ETRI ETRI DONG-EUI Univ. This document includes an analysis of multiple interfaces in a host and a description of scenarios of multiple interfaces with the respect of the relationship between layer 2 connection and layer 3 connection. The current TCP/IP mechanism and networking methods are suitable for single network interface. When a host has multiple interfaces, the current TCP/IP mechanism and networking methods cannot directly be used for them. A network interface establishes layer 2 connection to layer 2 entity (e.g., WLAN Access Point) and it does not mean providing proper layer 3 connection. So every active network interfaces do not guarantee successful IP layer operations. In this document, we describe some problems for a host which has multiple interfaces as an aspect of host's operations and usage scenarios of multiple interfaces in a host.