Actually on the client side you want to open 5 ports (1 additional for the 
client configuration wizard).  I don't know what the other 2 ports are for 
above 7937 (nsrexecd) and 7938 (lgtomapper).  

I do know that the portmapper service (the built-in @ 111 or lgtomapper at 
7938) will map the ONC RPC program number to a particular port.  When the 
server wants to contact the client to establish a "direct" connection to the 
nsrexecd process it contacts the portmapper service to find out what port 
number the RPC packets should be sent.  

I "heard" the client ports are for: 

nsrexecd 2 (portmapper and remote execution)
client configuration wizard (1 per client config wizard running)
local host resources (1 for administering local host resources through the 
Admin window)
NDMP (1 transient port used when an NDMP filer is backed up)

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