[ovs-discuss] DHCP IP addresses range of OVN's internal DHCP server

[Numan Siddique]

On Thu, Jan 11, 2018 at 8:27 PM, Dominik Holler <dholler at redhat.com> wrote:

> On Thu, 11 Jan 2018 18:31:25 +0530
> Numan Siddique <nusiddiq at redhat.com> wrote:
>
> > On Thu, Jan 11, 2018 at 5:31 PM, Dominik Holler <dholler at redhat.com>
> > wrote:
> >
> > > Hello,
> > > what is the range of offered IP addresses by OVN's internal DHCP
> > > server?
> >
> > Hi Dominik,
> > Internal DHCP offers the IP address set in the logical_switch_port's
> > addresses column. So, the CMS (cloud management system)  is expected
> > to set it.
> >
> >
> > > I am also interested in locating the source code which calculates
> > > this range.
> > >
> >
> > Alternatively, OVN supports basic IPAM implementation which actually
> > assign's IP address to the logical switch ports from the configured
> > range.
> >
>
> Hi Numan,
> this is the feature I am interested.
>
> > All the documentation is available in "man ovn-nb" (grep for "IP
> > Address Assignment"  and "DHCP") and "man ovn-northd".
> >
>
> Even I use this man page quite often, I did not find the concrete range
> in the man page.
>
> > For IPAM you can find the code here -
> > https://github.com/openvswitch/ovs/blob/master/
> ovn/northd/ovn-northd.c#L1114
> >
>
> Thanks. Looks like IPAM returns for IPv4 the next smallest unused
> address in the range of subnet address +1 (e.g. x.x.x.1) to biggest
> subnet address-1 (e.g. x.x.x.254).
>
> But from my experience the first port usually gets x.x.x.2.
> Can you give me a hint why it does not get x.x.x.1?
>

The x.x.x.1 is assumed to be reserved for router IP -
https://github.com/openvswitch/ovs/blob/master/ovn/northd/ovn-northd.c#L553
So it is marked as taken. When the first logical port is created x.x.x.2
will be assigned.

Thanks
Numan


> > For DHCP here -
> > https://github.com/openvswitch/ovs/blob/master/
> ovn/northd/ovn-northd.c#L2662
> >
> > Thanks
> > Numan
> >
> > Thanks and regards
> > > Dominik
> > >
>
>
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