Specify a netmask for the ip addresses to pass to ./bin/pipework.
Without it, you get the following error.
$ make riak-container
./bin/start-cluster.sh
The IP address should include a netmask.
Maybe you meant 33.33.33.10/24 ?
make: *** [start-cluster] Error 1
Merge pull request #1 from hnakamur/specify_net_mask

Specify a netmask for the IP addresses passed to Pipework.