Hello all,

I've got a multi-NIC machine on which I am running Centos 6.2. I am trying
to have a NIC configured with an IP address but not connected to anything.
The reason for this is to create a network currently only used by VM's
residing on the machine, with that NIC configured to have an IP address
that is a part of that network, with a view of connecting real machines to
the same network in the future. How can I implement that? Currently ifup
just refuses to bring that NIC up.

Thanks.

Boris.
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On 05/01/12 10:38 AM, Boris Epstein wrote:
> I've got a multi-NIC machine on which I am running Centos 6.2. I am trying
> to have a NIC configured with an IP address but not connected to anything.
> The reason for this is to create a network currently only used by VM's
> residing on the machine, with that NIC configured to have an IP address
> that is a part of that network, with a view of connecting real machines to
> the same network in the future. How can I implement that? Currently ifup
> just refuses to bring that NIC up.

create a bridge interface that isn't bridged to any NICs



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john r pierce N 37, W 122
santa cruz ca mid-left coast

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On Tue, May 1, 2012 at 1:46 PM, John R Pierce <pierce@hogranch.com> wrote:

> On 05/01/12 10:38 AM, Boris Epstein wrote:
> > I've got a multi-NIC machine on which I am running Centos 6.2. I am
> trying
> > to have a NIC configured with an IP address but not connected to
> anything.
> > The reason for this is to create a network currently only used by VM's
> > residing on the machine, with that NIC configured to have an IP address
> > that is a part of that network, with a view of connecting real machines
> to
> > the same network in the future. How can I implement that? Currently ifup
> > just refuses to bring that NIC up.
>
> create a bridge interface that isn't bridged to any NICs
>
>
>
> --
> john r pierce N 37, W 122
> santa cruz ca mid-left coast
>

John,

Thanks! But if it is not connected to any NIC's then how would I connect
external devices to it in the future?

Boris.

>
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> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
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On 05/01/12 10:48 AM, Boris Epstein wrote:
> Thanks! But if it is not connected to any NIC's then how would I connect
> external devices to it in the future?

connect the bridge to a network adapter


--
john r pierce N 37, W 122
santa cruz ca mid-left coast

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On Tue, May 1, 2012 at 1:56 PM, John R Pierce <pierce@hogranch.com> wrote:

> On 05/01/12 10:48 AM, Boris Epstein wrote:
> > Thanks! But if it is not connected to any NIC's then how would I connect
> > external devices to it in the future?
>
> connect the bridge to a network adapter
>
>
>
That's precisely what I planned on doing - but I believe the network
adapter needs to have an address first. Then you bridge pseudo adapters to
it. It would all be fine but I can't take this initial step of assigning an
IP address to the NIC in question.

Boris.
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On 05/01/12 11:03 AM, Boris Epstein wrote:
> That's precisely what I planned on doing - but I believe the network
> adapter needs to have an address first. Then you bridge pseudo adapters to
> it. It would all be fine but I can't take this initial step of assigning an
> IP address to the NIC in question.


no, no. the BRIDGE pseudodevice has the IP, network adapter(s) that are
bridged to it don't have their own IP at all


--
john r pierce N 37, W 122
santa cruz ca mid-left coast

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On 05/01/2012 02:46 PM, John R Pierce wrote:
> On 05/01/12 11:03 AM, Boris Epstein wrote:
>> That's precisely what I planned on doing - but I believe the network
>> adapter needs to have an address first. Then you bridge pseudo adapters to
>> it. It would all be fine but I can't take this initial step of assigning an
>> IP address to the NIC in question.
>
>
> no, no. the BRIDGE pseudodevice has the IP, network adapter(s) that are
> bridged to it don't have their own IP at all

If it helps, I show how to create a bridge as part of a bigger tutorial.
I show ethX -> bond -> bridge, but you can drop the bond and go straight
from ethX -> bridge.

https://alteeve.com/w/2-Node_Red_Hat_KVM_Cluster_Tutorial#Creating_Some_Ne twork_Configuration_Files

--
Digimer
Papers and Projects: https://alteeve.com
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On Tue, May 1, 2012 at 3:12 PM, Digimer <lists@alteeve.ca> wrote:

> On 05/01/2012 02:46 PM, John R Pierce wrote:
> > On 05/01/12 11:03 AM, Boris Epstein wrote:
> >> That's precisely what I planned on doing - but I believe the network
> >> adapter needs to have an address first. Then you bridge pseudo adapters
> to
> >> it. It would all be fine but I can't take this initial step of
> assigning an
> >> IP address to the NIC in question.
> >
> >
> > no, no. the BRIDGE pseudodevice has the IP, network adapter(s) that are
> > bridged to it don't have their own IP at all
>
> If it helps, I show how to create a bridge as part of a bigger tutorial.
> I show ethX -> bond -> bridge, but you can drop the bond and go straight
> from ethX -> bridge.
>
>
> https://alteeve.com/w/2-Node_Red_Hat_KVM_Cluster_Tutorial#Creating_Some_Ne twork_Configuration_Files
>
> --
> Digimer
> Papers and Projects: https://alteeve.com
> _______________________________________________
>

I found a solution that seems to work best for now. If you go into
/etc/sysconfig/network-scripts/ and edit the ifcfg file corresponding to
the NIC in question (in my case, ifcfg-eth1) and change the ONBOOT flag to
"yes":

ONBOOT=yes

then the interface comes up with the right address regardless of whether it
is physically connected to anything via an ethernet cable. I intend to
bridge both virtual and physical devices to it but that will be the next
step.

Thanks to everyone who helped.

Boris.
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