File Portion of URL - HI Policy for Definitions

We have three SEPMs running 12.1.6 MP4 with clients mixed between 12.1.6 MP1 - 4.  We have an HI policy in place that checks that the AV defs are no more than three days old.  Currently we have it configured that if the defs are beyond three days the clients should check in with the Symantec LU servers for the latest defs.  I would like to change this to our internal LUA servers however I'm not sure what to put for the file name to download the lates definitions.  LUA is version 2.3.4.16.