[openstack-dev] [ironic] the possible use of dhcp client id

Carl Baldwin carl at ecbaldwin.net
Thu Nov 13 00:25:36 UTC 2014

Hi Chuck,

I should probably chime in since I made the initial comment in the
first place.  I hate to derail the progress you've made with the
blueprint you have up now but this is worth some discussion.

On Wed, Nov 12, 2014 at 3:38 PM, Chuck Carlino <chuckjcarlino at gmail.com> wrote:
> It has been proposed that both issues could be at least partially addressed
> by adding the ability to use dhcp client id to neutron.  In this solution,
> the dhcp client is configured to use a dhcp client id, and the server
> associates this client id (instead of mac address) with the ip address.
> Note that this idea just came up today, so no code exists yet to try things
> out.

I think changes to the Neutron code to support a client id in the DHCP
server would not be too bad.  We would need some sort of switch to
turn it on because I don't think we could replace the current
MAC-address-as-identifier method that we've got now.  Would we turn it
on per port, per network, per tenant, per deployment?  I don't know.
Per port seems like maybe the right answer but I haven't thought much
about it.

> My questions:
> For 1, the mac address of the neutron port will be left different from the
> actual nic's mac address.  Is that a problem for ironic?  It makes me feel
> uneasy, and might confuse users, but that's all I got.

This is a good point.  It makes me feel "a bit uneasy" too.  Maybe the
API you've proposed to update the port's mac address would still be
needed just for this.

> In general, does using dhcp client id present any issues for booting an
> ironic server?  I've done a bit of web searching and from a protocol
> perspective it looks feasible, but I don't get a sense of whether it's a
> good general solution.

I'm looking forward to hearing others' thoughts on this too.

> If you have any off-the-top 'there's no chance that'll work' or better
> things to try kind of feedback, it would be great to hear it now since I'm
> about to start a POC to try it out.

The problem that came to mind when I wrote my comment is that
typically we don't assume any kind of control over the guest image and
how would we feed the client identifier in to the instance at boot?
We don't have access to a meta-data service yet.  Would nova do it?  I
guess if this were an optional feature and, in your case, you could
send a client identifier then maybe this would be a good idea.


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