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I have two VMs ( linux based VM ) running on a UBUNTU/QEMU KVM. I am looking at a simple networking model, where in the VMs have public address and need to talk to the outside world and the outside world should be able to talk to the VMs as well. I did this

  • Created a bridge with A.B.C.D/16 ( class B address )
  • eth2 is part of the brige with A.B.C.E /32 host address
  • VM's interface ( through TAP ) has A.B.C.F / 16 address

eth2 and VM interface are both part of the bridge. Now however, I am unable to ping these address from the outside world. If i remove eth2 from the bridge, I am able to ping the eth2.

Please let me know what is going on.


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You need something to tell the outside world to route A.B/16 to your bridge, this involves some kind of router and possibly some kind of virtual router.

I'm not sure if learning this kind of routing is your goal or if simply getting VMs bridged is your goal.

If you just want your VMs bridged, then bridge them onto the same network as your host.


$ sudo brctl show br0
bridge name     bridge id               STP enabled     interfaces
br0             8000.001fd085d98b       no              eth0

tap0 is added to my br0 bridge. eth0 and eth2 are physical nics in my VM host.

now when I start KVM I tell it to use tap and it will use tap0.

sudo kvm -m 1024 -smp 2 ... -net tap ...

It will be "on my LAN". This is as simple as I can suggest.

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