# How to understand the bridge_mappings?

# Comma-separated list of <physical_network>:<bridge> tuples mapping physical
# network names to the agent's node-specific Open vSwitch bridge names to be
# used for flat and VLAN networks. The length of bridge names should be no more
# than 11. Each bridge must exist, and should have a physical network interface
# configured as a port. All physical networks configured on the server should
# have mappings to appropriate bridges on each agent. Note: If you remove a
# bridge from this mapping, make sure to disconnect it from the integration
# bridge as it won't be managed by the agent anymore. Deprecated for ofagent.
# (list value)
bridge_mappings =


I am trying to setup vlan type tenant network use ml2 + ovs. But the configure bridge_mappings confused me. Above said it is physical network names map to ovs bridge. But!!! What is a physical network name? The network you created with neutron net-create command? But that network should not be created yet at the time I edit this config.

Another guess here is that there is some predefined network names that neutron understand. But where I can find those predefined name if it is the case?

I am using ovs + ml2 to create vlan tenant network.

I try to create two tenant network net1 and net2, both with vlan type. Then try to create provider network external with flat type.

I want the net1 and net2 use ovs bridge called br-vlan and external use ovs-bridge called br-ex.

So I config the bridge_mappings to

bridge_mappings = net1:br-vlan, net2:br-vlan, external:br-ex


But this is wrong. The server said

Parsing bridge_mappings failed: Value br-vlan in mapping: 'vlan2:br-vlan' not unique. Agent terminated!


So how should I config?

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Each label must be mapped to a unique bridge. A given bridge is only good for a single flat network, since it is untagged traffic. Thus, if you want to have two flat networks you would need two different label/bridge mappings, and two different server interfaces - one in each bridge.

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.

more

https://access.redhat.com/documentati...

This link will give some basic idea to understand the bridge mappings.

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