CentOS virt - Jun 2010 - KVM with bridge in one interface

Hi,

I have only one ethernet port in a remote server. (eth0)

I have a public address with x.x.x.164 netmask 255.255.255.240 gw x.x.x.161

and want to use in my guest OS the next available ip address (x.x.x.165 netmask
255.255.255.240 gw x.x.x.161)

Is this posible with brctl to achieve this?

I did a file called ifcfg-xenbr0 with:


DEVICE=xenbr0

TYPE=Bridge

BOOTPROTO=dhcp

ONBOOT=yes

then reboot, after that i use:

# brctl addif xenbr0 eth0

I was connected to my remote server but problems begin when I assigned the
x.x.x.165 ip addres to the guest OS with

virt-manager to begin installation. I lost the remote connection. Maybe I miss
something like this? :

iptables -I FORWARD -m physdev ?physdev-is-bridged -j ACCEPT

to avoid loosing the connection ?

i'm still receiving ping from x.x.x.165 but x.x.x.164

:(

I am having a couple of iptables issues with this type of setup
myself.  The RH manual says to insert a rule into the FORWARD chain
like this:

-A FORWARD -m physdev --physdev-is-bridged  -j ACCEPT

However, for the host does this not mean that every packet is
accepted.  As far as I can discern from the documentation, when one
sets up a physically bridged network on a kvm host then every packet
arrives across the bridge interface and, insofar as the host is
concerned, anything that it does not orginate itself is forwarded.

I may be wrong on this, but the behaviour of my ssh filters since
putting that command in the FORWARD chain indicates that something
along those lines is occurring.  The i/f eth0 seems to have no
relevence to iptables rules for the host instance.

-- 
***          E-Mail is NOT a SECURE channel          ***
James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
Harte & Lyne Limited          http://www.harte-lyne.ca
9 Brockley Drive              vox: +1 905 561 1241
Hamilton, Ontario             fax: +1 905 561 0757
Canada  L8E 3C3

I am having a couple of iptables issues with this type of setup
myself.  The RH manual says to insert a rule into the FORWARD chain
like this:

-A FORWARD -m physdev --physdev-is-bridged  -j ACCEPT

However, for the host does this not mean that every packet is
accepted.  As far as I can discern from the documentation, when one
sets up a physically bridged network on a kvm host then every packet
arrives across the bridge interface and, insofar as the host is
concerned, anything that it does not orginate itself is forwarded.

I may be wrong on this, but the behaviour of my ssh filters since
putting that command in the FORWARD chain indicates that something
along those lines is occurring.  The i/f eth0 seems to have no
relevence to iptables rules for the host instance.

-- 
***          E-Mail is NOT a SECURE channel          ***
James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
Harte & Lyne Limited          http://www.harte-lyne.ca
9 Brockley Drive              vox: +1 905 561 1241
Hamilton, Ontario             fax: +1 905 561 0757
Canada  L8E 3C3

On Fri, Jun 25, 2010 at 3:26 AM, Armando Montiel
<armando.montiel at gmail.com> wrote:
> Hi,
>
> I have only one ethernet port in a remote server. (eth0)
>
> I have a public address with x.x.x.164 netmask 255.255.255.240 gw x.x.x.161
I am assuming the above is assigned to the physical device eth0, right?
>From your netmask information the following is your IP params for your
subnet.
Network range		- x.x.x.160 - x.x.x.175
Usable range		- x.x.x.161 - x.x.x.174
>
> and want to use in my guest OS the next available ip address (x.x.x.165
netmask 255.255.255.240 gw x.x.x.161)
>
> Is this posible with brctl to achieve this?
>
> I did a file called ifcfg-xenbr0 with:
>
>
> DEVICE=xenbr0
>
> TYPE=Bridge
>
> BOOTPROTO=dhcp
>
> ONBOOT=yes
>
> then reboot, after that i use:
>
> # brctl addif xenbr0 eth0
>
> I was connected to my remote server but problems begin when I assigned the
x.x.x.165 ip addres to the guest OS with
>
> virt-manager to begin installation. I lost the remote connection. Maybe I
miss something like this? :
>
> iptables -I FORWARD -m physdev ?physdev-is-bridged -j ACCEPT
You have not disclosed how you are connecting to the "host" OS a
priori your VM installation.   Do you mean the above rule should be on
the "host" OS?  I don't think so unless you have enabled firewall
on
the host.  I would suggest to disable the firewall until you are done
with the VM setup.
>
> to avoid loosing the connection ?
>
> i'm still receiving ping from x.x.x.165 but x.x.x.164
>From the above it appears you are doing Xen virtualization.   I have
no experience with Xen but do with the Linux KVM  and I do think that
the basic networking fundamentals would be uniform, irrespective of
the virt platform.

(1) With Bridge, you cannot assign an IP to the physical interface, in
your case eth0.
(2) The IP number is assigned to the bridge instead, in your case
x.x.x.164 would be assigned to the bridge.
(3) My KVM setups  need "tap" (tunctl) interfaces to be bound to the
bridge interface.
(4) The VM  guest sees a regular NIC (as emulated by the host VM
environment), which is bound to the "tap" interfaces on the host OS.
The bridge being bound to the tap becomes the ethernet viaduct between
the guest VM and the rest of the world.

Therefore, I believe you need to move your host IP to the bridge,
define a tap which is bound to the bridge and then present the tap to
the VM in whichever way it is supposed to be for your virt. platform.

HTH
-- Arun Khan