Pippin Williamson

Easily put your site into maintenance mode with this plugin so that you can perform updates. The plugin works by taking a selection of IP addresses and comparing them to the visitor’s IP address.
Users whose IP addresses match those specified in the settings page can view the site normally. Users who do not have IP access are directed either you a WordPress page (which you pick), or to any external url.
It’s extremely simple to use:
<ul>
<li>activate the plugin</li>
<li>go to the “Maintenance Mode” settings</li>
<li>check the “Enable Box”</li>
<li>enter the IP addresses that should have access</li>
<li>choose whether to redirect non-authorized users to a page or url</li>
<li>choose the page or enter the url</li>
</ul>
Once your site is ready to be made available again, simple uncheck the “Enable” box.

CGC Maintenance Mode

Good options, no check if the URL is on the same domain which causes redirect loop.



Almost there

This plugin allows you to put your site into maintenance mode, by allowing only users with specified IP addresses to view the site.

wedevpt

This plugin allows an administrator to restrict specific users to login into the wordpress only on a specific IP newtword 
This plugin needs 2 steps to work 
 – first setup the IP to filter the login under the menu “Options” -> “Limit IP Admin” 
 – second is need that you edit the user and activate the checkbox to limit the login for the specific user , inside of User edit page

CGC Maintenance Mode vs WD Limit IP Admin