Xen users - May 2009 - NAT routing + HVM DomU''s

Hello,

I am attempting to setup a Xen environment hosting several internal
web apps (mostly Ruby on Rails).  I will have an OpenSuse 11 Dom0 with
Ubuntu 9.04 (server) DomU''s.  I am only given one IP address for my
server, and none of the DomU''s will need to be reachable directly, as
Apache will be handling the proxy load between apps on the DomU''s.
What I need is for the Dom0 and all DomU''s to be able to communicate
and for the DomU''s to be able to communcate with the internet via
routing through Dom0.

However, the issue I appear to be running into, is that running the
DomU''s HVM are attempting to communicate via the tapX device instead
of the vifX devices.

Here is a sample of my configurations:

ifconfig on dom0

eth0      Link encap:Ethernet  HWaddr 00:23:7D:51:19:3E
          inet addr:172.26.6.17  Bcast:172.26.7.255  Mask:255.255.254.0

vif1.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          inet addr:10.0.2.128  Bcast:0.0.0.0  Mask:255.255.255.255

vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          inet addr:10.0.1.128  Bcast:0.0.0.0  Mask:255.255.255.255


route -n on dom0

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.2.1        0.0.0.0         255.255.255.255 UH    0      0        0 vif1.0
10.0.1.1        0.0.0.0         255.255.255.255 UH    0      0        0 vif2.0
172.26.6.0      0.0.0.0         255.255.254.0   U     0      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
0.0.0.0         172.26.6.127    0.0.0.0         UG    0      0        0 eth0

Relevant configuration information for VM''s:

builder="hvm"
extid=0
device_model="/usr/lib/xen/bin/qemu-dm"
kernel="/usr/lib/xen/boot/hvmloader"
vif=[ ''mac=00:16:3E:C2:AA:XX'' ]

I am using dnsmasq to offer DHCP to the DomU''s as per the setup
documented here:
http://www.nikhef.nl/pub/projects/grid/gridwiki/index.php/Xen_3.2,_CentOS_5.1_and_NAT_HOWTO

I have also tried a static networking setup passing ip=x.x.x.x on the
vif line in the DomU configuration.

Reading through the archives I''ve seen a couple things mentioning
documented issued with routing in HVM DomU''s, but nothing recently
(3.3+).  Has anything changed, or are there any special considerations
when dealing with this type environment?

Any help is much appreciated.



-Steve

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Dear All, 

Can anyone please suggest me how to generate uncompressed kernel from
vmlinuz available in /boot, I doubt if gzip will work. I am trying to run
oprofile on rhel5.2 xenified kernel.

Thanks!
Ata


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On Wed, May 20, 2009 at 1:25 AM, Steve Copous <jaofos@gmail.com>
wrote:
> What I need is for the Dom0 and all DomU''s to be able to
communicate
> and for the DomU''s to be able to communcate with the internet via
> routing through Dom0.
>
> However, the issue I appear to be running into, is that running the
> DomU''s HVM are attempting to communicate via the tapX device
instead
> of the vifX devices.
Correct.
>
> Here is a sample of my configurations:
>
> ifconfig on dom0
>
> eth0      Link encap:Ethernet  HWaddr 00:23:7D:51:19:3E
>           inet addr:172.26.6.17  Bcast:172.26.7.255  Mask:255.255.254.0
>
> vif1.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
>           inet addr:10.0.2.128  Bcast:0.0.0.0  Mask:255.255.255.255
>
> vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
>           inet addr:10.0.1.128  Bcast:0.0.0.0  Mask:255.255.255.255
>
So I assume you use network-route and vif-route scripts or its variant?
You have two options :
- install PV drivers for HVM domU so traffic can go through vif. AFAIK
none is available for the default Ubuntu kernel, so the easiest way si
actually to convert your Ubuntu HVM to PV.
- use bridging setup, and setup NAT with iptables. This is what
libvirtd does, giving NATed address 192.168.122.0/24

-- 
Fajar

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