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What's the neutron traffic flow between VMs?

I recently focused on neutron traffic flow between VMs, and got confused about this part of the instructions on the OpenStack Docs: East-west scenario 1: Instances on the same network

I used my local environment to do following tests:

env

  1. CentOS7
  2. OpenStack Newton

Deployment

  1. 1 Controller 1 Compute 1 Network
  2. Two VMs which belongs to the same selfservice subnet on the Compute Node with floating ip

Action

SSH into one VM and do icmp request to another one

Result

It's interesting to find there are packets forwarding through overlay interface of Network Node, and also tap interface of l3-agent router.

But according to the previous OpenStack Docs, VMs on the same network should communicate directly.

Questions:

  1. VMs on the same network should communicate directly, floating ip or fixed ip? I think there are differences.

  2. What's the reason caused VMs on the same network in my deployment communicate with Network Node? Some mistakes in neutron configurations?


Configurations that may make sense:

/etc/neutron/neutron.conf

[DEFAULT]
auth_strategy = keystone
core_plugin = ml2
service_plugins = router

/etc/neutron/plugin.ini

[ml2]
type_drivers = flat,vlan,vxlan
tenant_network_types = vxlan
mechanism_drivers = openvswitch,l2population
extension_drivers = port_security

[ml2_type_vxlan]
vni_ranges = 1:1000

[ml2_type_flat]
flat_networks = provider

[securitygroup]
enable_ipset = true

/etc/neutron/plugins/ml2/openvswitch.ini

[agent]
tunnel_types = vxlan
l2_population = true

[ovs]
local_ip = **
bridge_mappings = provider:br-provider

[securitygroup]
firewall_driver = iptables_hybrid