Network simulator

I would like to clone a network environment that exists at our work place. Our network has a Domain, 3 VLANs, 3 manageable HP switches, VMware and standard servers that are running server 2003, Exchange. We also have FTP Linux server (which I don’t know much about at this stage), 2 firewalls, email appliance and web appliance (proxy). I have OK understanding of the way everything works, however; not enough for me to feel very comfortable in case something goes wrong. I want to be able to make changes to reinforce my knowledge or improve things without touching a live network.
Is there a simulator or other software (free would be nice) that I can use to clone our network?
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I don't think so.  It's too big and would almost exactly resemble the real thing.  You can't really "simulate" Windows, if you want to be able to make changes etc.  The best you can do is make Virtual Machines of it all, using something like VMWare Converter, and then set it up on a big virtual server that can run all those VMs.  Of course, licensing issues apply here, as you shouldn't be copying and using Windows.

For your VLANs and switches, you can use a network simulator like GNS, but I don't think you can plug this into your VM/Windows environment described above.  You shouldn't be okay without it though.  I can't see that the VLANs and switches will make too much difference to the way that your actual servers talk to each other.  You'll just have to test network and server things separately.

Perhaps I stand corrected.  When I was looking for a link for you for GNS3 I found this video showing how to connect to real equipment
I haven't actually used GNS3 (I've used other similar ones) so you'll have to try it out for yourself.

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Network infrastructure such as HP switches are not really possible to simulate.
(P.S. HP witches are generally a pretty nasty choice as far as managed switch products are concerned)   You would need to buy real switches for your 'simulation' environment,  to emulate that element.

There is no software to do this automatically, you basically have to do it manually.

You can build a server to run VMware or KVM and run virtual machine copies of all those computer servers in an isolated environment that you build,  for example VMware ESXi on a dedicated machine,  but you will need to read up on VMware's hardware requirements first to do this,  as it adds a few layers of complexity  (and consolidation) to your simulation that doesn't exist on the real network.

You may want to spend a few weeks learning VMware and about its hardware requirements, before you consider trying to build a sim using it.

In addition, you may have to do everything from server OS install manually inside the sim environment,  or else,  install a VMware converter on real servers, to perform the cloning, and (in theory), running the VMware converter could negatively impact production server, especially in the case of Exchange or SQL.

You would configure the network like this in VMware:
-  Have 1 dedicated virtual switch   allowing you to connect to the VMware server.  Call this "the vSwitch connected to the outside world for management of VMware server"
-  Delete the default "VM Network"  (port group under vSwitch properties),  since you will be creating it on an isolated vSwitch.

    If you want to forego emulating the HP switches...
          -  1 additional virtual switch in VMware to connect all the VMs to.
              Basically, you would create a 'VMware virtual network',
              or  port group on the second vSwitch, for each VLAN.
              And not assign any network cards to it.
          -   Create a port group called 'VM Network', the default network that
               new VMs get placed in.

     Then when creating a VM  (or before starting a new VM),  edit it and change
     the network card  to be connected to the proper network.

    If you want to emulate the HP switches, you can use multiple supported network cards on your VMware server,  generally these need to be well-known gig cards such as Intel Pro/1000PT, though, and  ESX(i) is finicky about what network cards and other hardware (such as RAID cards) are supported.     Create different 'Virtual switches'  in VMware, and assign different network cards to different switches.

No matter how you go about emulating the VLAN topology, an additional need you will have is something to emulate a router  on a stick for inter-vlan routing.

If you went all out with physical managed switches,  you may want to  obtain, config, and use a real router on a stick at this point.

Or use a  virtual machine to handle this.
You could use a firewall virtual appliance such as pfsense or just a generic Linux virtual install to simulate 'a generic router',

Add multiple virtual network cards to the VM, one in each  'VLAN port group',
enable IP forwarding, and configure the IP addresses accordingly.

Licensing Windows/any third party software for this could indeed be an issue, and might cause technical problems too, especially if you ever want to connect your sim environment to the Internet, for updates or some other reason.   I would suggest isolating the virtual network from the production network completely,  and  go buy a suitable MSDN subscription from Microsoft to support your personal Development/testing activity: and ensure you are compliant to use those licenses for your simulation infrastructure.

Any third party software you want to simulate may have its own requirements.

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