[libvirt-users] I have ping through bridge , net has been started , But IPs they're not equivalent.

Fri Apr 29 15:22:42 UTC 2016

On 04/28/2016 10:44 PM, Mohsen Pahlevanzadeh wrote:
> Dear All,
>
> I have the following configuration and I have ping from bridge :
>
> /////////////////////////////////////////////////////
> iface eth0 inet static
>         address 192.168.1.4
>         netmask 255.255.255.0
>         network 192.168.1.0
>         broadcast 192.168.1.255
>         gateway 192.168.1.1
> auto ivbr0
> iface ivbr0 inet static
>         address 192.168.1.4
>         netmask 255.255.255.0
>         network 192.168.1.0
>         broadcast 192.168.1.255
>         gateway 192.168.1.1
>         bridge_ports eth0
>         bridge_stp on
>         bridge_maxwait 0
>         bridge_fd 0

You misunderstood the instructions for putting your ethernet behind a 
bridge.

You should *never* give an IP address to both the bridge and the 
ethernet device that is attached to it. If an ethernet is attached to a 
bridge, remove *all* IP config information for the ethernet. For 
debian/ubuntu this means removing the entire "iface eth0" section. If 
you read the instructions on the wiki page carefully, you'll see that it 
is telling you to *replace* the line that says "iface eth0 ...." with 
one that says "iface br0...", *not* to add an entire new section for the 
bridge while leaving the section for eth0 intact.

>
> /////////////////////////////////////////////
> # brctl show
> bridge name    bridge id        STP enabled    interfaces
> ivbr0        8000.18037360b44e    yes        eth0
> /////////////////////////////////////////////
> my network xml file :
> <network>
>   <name>myintranet</name>
>   <uuid>465ce6cb-0a69-4f89-92ba-629349741e73</uuid>
>   <forward mode='nat'>
>        <interface dev="eth0" />
>   </forward>
>   <bridge name='ivbr0' stp='on' delay='0' />
> <mac address='52:54:00:0f:f4:f0'/>
>   <ip address='192.168.1.4' netmask='255.255.255.0'>
>     <dhcp>
>       <range start='192.168.1.3' end='192.168.122.254'/>
>     </dhcp>
>   </ip>
> </network>

You have misunderstood  the working of libvirt's virtual networks. You 
should *not* assign a bridge device that is already in the host system's 
network config to be used by a libvirt virtual network with a forward 
mode of nat, route (or no forward mode). libvirt creates the bridges for 
those types of networks itself, and they should *never* be listed in the 
system's network config.

Since you've mixed the use of a host-system-managed bridge (normally 
used when you want the guests to have an IP address that is 
visible/reachable directly from the physical network) with a 
libvirt-managed virtual network in NAT mode (normally used when the 
guest will only be used for outbound traffic (+ incoming only from the 
host)), I'm not sure which you want.

1) If you want the guests to be directly on the physical network, do this:

* edit /etc/network/interfaces and *remove* the entire section that 
starts with "interface eth0 inet static"

* "virsh net-edit myintranet" and change it to this:

<network>
   <name>myintranet</name>
   <uuid>465ce6cb-0a69-4f89-92ba-629349741e73</uuid>
   <forward mode='bridge'/>
   <bridge name='ivbr0'/>
</network>

(this make the libvirt network a simple unmanaged (by libvirt) pointer 
to an existing bridge named ivbr0. All bridge device configuration will 
be handled by the host system network config.)

* virsh net-destroy myintranet && ifup ivbr0 && virsh net-start 
myintranet && virsh net-autostart myintranet

(ifup ivbr0 will restore the system IP config of the bridge)

Any guests connected to this network will be connected directly to the 
physical network (assuming that ivbr0 is functioning properly)

2) If, on the other hand, you wanted your guests to be connected to a 
network that was NATed behind the host system's physical IP address, and 
be unreachable for incoming connections anywhere beyond the host, you 
should do this:

* edit /etc/network/interfaces and *remove* either the entire section 
that starts with "interface eth0 inet static" (if you want to maintain 
the option of connecting some guests directly to the physical network) 
*OR* the entire section that starts with "auto ivbr0" (if you don't want 
the option of connecting guests directly to the physical network).

* "virsh netedit myintranet" and make the following changes:

    * remove this line:   <interface dev="eth0" />
    * remove this line:  <bridge name='ivbr0' blah blah/>
    * correct the ending address of the dhcp range:
          <range start='192.168.1.3' end='192.168.1.254'/>
      (I'm surprised that didn't generate an error)

* virsh net-destroy myintranet && ifup ivbr0 && virsh net-start 
myintranet && virsh net-autostart myintranet

This will restart the myintranet network using a new bridge device 
(automatically named and created by libvirt), as well as restoring the 
original ivbr0 interface (or eth0 interface, depending on which section 
you removed from /etc/network/interfaces)

> Now , I have ping of my modem and internet.
> Then I did the following command :
> # ip l set dev ivbr0 down
> # brctl delbr ivbr0
> # virsh net-start myintranet
> Network myintranet started
>
> According to above , myintranet network has been started. But with the 
> following IP address :
> # ip a show dev ivbr0
> 17: ivbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue 
> state DOWN group default
>     link/ether 52:54:00:0f:f4:f0 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.122.1/24 brd 192.168.122.255 scope global ivbr0
>        valid_lft forever preferred_lft forever
> ////////
>
> 192.168.122.1 ?
> Question is , Where I change this address?(I set in myxml file.)

Did you edit the files in /etc/libvirt directly? You should never do 
that. Only edit them via virsh net-edit (or some other program that uses 
the libvirt API to retrieve and save the config).

>
> --best regards
> Mohsen
>
>
>
>
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