Time Machine backup on network

step 1. In the terminal enter the following:
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

step 2. Create what is called a sparse bundle on your mac(this is like a container for a virtual disk):
sudo hdiutil create -size 495g -type SPARSEBUNDLE -nospotlight -volname "mbp" -fs HFS+J -verbose ~/Desktop/mbpname_macaddresswithoutdividers.sparsebundle -imagekey sparse-band-size=131072

size = size in gigs
volname = the name of the volume in the sparse bundle
macaddresswithoutdividers = the mac address for the mac (eg 0023def4 etc)
The sparsebundle will be 200-300 meg

step 3. Copy sparsebundle over to network share.

step 4. open time machine and point it to wherever you put the sparse bundle

step 5. ?? (included for tradition's sake)

step 6. wait for the first backup to complete

Tip:
if you try starting time machine without the sparse bundle after the first step it will create the file name you need to use in the sparse bundle creation line similar to mycomputername_00023023d3.tmp.sparsebundle while it is working. Remove the "tmp" and you have the correct sparsebundle file name

Known issue:
If you put your machine to sleep or turn it off during a time machine backup the backup will be unrecoverable