A MANET has no fixed infrastructure, and services on the Internet might not be available in such networks. However, it is likely that nodes in an ad-hoc network in many cases want to connect to nodes on some external network, using services available there. For a widespread and successful deployment of MANETs, the ability to provide easy access to the Internet is therefore a prerequisite.
A common approach is to let a MANET node with Internet access operate as an Internet gateway and provide Internet access to other nodes in the MANET. There can naturally be several MANET nodes operating as gateways on the MANET at the same time. In OLSR, HNA messages, as explained in section 4.1, are used to announce the gateway service.