MANET (Mobile ad-hoc network) mitigates the requirement of common control or access point for forming a transient network. The extensive growth of wired and wireless devices due to rapid enhancement in technology has led to more emphasis on this network. The tremendous use of mobile devices by the users forms temporary connection between mobile devices which form MANET. This network is although very effective in the sense that it does not need any prior infrastructure but it has limitation too like low bandwidth, frequent disconnection , limited features and low battery problem. MANET also allows internet connection with the help of Internet Gateways .These Gateways are bridge between infrastructure based and MANET based network. Several mechanisms had been proposed for the Gateway Discovery in ad-hoc network. This paper tries to analyze several Gateway discovery mechanism proposed earlier and gives a critical evaluation of those technique. The survey concludes with future scope in this area.