Red Hat Bugzilla – Bug 693711
Libvirt does not allow several client to communicate with the host using the same bridge
Last modified: 2012-01-25 01:09:38 EST
Description of problem:
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Create a virtual network virbr1
2. Create two guests, connect both to the virtual network
3. The mac address of the guest started first is copied to the virbr1. The second guests mac address is different.
4. Try to connect to the host from both guests. The second guest works. The first guest does not work because guest and host share the same mac address.
Communication between the first guest and the host is not possible.
Communication should be possible.
Could it be that the problem is caused by the MAC address of the bridge *changing* when the 2nd guest is started, thus confusing the 1st guest? What happens when you start only guest 1, or only guest 2? are both able to communicate with the host in those cases?
The way that a Linux bridge device works is that it always takes on the lowest numerical MAC address of all the interfaces that are directly connected to it. So, by definition, there is no problem with the MAC address of the guest's tap interface and the MAC address of the bridge matching - this is just how things work.
However, problems can arise if a new guest with a lower MAC address is started/attached to the bridge - the MAC address of the bridge changes, and this causes problems. (I haven't heard of it causing a loss of network connectvity though, only that it causes MS Windows guests to believe they've connected to a new network).
This has been solved upstream by creating a dummy tap device with a MAC address guaranteed lower than any guest tap, and connecting that tap to the bridge. This way the bridge has a MAC (required for forwarding to work), but the MAC never changes.
The upstream commit is:
Subject: Give each virtual network bridge its own fixed MAC address
It is in just-released libvirt-0.9.0, which will hopefully show up in the F14 virt-preview repo soon.
Please give that version of libvirt a try if you can.,
This package has changed ownership in the Fedora Package Database. Reassigning to the new owner of this component.
Closing as INSUFFICIENT_DATA (and F14 is EOL)
Sorry for not replying. It works fine on Fedora 16.