Tag Archives: Internet

GNS3 – doesn’t work ping through the cloud on VM

First of all I would like to mention that all actions published here have as scope educational purpose. A lot of people who are trying to use GNS3 for testing/lab purpose meet the problem with connection to Internet through cloud.

My problem was: I couldn't ping from router in gns3 any external host. I meet this problem several times on different Operating Systems with different versions of GNS3. I researched on Internet for the solution many times and every time gave up in front of the problem. This is why I decided to write this article. It could be useful for someone in the same situation.

Let's begin with topology:

  1. I decided to install GNS3 on the Linux Ubuntu 14.04. Big Thanks to people who wrote this article http://www.computingforgeeks.com/2014/12/best-way-to-install-gns3-version-12-in.html and special thanks for those who wrote installation script.
  2. One of the most important things is that I decided to install GNS3 on VM using as hypervisor ESXi. Below you can see the topology. So I selected VM1 for this purpose.
  3. I connected ESXi host to the Cisco's switch using two cables. Cable connected to the G0/1 interface was set to trunk. Cable on G0/2 wasn't used (we will use it for debug purpose later).
  4. My VM1 has two interfaces. One is for remote management and the second for testing purpose.
  5. From VM1 I could ping from VLAN 10 interface User PC.


Let's move to GNS3 and create topology:

I am not going explain how to create topology and connect to the cloud you could easy find how to do it on internet. I will just publish screen from my topology:

VMware_GNS3_topologyAfter topology creation I was configured Interface Fa0/0 to get ip address via DHCP:

R1(config)#int fa0/0
R1(config-if)#ip add dhcp
R1(config-if)#no sh
*Mar  1 00:03:35.071: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar  1 00:03:36.071: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
*Mar  1 00:03:48.367: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0 assigned DHCP address, mask, hostname R1

Ok I have confirmation that packets are going through cloud. Everything is good. Next test is to ping CR2 interface ip address:

R1(config-if)#do ping

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

 Hmm.. Maybe ICMP packets were suppressed. Let's try to send ping from VM – ping test passed. So we have the situation when some packets could reach GNS3 and some others couldn't. Let's try to find where is the exactly the problem. Packets could be stuck on VM or somewhere in the network. We are connected to the Cisco switch and we have option to configure SPAN or port mirroring in order to check out suppositions. Let's do it.

C2960(config)#monitor session 1 source interface gigabitEthernet 0/1 both

C2960(config)#monitor session 1 destination interface GigabitEthernet 0/2

Please keep in mind that Gi0/2 interface couldn't send legacy user traffic after this configuration. In our case this is not a problem because I don't use this interface. On the VM2 I run Wireshark application and from R1 in GNS run again ping command. In the wireshark I see that packets leave VM and return back to the host. So problem seems to be somewhere on the VM. It could be SElinux or iptables.

Let's try another thing. Let's check how is set vmnic0 interface for VLAN10 in security tab. For this go the vSphere Client -> Configuration -> Networking -> Properties -> Double-click on your VLAN -> Press Security tab. I had the following configuration:

VMware_GNS3_errorLet's try to change promiscuous mode from Reject to Accept and repeat test again. The results:

R1(config-if)#do ping

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/20/44 ms

Here was my problem. Promiscuous mode allows vSwitch to forward all frames including those which are not directed to VM. Router in GNS3 acts as virtual interface inside of VM. From security purpose VMware block frames which are addressed to VM.

I hope that this article could be useful for you.