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Re: [Xen-users] Multiple IPs in a domU

To: Dan Parsons <dparsons@xxxxxxxx>
Subject: Re: [Xen-users] Multiple IPs in a domU
From: Tim Post <tim.post@xxxxxxxxxxxxxxx>
Date: Mon, 26 Feb 2007 18:05:53 +0800
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On Sun, 2007-02-25 at 21:54 -0800, Dan Parsons wrote:
> I've been trying to make multiple public IP addresses work in a domU,  
> and have been unable to do it. I've tried every method mentioned in  
> the xenu-users archive as well as through a lot of stuff mentioned in  
> google.

>  Then the IP works. So,  
> it's a MAC/ARP issue.

Most cisco routers take up to ~9 minutes to re-arp these changes. Static
MACS must be used. 

You could tri arping'ing the gateway just specifying the address and
interface (i.e. eth0:1) or pass a -U. This should trick the router into
doing it.

The best way, use static macs when bringing up the vifs within the
dom-u. Remember, you can have only 3 physical eth devices within a
guest, as far as I know this limitation has not yet increased. 

So, its much easier to bring them up as vifs from within the dom-u
itself, just specify macs for each one. 

> But why isn't the MAC for eth1 being announced?

It is. apring is being called each time its brought to an up state to
make sure the IP does not already exist on the network. You either have
to wait 10 minutes, send traffic from it (i.e. ping -I eth0:1 -c1 -w5 > /dev/null 2>&1 in the postup init script. It really depends on
the router.

> I've tried specifying  
> the IPs in the domU config various ways and that also didn't help.

That's not going to make much of a difference. I often just specify
bridge, vifname and mac and handle the rest inside of the guest.

> This is on Fedora Core 6, using Xen 3.0.3. domU is also FC6 using the  
> same kernel. kernel is 2.6.19-1.2911.fc6xen. Below is a bunch more  
> info, please tell me if I've forgotten to include anything.

Just flushing the router's arp hehehe :)
> domU config file:
,,, looked just fine to me.
[ snip ]

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