Using Dynamips for CCIE Lab Preparation on Mac OS X

By: Josh Finke, Brian Dennis, CCIE #2210 (R&S, ISP Dial, Security, Service Provider, Voice)

Since the beginning of networking related certification one of the recurring problems that have faced candidates is getting access to hardware to familiarize themselves with how network operating systems work. Traditionally candidates have been limited to hunting for great deals on old or refurbished equipment to buy, renting equipment time from rack rental vendors, using severely limited router simulator programs, or testing configurations on live customer networks and praying that the help desk's phone doesn't ring. Today candidates now have an additional option for creating a Cisco IOS testbed, a router hardware emulation program known as “Dynamips".

Started in August of 2005 by Christophe Fillot, Dynamips is a Linux and Windows based application that is used to emulate the hardware of the Cisco 7200 and 3600 series routing platforms. Unlike traditional router “simulators" Dynamips allows you to boot real Cisco IOS software images and build complex network topologies to test the functionality of IOS on your desktop PC. As of November 2006 Dynamips currently supports Ethernet, Serial, ATM, and POS interfaces for the 7200 series routers and Ethernet, Serial, and Etherswitch modules for the 3600 series routers. Best of all Dynamips is open-source and free to download!

This brief walk through documents the steps used to set up Dynamips and Dynagen on Intel based Apple computers running Mac OS X. Our development computer is a MAC Mini, with a 2Ghz Processor, and originally equipped with 1 gig of memory, which we swapped out for 2 gigs worth of RAM from http://www.macsales.com

A new installer package for Intel Based computers running Mac OS X has been released, creating a more straight forward process. The link to download can be found here. This package contains Dynamips, Dynagen and a helpful readme that explains some basics such as file location as well as how to associate .net files with Dynagen.

After downloading the software package, follow the readme and place the Dynagen folder in your desired location. The readme will recommend Applications, which associates with the path structure laid out in Internetwork Expert's .net files.

Next you'll need a Cisco IOS software image for a 7200, 2600, 2600XM, 3600 or 3700 series router depending on which platform you will be emulating. IOS images can be downloaded from http://www.cisco.com for users with a valid service contract. Once you have downloaded the appropriate IOS image it is recommended that you extract the image to save time in the Dynamips booting process. This can be accomplished with programs such as Stuffit Expander.

Next you need to build a Dynagen .net file to provision the Dynamips emulator, or you can download prebuilt ones to emulate the Internetwork Expert Routing & Switching and Service Provider topologies from here:

Click here to download the Internetwork Expert Topologies for Dynagen

Note that these files may need minor modification to specify your working directories and the names and locations of your Cisco IOS images. Also included in the Internetwork Expert topologies for Dynagen is a router instance that is designated as a Terminal Server (Access Server). This instance can be used like a Cisco 2511 series router to reverse telnet to the console ports of the virtual Dynamips router instances, similar to how the Terminal Server is used in the CCIE Lab Exam.

To use the Terminal Server instance, note that the addresses used for the reverse telnet process are the localhost of your machine (127.0.0.1 port 2000-2011)

Now boot the Dynamips hypervisor, which can be launched using the Dynamips Server icon. Next run the appropriate .net file for Dynagen, and “start" your devices from the Dynagen command line. Once booted, the Dynamips router processes can be telneted to with any terminal emulation software such as Terminal in Mac OS X, or Z-term a popular piece of software for MAC OS X that offers tabbed terminal instances.

Note that as the number of devices you boot in Dynamips increase the processor, memory, and disk space requirements of your desktop will as well, which is largely the reason for the use of MAC OS X and it's great memory utilization capabilities.  Using the recommended Mac Mini with 2 gigs of RAM you shouldn't have any problems running the 13 devices needed assuming your idle-pc values are set correctly.

Two last steps that we would like to include are setting optimal Idle PC values, and defining a second NIC card allowing for external connections to the box running dynamips (i.e. to a real router or real switch). The Idle PC value allows for greater control over memory and processor utilization for each virtual device you boot. To obtain the optimal value, boot a device, and from the Dynagen console, type "Get Idle PC Router 1". This value can then be added to your .NET file, and will help prevent a "memory leak". For more functionality you can add a second NIC to you mac, as we did with a USB to ethernet external NIC. To add this device to Dynamips, make sure your USB adapter drivers are installed and use the "ifconfig" command in your terminal to find the device "name" and hardware address. With this information, replace the line  "# F0/0 = NIO_gen_eth:en0" in your .NET file, and make sure to uncomment the line. Make sure that Dynamips and Dynagen are run as the root user (sudo) in order to map a router's interface to a real external interface on your Mac.  If additional interfaces are needed the common solution is to use USB-to-Ethernet adapters.

Useful links for Dynamips/Dynagen:

Dynamips: http://www.ipflow.utc.fr/index.php/Cisco_7200_Simulator
Dynagen: http://dyna-gen.sourceforge.net/ or http://dynagen.org/
Dynamips/Dynagen Forum: http://7200emu.hacki.at/

Auto determination of the idle-pc values:
http://dynagen.org/tutorial.htm#_Toc176827651

Packet capture support
http://dynagen.org/tutorial.htm#_Toc176827660

Using Dynamips for CCIE Lab Preparation on a PC