While working on a virtual pentest lab in VMWare Fusion. I had the desire of emulating a Cisco router device on a virtual network. The tool I used Dynamics did exactly that. However, it was eating up all CPU resources, making other guests almost unusable.

Below shows VMware Fusion process running in Activity Monitor:

VMware Fusion CPU


Open the Dynagen Management console dynagen /opt/config.net and run idlepc get R1 (R1 is the name of the router) which will calculate a better Idle PC Value for the current guest. This may take a few seconds and should present you with the following:

dynagen management console

As screenshot reads, select a number best suited for your system hinted by an (*). This change will apply for the current session only, meaning it will have to be set again once the program restarts.

Persistent Change

To make changes persistent, edit your configuration file e.g. /opt/config.net and include the idlepc keyword and the value calculated previously, in my case:

# Simple lab


    image = /opt/7200-images/c7200-jk9o3s-mz.124-25d.image
    npe = npe-400
    ram = 256
    # keep CPU usage below 100%.
    idlepc = 0x6079ca5c

    [[ROUTER R1]]
    f0/0 = NIO_linux_eth:eth0
    f1/0 = NIO_linux_eth:eth1

I’ll post the full workings of my virtual network architecture in the near future.