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Re: [Xen-users] Multiple IPs in a domU (I am using static macs)

Tom, thanks for replying. I started off doing the simple eth0:1 eth0:2 method. It didn't work - no traffic to the aliased IPs came in. eth0 would work but not eth0:1 or eth0:2. The outside world couldn't ping them, though the outside world could ping eth0. I would very much prefer to use aliases and not separate interfaces.

I haven't done any big config changes, nothing to xend conf or bridge scripts or anything like that. domU eth0 works fine from outside world, domU eth0:1 does not.

I really appreciate the help, I'm under the wire here and have to get this going :(

Xen 3.0.3 on fc6; here's my domU conf:

# Automatically generated xen config file
name = "ns"
memory = "128"
disk = [ 'phy:vg0/VM_ns,xvda1,w' ]
vif = [ 'bridge=xenbr1, mac=00:16:3E:6A:24:16' ]

uuid = "8141e049-0168-2bae-9d8d-b471220520ad"
on_reboot   = 'restart'
on_crash    = 'restart'

Dan Parsons

On Feb 26, 2007, at 2:34 PM, Tom Brown wrote:

On Mon, 26 Feb 2007, Dan Parsons wrote:

Thanks for the suggestions. Did something I say make you think I'm using a HVM? I'm using a plain old paravirtualized VM here. Does this change any of your suggestions?

My worry about the ping fix is that if there is no traffic on that IP for a long time, the arp record created by the ping will die. And then the router issues another arp who-has, and we have the same problem. Indeed,

what problem?

I use IP aliases in domUs all the time and have no trouble.

it looks as if Xen is ignoring who-has requests for eth1's IP.... Also, how can it be upstream when the eth0 ip works just fine? It's just eth1's ip that's bad. What is xen doing to make eth0 work, that it's not doing for eth1? And why?

why are you creating multiple interfaces if you don't want them on separate networks/bridges? Just use aliases of eth0

ifconfig eth0:1
ifconfig eth0:2

obviously I'm joining the thread late, so my apologies if there
is a clear issue I've missed.


tbrown@xxxxxxxxxxxxx   | Courage is doing what you're afraid to do.
http://BareMetal.com/  | There can be no courage unless you're scared.
                       | - Eddie Rickenbacker

Dan Parsons

-----Original Message-----
From: Tim Post <tim.post@xxxxxxxxxxxxxxx>
Date: Mon, 26 Feb 2007 19:30:21
Subject: [QUAR] Re: [Xen-users] Multiple IPs in a domU (I am using static macs)

On Mon, 2007-02-26 at 10:18 +0000, Dan Parsons wrote:
Thank you, but I actually am using statically defined MACs in the domU config.. So I don't believe what you said applies. Please correct me if I'm wrong.

Ah no, you're right I had a brainfart. Mac was staring right at me in
your config file.

Do you have further suggestions?

I haven't run into this, but only a few of my guests are HVM. You could
try a couple of things.

If you are using Xen's network-bridge script to bring up your bridges, try letting init do it and use a network-dummy script in its place, play
with the bridge settings and see if it helps.

forward delay, helo, maxwait, should be set to 0. I am not entirely sure
that they are set to 0 by default by brctl.

Or a quick fix, call ping during the boot process on the guest slightly modifying the init strings until you can rule out exactly what the issue

I'm tending to lean in the direction of something upstream, though.


Dan Parsons

-----Original Message-----
From: Tim Post <tim.post@xxxxxxxxxxxxxxx>
Date: Mon, 26 Feb 2007 18:05:53
To:Dan Parsons <dparsons@xxxxxxxx>
Subject: [QUAR] Re: [Xen-users] Multiple IPs in a domU

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

 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 ]

tbrown@xxxxxxxxxxxxx   | Courage is doing what you're afraid to do.
http://BareMetal.com/  | There can be no courage unless you're scared.
                       | - Eddie Rickenbacker

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