Pavel, I think you are right! Thanks!

I didn't take into consideration that there is another oVirt environment that has some VMs on this vlan..

And I found a VM with the same mac 00:1a:4a:16:01:51 (and a different ip)

Now I powered off that other VM, restarted my one and things seem ok.

What is the best way to manage when more oVirt environments has VMs on the same vlans?

BTW: before finding the problem related to the mac I found my documents when I used qemu-kvm on CentOS 6.3 on the same hardware pieces and I had similar problems (it was mid 2012) and in that case I had to set tx-checksumming off for the interfaces where I had the bridges (managed by libvirt).

I created an init script that did the setting at boot.

I have verified that by default my network interfaces in CentOS 7.3 start with the parameter set to on. Of course changing the setting didn't solve my problem because was mac related...

But Is there any reference about it and what would be the best setting and why?

Thanks again in the mean time ;-)