[CentOS-virt] Centos 6.2 / KVM troubles with network

Sat Jan 14 14:08:53 UTC 2012
Dennis Jacobfeuerborn <dennisml at conversis.de>

On 01/14/2012 02:59 PM, Radek Bursztynowski wrote:
> Hi,
> I have installed CentOS 6.2 x86_64 and KVM/Qemu and I have some troubles
> with network.
> The first case:
> -----------------
> The configuration is:
> - CentOS 6.2 (hardware machine) has one Ethernet interface with static IP
> address (eth0).
> - Virtual machine has bridge network interface with eth0 interface on
> CentOS 6.2. This bridge is created using wizard integrated with virt-manager.
> - Bridge interface on virtual machine receives IP addres from DHCP server.
> IP address is received well.
> - All firewalls and SELinux are closed.
> Virtual machine has no any connection with CentOS 6.2 hardware machine, and
> CentOS 6.2 has no any connection with virtual machine. But every others
> machines have all connection with both virtual and CentOS 6.2 machine.
> The question: Why?
> The second case:
> ----------------------
> The configuration is:
> - On CentOS 6.2 (hardware machine) I created bridhe (br0) with eth0
> hardware interface. Two situations:
> + I force two different IP addresses for eth0 and br0 interfaces - there no
> any connection with this server. So I don't test this case.
> + I forced one IP addres for both eth0 and br0 interfaces. ifconfig shows
> that eth0 has no IP address, br0 has IP address. So, I test this case.
> - I use Red Hat documentation:
> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html-single/Virtualization/index.html#sect-Virtualization-Network_Configuration-Bridged_networking_with_libvirt)
> - On virtual machine I created bridge connection with br0 interface on
> CentOS 6.2.
> - All machines have all connections.
> - All firewalls and SELinux are closed.
> NFS server on CentOS 6.2 (hardware machine) doesn't serve exported file system.
> The questions:
> 1. Is it proper that eth0 has no IP addres and bridge (br0) interface has?
> 2. What about my NFS? NFS server worked well before starting virtualization.
> Who can me help with my troubles?

You say you create bridge interfaces in your virtual machines. Why? Usually 
you don't do that you create a bridge only on the host.

You also say you "forced" one IP address for both eth0 and br0. There is no 
need to force anything. eth0 shouldn't have an IP but br0 should have this 
IP instead.