[openstack-dev] [neutron][dvr] Wasting so many external network IPs in DVR mode?

zhi changzhi1990 at gmail.com
Wed Jun 1 15:48:46 UTC 2016

hi, all

    I have some questions about north/south traffic in DVR mode.

    As we all know, packets will be sent to instance's  default gateway (qr
interface) when an instance want to communicate to the external network.
Next, these packets will be sent from rfp interface(qrouter interface) to
the fpr interface(fip namespace) after NAT by iptables rules in qrouter
namespace, Finally, packets will be forwarded by fg interface which exists
in the fip namespace.

    I was so confused by the "fg" interface.

    The device owner of "fg" interface is
"network:floatingip_agent_gateway" in Neutron. It is a special port which
allocated from the external network. I think, in this way, we have to
wasted many IP addresses from the external network. Because we need a
dedicated router IP per compute node, didn't we?

    In DVR mode, why not we use "qg" interface in qrouter namespace? Just
like the "Legacy L3 agent mode" !  We can also setup "qg" interface and
"qr" interfaces in qrouter namespaces in DVR mode.

    Maybe my thought was wrong, but I want to know what can we benefit from
the "fip" namespace and the reason why we do not use "qg" interfaces in DVR
mode just like Legacy L3 agent mode.

    Hope for your reply.  ;-)

Zhi Chang
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