Passive network latency monitoring

A method measures a resident delay for each port in a node in a network and a peer delay between each pair of neighbor nodes in the network. From these resident delays and peer delays, latency between each pair of neighbor nodes in the network is determined. The method includes weighting a route for a data packet going through the nodes in the network using the determined latencies. Each node includes a switch having switchable connections and is configured by a controller to send probe packets from an output port to a port in a neighbor node. The packet may include a time stamp and an identifier.