How does the bridge network talk to the outside world?

asked 2015-02-15 20:38:45 -0600

anonymous user



I am new to openstack and learning the vlan manager. I came across some network diagram to explain the network topology of nova-net vlan manager.

Suppose I have two compute nodes:

Node 1                        Node 2
  eth0 (outgoing)              eth0(outgoing)          
  br0  (vlan1)                    br0  (vlan1)
  |-  vnet0                        |- vnet2
  |-  vnet1                        |- vnet3

Suppose I ping from vnet0 to vnet2. How does br0 of Node 1 knows the outgoing interface is Eth0 of Node 1?


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answered 2015-02-16 08:49:57 -0600

updated 2015-03-11 12:28:25 -0600

Your route configuration for vmnet0 will route requests like ICMP to a 'gateway' using a routing table. Likely, you're gateway is the same IP as eth0 on Node 1. On most bash CLI, you can type 'route' to see these.

A 'bridge' is supposed to 'bridge' two circuits into 1 complete circuit. So vmnet0 and vmnet1on br0 should be able to 'talk' directly, without going through the routing gateway.

since br0 and eth0 are on the same host, and the TCP/IP protocol doesnt care about devices as much as it does IPs, requests to something like are 'routed' to an IP that is binded with a device. This allows "public" requests on to go through (be routed to) eth0 with the public vlan tag, while requests for might go through the "management" vlan on eth0.

I should also add that in vlans there are multiple networks at play here, and much more going on with the ARP tables and ethernet frames. The core service for this is neutron, and most of your configuration is defined within the scope that service.

For example, the Open vSwitch service running on a compute node should be handling the vlans for your public L3 agent traffic's inbound requests from the floating IPs.

This can also be summed up with the image here: image description

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the question is for nova-network, not neutron

darragh-oreilly gravatar imagedarragh-oreilly ( 2015-03-11 13:47:56 -0600 )edit

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Asked: 2015-02-15 20:38:45 -0600

Seen: 184 times

Last updated: Mar 11 '15