xen-vm install with FAI - dhcp requests being ignored as "not authoritative"

[Henning Sprang]

Hi, 
On my way to install a xen vm with FAI over the network. I have a ip
autoconf-enabled kernel, but am experiencing the following problem. On the
xen-users list nobody had an idea, it seems the xen kernel makes "wrong"
dhcp requests, as my dhcp server works perfect with all other machines amd
setups. Maybe some other FAI user has an idea why this happens with xen
3.0.2:

When trying to get an IP adress, nfs root host and directory information
for the xen vm from dhcp, the dhcp server's syslog reads:

May  4 05:13:21 amalgam dhcpd: DHCPREQUEST for 255.255.255.255 (1.2.3.4)
>from 00:16:3e:00:00:11 via eth0: ignored (not authoritative).

And so I get no ip address and other installserver info.

However, if I boot the same vm config without the nfs root option, and
let it request ip configuration from nfs with the userland dhcp client,
everything is fine, but syslog looks slightly different:

May  4 05:09:49 amalgam dhcpd: DHCPDISCOVER from 00:16:3e:00:00:11 via eth0
May  4 05:09:49 amalgam dhcpd: DHCPOFFER on 192.168.0.57 to
00:16:3e:00:00:11 via eth0
May  4 05:09:49 amalgam dhcpd: DHCPREQUEST for 192.168.0.57
(192.168.0.133) from 00:16:3e:00:00:11 via eth0
May  4 05:09:49 amalgam dhcpd: DHCPACK on 192.168.0.57 to
00:16:3e:00:00:11 via eth0

(How)Do I need to tweak xen's or my dhcp's config? Or maybe try another
dhcp server? I am using the isc server from the dchp3-server package on
Debian Sarge.

The vm install also works when I give the nfs root location and ip in the
xen config, but I'd rather like to get that from dhcp.

Henning