Domain and Forest functional level

Hi,

Can keep Forest functional level 2003 and domain functional level 2008 R2?

Also Can I set Parent domain FFL 2003 and Child Domain DFL 2008 R2 ? If yes how can and what can be impact on other applications?

Also I have in same forest, existing 2 tree which are running on windows 2003 DCs with DFL 2003 and have Forest, external trust, parent -child trust and tree root trust.



Is there any impact on to increase DFL 2008 R2 and keep FFL 2008 on Trust part and application part?