root@db \~# cat /etc/hosts.deny
hosts.deny This file contains access rules which are used to
deny connections to network services that either use
the tcp_wrappers library or that have been
started through a tcp_wrappers-enabled xinetd.
The rules in this file can also be set up in
/etc/hosts.allow with a 'deny' option instead.
See 'man 5 hosts_options' and 'man 5 hosts_access'
for information on rule syntax.
See 'man tcpd' for information on tcp_wrappers
sshd:all:deny
root@db \~#