In loose mode each incoming packet's source address is tested against the FIB. The packet is dropped only if the source address is not reachable via ''any'' interface on that router.{{efn|name=command}}<!--[[User:Kvng/RTH]]-->
RPF is often incorrectly definedinterpreted as reverse-path ''filtering'', particularly when it comes to unicast routing. This is an understandable misinterpretationalternate interpretation of the acronym in that when RPF is used with unicast routing as in RFC 3704, traffic is either permitted or denied based upon the RPF check passing or failing. The thought being that traffic is denied if it fails the RPF check and is therefore filtered,. howeverWhile asuRPF peris RFCused 3704as thean correct interpretation is that traffic isingress '''forwarded'filtering'' ifmechanism, it passesis the RPF check. Several examples of the proper usage can be seen in documentsaffected by [http://www.juniper.net/techpubs/software/junos/junos56/swconfig56reverse-interfaces/html/interfaces-family-config15.htmlpath Juniper], [http://www''forwarding''.cisco.com/web/about/security/intelligence/unicast<!--rpf.html Cisco], [http[User:Kvng//www.openbsd.org/faq/pf/filter.html#urpf OpenBSDRTH]], and most importantly RFC 3704 which defines the use of RPF with unicast.-->
While uRPF is used as an ingress ''filtering'' mechanism, it is affected by reverse-path ''forwarding''.
