[CentOS-virt] Finally switching from Xen to KVM - question about networking

[Steve Campbell]

On 6/10/2014 12:43 PM, Digimer wrote:
> On 10/06/14 12:38 PM, Steve Campbell wrote:
>>
>> On 6/10/2014 12:05 PM, Digimer wrote:
>>> On 10/06/14 11:46 AM, Steve Campbell wrote:
>>>>
>>>> On 6/10/2014 10:46 AM, Digimer wrote:
>>>>> On 10/06/14 10:03 AM, Steve Campbell wrote:
>>>>>> I had so much trouble putting Centos 6 guest VMs on a Centos 5 host
>>>>>> that
>>>>>> I finally switched to a Centos 6 host.
>>>>>>
>>>>>> I've not needed more that test VMs, so I've used Virtual Machine
>>>>>> Manager
>>>>>> on the old system, which worked pretty well, so I decided to 
>>>>>> create my
>>>>>> first KVM guest machine. I noticed when I created it, I only had the
>>>>>> options of NAT for my network interface, so I used that (obvious).
>>>>>>
>>>>>> Well, after starting the VM, I find I don't have connectivity with
>>>>>> that
>>>>>> interface. Reading, I find examples where I need to create bridges
>>>>>> perhaps. Xen did most of this for me, so it's a little new to me.
>>>>>>
>>>>>> Can anyone throw me a clue, please?
>>>>>>
>>>>>> steve campbell
>>>>>
>>>>> Setting up a bridge is not that hard, and it will give your VMs 
>>>>> direct
>>>>> access to the outside world, and host <-> VM access just fine as 
>>>>> well.
>>>>>
>>>>> Here is a link showing how to setup a bridge connected to a bond
>>>>> device. Ignore the bond and pretend it is a straight ethX device:
>>>>>
>>>>> https://alteeve.ca/w/AN!Cluster_Tutorial_2#Configuring_our_Bridge.2C_Bonds_and_Interfaces 
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> The host has a device named virbr0 that is installed during system
>>>> installation. It also has a network device vnet0. There are no 
>>>> files in
>>>> /etc/sysconfig/network-scripts for these.
>>>>
>>>> Shouldn't I be able to use the virbr0 virtual bridge for this? I've
>>>> tried setting up the VM's device with all of the options that is 
>>>> listed,
>>>> but to no avail.
>>>>
>>>> Should I need to set up another bridge for this?
>>>>
>>>> And thanks for the link.
>>>>
>>>> steve
>>>
>>> virbr0 is created and managed by libvirtd. If you open Virtual Machine
>>> Manager, connect to localhost and then double-click on 'localhost',
>>> you will see a tab for creating/managing bridges (NAT'ed, generally).
>>> I disable 'virbr0' as NAT'ing is generally not what I want.
>>>
>>> The 'vnetX' devices are dynamically created to link a VM's interface
>>> to a bridge. Think of them as virtual network cables. They get created
>>> and destroyed as needed.
>>>
>>>
>> Sorry, but I'm confused:
>>
>> My host server has a real NIC and IP address with a real gateway to the
>> outside:
>> virtbr0 IP: 192.168.122.1
>> Host IP: 10.0.5.16
>> Gateway IP: 10.0.5.1
>> on eth0 and this works
>>
>> My VM server has all fake stuff currently:
>> Host IP: 10.0.5.17
>> Gateway IP: 10.0.5.1
>> on eth0 and this is like NIC without a cable.
>>
>> So I need to create a bridge device on both the host and VM (lets say I
>> name it br1). I change the eth0 config file on both host and VM to point
>> to br1 and give the br1 config file on both host and VM the correct IP.
>> But won't this just let the two talk to each other. How will the VM
>> server get outside?
>>
>> steve
>
> The bridge is created only on the host. Think of the bridge as being 
> like a virtual switch. When a VM is created, you tell it to connect to 
> the bridge, similar to how you would plug a physical wire into a real 
> switch. That provides the link to the network, and then you configure 
> the virtual server's network just as if it was a real network.
>
> On the host, you don't set the IP on the ethX device, instead you tell 
> ethX to connect to the bridge (look at 'bond2' in the link above for 
> the 'BRIDGE="..."' line). Then you move the host's IP address/config 
> to the bridge itself (look at the 'vbr2' in the link above).
>
> If you're still stuck, tell me the IP addresses you want to set in the 
> host and VM and I'll see if I can bang out a couple sample 'ifcfg-X' 
> files.
>
I'm running into some problems with my config files where I get a 
message that says the network can't determine my interface names. I'll 
look further, but the IPs above are what I need. 10.0.5.1 is a firewall 
that NATs the 10.0.5.0/24 network to another outside public firewall.

Thanks
steve