If you are trying to run many linux machines at a time it can become difficult to keep them in sync. One solution that many use is to mirror the repository(s) to a local network to save on internet bandwidth. While this is a solution it does require a lot of setting up, uses a lot of valuable space, takes a lot of time for the initial download and requires you to store programs that your machines will probably never use.
There is a lot quicker way that only requires you to store what you use, uses less hard disk space and reduces the internet load. It involves using NFS to share the apt cache among your linux machines. Here's how to set it up.