Re: Simple way of putting a VM on a LAN

[Bill Davidsen <davidsen@tmr.com>]

Stuart Jansen wrote:
> On Fri, 2008-07-25 at 12:44 -0400, Bill Davidsen wrote:
>> But when the host is really on the network, it uses DHCP to set the IP, 
>> while in a VM it never sends any DHCP packets, the setting of the IP 
>> times out, and I wind up with no IP until I set it. I have checked with 
>> tcpdump, the DHCP requests for IP appear on the bridge, but not on the 
>> eth0 NIC, and so are never seen by the DHCP server.
>>
>> Do you see this problem, or have any information about it? Obviously 
>> suggestions on fixing this are needed, since the dhcp server is a 
>> candidate for virtualization in the future.
> 
> Just to be certain of the obvious, you added eth0 to the bridge, right?
> 
> brctl addif br0 eth0

Yes, everything works except the DHCP discovery. Once I bring up the VM 
NIC by hand and set the default route everything works really well with 
TCP, UDP, and ICMP, as well as the usual ARP packets, etc.
> 
> And the tap device is active, right?
> 
> ifconfig tap0 up

UP and based on something I saw in another script is tried adding 
promiscuous, which really didn't change anything.
> 
> Assuming it isn't something so obvious, I'm suspecting spanning tree.
> 
> brctl stp br0 off

It was never on (unless it was turned on by something more automated 
than my fingers, but it's definitely off now, and make no difference.

For a test I modified the network setup to a static IP and routing. That 
did work, although it is undesirable, since it invites having the DNS 
wrong. I moved to DHCP to be sure that the IPs are always right, a 
master list gets turned into entries in both dhchd.conf and the 
appropriate DNS files (forward and reverse lookeps are always right, 
too). Shot myself in that foot way back in ARPAnet days :-(

Thanks for the ideas, I have one more, but I have to do a little 
research before I can ask an intelligent question.

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot