Windows Server 2008 Start > Settings > Network Connections.
There is a 'Local Area Connection' network. It is a physical network adapter for Hyper-V Virtual Network.
Right click 'Local Area Connection' and select 'Properties'.
Click 'Internet Protocol Version 4(TCP/IPv4)' and select 'Properties'.
Windows Server 2008 Start > Programs > Administrative Tools > Hyper-V Manager.
Click "Virtual Network Manager..." in the right side "Actions" panel.
Select 'External' and click 'Add'.
There will have a new warning window. Click 'Yes' to apply the changes
Note:
The network may be disconnected if you use a static IP. Please re-config the 'Local Area Connection 4' as the old Local Area Connection.
Windows Server 2008 Start > Settings > Network Connections.
There is a new 'Local Area Connection 4' network. It is the External Virtual Network that has been created.
Right click 'Local Area Connection' and select 'Properties'.
There is only 'Microsoft Virtual Network Switch Protocol' enabled after installed External Virtual Network.
Right click 'Local Area Connection4' and select 'Properties'.
It will have the same settings to the Local Area Connection's old settings
Click 'Internet Protocol Version 4(TCP/IPv4)' and select 'Properties'.