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What is the physnet?

asked 2016-07-03 02:20:10 -0500

kramer gravatar image

When configure the bridge_mappings of ovs-agent configuration. Some docs will give examples like

bridge_mappings = physnet:br-ex,vlan:br-vlan


bridge_mappings = provider:br-ex, vlan:br-int

From my understanding, the word provider,vlan,physnet should be network names. Like the object you created with neutron net-create

But during the time you config the bridge_mappings. Those network may not be created yet. Does it matter? Does it mean we must create networks with same name latter?

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answered 2016-07-03 14:47:07 -0500

james-denton gravatar image

Per host you can have:

  • 1x integration bridge where VMs connect
  • 1x tunnel bridge used for overlay (vxlan /gre) traffic
  • 1x or more provider bridges that connect to physical interfaces used for tagged (vlan) and untagged (flat) traffic

bridge_mappings defines the mapping of a label (or name) to an actual bridge. The label name is arbitrary, but must be mapped to an actual bridge on the host. The bridge should contain a physical server interface that likely connects to a physical switch, such as eth1. The OVS agent will connect the provider bridge to the integration bridge. When you create a provider or external network using the net-create command, you can specify the provider label to ensure traffic on that network utilizes the mapped bridge and respective interface.

You can have more than one provider bridge, each with its own physical interface or bonded interface. This is useful when you have, say, a 1G network and a 10G network:

bridge_mappings = slownet:br-eth1,fastnet:br-eth4

The br-eth1 bridge would contain eth1, a 1G interface. The br-eth4 bridge would contain eth4, a 10G interface. The labels must be consistent across all hosts, but the bridges they map to can be unique to that host. As a result, I would make the labels fairly generic and not identify some interface name that may not be consistent across hosts. Same goes for the bridge, too, if it may not always contain eth1 or eth4.

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@james-denton Thanks. This explains very clear.

kramer gravatar imagekramer ( 2016-07-03 21:15:13 -0500 )edit

very, very useful. thank you

masber gravatar imagemasber ( 2018-11-21 20:20:11 -0500 )edit

Wonderful answer.

hr858f gravatar imagehr858f ( 2019-02-07 17:05:36 -0500 )edit

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Asked: 2016-07-03 02:20:10 -0500

Seen: 2,231 times

Last updated: Jul 03 '16