Port security in Openstack

Openstack Neutron provides by default some protections for your VMs’ communications, those protections verify that VMs can not impersonate other VMs. You can easily see how it does that by checking the flow rules in an OVS deployment using:

ovs-ofctl dump-flows br-int

If you look for a certain qvo port (or the port number, depending on the deployment), this will show the following lines

table=24, n_packets=1234, n_bytes=1234, priority=2,arp,in_port="qvo",arp_spa=10.10.10.10 actions=resubmit(,25)
table=24, n_packets=1234, n_bytes=1234, priority=0 actions=drop

Table 24 by default will drop all the packets originated from a VM unless they are resubmitted to table 25. The criteria for submitting to table 25 is simple: That the source IP for this traffic is the one that has been assigned to that VM, if not it will drop the packet at the end of table 24

In addition , there’s a protection from changing the MAC address of the interface, it’s implemented via the following rule

table=25, n_packets=1234, n_bytes=1234, priority=2,in_port="qvo",dl_src=aa:aa:aa:aa:aa:aa actions=resubmit(,60)

which basically compares the source MAC address of the packet with the expected MAC address of the VM.

In some use cases, you may want to drop this protection, it can be done using

neutron port-update $PORT_ID --port-security-enabled=false

This will ensure there’s no openflow rules in br-int that will drop your packets if they don’t adhere to the MAC/IP requirements

Good Luck !