The number of gateways depends on the number of networks. Each of the applications at the networks should be reachable to a gateway over a private network. We may need to have same number of gateways as the network to configure it this way. More number of gateways may be needed for a network if different types of access( IP level, web level or client less access) are planned. We can configure the failover and load balancing by having more number of gateways sharing the same application access.