Xen users - Sep 2009 - Sending DHCP-Offer from DomU in routed-mode doesn''t work

Hello,

I''m currently working with Xen in routing mode. So I changed the
xend-config file and changed the mode to:
        (network-script network-route)
        (vif-script vif-route)
So by default, ip_forwarding and prox_arp is now enabled (i checked it)
on eth0.

My config for the domU''s looks as follows:
        kernel = "/boot/vmlinuz-2.6.26-2-xen-686"
        ramdisk = "/boot/initrd.img-2.6.26-2-xen-686"
        memory = "512"
        name = "ubuntu2"
        vif = [ ''ip=192.168.0.98,
mac=00:01:02:03:04:05,vifname=ub2.0'' ]
        disk = [''file:/.../ubuntu.9-04.x86.img,sda1,w'']
        root = "/dev/sda1 ro"
        extra = "xencons=tty1

Now when I start the domU domain named ubuntu2 the routes where created
and if I specify the given Ip by myself in the Userdomain everything
works fine and I can connect to the world.

But now I when I''m going to run a DHCP-server on dom0 to handle
requests
from the domU''s the offers do not even arrive on the vif-Interface of
the domU (named ub2.0)?
And I''ve no explanation why? I checked the iptables rules, so the
default rules for FORWARDING also DHCP request have been set. (I also
experimented with deleting them, reconfigure and so on) But as it shows
no effect to the DHCP-Request and the fact that I think I should have
seen them at least at the ub2.0 Intefaces I''m thinking that Xen is
maybe
blocking the request?

Does anybody know how, why or what is exactly going on there?

Thank you in advance and sorry for my bad english :)


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Patrick Straub <pastraub@hs-furtwangen.de> writes:
> Hello,
>
> I''m currently working with Xen in routing mode. So I changed the
> xend-config file and changed the mode to:
>         (network-script network-route)
>         (vif-script vif-route)
> So by default, ip_forwarding and prox_arp is now enabled (i checked it)
> on eth0.
>
> My config for the domU''s looks as follows:
>         kernel = "/boot/vmlinuz-2.6.26-2-xen-686"
>         ramdisk = "/boot/initrd.img-2.6.26-2-xen-686"
>         memory = "512"
>         name = "ubuntu2"
>         vif = [ ''ip=192.168.0.98,
mac=00:01:02:03:04:05,vifname=ub2.0'' ]
>         disk = [''file:/.../ubuntu.9-04.x86.img,sda1,w'']
>         root = "/dev/sda1 ro"
>         extra = "xencons=tty1
>
> Now when I start the domU domain named ubuntu2 the routes where created
> and if I specify the given Ip by myself in the Userdomain everything
> works fine and I can connect to the world.
>
> But now I when I''m going to run a DHCP-server on dom0 to handle
requests
> from the domU''s the offers do not even arrive on the vif-Interface
of
> the domU (named ub2.0)?
> And I''ve no explanation why? I checked the iptables rules, so the
> default rules for FORWARDING also DHCP request have been set. (I also
> experimented with deleting them, reconfigure and so on) But as it shows
> no effect to the DHCP-Request and the fact that I think I should have
> seen them at least at the ub2.0 Intefaces I''m thinking that Xen is
maybe
> blocking the request?
>
> Does anybody know how, why or what is exactly going on there?
>
> Thank you in advance and sorry for my bad english :)
Dhcp uses broadcast and broadcast is not routed. You need to run a
dhcp forward/proxy on the router (dom0) or use bridged mode.

MfG
        Goswin


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