Interactive Connectivity Establishment (ICE) /RFC 5245/ has not yet widely implemented although it is an exciting protocol. It is the only ultimate solution to overcome NAT traversal problem and much more. It is using STUN /RFC 5389/ for the negotiation and TURN /RFC 5766/ for the relay. It helps to negotiate what kind of communication connections could be established between the parties who want to establish new communication connections. This technique helps to overcome the Network Address Translation (NAT) and other Firewall issues. Furthermore it helps to negotiate between endpoints that are able to communicate on different or multiple IP protocol (IPv4 only, IPv6 only, dual-stack IPv4/IPv6). In my presentation I will explain how this protocol is working. This presentation is for experts only, and deep knowledge in the Real-Time Communication area is required to understand it.