[fedora-virt] Bridged Networking - Virtual Environments

[Emmett Culley]

On 01/17/2012 02:57 PM, Jorge Fábregas wrote:
> Hello everyone,
> 
> I'm learning about bridged networking and how it is applied to virtual
> environments (bypassing all the automation provided by libvirtd etc) .
> I have a question regarding ip configuration for the virtual bridge.
> 
> Let's say I have a host (my machine) where I want to run 3 VMs bridged
> to my home network (thru eth0).  I have a DHCP server running on my DSL
> router, and I have dhcp enabled on my 3 VMs so they all should get a
> lease from the DHCP.
> 
> As far as a I know these are the raw steps needed to accomplish this:
> 
> 1- create br0
> 2- remove current ip address from eth0
> 3- enslave eth0 to br0
> 4- create tap devices
> 5- attach tap devices to br0
> 6- assign tap devices to every VM
> 
> As you can see I haven't assigned an ip address to the virtual bridge
> (br0).  Why is it that (on almost any site that I visit with this setup)
> they always end up assigning an ip address to br0?
> 
> Thanks in advance!
> Jorge
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There should be no reason to use tap devices as the bridge device can be assigned as a network controller like so:

    <interface type='bridge'>
      <mac address='52:54:00:22:92:24'/>
      <source bridge='br0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <interface type='bridge'>
      <mac address='52:54:00:7c:0c:db'/>
      <source bridge='br1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </interface>

Using virtmanager to create the network interface would add the above tags and attributes to the guest's config file by creating a Bridge type interface.

Assign the host's IP addresses to the brX devices:

br0       Link encap:Ethernet  HWaddr BC:AE:C5:BE:07:DD                          
          inet addr:ww.xxx.yyy.zz  Bcast:ww.xxx.yyy.yy  Mask:255.255.255.240   
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1                     
          RX packets:28384 errors:0 dropped:0 overruns:0 frame:0                 
          TX packets:16265 errors:0 dropped:0 overruns:0 carrier:0               
          collisions:0 txqueuelen:0                                              
          RX bytes:34899139 (33.2 MiB)  TX bytes:2018000 (1.9 MiB)               


It would look like eth0 on the guest.

And the guest IP address to ethX:

eth0      Link encap:Ethernet  HWaddr 52:54:00:1B:A4:E6
          inet addr:ww.xxx.yyy.xz  Bcast:ww.xxx.yyy.yy  Mask:255.255.255.240
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3291 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2140 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:995099 (971.7 KiB)  TX bytes:414119 (404.4 KiB)
          Interrupt:11


On the host ifcfg-br0:

DEVICE="br0"
TYPE="Bridge"
BOOTPROTO="none"
ONBOOT="yes"
DELAY=0
GATEWAY="ww.xxx.yyy.zz"
IPADDR="ww.xxx.yyy.zx"
NETMASK="255.255.255.240"
IPV6INIT=no

On the host ifcfg-eth0:

DEVICE="eth0"
HWADDR="00:00:00:00:00:00"
ONBOOT="yes"
BRIDGE="br0"
IPV6INIT=no

On the guest ifcfg-eth0:

DEVICE="eth0"
BOOTPROTO="none"
HWADDR="52:54:00:22:92:24"
ONBOOT="yes"
IPADDR="ww.xxx.yyy.xz"
NETMASK="255.255.255.240"
GATEWAY="ww.xxx.yyy.zx"
DNS1="ww.xxx.yyy.xx"

Emmett