The demarc is an abbreviation of demarcation point. It refers to the point at which the ownership change from an organization to a service provider. In telephone connections, the demarcation point is at the MDF. Also, when we talk about Wide Area Network (WAN) connections the demarction point is at the Channel service unit/Data service unit (CSU/DSU). The network administrator test for network connectivity on both ends of the demarc to verify whether the problem is internal or external.