[ovirt-users] MacPoolRanges not working as expected

[Xavier Naveira]

Hi everyone,

First of all I'd like to say that we have been using oVirt successfully 
for more than a year, creating an automated deploy system with help of 
foreman and puppet.

That being said, we're currently facing the first serious problem and 
we'd appreciate some help.

Everything was working fine until we exhausted the default 
MacPoolRanges. After looking for a solution to the error message we 
found this document: 
http://www.ovirt.org/Engine_config_examples#MacPoolRanges

Following the instructions on it we executed the following commands:

First we found out what our current pool was:

# engine-config -g MacPoolRanges
MacPoolRanges: 00:1a:4a:24:26:00-00:1a:4a:24:26:ff version: general

So we proceeded to expand it:

# engine-config -s "MacPoolRanges=00:1a:4a:24:26:00-00:1a:4a:24:27:ff"
# service ovirt-engine restart

After this we were able to create new machines but none of them seemed 
to have network.

After some unsuccessful troubleshooting  we restored the original pool 
and instead added a new one:

# engine-config -s "MacPoolRanges=00:1a:4a:24:26:00-00:1a:4a:24:26:ff"
# service ovirt-engine restart

# engine-config -s 
"MacPoolRanges=00:1a:4a:24:26:00-00:1a:4a:24:26:ff,00:1a:4a:24:27:00-00:1a:4a:24:27:ff" 

# service ovirt-engine restart

After doing this and test to create a new host everything seemed to work 
fine.

The problem is that after the successful creation of some hosts the 
original problem where the new hosts didn't seem to have network, 
reappeared.

Trying to narrow down the problem what we've find out so far is:

This oVirt environment kickstarts hosts via PXE, when trying to PXE boot 
a new host, the DHCP process fails (timeout).

Tracing the network packets, we are able to see that the virtual host 
sends the dhcp request, the dhcp server receives it and acknowledges it 
and it sends the dhcp offer back. The dhcp offer reaches the hypervisor 
to the vnetxx network interface BUT it doesn't go further and it doesn't 
reach the virtual host. This behavior is consistent through different 
hypervisors and vlans, including the ones that have been used/created 
before the problems appeared.

The only pattern that we've been able to identify so far is through 
issuing the command "brctl showmacs <bridge_name>"

This command list the mac addresses for the interfaces connected to the 
bridge. In the cases where everything works fine the output looks like this:

port no mac addr                is local?       ageing timer
2       00:1a:4a:24:27:e0       no                 0.01
2       fe:1a:4a:24:27:e0       yes                0.00

The virtual host MAC address begins with "00" and it has a corresponding 
address beginning with "fe" which is assigned to the "vnetxx" interface 
in the hypervisor.

In the cases where the virtual host doesn't get the dhcp answers the 
output of "brctl showmacs <bridge_name>" is:

port no mac addr                is local?       ageing timer
6       fe:1a:4a:24:27:a0       yes                0.00

This is, the actual virtual host's MAC address is missing from the bridge.

We haven't been able to find a detailed explanation on how the network 
internals of oVirt should work but hopefully someone in this list can 
point us to the right resource.

Thank you.

Xavier.