[colug-432] DHCP/bootp broadcast question

R P Herrold herrold at owlriver.com
Tue Nov 10 17:59:24 EST 2015

On Tue, 10 Nov 2015, Stephen Potter wrote:

> I've got a bit of a strange situation.  I'm probably just missing 
> something easy, but right now I'm stuck.
> I'm building a new Satellite 6 virtual machine including DHCP, PXE, 
> Kickstart, etc.  I've got an existing Satellite 5 VM running on the same 
> ESX host on the same VLAN, same portgroup, same services but difference 
> DHCP scope.  I've attached the S6 to my vCenter, so I can do one stop 
> provisioning.  When I create the new VM in Satellite6, I can see it get 
> created on a different ESX host by vCenter and powered up, but the DHCP 
> times out and the actual build never happens.
> If I run tcpdump on both the S5 and S6 (remember, same ESX host, same 
> VLAN, same portgroup), on S5 I can see the DHCP request traffic.  On the 
> S6 host, I don't even see the traffic.  I've disabled the firewall and 
> SElinux on the S6 box, so they aren't getting in the way.  Normal 
> networking between the two ESX hosts, nothing blocking traffic from the 
> switch standpoint.
> What am I missing?

You mention: 
	normal networking between the two ESX hosts

but VLANs are complicating.  DHCP forwarders come to mind and 
can be touchy

The basic testing setup would be two chassis, each running 
ESX, and a network cable, switch or hub, and network cable; or 
a cross-over cable.  As I say, the presence of VLAN's also 
implies possible network packet impairing kit in the way.  
I'd reduce the diagnostic setup to:
	host -- cable -- hub -- cable -- host

and 'sniff' on the hub.  Rule out the VLAN issue.  See which 
host is truly not letting dhcp requests transit its virtual 
networking, or not letting replies back in across the same 
virtual networking

One has to think that perhaps bridging or such are in play in 
the implementation, and that layer two non-forwarding of 
packets is in play with the later version.  We have to take 
special steps with 'ebtables' rules under KVM / libvirt for 
multiple dom0 to all be served from (and only from) the 
desired authoritative DHCP server

But I suppose as a authorized receiver of ESX binaries, you 
might ask them for the source so you can check that out


Oh -- yeah -- Linux based ESX is not open source, per VMWare

Ah, well

-- Russ herrold

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