[openstack-dev] [neutron] Why neutron-openvswitch-agent use linux-bridge?

George Shuklin george.shuklin at gmail.com
Wed Nov 27 19:29:16 UTC 2013

Thank you for reply!

Few more question:

AFAIK bridge tools is not very fast (compare to OVS), so adding them
between OVS and tap (instead of yet another OVS switch) is kinda slow
everything down. Why just not use yet another openvswitch switch to connect
tap to veth devices?

Why iptables, not internal openvswitch flow rules? Those rules allows to
filter packets on L2-L4 headers and operates very fast. Is some
iptables-only features used in ovs-agent?

27.11.2013 20:55 пользователь "Lorin Hochstein" <lorin at nimbisservices.com>

> Hi George:
> On Wed, Nov 27, 2013 at 1:45 PM, George Shuklin <george.shuklin at gmail.com>wrote:
>> Good day.
>> I looking at the internals of bridge layout of openvswitch agent at
>> http://docs.openstack.org/network-admin/admin/content/
>> figures/2/figures/under-the-hood-scenario-1-ovs-compute.png
>> and wondering, why this scheme is so complicated and why it use linux
>> bridge and vethes with openvswitch together? Why no just plug tap device
>> directly to openvswitch bridge without intermediate brctl bridge?
>> I guess that was caused by some important consideration, but I unable to
>> find any documents about this.
>> If someone know reasons for that complex construction with different
>> bridges, please response.
> If you look a little further down on the page with that figure, the
> documentation reads
> Ideally, the TAP device vnet0 would be connected directly to the
> integration bridge, br-int. Unfortunately, this isn't possible because of
> how OpenStack security groups are currently implemented. OpenStack uses
> iptables rules on the TAP devices such as vnet0 to implement security
> groups, and Open vSwitch is not compatible with iptables rules that are
> applied directly on TAP devices that are connected to an Open vSwitch port.
> Take care,
> Lorin
> --
> Lorin Hochstein
> Lead Architect - Cloud Services
> Nimbis Services, Inc.
> www.nimbisservices.com
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> OpenStack-dev at lists.openstack.org
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