When deploying uPortal at your organization you will likely want to insulate your local build process from having to access external resources. The primary external service access issue with Maven is dependency retrieval from Maven repositories on the internet. There are several free Maven caching proxy solutions that can be used for both local caches of these public repositories as well as hosting your own repository if you need a place to put locally developed artifacts. A caching proxy mitigates the effects of one of these public Maven servers being down as well as speeding up your local builds.
Caching Proxies
The following are some of the freely available Maven 2 proxies.