We present the details of a novel method for passive resource discovery in cluster grid environments, where resources constantly utilize internode communication. Our method offers the ability to nonintrusively identify resources that have available CPU cycles; this is critical for lowering queue wait times in large cluster grid networks. The benefits include: 1) low message complexity, which facilitates low latency in distributed networks, 2) scalability, which provides support for very large networks, and 3) low maintainability, since no additional software is needed on compute resources. Using a 50-node (multicore) test bed (DETERlab), we demonstrate the feasibility of our method with experiments utilizing TCP, UDP, and ICMP network traffic. We use a simple but powerful technique that monitors the frequency of network packets emitted from the Network Interface Card (NIC) of local resources. We observed the correlation between CPU load and the timely response of network traffic. A highly utilized CPU will have numerous, active processes which require context switching. The latency associated with numerous context switches manifests as a delay signature within the packet transmission process. Our method detects that delay signature to determine the utilization of network resources. Results show that our method can consistently and accurately identify nodes with available CPU cycles (<;70 percent CPU utilization) through analysis of existing network traffic, including network traffic that has passed through a switch (noncongested). Also, in situations where there is no existing network traffic for nodes, ICMP ping replies can be used to ascertain this resource information.