Systems and methods for setting a Network Allocation Vector (NAV) in a PLC node are disclosed. In a PLC standard, coexistence is achieved by having the nodes detect a common preamble and backing off by a Coexistence InterFrame Space (cEIFS) time period to help the node to avoid interfering with the other technologies. In one embodiment, a PHY primitive is sent from the PHY to the MAC know that there has been a preamble detection. A two-level indication may be used—one indication after receiving the preamble and other indication after decoding the entire frame. The MAC sets NAV to EIFS if a native preamble is detected. The MAC sets NAV to cEIFS if only a coexistence preamble is detected or if a non-native preamble is detected.