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Using field as comment . Per Arie Bregman blog http://abregman.com/2016/01/03/openstack-neutron-l2-l3-agents/

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Using field as comment . Per Arie Bregman blog http://abregman.com/2016/01/03/openstack-neutron-l2-l3-agents/

L2 Agent functionality
Its main responsibility is to wire new devices (TAP interfaces created by Nova) 
and to configure the software bridges on the compute nodes. There are usually 
two bridges: br-int and br-tun.
br-int is the integration bridge. It’s the bridge that takes care of tagging & untagging 
the traffic which coming in or out of the VMs. To tag the traffic, it uses local vlan id 
and assign it to the network.
br-tun is the tunneling bridge. It takes care of translating the tagged traffic. 
It translates the vlan id into segmentation and using it then for tunneling. 
If for example you use GRE tunnels, the segmentation id is used to specify the tunnel id.
The L2 agent is also responsible for applying security group rules 
(firewall rules) which implemented in neutron by using iptables and ip sets.
L2 constantly communicates with neutron-server using RPC.

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