[Openstack] instances without a floating ip address

Aqsa Malik aqsamm at gmail.com
Tue May 3 04:27:14 UTC 2016

This is by design in OpenStack. A VM can't access the external network
unless assigned a floating IP.
Each private network exists behind the router and access to external
networks all happens via SNAT or Floating IPs. Each router uplink and
floating IP is allocated from the external network subnet.
Just as an add on,  Hosts without floating IPs can still create outbound
connections to the external network, as the provider router performs SNAT
to the router's external IP. The IP address of the physical router is used
as the gateway_ip of the external network subnet, so the provider has a
default router for Internet traffic.
The internal network is for traffic between virtual machines in OpenStack,
and between the virtual machines and the network nodes that provide l3
routes out to the public network (and floating IPs for connections back in
to the VMs).
I hope this helps.

On Tue, May 3, 2016 at 8:32 AM, Jagga Soorma <jagga13 at gmail.com> wrote:

> Hi Guys,
> Need some clarification regarding routing for instances without a floating
> ip address. Basically we have instances connected to a priv network that is
> also connected to our external network and our security group allows all
> egress traffic. However, we can't seem to get to any resource on our
> external network till a floating ip address is assigned. Once we assign a
> floating ip address we can get out.  Is that by design or is there
> something wrong with our configuration?
> Thanks.
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Aqsa Malik
Military College of Signals NUST

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