This may be of interest to some here...additions to the contiki code has allowed a 6LoWPAN RPL mesh to be formed by a border router that runs within cygwin on the Windows host. Formerly the Raven USB stick or other RF device had to implement the border router which limits the size of and access to the routing tables. With the border router running on the host the stick can just use its original build as a RNDIS to 6LoWPAN bridge.
Debugging is much easier since the RPL traffic appears on the RNDIS interface; no need for an 802.15.4 sniffer to see it. Additionally the host has rapid access to the routing tables.
Details are at http://www.sics.se/contiki/wiki/index.php/A_RPL_network_on_the_minimal-net_platform. Basically it uses two wpcap tees to connect to two interfaces, ethernet for the host traffic and RNDIS for the RPL traffic. Intermediate and end nodes can be emulated on the host as well, and share the RPL DAG with RF motes.
Probably something similar would work on *nix if pcap were used to connect to the two interfaces. Right now the *nix version uses a tun0 bridge to ethernet only.