I would like to simulate or emulate the design of a replacement network which will be L3 routed (the easy part) but will have a lot of simultaneous L2 VLAN bridging (or tunnels) to accommodate the transition from the existing network.

I am perfectly happy to get the VIRL subscription from Cisco, my question is not about cost, but I am unable to tell if it solves my problem, either alone or with GNS3, and would prefer to avoid wasting the time if the answer is "not a good approach".

The plan is to use EIGRP and L3 routing mostly, but during the transition have to bridge a lot of legacy VLAN's (and/or tunnel them); we also want to experiment with various configurations of two microwave rings involved (easily simulated by an L2 switch in various configurations) and how those interact with the p2p fiber connections used for a second or third redundancy. So the closer to functional equivalency the better. All private fiber or microwave, no VPN or encryption involved at this point, no ASA's (we will have some but that's a separate and easily handled aspect) and no IOS routers just the L3 switches.

I have GNS3 running (never used it before) and it is very cool for old IOS routers, but I am reading conflicting info (perhaps due to changes over time) on how well either VIRL alone or GNS3 with IOSVL2 and IOSVL3 images from VIRL can emulate catalyst switch functionality (especially L3). I have yet to find any side by side feature comparison of what will, and will not, be similar to the Catalysts. We will be using 3650's and 3560CX's at most locations (about 15 total so under the VIRL 20 limit for PE).

So basic question: How close can I get to a reliable simulation in this way?

Related question: Assuming I can find the functionality I need, how reliable is it to assume if it works in simulation it works in reality the same way (again, performance aside)?

Bonus question: how close will the configs be to actual configs needed for the Catalysts?

  • Since the question is Simulate a real L3 WAN, can you tell me what you desire to simulate? A) The service provider network. B) An enterprise network and its uplink. Commented Oct 28, 2017 at 15:58
  • No, this is al(most) all private microwave links and fiber. The Microwave is today point to point, later will be multiple rings with NEC's provisioning making the microwave look like a simple layer2 switch (it will handle ERP). There is an existing, fairly large L2 bridging over all this, with manual loop management. The goal is to move replace all the gear and end up L3 entirely, but during the transition we need to keep bridging (or tunneling, but I think not possible on the switches) the legacy vlans.
    – Linwood
    Commented Oct 28, 2017 at 17:04
  • PS. Not to leave that "almost" hanging, even where a service provider is providing the fiber it is configured as private. There are internet connections but that is not really part of the redesign (or more precisely it touches only at the edges).
    – Linwood
    Commented Oct 28, 2017 at 17:06

2 Answers 2


You can simulate the L2 or L3 WAN, but only when it is functioning correctly. You won't be able to effectively simulate problems like signal fade, or unidirectional links. GNS3 and VIRL (and now EVE) are designed to simulate network devices, not L1 devices.

  • That's great. It was the L3 stuff that worried me, as I saw only references to IOSvL2 on the Cisco sites (GNS3 refers to IOSvL3).
    – Linwood
    Commented Oct 28, 2017 at 19:04
  • Keep in mind that GNS3 simulates devices, but emulates the operating system. IOS on GNS3 (dynamips) means that image file is run. Commented Oct 29, 2017 at 6:55

Also, consider on GNS3 you can run on VM instances to contain the devices you are building. Potential is to use the inter-VM connectivity to determine some L1 scenarios e.g. VMNet0 using Wifi adapter etc.

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