System to detect network egress points

Described are techniques for detecting network egress points. A source device on a first network may generate a probe data with loose source route data that includes internal routing data to a designated subnet within the first network. The ultimate destination of the probe data is outside the first network. Once at the designated subnet, the probe data is handled by the egress network devices, such as a router, that services the subnet. Ultimately, the probe data may arrive at a destination device by way of a second network. The destination device determines the egress point from the first network used by the probe data. By comparing the actual route data with known egress points, known egress network devices may be confirmed and unknown egress network devices may be determined.