Hi

I'm Bartek and I cooperate with Michal on vCPE.

I managed to find the root cause of the issue which is security groups in 
Openstack. Although they are turned off for network and for port of the vBRG 
and vBNG VNF, neutron still applies anti spoofing rules in iptables:

> 
> 
> 
> 
> Chain neutron-linuxbri-oab4fd8e9-1 (2 references)
> 
> 
> 
> (...)
> 2618  833K DROP       udp  --  *      *       0.0.0.0/0           
> 0.0.0.0/0            udp spt:67 dpt:68 /* Prevent DHCP Spoofing by VM. */
> (...)
> 
> 

"neutron-linuxbri-oab4fd8e9-1" is a chain associated with tap interface of vBNG 
which is proxying DHCPOFFERs to vBNG, thus this traffic is being dropped as 
"spoofed". Once  this rule is deleted vBRG gets it's lease from dhcp server. 
Nova probably cleans/adds those rules upon restart and  there's a brief period 
of time when the rules aren't applied and that reveals why the packets 
eventually "sneaked" by.

Anti spoofing rules shouldn't be applied as we have "port_security_enabled -> 
False", but there seems to be a bug: 
https://bugzilla.redhat.com/show_bug.cgi?id=1406263 fixed in this errata: 
https://access.redhat.com/errata/RHBA-2017:0314
In our Openstack version it should be fixed but for some reason it's still 
hitting us.

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