The allowed hosts list is a list of IP addresses that are permitted to initiate a Debugger session on the Web server on which Zend Server is installed.
The default value for zend_debugger.allow_hosts intentionally covers a wide range of IP addresses. This is to make the initial installation of Zend Server
compatible for a large selection of environments.
However, this also can be a security risk, as you are permitting a wide range of IP addresses to access your Web server. Therefore, we recommend that you limit accessibility and create a secure environment by only using specific hosts (full IP address) recognized by you that you are sure you want to permit to connect.
To change this value in the Administration Interface, go to Server Setup | Debugger, remove all the IP range settings and set the specific IP's that you permit to connect to Zend Server .
Depending on if you are working on a development or production environment, you may want to consider different defaults.
In development environments, all the machines that require access to debug should be allowed. In production environments, it is safer to limit access or even allocate a single machine to allow access. Not only will this make your environment more secure, it may also help limit and prevent unnecessary traffic on your production server