How can ssh access to an AIX 7 system be restricted to the 192.168.0.1/24 subnet? 

Add the following entry to the hosts.allow file: sshd : *@192.168.0.1/24
Add the following entry to the hosts.deny file: sshd : ALL 

Add the following entry to the /etc/ssh/sshd_config file: AllowUsers *@192.168.0.* 

Set AIXPert to High Level Security
Add the AIXPertGroup xml tag in /etc/security/aixpert/core to 22
Add the AIXPertArgs xml tag in /etc/security/aixpert/core to allow=*@192.168.0.* deny=all 

Add the service filter through RBAC with mkauth id=192.168.0.* ssh