From Linux NFS
NetEm is a tool aimed to emulate a WAN network by means of several tunable parameters: delay, packet loss, packet reordering, packet duplication, ...
NetEm has been derived from NIST-Netby Stephen Hemminger at OSDL.
We (at Bull) have experimented with NetEm and our conclusions are that this tool is easy to put at work with fresh kernels already patched with NFSv4 from CITI and that it provides useful features for testing NFSv4 over (an emulated) WAN.
You will find more technical detailed information in the following Bull news about NetEm, which provides a How-to put NetEm at work Guide).
A NetEm GUI is available: PHPNetEmGUI.
See also the Netem section of the linux networking wiki.