Problems with real networks:
They do not stay still, routes change, links are upgraded, pings are blocked, hosts
go down, hosts have configurations changed, routers are misconfigured and/or
crash
Must avoid impacting production traffic, need agreement of remote administrators
and/or network folks
Many of the stacks are alpha or beta releases and are
in the kernel: kernel crashes, developer wants to add new feature, measurer
wants stability or throw out previous measurements. Some stacks were not
available in time (Westwood+, GridDT)