CentOS virt - Nov 2009 - Question - Xen host, DHCPD and guest VMs

I have a question about a Xen host that runs dhcpd and installing 
guest/running guest VMs on that host (that use DHCP)...

On other hosts or hosts running VMs, they are absolutely able to get DHCP 
addresses no trouble...  However, the fun begins when the machine I run 
dhcpd on is also hosting VMs.  I can see in /var/log/messages the request 
and ack from dhcpd but the guest VMs never hear it.  If I should bounce dhcpd
prior to a guest install or start a guest VM
- everything works just fine.

I'm guessing, perhaps, there is some iptables rule I need to set up? Based 
on the init scripts, dhcpd definitely starts before xend and xendomains 
and ultimately the xen bridge...

Anybody know what I need to do :)  I've been bouncing dhcpd in 
/etc/rc.local and starting any VMs there.  Although annoying, I'd rather 
do it "right" so I can auto start my Xen guests...

Thanks ahead of time!

Scot P. Floess
27 Lake Royale
Louisburg, NC  27549

252-478-8087 (Home)
919-890-8117 (Work)

Chief Architect JPlate   http://sourceforge.net/projects/jplate
Chief Architect JavaPIM  http://sourceforge.net/projects/javapim

Architect Keros          http://sourceforge.net/projects/keros

Scot:
> I have a question about a Xen host that runs dhcpd and installing 
> guest/running guest VMs on that host (that use DHCP)...
I just thought of something:

Do you have logs enabled at the bottom of your iptables
rules?  If something is hitting the firewall, you will see
it in the log.

	Neil

--
Neil Aggarwal, (281)846-8957, http://www.JAMMConsulting.com
CentOS 5.4 KVM VPS $55/mo, no setup fee, no contract, dedicated 64bit CPU
1GB dedicated RAM, 40GB RAID storage, 500GB/mo premium BW, Zero downtime

----- "Scot P. Floess" <sfloess at nc.rr.com> wrote:
> Anybody know what I need to do :)  I've been bouncing dhcpd in 
> /etc/rc.local and starting any VMs there.  Although annoying, I'd
> rather 
> do it "right" so I can auto start my Xen guests...
If you want to do it correctly, don't run dhcpd in domain 0. :) You're
exposing your host to traffic that it doesn't need to deal with, which can
be bad for performance and is bad for security. You're also putting one
extra service there that isn't solely related to keeping the ground beneath
the guests, the only thing domain 0 should be doing. Start a guest to run dhcpd
in auto and name the sym link in auto something like "00-guestname" so
it runs before the other guests. If you have two or more physical hosts and you
run ISC dhcpd, run another one of these guests as a dhcp failover peer on
another host.

-- 
Christopher G. Stach II