Microsoft Dynamics CRM 4.0 supports IPv6. http://support.microsoft.com/kb/954313
Microsoft Dynamics CRM 2011 supports IPv6. http://technet.microsoft.com/en-us/library/gg554883.aspx
Microsoft Dynamics CRM Online requires IPv4 to connect to the Dynamics CRM application. We currently do not offer support for users connecting to the Dynamics CRM Online application from networks that exclusively use IPv6. Users can connect from networks that use both IPv4 and IPv6. We will be looking to address this need in a future update to the Online Service.