After Grizzly release Quantum was renamed Neutron. View:
https://openstack.redhat.com/Neutron_...
L2 agent - agent which talks with the layer 2 plugin like OVS (Open vSwitch) or LB (Linux bridge) etc.
http://docs.openstack.org/training-gu...
The original OpenStack Compute network implementation assumed a very basic model of performing all isolation through Linux VLANs and IP tables. OpenStack Networking introduces the concept of a plug-in, which is a pluggable back-end implementation of the OpenStack Networking API. A plug-in can use a variety of technologies to implement the logical API requests. Some OpenStack Networking plug-ins might use basic Linux VLANs and IP tables, while others might use more advanced technologies, such as L2-in-L3 tunneling or OpenFlow, to provide similar benefits.
OpenStack Networking also includes additional agents that might be required depending on your deployment:
plugin agent (quantum-*-agent):Runs on each hypervisor to perform local vswitch configuration. Agent to be run depends on which plug-in you are using, as some plug-ins do not require an agent.
dhcp agent (quantum-dhcp-agent):Provides DHCP services to tenant networks. This agent is the same across all plug-ins.
l3 agent (quantum-l3-agent):Provides L3/NAT forwarding to provide external network access for VMs on tenant networks. This agent is the same across all plug-ins.