This network lab provides an easy way to simulate complex networks. You can configure any topology of your liking in generate.rb and run it (it will probably currently complain about missing files, just create those until I cleaned it up).
You can then start a Vagrant VM (vagrant up && vagrant ssh). In there become root, switch to /vagrant/ and run the included setup.sh.
Then you can run the up.sh script. This sets up the topology described in generate.rb. Using tmuxinator start -p tmux.yaml you get a shell into every defined router as well as running bird daemons and shells into each of those (mouse-mode in tmux is enabled so you can click the panes).
When you change anything on your topology you can use CTRL-b X y to exit the tmux session, then run ./down.sh && ./up.sh to recreate the topology.
generate.rb also produces GraphViz: ruby generate.rb && cat graph.dot|dot -Tpng -o out.png && open out.png