openstack team mailing list archive

[Lorin Hochstein <lorin@xxxxxxxxxxxxxxxxxx>]

I'm trying to wrap my head around how Quantum works. If understanding
things correctly, when using the openvswitch plugin, a packet traveling
from a guest out to the physical switch has to cross two software bridges:

1. br-int
2. br-ethN or br-tun (depending on whether using VLANs or GRE tunnels)

So, I think I understand the motivation behind this: the integration bridge
handles the rules associated with the virtual networks defined by OpenStack
users, and the (br-ethN | br-tun) bridge handles the rules associated with
moving the packets across the physical network.

My question is:  Does having two software bridges in the path incur a
larger network performance penalty than if there was only a single software
bridge between the VIF and the physical network interface?

If so, was Quantum implemented this way because it's simply not possible to
achieve the desired functionality using a single openvswitch bridge, or was
it because using the dual-bridge approach simplified the implementation, or
was there some other reason?

Lorin
-- 
Lorin Hochstein
Lead Architect - Cloud Services
Nimbis Services, Inc.
www.nimbisservices.com