1.  Goto the Dynagen page and then to the Downloads
2. Select the OS X Intel Package and download the most recent DMG. As of this entry the most recent was Dyngen-0.10.1 and Dynamips-0.2.8-RC1. (Dynagen-0.10.1_Dynamips-0.2.8-RC1.DMG – Local Mirror)
3. Mount the image(this is usually done automatically upon downloading a DMG image, but browsers/settings may vary) and you will find a Dynagen Folder and an Readme file.
4. Drag the Dynagen Folder to your /Applications/ folder and open it up.
   1. Double-clicking on Dynamips Server now(after authenticating for sudo) will produce the following error “sudo: unable to execute /Applications/Dynagen/dynamips: Bad executable (or shared library)”
5. So now we need to fix Dynamips so that it will run properly. To do this we need to download a different version of the binary that has been updated to work on Leopard. It is available on 7200emu.hacki.at about the 3rd post in… (Dynamips-0.2.8-RC1-Intel-Fixed.bin for Leopard – Local Mirror)
6. In your current Dynagen folder you will find a file named dynamips with an icon like . I would suggest renaming this file to dynamips.old just in case you need it at some point. Take the second file you downloaded and move it into the /Applications/Dynagen/ folder.
7. Rename the file to dynamips and the icon should change to the , if it doesn’t use Finder’s Get Info command to unhide the extension and remove the extension.
8. Now double-click Dynamips Server and you should get a new Terminal window with:
   • Cisco Router Simulation Platform (version 0.2.8-RC1-x86)
   • Copyright (c) 2005-2007 Christophe Fillot.
   • Build date: Oct  6 2007 19:49:12
   • Hypervisor TCP control server started (port 7200).
9.  You’re done! Dynagen itself should already be working, but it is up to you to provide your own IOS images and network configuration files.

On a side-note: In the Readme file that was in the Dynagen dmg file there are additional instructions on how to associate your .net files to dynagen. I personally don’t use it and instead have a bash alias to run it from terminal directly. Also I have included a local mirror of the files not because I particularly feel like being a mirror, but rather I always find it annoying to follow instructions for files that don’t exist anymore. I highly encourage you to download the files from the individual sites themselves and leave a thank you for the developers.