Re: [Xen-users] Sending DHCP-Offer from DomU in routed-mode doesn't work

[Goswin von Brederlow <goswin-v-b@xxxxxx>]

Patrick Straub <pastraub@xxxxxxxxxxxxxxxx> 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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