Cisco optimize

Practice Cisco router configuration using a free emulator

With a simulator, there are always missing commands and programming errors, and it can never really be as complete as the real IOS. However, because an emulator runs the IOS, you get every feature that the real IOS has.

A few months ago, I wrote "Eight ways to strengthen your Cisco networking skills," and the second suggestion I listed for improving your abilities was to use a simulator. However, while simulators are useful, there's something even better that you can get for free -- an emulator.

What's the difference? A simulator attempts to re-create the Cisco IOS using a programming language, but an emulator takes the real IOS router code, which you supply, and emulates the hardware behind it so you can run the real IOS on your PC.

With a simulator, there are always missing commands and programming errors, and it can never really be as complete as the real IOS. However, because an emulator runs the IOS, you get every feature that the real IOS has (based on the limitations of the emulated hardware, of course).

For example, if your emulated hardware has a Gig Ethernet interface, and the IOS supports a Gig Ethernet interface on that platform, then you can use the Gig Ethernet interface. If, however, your emulated hardware doesn't have a VoIP FXS card, then you wouldn't be able to configure one in the Cisco IOS, even if the IOS supported it.

What is Dynamips?

You can use the Dynamips Emulator for training purposes and testing configurations. You can create configurations and later deploy them to real routers. The Dynamips Emulator can boot IOS images from 7200, 3600, 3700, and 2600 series routers, even including the latest and greatest 12.4T IOS (something that my old 2600 router can't do because it doesn't have enough RAM).

One caveat is that you must supply the IOS for any router that you're going to emulate. It is, of course, illegal to distribute the IOS and only legal to obtain it by purchasing and downloading it from Cisco. However, if you already have a router that's one of these models, you can copy that IOS into the Dynamips Emulator for testing and training purposes.

What is Dynagen?

Dynagen is the text-based front end for the Dynamips Emulator. It allows you to automatically provision Dynamips-emulated networks. It has a large following, supported through 7200emu.hacki.at Forum for Dynamips & Dynagen.

Now, as much as I like using Dynamips and Dynagen together, their configuration can be challenging for new users to understand. However, a package called GNS3 helps make it easier.

What is the Graphical Network Simulator?

A new open source project that helps improve on Dynamips is the Graphical Network Simulator (GNS). Linked to Dynamips and Dynagen, GNS3 is available precompiled for Windows, and the source is available if you want to run it on Linux or Mac OS X.

The GNS3 Windows all-in-one installation package includes Dynamips, WinPCAP, and GNS3. Let's walk through installing and using GNS3.

First, I downloaded the GNS3 Windows all-in-one package and installed it. To install WinPCAP, I did have to reboot my PC. Once installed, I ran GNS3 from the desktop icon the installation process created.

This brought up a nice GUI interface that was similar to some of the Cisco IOS simulators I've seen. I was able to quickly create a sample network by dragging and dropping router icons and then connecting them with the Connection tool. Figure A offers a screenshot of what it looked like.

Figure A

Figure A

After creating the network, I did have to add my IOS images because GNS3 didn't provide them. To add IOS images, go to Edit | IOS Images and Hypervisors. Figure B shows a screenshot of what it looked like after I finished.

Figure B

Figure B

Next, I started the Dynamips Emulator by go to Preferences | Dynamips and clicking Test. Figure C offers a screenshot.

Figure C

Figure C

From here, I could configure the specifications for the router -- amount of RAM, Flash, cards in slots, and configuration-register. Next, to use the network, click the Emulation Mode button. Once in Emulation Mode, click the Play button to start the IOS instances of all routers. Figure D offers a screenshot.

Figure D

Figure D

This launches a console for each router, and it boots up the routers, as shown in Figure E.

Figure E

Figure E

As you can see, just like a real test lab with multiple routers, I was able to configure these two routers to communicate with each other by configuring IP addressing, enabling the interfaces, and configuring a routing protocol. Figure F shows how I configured basic RIP routing and how the router received a RIP route from the other router.

Figure F

Figure F

While I recommend building your own lab so you can get a better understanding of how it works, there are also some sample labs available when you install Dynagen. I've also seen some sample labs and an entire CCIE commercial lab workbook, all based on using Dynamips, on the Internetwork Expert Web site.

Conclusion

The ability to run multiple routers inside your PC is very useful for testing and training. It can save you the time and trouble from having to invest in a test Cisco network, and it certainly makes it more convenient. I hope that by trying and using GNS and Dynamips, you can become a better Cisco network administrator.

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42 comments
chagbert
chagbert

Great start to Cisco routing - thanks. I can easily configure my nodes. Chagbert

Dave Jong A Lock
Dave Jong A Lock

I can also add routers and send commands, but not for the one we have in our company. The cisco 1921 router. Whenever I search on google on how to add this router I end up with the 1900 switch series. Does anyone know how to get 1900 router series functionality in gns3?

steelejedi4
steelejedi4

Well i I downloaded the GNS 3 package to study for CCNP, it launches fine. I can actually configure routers 1 and sometimes router 2, the only question I have is. Why does it loose connection with the default server and never reappear? The message I get are Router 1 connection lost with 127.0.0.1:7200 Router 2 connection lost with 127.0.0.1:7200 Router 3 connection lost with 127.0.0.1:7200 I believe these are the pre-established IP and port addresses for the software, I have asked for clarification of this problem from the GNS 3 team, but I am still awaiting an answer. It does not matter how many times I uninstall and re-install it I still get the same messages when I try to run it. Anybody got any ideas out there as to how to resolve this matter?

osama79
osama79

Sounds really good. How and where do I download this from? Thanks

TheMetru
TheMetru

Can anyone asist me. my machine is freezing when i try to press the play button on GNS3, it taking for ever long to go into the simulation mode. What could be wrong? It has 1.93 Gig RAM and 160 Gig drive with 120 free space

DavidParkerCCAI
DavidParkerCCAI

Packet tracer belongs to Cisco and it's my understanding they don't like [as in sue the daylight out of] anyone who isn't in the Cisco Academy or an alumnus/a of one.

DavidParkerCCAI
DavidParkerCCAI

What is Cisco's stance on duplicating images [even though you own the machines] for purposes other than backing up the routers? I would assume it would be hard for them to sue someone who has 1 copy in storage, even though it can be accessed by a non-Cisco product. That's a big concern at the school I teach at.

udp500mo
udp500mo

When I try to download GNS3 windows complete package I receive warning from McAfee that the software (GNS3) contains potentially harmful spyware or Adware. What it in this download to cause that warning? I aborted the download to be on the safe side.

MPG187
MPG187

Do you need to get IOS Images? Where can you get them from? I have a CD that came with my Cisco CCNA book. It has Router Simulations, but only for labs. I want a simulation where I can do whatever I want and just play around, not what the lab tells me. If the images are copyrighted are there open source clones that aren't copyrighted by Cisco, but do the same thing and are legal?

madhanram
madhanram

c guide me ho config n router

sh.dileep.kr88
sh.dileep.kr88

it is a good project i thing that if all network engineer have a this knowledge that its project is very femous and develop.

Mostina
Mostina

Please try to give more imformation on each Router and Switchs,and their Configuration Tables. This is my Emial Address tupe533@yahoo.com. Thanks Freeman Blackie Cisco Student from Liberia

kenneth.cho
kenneth.cho

A new Facebook application available to you from Cisco. It is Edge Quest 2 at http://apps.facebook.com/edgequesttwo and it contains a shockwave game of the same name. The game will also be involved in a tournament with the opportunity for your users to win prizes based on how they do. The Edge Quest 2 tournament starts on Monday, February 23, 2009 and ends on Friday, March 6, 2009. Play as many times as you want to master the game ? your top score may qualify you to win! Your members can practice their skills within Facebook at http://apps.facebook.com/edgequesttwo. When time for the actual tournament, they will play the game at http://tools.cisco.com/GCT/PCTPST/game_public/EQ2/CiscoGameEQ2LandingPage.jsp. Potential prizes include ? Grand prize: US$500 gift card and a Cisco Wireless Home Audio Solution ? First prize: US$300 gift card ? Second prize: US$100 gift card Prizes will be awarded to each week's top eligible scorers.

kylemcgowan
kylemcgowan

How is this "perfect for a CCNA student" who has no access to IOS images?

daniel
daniel

I just started using this tool on my PC and MAC...very nice. The install and setup was easy. Just have your IOS image(s) and away you go. Wonderful if you cannot afford real hardware. Can be memory intensive.

biswas_sai
biswas_sai

i have downloaded the graphical network stimulator and loaded in my computer but i am not understanding how to use it and how to configure it .please give details information.

amit.k.raja
amit.k.raja

How can i get cisco IOS image to use with this emulator?

bkerwood
bkerwood

The screen shots show routers using serial connections, but GNS3 doesn't support wic modules. How was a serial connection accomplished??

James Jelinek
James Jelinek

This rocks! Free tools, especially ones that that work are always a great thing!

Exp
Exp

Thanks for the post, I will give a try. Personally, I use Packet Tracer 4.1 which is quite good except you can't do debug and couple other things.

CrimsonPaw
CrimsonPaw

I've been running this for about a month / month and a half and I've found that with 1.5GB of RAM I can run 3 routers at once, 4 if I don't mind slowdown. Once you go over that your system is garbage ... i.e. make sure you allocate enough resources for your testing. Also, I've found that on Windows you may want to go in and set the Dynamips process to Low Priority in Task Manager, this way when it hits 99% CPU utilization you can still use your PC. Other than that, the emulator does exactly what David has stated, it's an excellent tool. Also, not sure if he mentioned it, you can INTERFACE WITH YOUR REAL NIC to attach it to a real world network to test Internet functionality.

mmantei
mmantei

Of all the tips you've published, I think that this could be the most useful yet. If it does everything you say it does, it will be an indispensable tool for anyone doing work on Cisco gear.

wizard57m-cnet
wizard57m-cnet

repost in Q&A. Try re-posting in the Q&A section.The 'Discussion' forum is for matters of general discussion, not specific problems in search of a solution. The 'Water Cooler' is for non-technical discussions. You can submit a question to 'Q&A' here: http://www.techrepublic.com/forum/questions/post?tag=mantle_skin;content There are TR members who specifically seek out problems in need of a solution. Although there is some overlap between the forums, you'll find more of those members in 'Q&A' than in 'Discussions' or 'Water Cooler'. Be sure to use the voting buttons to provide your feedback. Voting a '+' does not necessarily mean that a given response contained the complete solution to your problem, but that it served to guide you toward it. This is intended to serve as an aid to those who may in the future have a problem similar to yours. If they have a ready source of reference available, perhaps won't need to repeat questions previously asked and answered. If a post did contain the solution to your problem, you can also close the question by marking the helpful post as "The Answer". . .

DavidParkerCCAI
DavidParkerCCAI

you WILL need images, but if you have cisco routers, you can upload them via tftp to a server and use that location with gns3

larrsland
larrsland

Cisco has the new packet tracer 5 and works great. I have a whole network setup right now with ip phones, fiber, printers, etc. The server modules will even do DNS, DHCP, and Web Servers. Great product.

adewalexdavid
adewalexdavid

I have been using Packet tracer , hope this will be more advanced to use. Keep it up i always enjoy your write up

LievenV
LievenV

Have you tried to calculate the idle values in GNS3? This way the routers don't consume all your resources when idling. If not, read the documentation provided with GNS3 to calculate these values.

dion2herrera
dion2herrera

hi guys, I downloaded the cisco emulator and unziped to my destop, now I need some help installing it on my pc. Do you have any installation instructions.

trustmubaiwa
trustmubaiwa

i woulding agree with you more. this is so good.

avila_mj
avila_mj

What a great tool for Network engineers..!

CrimsonPaw
CrimsonPaw

Yeah, I've run the Idle Values and put them in, but my CPU still goes up to 99%. I found it easier just to remember to lower the priority than spend time figuring out why the Idle Values aren't working (which I've posted on their message board and many other are having the same problem).

Mdallen70
Mdallen70

Hello dion2herrera, I need help also, have you figure out on how to get it configure? If so can you help me too? Thanks, Mace mdallen70@hotmail.com

ktaisia
ktaisia

It a few months on now. Are you still using the emulator and have you sorted the idle pc values problem?