Windows Firewall blocking OAB connections

I am running Exchange 2010 SP1 RU7 on a Windows 2008 R2 server. When I run the Get-OabVirtualDirectory command from and Exchange Server (I have separate CAS and Mailbox Servers) I get an unspecified error.

When I turn the Windows Firewall off on the CAS, the mailbox can then communicate the OAB updates. I have checked the CAS and all the Windows Firewall exceptions for Exchange seem to be there. I want to write an addtional one for the OAB communications but can not find what port to open.

I am sure someone ran into this and I do not want to run Exchange with the Firewall off

Thank you

Steve