Re: [Xen-users] DomU networking help please

[Marcus Brown <marcusbrutus@xxxxxxxxxxxxxxxx>]

Andrew Olds wrote:
> I have tried that and no joy.
> What I really want to know is which device in dom0 correlates to the eth0 in 
> domU

the vif (virtual interface)

> and do I need to attach an IP address to it.

no, dom0 has the vif attached to the bridge, the bridge needs an IP

> I'm sorry but I just need someone to explain in basic terms how it hangs 
> together.
> I realise I am probably doing something fundementally wrong here. I just 
> can't figure out what it is.
> 
>>They appear to be on different subnets - are you using an external 
>>router?  - if so, make sure you have a default route to the gateway, 
>>otherwise try setting the DomU's IP to something the in the Dom0's 
>>network...
>>
I agree, the IP address of domU should be in the same subnet as dom0
(as you are bridging, not routing)
eg. something like 10.0.0.6

>>
>>>Hi please forgive this if it seems a dumb question but I am new to xen and 
>>>linux.
>>>I have Xen running in Centos and another Centos Partition DomU running.
>>>But I cannot seem to get networking running between 0 and U.
>>>All the doco appears to assume you know everything about networking bridging 
>>>and the like.
>>>Does anyone have a simple how to step by step on how to get a single dom0 
>>>talking to a single DomU.

I guess the docs are as simple as it gets :) ...
ie. networking becomes simpler with experience

>>>All I am looking for is a really simple explanation of what all the 
>>>interfaces do
>>>and how to get the doms talking to each other.

here's my attempt to explain bridging:

======================================================================

Before booting any domUs:

    ______P_h_y_s_i_c_a_l__M_a_c_h_i_n_e_______
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |                                         |
    |     _______________________________     |
    |     |                             |     |
    |     |                             |     |
  ==|=====|eth0         dom0            |     |
    |     |                             |     |
    |_____|_____________________________|_____|



======================================================================

After bringing up a domU:

    ______P_h_y_s_i_c_a_l__M_a_c_h_i_n_e_______
    |                                         |
    |                                         |
    |                                         |
    |          _______________                |
    |          |             |                |
    |          |    domUn    |                |
    |       ___|             |                |
    |      /   |eth0         |                |
    |     /    |             |                |
    |  vifn.x  |_____________|                |
    |   /                                     |
    |  |  _______________________________     |
    |  |  |                             |     |
    |  |  |                             |     |
  ==|==+==|eth0         dom0            |     |
    | br0 |                             |     |
    |_____|_____________________________|_____|

IN DOM0:
- br0 (or xen-br0) is assigned the IP of eth0
- vifn.x is tied to the bridge (br0)
- neither vifn.x or eth0 require IP addresses now


======================================================================

Some commands that might help:
brctl show
ifconfig -a
route -n

Each of which has an excellent manpage, eg:
man brctl

Also of help:
http://wiki.xensource.com/xenwiki/XenNetworking
http://www.siliconvalleyccie.com/linux-hn/network-intro.htm
http://bridge.sourceforge.net/faq.html


Hope that helps a little,

Marcus.

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