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GNS3 VM is used to run GNS3 network simulations.
How can I connect from the network in the simulation to the physical network at Layer 2?

For example, create a GNS3 environment with the following configuration:

plantUML GNS3 Network Image

The ping from "Client 2" to the IP address of "Physical Device" is successful.
However, due to the presence of NAT in between, "Client 2" and "Physical Device" belong to different broadcast domains.

On the other hand, I connected "Client 1" to the "Cloud Device" expecting an L2 connection, but unfortunately the ping from "Client 1" to "Physical Device" is not successful.

From each of the packet captures below, it appears that many of the packets reaching eth2 from the outside also reach "Cloud" in the simulation.

  • Between "Cloud" and "Client 1"
  • eth2 of the GNS3 VM
  • the USB LAN adapter on the host PC

However, some Ethernet frames, such as broadcasts sent by "Client 1", disappear between the Host PC and "Cloud".

How can I make sure that all Ethernet frames between the GNS3 simulation network and the physical network reach each other?

Setting eth2 on the GNS3 VM to promiscuous mode did not make any difference.
ip link set dev eth2 promisc on

Note that the virtual network settings for the VMs were configured as follows for each hypervisor:

  • VirtualBox:
    • Assign the USB-LAN adapter (NIC) as a "Bridge Adapter" to "Adapter 3" of the VM
  • Hyper-V:
    • Create a "Virtual Switch" with the USB-LAN adapter (NIC) assigned as the "External Network" and assign it to a "Network Adapter" of the VM
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  • Broadcast domains are actually irrelevant here. Your problem with NAT are the different routing domains. "NAT" is likely a router - what kind of device is "Cloud"?
    – Zac67 ♦
    Commented Feb 7, 2023 at 9:25
  • How can I make sure that all Ethernet frames between the GNS3 simulation network and the physical network reach each other? seems to be a host/hypervisor question which is explicitly off topic here, see the help center.
    – Zac67 ♦
    Commented Feb 7, 2023 at 12:18
  • My understanding is that the GNS3 Cloud node bridges the NIC of the machine running GNS3 (it means GNS3 VM) and the GNS emulation network. However, the GNS3 documentation (docs.gns3.com/docs) does not provide a detailed description of the Cloud node. Therefore, it behaves differently to my understanding, which is troubling me.
    – longer
    Commented Feb 7, 2023 at 16:07
  • From the packet capture results, it appears that all Ethernet frames from the physical network reach the eth2 device of the GNS3 VM promiscuously. It means that the problem is not with the physical device on the host PC or the hypervisor, but with the GNS3. As GNS3 is a "tool used by network professionals", I recognise that this is an on-topic question for the Network Engineering community.
    – longer
    Commented Feb 7, 2023 at 16:07
  • The Virtualbox hypervisor (or rather its virtual switch) might be the problem - then your question is off topic here.
    – Zac67 ♦
    Commented Feb 7, 2023 at 17:53

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