A method of routing messages includes receiving a request message from an originating device to be forwarded to one of a plurality of target devices, the request message having a first network address as a source address identifying the originating device. The first network address of the request message is dynamically mapped to a second network address of a selected target device, and the first and second network addresses are stored in association with each other as address mapping information. The method also includes forwarding the selected target device using the second network address. The routing device receives from the target device an error message in relation to the request message, and identifies the originating device which originated the request message using the address mapping information and the second network address of the target device which issued the error message.