[DHCP][Provider Network] Instances get IP from external DHCP server

Ruslanas Gžibovskis ruslanas at lpic.lt
Sun Jan 31 08:46:03 UTC 2021

Depends on the usage.
If your instance will be the only one on that dhcp network, then on
port/server would be better, but if you will need to create more instances
on such dhcp usecase, then I would go for a network port security.

On Sun, 31 Jan 2021, 05:54 dangerzone ar, <dangerzonen at gmail.com> wrote:

> Hi Slawek and Ruslans, thanks for the response. In this case the instance
> is connected to an unknown dhcp network and requests ip from that network
> to get access to the lan/internet. Thus, there is no known ip
> range/gw/dns/subnet that configures on the neutron network. From Ruslanas
> in the email, propose to set subnet as and disable port
> security ( on the instance itself or on the network that should be
> disabled???).
> The use case is I have a computer that has been configured as an openstack
> and with 2 nic ports. An instance created with attached to eth0 and eth1.
> This is a mobile mini computer that is used for demo purposes...
> The management openstack is set to network (eth0) and
> the second port eth1 is the one that will be connected to the external dhcp
> network. For example I bring the computer to customer site A for a demo...
> and connect eth0 to notebook for local management and then connect eth1 to
> site A to get ip from dhcp server for my instance to access lan/internet
> from site A network.
> I understand if we have the details of IP range/gw/etc that can be defined
> as a network, but the scenario here....we don't know the network and
> requesting ip from unknown dhcp network.
> Hope it gives some ideas... Thanks
> On Fri, Jan 29, 2021 at 4:07 PM Slawek Kaplonski <skaplons at redhat.com>
> wrote:
>> Hi,
>> On Fri, Jan 29, 2021 at 12:20:15PM +0800, dangerzone ar wrote:
>> > Hi, appreciate some advice on how instances in openstack get ip from
>> > external DHCP server. For example instance is attached to port eth1
>> > (physical port) and this port is connected to home/office lan port and
>> > requests dhcp ip. How this can be achieved.
>> > ***User don't know the dhcp ip range/gw/dns that will be provided by the
>> > dhcp sever to that instance...instance just attach to eth1 and request
>> > ip.***
>> > Similar like our pc/notebook request dhcp ip via wifi or lan port.
>> > How to establish this in openstack. Please advise and help me.
>> > Thank you
>> You need to disable port security on such instance. Otherwise Neutron will
>> block traffic from such IP address which is unknown.
>> Or You need to add this IP address which VM get to the
>> allowed_address_pairs of
>> the VM's port.
>> Also, please keep in mind that You will have different IP associated to
>> that VM
>> in the Neutron, and that will be visible in OpenStack API and different
>> one will
>> be really used.
>> --
>> Slawek Kaplonski
>> Principal Software Engineer
>> Red Hat
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