Methods and apparatus for providing path characterization information relating to a network characteristic such as network congestion to nodes in a data network using data units being forwarded from a source to a destination via a plurality of nodes in the network, the method comprising: receiving, at a first proxy node, data units from a source, each data unit comprising a destination indication indicative of an intended destination; identifying, in respect of an intended destination indicated, a second proxy node in the network to which data units may be forwarded before being forwarded to the intended destination; and forwarding a first and at least one subsequent data unit from the first to the second proxy node via ‘one or more intermediate nodes; the method further comprising assigning conditions to path characterization metrics in respect of data units traversing a path across the network from the first to the second proxy node, the initial condition being dependent on information received by the first from the second proxy node.