Source and destination addresses in IP remain consistent from the source to the destination hosts, with individual hops being coordinated at layer 2. One instance where this is important is if changes are made to these addresses during transmission, or if the source address doesn't appear to be from the right address. For example, source addresses might be changed to subvert access control lists, or to direct traffic incorrectly. This could be to allow information to leave the system (for example, by sending a request from a legitimate host, but having the return address outside the corporation), or as a means of hiding the originator's identity.