Replication monitor is the GUI tool which is introduced Windows Server 2003 Support Tools to monitor and control the AD DC replication. You can avail this either with the operating system CD or from Microsoft download centre. The Replmon graphical user interface tool was removed from Windows Server 2008 and later and it is replaced by CLI utility ‘repadmin’. More details of using repadmin is available in http://technet.microsoft.com/en-us/library/cc770963.aspx
However you can still install and use replmon in server 2008 and later by following these steps.
1.Download the replmon from the above below link.
2. Run ‘Supptools.msi’, you may need to run it with Administrative Privileges (Right-click > Run as Administrator).
3. You'll get a compatibility message, Click ‘Run Program’ to continue with installation.
4. You will have the welcome window, continue to complete the installation.
5. Once the installation is completed Open the "C:\Program Files (x86)\Support Tools" folder and locate Replmon.exe. Double-click on it to launch.
6. Right click on ‘Monitored server’ and select ‘Add monitored server’.
7. You can either select ‘Add the server explicitly by name’ which will help you to specify the server name manually or ‘Search the directory for the server to add’ this will automatically identify the directory service and list. I have preferred to go with second option.
8. On next windows select the server that you want to add to monitoring list and click ‘Finish’.
9. Repeat the above steps to add more servers to your monitors list.