The L2 Population driver enables broadcast, multicast, and unicast traffic to scale out on large overlay networks. This traffic is sent to the relevant agent via encapsulation as a targeted unicast.
Current Open vSwitch and Linux Bridge tunneling implementations broadcast to every agent, even if they don’t host the corresponding network as illustrated below.
As broadcast emulation on overlay is costly, it may be better to avoid its use for MAC learning and ARP resolution. This supposes the use of proxy ARP on the agent to answer VM requests, and to populate forwarding table. Currently only the Linux Bridge Agent implements an ARP proxy. The prepopulation limits L2 broadcasts in overlay, however it may anyway be necessary to provide broadcast emulation. This is achieved by broadcasting packets via unicast only to the relevant agents as illustrated below.
The partial-mesh is available with the
Open vSwitch and Linux
Bridge agents. The following scenarios will
use the L2 population mechanism driver with an
Open vSwitch agent and a
Linux Bridge agent. Enable the
l2 population driver by adding it to the list of
mechanism drivers. In addition, a tunneling driver must
be selected. Supported options are GRE, VXLAN, or a
combination of both. Configuration settings are enabled in
ml2_conf.ini:
[ml2] type_drivers = local,flat,vlan,gre,vxlan mechanism_drivers = openvswitch,linuxbridge,l2population
