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Create isolated network on Virtual Machine Manager - Centos 6.5

Since most of the Linux administration practice is done in a virtual environment, I thought I should create a video about it, as I am aware that some students at my college struggle with it in their labs. Please let me know if I missed anything or did not explain anything clearly.



  1. hi,
    i want to know that if these vms on isolated network can run internet on them OR can ping or some other website
    if this is possible, please tell me how to configure it.

    1. it is definitely possible. There are two ways. either you can add another NIC which would be configure as a "NAT" to all the VM. All the external traffic will go to that NIC automatically. The other way is through firewall masquerading, on one of the VMs which has two NIC cards.
      Lets say you have three VMs on an isolated network, one VM has two NIC(configured as NAT) cards and all the others have one NIC. The other two VMS will forward all the traffic orginating for external network to the VM which has two NICs and that VM will forward it to the host. When host receives a reply it is going to forward it back to the VM with 2 NIC, and that NIC will forward the Traffic to respective VMs. How exactly are you going to do it? that deserves its separate blog entry :)

    2. i want to explain it to you in detail
      can you send your email id????
      mine is
      please send me email on this id

    3. i have 3 vms with one nic each on them in vitual machine manager and they have static ip =,129,130/24 respectively. they can ping host with ip of on virbr0 virtual nic , BUT they cannot ping outer network.
      this is a big problem for me. please help me to solve this..........
      i have tried this iptables command:
      iptables -t nat -A POSTROUTING -p tcp -o eth0 -j MASQUERADE
      on host machine and then put
      echo 1 > /proc/sys/net/ipv4/ip_forward
      but this does not work
      check this website ===

    4. This comment has been removed by the author.

    5. sorry i am a bit busy these days, I will get back to you as soon as i get some time. Meanwhile, try looking and understanding how POSTROUTING and PREROUTING works.


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