During a Maven build, you need to connect to external repositories outside your firewall. In a tight and secured environment, any outbound connection has to go through an internal proxy server. The following configuration in MAVEN_HOME/conf/settings.xml shows how to connect to an external repository via a secured proxy server:

<proxy>
  <id>internal_proxy</id>
  <active>true</active>
  <protocol>http</protocol>
  <username>proxyuser</username>
  <password>proxypass</password>
  <host>proxy.host.net</host>
  <port>80</port>
  <nonProxyHosts>local.net|some.host.com</nonProxyHosts>
</proxy>

The proxy child element must be defined under the proxies element, with the appropriate configuration. There can be multiple proxy elements, but only the first proxy element where the value is active will be picked by Maven. If you also have a corporate Maven repository deployed behind a firewall, then the corresponding hostname should be defined under the nonProxyHosts element. When Maven talks to this repository, it won't go through the proxy.