First of all, may I welcome you to my site. My name is Chris and I'm from the UK and work as a Systems Engineer for Cisco. This blog was initially created to post up my subnetting technique but has now got more stuff to do with attaining Cisco certifications. Either way I really hope that the content is sufficent for your needs and I look forward to hearing your feedback. If you find that the content really helps you please feel free to donate using the PayPal link on the right.

To view the index of all my articles please click here.

GNS3 Configuration Guide

What is GNS3 I hear you cry? Well, imho, it is the best tool on the market to practice router configuration without having an actual router in front of you. What sets it apart is that it is a Cisco IOS emulator, not one of those nasty simulators that constrain the commands that can be used. The caveat is that you will need a Cisco IOS, for example I use the 3660 Crypto IOS. I have a support contract with Cisco so I can access an IOS however if you look around enough you will be able to find a Cisco IOS for yourself.

GNS3 is actually the graphical front-end of Dynamips/Dynagen and allows you to drag-and-drop routers onto a stage, connect them up, run IOS on them, and save their configs, just as if you had your own network. It can be a little confusing to set up first of all so I will present a step-by-step guide below of how to install and configure GNS3 including a couple of advanced options which will allow you to run Cisco Security Device Manager (SDM) on your PC.

Installation and Configuration

This process needs to be done only the once.

1. Download GNS3 from here and choose the installer which includes Dynamips, WinPCap and the binary version of GNS3 and install, accepting the various licence agreements etc.

2. You now need a Cisco IOS. Get one from Cisco if you have a CCO account with Support or find an IOS on Google.

3. Now open up GNS3.

Users of GNS3 version 0.5 will see the following:

4. Now click on Step 1.

You will see something similar to the following:

5. The executable path should point to the dynamips-wxp.exe in the Program Files directory. Change the Working Directory to a desired folder then click on the Test button. You should see that Dynamips has successfully started, if so click Apply then OK. If not you should double-check the Executable Path and the Working Directory:

6. Go back to the Setup Wizard and choose Step 2 and you should get a screen similar to below:

7. In the Settings section you need to point to the IOS image you copied in Step 2 and select the platform and model, then click on Save. The value of the IDLE PC section will be blank and leave blank for now. Now click on Close. Click on OK to close the Setup Wizard.

8. On the main screen drag a router onto the main screen then right-click on it, select Start and wait for the IOS to start and then right-click and select Console. You should now get a DOS screen open up with a telnet session for the router. NOTE: The length of time you have to wait for this to start depends on the speed and memory of your PC.

9. Say “No” to initial configuration dialog until you get to the Router> prompt. Now type enable to go into Enable mode.

10. Go back to the GNS3 session KEEPING THE CONSOLE SESSION OPEN.

11. Type idlepc get your-router-name for example idlepc get R0 and wait for some idlepc values to be displayed. Make a note of these values and click Cancel.

12. By default Dynamips will take up 100% of your CPU usage and you need to specify an idlepc value to get that changed. Close down the console session and open up Task Manager on your PC (usually CTRL-ALT-DELETE) then go to the Performance tab.

13. Go to Edit-->IOS Images and Hypervisors and select the IOS you identified in Step 4 then click on Edit. Enter the first idlepc value you wrote down from Step 12 then click on Save then Close.

14. Start the IOS again as you did in Step 8 then console to the router. View the CPU utilisation in Task Manager and see if it falls below 5%. If it stays at 100% then go back to step 14 and change the idlepc value to the next one in the list. Repeat this until you get an idlepc value that has the CPU utilisation at around 5% or less.

You have now successfully installed and configured GNS3.

Configuring a Serial Interface on a Router

By default the 3660 image that I use comes with 2 FastEthernet interfaces. In order to simulate WAN links you need to add serial interfaces to the router as outlined below.

1. Right-click on your router, choose Configure, then click on your router name.

2. Click on the slots tab and change slot 1 (or any other slot other than slot 0) to NM-4T. This will provide you with 4 serial interfaces. NOTE THAT THE SLOT NAME MAY BE DIFFERENT DEPENDING ON WHICH IOS YOU USE.

3. Click on Apply then OK.

Adding a switch module to your router

Follow the same steps as you did for configuring a serial interface but choose the NM-16ESW module from the drop-down list.

Connecting two or more routers

You will come to the point where configuring just one router is not sufficient such as when you want to run a routing protocol. The following guidelines show you how to connect routers together.

1. Drag two or more routers onto the stage and configure their slots if required. Display their hostnames by pressing the ABC button on the toolbar if they are not already displayed.

This is a personal preference and allows you to track which router is which.

2. Now click on the interface button on the toolbar and select Manual.

The interface button changes to a red cross.

Now left-click on a router and select an interface which you want a cable connected to. Now click the router to which you want to connect to and select the interface on that router for the other end of the link. You should now see the link has been drawn. Once you have finished configuring the interfaces click the interface button (red cross) to get out of interface configuration mode (the icon will revert to the telephone jack symbol). The picture below shows three routers with a FastEthernet connection and the other with a Serial link (zig-zag line).

3. Notice that each link has got a red dot on it. When you start the IOS each dot should turn to green which denotes that each router has successfully started the IOS.

Saving your configuration

After all your hard work on the command line you will probably want to save your configuration and reuse it on another day. Follow the steps below to save your work:

1. Go to File-->Save As and save your topology where you want as a .net file. When it comes to reusing this topology just double-click on the .net file to open it up in GNS3.

2. On each router save your config using copy run start

3. Back in GNS3 type save /all in the bottom half of the screen to save all of the configs into the .net file. If you want to save the config of only one router you can replace the keyword all with the name of the router you wish to save the config of. You can also extract the configs by clicking on the "Extract all start-up configs" button on the toolbar.

Configuring a host in the network (Advanced)

There may be an occasion when you want to connect a host in your topology such as running Cisco’s Security Device Manager (use of this may figure in future CCNA exams). To do this you must first configure a Loopback Adapter on your PC.

1. Go to Control Panel-->Add Hardware then click Next

2. Yes I have already connected the hardware

3. Scroll to the bottom and click on Add a new hardware device then Next

4. Install the hardware that I manually select from a list (Advanced)

5. Click on Network Adapters then Next

6. Select Microsoft as the Manufacturer then on Microsoft Loopback Adapter under Network Adapter then click Next then Next again.

7. Open up Control Panel-->Network Connections to see the adapter in place.

Now that you have created a loopback adapter you will want to connect it to a router. To do this, follow these steps:

1. In the GNS3 installation directory run the Network Device List.bat file which will give you the Ethernet address of your Loopback Adapter.

Notice the second adapter shown where description is MS Loopback Driver. I have renamed the adapter as Loopback Adapter for SDM. We are interested in the NIO_gen_eth string.

2. Go into GNS3 and drag a cloud onto the stage.

3. Right-click the cloud and select configure.

4. Choose your cloud from the list.

5. In the Generic Ethernet NIO section select your Loopback Adapter from the drop-down list (the one that matches what is shown in Step 1) and click on Add, Apply, the OK.

6. Now connect a FastEthernet port on your router to the cloud as you would connect two routers.

7. Configure an IP address and subnet mask on the router interface connected to the cloud and bring the interface up.

8. Go to Control Panel-->Network Connections and right-click your adapter. Choose Properties then Internet Protocol (TCP/IP) and give it an IP address in the same subnet as the router’s FastEthernet interface with the same subnet mask and with a default gateway matching the IP address of the router’s interface.


Router’s FastEthernet 0/0 interface connected to the cloud:

On the router I would have something like:
Router(config)#int fa0/0
Router(config-if)#ip address
Router(config-if)#no shut

On the PC I would have something like:
IP address =
Subnet Mask =
Default Gateway =

You should now be able to ping between your PC and the router

Running SDM (Advanced)

There may be a need to practice using the Cisco Security Device Manager (SDM) for your exam and the following steps show you how to configure it.

1. Download and install SDM from the www.cisco.com or from a share on the web.

2. Choose to only install SDM to your PC, NOT to the router.

3. Now configure your router with a hostname and a domain name in order for SSH to work:

Router#conf t
Router(config)#hostname SDMRouter
SDMRouter(config)#ip domain-name SDMDomain

4. Now configure your router with the following commands:

SDMRouter(config)#username your_username privilege 15 secret 5
SDMRouter(config)#ip http server
SDMRouter(config)#ip http secure-server
SDMRouter(config)#ip http authentication local
SDMRouter(config)#line vty 0 4
SDMRouter(config-line)#login local
SDMRouter(config-line)#transport input telnet ssh
SDMRouter(config-line)#privilege level 15
SDMRouter(config-line)#line cons 0
SDMRouter(config-line)#login local
SDMRouter(config-line)#transport input telnet ssh
SDMRouter(config-line)#privilege level 15
SDMRouter(config)#crypto key generate rsa gen mod 1024

5. Now double-click the SDM icon and enter the IP address of the router and tick the box asking about HTTPS then click on Launch.

6. Ensure you allow popups on your browser.

7. Enter username and password as defined after step 3.

8. Say yes to allow SDM to install.

You should now have a screen similar to the one below although this may be because I used a username and password of “cisco” which are the default.

9. Select a new username and password for the router then click OK. You should see the screen below then click OK.

10. You should now be in SDM and able to configure the router.

Posted byChris Bloomfield at 09:11  


Brad said... 16 January 2008 at 04:07  

Can I just say, I am absolutely in LOVE with you and this blog right now. I was going to actually buy some lame ass simulator software or buy a bunch of cisco equipment to prepare for my CCNA. I kept thinking to myself, if only there was a better way...

Thanks so much for not only the tip, but the detailed tutorial on how to setup and actually use GNS3. This is completely invaluable information.

fayda said... 16 January 2008 at 21:05  

Hi, just tested it.
It's very incredible, perfect.
Good work, if yoy have some tips for ccna please post.
I use gns3 and dynamips

Chris Bloomfield said... 20 January 2008 at 14:36  

Hey, glad to be of help :-)

Christopher Mark said... 18 February 2008 at 02:32  

This is awesome...I'm just wondrin if a similar software exist for Catalist Switch simulation, cause GNS3 does not allow me perform switch configuration...

Wireless said... 29 February 2008 at 05:25  

Hey where can i get that ISO Image files? Can you help me?? Because i can't find them??

Chris Bloomfield said... 29 February 2008 at 08:40  

Unfortunately there is nothing for Cat switches. You can do basic switch configuration using a switch module in the 3660.

To get an IOS try going to www.sadikhov.com/forum and check the shares section.

Anto said... 16 March 2008 at 17:40  

i have tried your good tutorial.. But when i start emulation mode, it has error which say "could not connect to server". I also have searched this problem in 7200emu.hacki.at, and i tried its solution.. but i still have a same problem.. I dont know why... can you tell me which part i am wrong... Thank u for ur help...

For your information i use this IOS : c7200-adventerprisek9-mz.124-9.T1.bin

Chris Bloomfield said... 18 March 2008 at 12:42  

The only suggestion I would make is to ensure that you are pointing to the correct location of Dynamips in Program Files and that your working directory actually exists.

Anto said... 19 March 2008 at 15:00  

When i test my Dynamips, it is working... But when i try in emulation mode, it says " could not connect to server"... :(...

Veeral said... 5 April 2008 at 12:19  

How can i acces command line for switch configuration. I would like to create VLAN, assign IP etc on switch using command line. GNS3 includes lot of router specific feature but has limited features with regards to switchs. Is that right or am i missing something here.

thanks for your help in advance.


Chris Bloomfield said... 5 April 2008 at 18:36  

GNS3 is a router emulator only so the switches built into it can only be configured by right-clicking on it and configuring it from there.

You can use a router with a switch module and assign VLANs from there if you wish.

sakal-woman said... 7 April 2008 at 05:13  

Hi Chris,

Thanks a lot with this guide. I have tried configuring a host in the network, the cloud connected to a router,but the host can only ping to router and not the router to the host. I have followed all your steps. Thanks

Chris Bloomfield said... 7 April 2008 at 08:36  

Hello sakal_woman a fellow Sadkhovian! A few things I can think of:

1. I've heard that Vista is decidely dodgy when it comes to Loopback Adapters.

2. Have you turned off your firewall as it may be blocking inbound ICMP?

sakal-woman said... 8 April 2008 at 17:25  

Hi Chris,
Thanks your reply. I have managed to get it right this time. Not quite sure what was the reason, tried many times till it worked. I didn't use XP and my firewall was disabled. too bad can't do much with switches.. :-) visited that forum almost every day.

wave said... 15 April 2008 at 01:04  

Great blog...buddy. I really appreciate your info on GNS3 and your tips with subnetting

Adriano said... 16 April 2008 at 19:32  

Hi Chris !!
Could you please help me with the technique of saving configuration.. necause i am getting this error in GNS3 v0.4Beta

Please Help me !!

=> save /all
*** Error: cannot find server section for device: R0
local variable 'serverSection' referenced before assignment

Chris Bloomfield said... 17 April 2008 at 08:19  

Have you seen the code at http://code.gns3.net/gns3-devel/file/3c21438d91c6/src/GNS3/Dynagen/console.py

The text you're looking for is:

# Find the config section for this device

627 if netfile.has_key(host + ":" + str(port)):

628 serverSection = host + ":" + str(port)

629 elif netfile.has_key(host):

630 serverSection = host

631 else:

632 error('cannot find server section for device: ' + device.name)

You did save the config on each router (e.g. wr mem or copy run start)?

Adriano said... 18 April 2008 at 16:52  

Thankz fr d help, actually i didnot save the configuration on each router hence i was facing a problem :)

Zey said... 15 May 2008 at 14:55  

This information is so useful yet simple. I'm able to run SDM with GNS3 now! Time for more practices!

Jacob said... 30 May 2008 at 00:09  

Thanks so much Chris for GNS3. i had problem with my sdm. When i try to launch sdm from desktop I am getting error message. The ip address is of router or http/https not enabled.

But i did the configuration exacltly as your configuration. I can ping from pc to router on the ip address what i am trying to login. Please help me what is the problem. Why i am not able to connect thru SDM launch button.

If i type ip address on IE it works but I have few options not GUI.

lunatichead said... 5 July 2008 at 03:24  

Well just started with CCNA studies and trying to get GNS3 working now, iam must say iam really thankful to u and a lot of Sadikovians for sharing their knowledge. hopefully all my quires will be anserd from here as well... Chris u are a great help

nyon said... 23 July 2008 at 00:05  

i´m using a router with a NM-16ESW slot to work like a switch, but my IOS doesnt have some switch cmds, like VTP mode, etc, is there a IOS that has a least more switch commands available?


Chris Bloomfield said... 23 July 2008 at 19:19  

Have you gone into vlan database from privileged exec mode?


Router#vlan database

You should find everything you need there.

Better still you would be advised to download c3725-adventerprisek9-mz.124-19b.bin
as that supports the VLAN commands in conf t, not vlan database as this is deprecated.


Erik said... 17 August 2008 at 02:57  

I must mirror what everyone else has said! This is absolutely STUPENDOUS! I thank you so very much for your time and effort in putting this blog together.


Pravee said... 13 October 2008 at 19:38  

Excellent procedure document Chris,

i am stuck in while adding loopback interface, i am running on Vista (i tried switching off my firewall as well no luck)

i am getting below mentioned error when i run network device list.cmd

c:\Program Files\GNS3>"Network device list.cmd"

Network adapters on this machine:

Unable to create lock file "c7200_i0_lock".
VM default: unable to create instance!
C7200: unable to create instance!

Use as follows:
F0/0 = NIO_gen_eth:\Device\NPF_{...}

Press any key to continue . . .

c:\Program Files\GNS3>

Anonymous said... 19 October 2008 at 13:53  

ERROR Unable to create lock file “c7200_i0_lock”

Problem npf driver for winpcap isn't running on VISTA
START->RUN: msinfo32
Go to Software Enviroment -> System Drivers and look for NPF if it's not started this is the problem.

Now u need to start the service:

1.START->RUN: regedid
2.Go to:computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NPF
3.Change Start VAlue to 2 (=AUTO)
4.Reboot Windows

All should be ok. U can run now "Network device list.cmd"


Anonymous said... 19 October 2008 at 13:54  


Anonymous said... 19 October 2008 at 13:55  


bonfission said... 11 November 2008 at 19:19  

Hi Constantin, I read your post on about installing sdm on windows vista.I have tried your approach to resolve the issue, but I still get this error message...
"ERROR Unable to create lock file “c7200_i0_lock".
VM default:unable to create instance!
C7200:Unable to create instance!"
...when I run the "Network device list.cmd" from Gns3.
I have checked the System Drivers and Nfs is running and its set to auto.
Please can you advise on how to resolve this.

repdetect2 said... 13 November 2008 at 02:19  

Awesome tutorial. I think the only thing you can't do for me is take my CCNA :) Keep up the good work, you have fans :)

Chris Bloomfield said... 20 November 2008 at 08:59  

Many thanks all. Sorry I haven't been around for a while - a few home issues to tend to.

I hope your problems are resolved.

sibaram said... 9 December 2008 at 10:57  


I have installed GNS3-0.5-win32 all in one exe file in My winxp system. Now when I am going to telnet the routers I am getting the error 'the system can not find the file specified."

Vipin Kumar said... 7 January 2009 at 17:44  

Hi Chris,
I am facing problem in running loopback adapter. I have tried all the solutions provided by you over here but all the hard work gone waste. I am running vista home operating system. Kindly help me to run SDM on my laptop.

Chris Bloomfield said... 7 January 2009 at 18:35  

Hi Sibaram,

Sounds as if you are running Vista which doesn't have the telnet client installed by default.

1. Click Start then select Control Panel.

2. Select Programs and Features.

3. Select Turn Windows features on or off.

4. Select the Telnet Client option.

5. Click OK.

6. A dialog box will appear to confirm installation. The telnet command should now be available.


Chris Bloomfield said... 7 January 2009 at 18:37  

Hi Vipin,

Now I'm no Vista man and I know that there have been problems in installing loopback adapters on it. Have you tried the following?

Download the DevCon compressed file, and then extract the files:
a. Visit the following Microsoft Web site for download: http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q311272
b. Save the Devcon.exe file to a folder on your computer, and then open the folder.
c. Double-click Devcon.exe.
d. In the Unzip to path box, type the folder where you want to unzip the files, and then click Unzip.
e. Click OK, and then Close to complete the unzip process.

2. Install the Microsoft Loopback Adapter:
a. At a command prompt, change directory to the folder where you extracted the DevCon files.
b. Change directory to the i386 folder.
c. Type devcon.exe install %windir%\inf\netloop.inf *msloop, and then press ENTER. You see output that is similar to the following:
Device node created. Install is complete when drivers are updated...
Updating drivers for *msloop from C:\WINDOWS\inf\netloop.inf.
Drivers updated successfully.

Vipin Kumar said... 7 January 2009 at 20:34  

Thanks Chris,
I found out another way to solve my problem. Finally it is solved.

Unable to create lock file "c7200_i0_lock".
VM default: unable to create instance!
C7200: unable to create instance!

Use as follows:
F0/0 = NIO_gen_eth:\Device\NPF_{...}

start => run => msconfig
disable user account control .... restart ...

swati said... 25 January 2009 at 05:42  

hey...i have vista installed on my system.... and i have enabled tyelnet client also...but it is still giving me error"the file specified cannot be found"...when i try to telnet to the router

acem@tty said... 19 February 2009 at 04:35  
This comment has been removed by the author.
acem@tty said... 19 February 2009 at 04:42  

Hi, I have tried all idlepc value as in the guide...still not able to bring down cpu utilization to 5% or less....I am doing this with single C3700...can u help pls?

Chris Bloomfield said... 19 February 2009 at 19:25  


Assuming you're using the latest GNS3 just right-click on the router and select idlepc. It will then calculate a new one for you.

Failing that you can always go to the menu and choose Edit-->IOS Images and Hypervisors then select your IOS and delete the idlepc value and choose Save.


Peter Chin said... 25 March 2009 at 11:52  

"Network adapters on this machine:

Unable to create lock file "c7200_i0_lock".
VM default: unable to create instance!
C7200: unable to create instance! "

For the network device list issue for vista can be solved by 'Turn User Account Control Off" under User Accounts under Control Panel.

It works for me. Let me know if it works for you all by email to me peterchin_oukl29@yahoo.com,

or add me to msn messenger using the same email address for group study.

chand72 said... 29 March 2009 at 06:13  

hi i am a newbie,i just followed accordingly but when i right-click on the router to start , i dont see any session starting..waited long enough. test dynamips is working.

Peter Chin said... 2 April 2009 at 16:37  


After u start the router, u just try to right click the router again and select console.



h77 said... 16 April 2009 at 00:09  

hi chris,

i added my ios images but i could not start any ios on gns3. the ios images i found on internet was .bin files. Am i supposed to add them the way they are or what? if i need to uncompress ..how?


jel220 said... 6 May 2009 at 00:49  

Hey hello, exellent blog
I need your help
I´ve had this problem with diferent exercises, i was configuring my router to support SDM, i could configure it correctly, and could access to SDM (i didn´t change the configuration with SDM), so i saved the running conf in star-up, and i saved the project, but when i opened that project everithing seemed to be normal but i telnet the router and you know what happened (the last screen),

so i can tellyou i dont have problem configuring the router o running the emulation , the problem is only when i save and i open the project and try to telnet the routers

I´ve tried with differents IOS, with different RAM values, with xp and vista

net file:

autostart = False
workingdir = C:\Documents and Settings\Administrador\Escritorio\GNS3\working
udp = 10000
image = C:\Documents and Settings\Administrador\Escritorio\GNS3\IOS\c1700-adventerprisek9-mz.124-19.bin
ram = 96
ghostios = True
idlepc = 0x8064047c
chassis = 1710
model = 1710
console = 2001
f0 = nio_gen_eth:\device\npf_{e07352d9-000e-4dfa-80f9-3e92de3f47a6}
x = -108.0
y = -4.0
[[Cloud C0]]
x = -24.5
y = -87.0
connections = R4:f0:nio_gen_eth:\device\npf_{e07352d9-000e-4dfa-80f9-3e92de3f47a6}

Thanks in advance

jel220 said... 6 May 2009 at 00:53  

Im sorry, when i try to telnet a router after saving and openins again the screen is like this:

##### [OK]


Chris Bloomfield said... 17 May 2009 at 20:51  

It looks as though you may not have unchecked the box which cleans the working directory after closing the program. Try unchecking that and see if that works. Have you also decompressed your IOS? If not use WinRAR and right-click the IOS and Extract and use the decompressed IOS for your needs. This will save on processing at router start-up.

susheel said... 11 June 2009 at 01:35  

hi, its a very good blog and it has provided the steps in a systematic way.thanks for that.

i need some help in running the gns3.
Things work fine till i click on console.wat i get is "connected to dynamips vm...... console port.

nuthing after that.i tried to get info from various websites bu nuthing till now.help me in this regard.u can also mail to raisushkr@gmail.com.thank you. i vl b waiting for ur reply here also

Chris Bloomfield said... 11 June 2009 at 20:51  

Hi Susheel,

This may sound a little basic but have you hit the Enter key when you get to that point?


surnar said... 12 June 2009 at 14:04  


Going thru the GNS3 documentation and Blindhog videos It seems pretty simple to connect a loopback interface of the PC via a cloud to a router in GNS3 and be able to ping a host on the internet from the router.

from GNS3
- my pc - ok
- default gateway - ok
- any outside network - failed

Disabled my firewall and antivirus

Do not know where I am messing up. Will be grateful for any help.

I am posting
1 .net file of the topology
2. router sh run config
3. output of ipconfig /all
4. pings from the router to the pc & internet
5. pings from the pc to the router & internet

Thank you.

autostart = False
workingdir = D:\GNS3\TEMP
udp = 10000
chassis = 3660
image = D:\IOS\ios-c3660\unzip-c3660-ik9o3s-mz.124-18.BIN
ram = 192
ghostios = True
sparsemem = True
idlepc = 0x606c1968
model = 3660
ghostios = False
console = 2000
f0/0 = nio_gen_eth:\device\npf_{cd0549f9-e871-4d47-a9a4-a856d6b5f7bf}
x = -200.0
y = -82.0
model = 3660
console = 2001
x = 36.0
y = -85.0
[[Cloud C0]]
x = -125.5
y = 8.0
connections = R0:f0/0:nio_gen_eth:\device\npf_{cd0549f9-e871-4d47-a9a4-a856d6b5f7bf}

hostname router
interface FastEthernet0/0
ip address
duplex auto
speed auto
ip default-gateway
ip route FastEthernet0/0


Adaptador Ethernet Puente de red :

Sufijo de conexión específica DNS :
Descripción. . . . . . . . . . . : Puente minipuerto MAC #2
Dirección física. . . . . . . . . : 02-00-4C-4F-4F-50
DHCP habilitado. . . . . . . . . : No
Dirección IP. . . . . . . . . . . :
Máscara de subred . . . . . . . . :
Puerta de enlace predeterminada :
Servidores DNS . . . . . . . . . .:


Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5),

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 0 percent (0/5)

Haciendo ping a con 32 bytes de datos:

Respuesta desde bytes=32 tiempo<1m TTL=254
Respuesta desde bytes=32 tiempo<1m TTL=254
Respuesta desde bytes=32 tiempo<1m TTL=254
Respuesta desde bytes=32 tiempo<1m TTL=254

Estadísticas de ping para
Paquetes: enviados = 4, recibidos = 4, perdidos = 0
(0% perdidos),


Haciendo ping a con 32 bytes de datos:

Respuesta desde bytes=32 tiempo=23ms TTL=255
Respuesta desde bytes=32 tiempo=15ms TTL=255
Respuesta desde bytes=32 tiempo=19ms TTL=255
Respuesta desde bytes=32 tiempo=26ms TTL=255

Estadísticas de ping para
Paquetes: enviados = 4, recibidos = 4, perdidos = 0
(0% perdidos),


Haciendo ping a con 32 bytes de datos:

Respuesta desde bytes=32 tiempo=1330ms TTL=237
Respuesta desde bytes=32 tiempo=1540ms TTL=237
Respuesta desde bytes=32 tiempo=1559ms TTL=237
Respuesta desde bytes=32 tiempo=1584ms TTL=237

Estadísticas de ping para
Paquetes: enviados = 4, recibidos = 4, perdidos = 0
(0% perdidos),

Chris Bloomfield said... 21 June 2009 at 20:49  

Have you tried enabling DHCP on your router's interface?

Rocky said... 6 July 2009 at 16:45  

Hey Chris, great work with the GNS support, specially the loopback adapter, that the coolest thing.. it is like you actually working on a router hardware from your system.. thank you so much for the step by step instructions.... I had a issues with generating the crypto keys.. i dont know why , but i dont have a option for that at all, tried 2691 , 3600, 7200 , but no luck, could u please help me in this, i am trying to get SSH and some SDM practicals...

Chris Bloomfield said... 6 July 2009 at 19:40  

Hey Rocky,

Sounds to me as though you don't have the correct IOS. Does it have "k9" in the name?



Rocky said... 7 July 2009 at 03:47  

Chrisssssss..THANK YOU SO MUCH BUDDY.. wow, this is great, so finally i can have hands on SDM .. simply great.....I am just entering the world of networking, taking my ccent this friday, and this stuff that you have out here is so fascinating .... love it....could you help me with last minutes advices on taking the ccent ...

mohamed said... 25 July 2009 at 06:09  

Hi Chris, as per your instruction I installed the GNS3 and reached to step 8. Drag the router to main screen, started the router(it is showing green in the topology summary pane). But when I go to console screen I am not getting the router console, it is showing " Connected to Dynamips VM "R0" (ID 0, type c3725) - Console port "
Kindly help as I am preparing for CCNA.

Chris Bloomfield said... 25 July 2009 at 10:41  

Hi Mohamed,

The things that spring to mind are:

1. Have you decompressed your IOS?
2. Have you hit the Enter button a few times as sometimes it remains idle until user input?


mohamed said... 27 July 2009 at 17:23  

Thanks Chris,

I changed the ios image file and it works fine.
Will there be any question about SDM in CCNA?

Thanks for every one who is helping others to become certified.

Chris Bloomfield said... 27 July 2009 at 22:02  

Glad it works for you. Unfortunately I am not fully au fait with the contents of the CCNA exam but if you are learning about it in the CCNA text then there is a likelihood that you will see a question on it.

Good luck!

btsomogyi said... 28 July 2009 at 15:54  

I don't know if this is common knowledge, but I was interested in running LMS & CSM against a GNS3 environment, but didn't have enough memory on one box for the apps and routers. By setting up GNS3 on a Win2K3 VM, setting up the loopback/cloud interface, then turning on IP routing under RRAS and entering some static routes, I am able to access the GNS3 routers from external hosts (such as the CSM & LMS machines). This has been a real boon in testing out proposed network topologies without committing to hardware.

Freeman said... 24 September 2009 at 18:21  

Hello Chris,

Thank you for your help.
for me, everything worked until step 7 after that, in the telnet console it says "connected to Dynamips VM "R1"......" and its not going any further at all. Please help me.


wafae said... 19 July 2010 at 14:57  

your article is very intersting but i still have some questions could you help me please? here are my questions:
what is the differnce between std and vxr?
what are the NPE drivers for c7200, and which one works?
i installed gns3 on a PC which has 2G, and i want to use the capacity of an other PC(that the both Pc could support the gns3)using the network cloud. HOW?
i wait for your help.
thank you

utkarsh said... 16 September 2010 at 22:16  

Though I am not going to say anything unique here but nonetheless, its out of gratitude that I am bound to say heartfelt THANKYOU for putting up such an in-depth blog for the first timers like me.
I would also like to thank invaluable inputs from the fellow users for providing the solutions of the problems they had faced while setting up GNS3.
Its because all of you that I was able to setup n configure GNS3 with SDM on my Windows 7 like a charm, coz for every problem I found the solution right here..!!
Now I am all set to go dirty with it.. :-)
Keep it up people..spread the knowledge..!!

utkarsh said... 16 September 2010 at 22:17  

Though I am not going to say anything unique here but nonetheless, its out of gratitude that I am bound to say heartfelt THANKYOU for putting up such an in-depth blog for the first timers like me.
I would also like to thank invaluable inputs from the fellow users for providing the solutions of the problems they had faced while setting up GNS3.
Its because all of you that I was able to setup n configure GNS3 with SDM on my Windows 7 like a charm, coz for every problem I found the solution right here..!!
Now I am all set to go dirty with it.. :-)
Keep it up people..spread the knowledge..!!

_Utkarsh, India

utkarsh said... 18 September 2010 at 10:30  

Okay seems I have a bit of problem.So I am looking forward towards the HELP.Here's what's causing the trouble :

1.I have configured the cloud and loopback adapter(as explained very clearly by Chris) and able to ping between the PC and the router..all works fine.But once I turn off my computer and get back to my saved topology the next time, the loopback adapter don't seem to identify the network already saved and I am not able to ping between the PC and the router.I tried uninstalling and reinstalling the loopback adapter, as if setting up for the first time, every time I turn on my computer to use that topology again and it works..but its quite a pain to do that.Is there any workaround for it?

2.My next question is somewhat trivial..Since I also have a NIC installed which I use it to connect to the internet and it obviously uses a default gateway which is different from what I have configured my loopback adapter with, for playing around in GNS3.The problem that I have is that while I am using GNS3, if I have to lookup something on the internet some websites won't come up, esp.google. I am assuming this is because of two different gateways(of my NIC and loopback adapter) and it creates some confusion for PC as to where to route the packets..am I correct??
I can always disable the loopback to get on to the internet but it would be helpful if anyone can provide me a solution to this as well.

Mauro said... 20 December 2010 at 20:43  

Hi all.
Do you know how to change the DCE/DTE on Routers or FRWS? thanks a lot. Mauro.

Chris Bloomfield said... 28 December 2010 at 19:28  

Have you seen this? https://learningnetwork.cisco.com/message/25917

Jaky Mix said... 13 April 2011 at 06:14  

Hi Chris

Great work indeed. Now I would to know if it's possible to use NMS tools, such LMS, EMC Smarts to manage GNS3 simulation?

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