Dear colleagues, I've been developing a tool for building and experimenting with virtual networks, primarily for use with teaching network protocols. It's an active work-in-progress, but I thought it might be time to reach out to NANOG in case anyone else might find it useful and/or might have feedback to offer. Here is the code: https://github.com/cdeccio/cougarnet It includes layer-2 switches, VLANs and trunking, and routers, all using Linux processes in their own namespaces as network "nodes". It was inspired by mininet (https://mininet.org) but it was developed from scratch to meet different needs. The README has additional information. If you install and run the code, *please* do it in a *virtual machine*. At this point, it requires superuser capabilities to run things like "ip link", "ip addr", and "sysctl", among other things, using sudo. Much on the to-do list, but it meets my immediate needs. Just wanted to share in the mean time. Cheers, Casey