Hope you have created a client install package with Basic content.
So by default as per product designed the clients will reachout to the internet to update the initial definitions once it is downloaded from the next time it will reach the LUA to update the definitions as per your configurations.
My suggestion is Create a package with All Content and deploy it on workstations so clients will not reach the internet for liveupdate session. it will contact ur LUA.
How to export Symantec Endpoint Protection (SEP) client install packages without any definitions or package with Basic Content.
http://www.symantec.com/docs/TECH178698
All Content: This option will have content version at the time of the deployment.
Basic Content: This option provides small client deployment packages, the definition (content) are downloaded via LiveUpdate after client installation.