[ovs-dev] [PATCH] pinctrl: Check requested IP in DHCPREQUEST messages

[Numan Siddique]

On Tue, Nov 20, 2018 at 1:37 AM Gregory Smith <gasmith at nutanix.com> wrote:

> Numan Siddique wrote:
> > On Fri, Nov 16, 2018 at 11:03 PM Gregory Smith <gasmith at nutanix.com>
> wrote:
> >
> > > See RFC 2131, section 4.3.2. When handling a DHCPREQUEST message, the
> > > server should validate that the client's requested IP matches the
> > > offered IP.
> >
> > When we added the native DHCP support in OVN, we primarily had
> > OpenStack in mind and wanted to get rid of neutron dhcp agent service.
> > In the case of OpenStack, when a port is created, the IP address is
> > assigned to it by the Neutron IPAM. This IP address will most likely
> > will remain the same for the port. So we added a simple native DHCP
> > implementation.
> >
> > I want to understand the use case for this requirement. Can you please
> > give more details. Does a CMS update the address of a logical port at
> > a later point of time ?
>
> We’ve been cloning windows VMs, and we’ve observed that the clone
> sometimes requests its parent’s IP address during boot, despite having
> been assigned a new adapter MAC address. The Windows DHCP client gets
> confused when it gets a DHCPACK for a different address, and reacts by
> repeating its original DHCPREQUEST. After a few retries, it gives up and
> uses the old address. It never sends a DHCPDISCOVER. By contrast, when
> the Windows DHCP client recieves a DHCPNAK, it immediately sends a
> DHCPDISCOVER to discover its new address.
>

Thanks for sharing this.


>
> Regarding OpenStack: I understand that it is not common to change a
> Neutron port's IP address assignment, but this is certainly a supported
> workflow. Are there any other parts of OVN that assume the port's IP
> address assignment is immutable?
>

No. CMS can change the port's IP addresses at any point and OVN should
handle it.
I was just curious to know the use case.

I will take a look at the patch.

Thanks
Numan


>
> Greg
>