[kea-dev] link-local-only operation

[Templin, Fred L]

Hi Tomek,

Responses below:

> -----Original Message-----
> From: kea-dev-bounces at lists.isc.org [mailto:kea-dev-bounces at lists.isc.org] On Behalf Of Tomek Mrugalski
> Sent: Friday, May 15, 2015 8:36 AM
> To: kea-dev at lists.isc.org
> Subject: Re: [kea-dev] link-local-only operation
> 
> On 15.05.2015 16:56, Templin, Fred L wrote:
> > I have a DHCPv6 PD use case where the DHCPv6 server (acting also as a delegating
> > router) is always on the same link as the DHCPv6 client (acting also as a requesting
> > router). There is therefore no reason that I should have to assign a non-link-local
> > address and prefix to the link, since link-local-only would get the job done. But,
> > kea does not appear to allow for link-local-only configurations.
> >
> > In a configuration like this, it should be possible to tell the kea server to service
> > all clients connected to the link even though the link itself does not have a
> > non-link-local address and prefix assignment. Much in the same way that you
> That is already supported. See Section 8.2.13. Note the "interface"
> parameter. For any subnet, you can say that it is reachable over local
> interface directly.
> 
> If I understand it correctly, you want a configuration that:
> - does not assign addresses (IA_NA)
> - does assign prefixes (IA_PD)
> - is connected directly (not via relays)
> - the interface your server connects to your clients has only link-local
> address
> 
> If my understanding i correct, the following config should address your
> needs:
> 
> {
> "Dhcp6":
> 
> {
> # Kea is told to listen on eth0 interface only.
>   "interfaces-config": {
>      "interfaces": [ "eth0" ]
>   },
> 
>   "lease-database": {
>     "type": "memfile"
>   },
> 
>   "preferred-lifetime": 3000,
>   "valid-lifetime": 4000,
>   "renew-timer": 1000,
>   "rebind-timer": 2000,
> 
> # The following list defines a subnet. There's only one subnet
> # in this case and it is reachable directly over eth0.
>   "subnet6": [.
>     {
>       "pools": [ ],
>       "pd-pools": [
>             {
>                 "prefix": "2001:db8:1::",
>                 "prefix-len": 56,
>                 "delegated-len": 64
>             }
>         ],
> 
> # That doesn't really matter. Kea will be unhappy if there's no
> # subnet parameter.
>       "subnet": "2001:db8::/64",
> 
> # This tells kea that this subnet is reachable locally over eth0
>       "interface": "eth0"
>     }
>   ]
> }
> 
> }
> 
> This will cause Kea to communicate over eth0 using link-local addresses
> only.

Yes, that is what I want. This is what I am already doing.

> It will delegate /64 prefixes out of its 2001:db8:1::/56 pool.

Good. Also what I want.

> If clients ask for addresses (send IA_NA), they will get NoAddrsAvail in
> their IA_NA responses.

Should never happen, so it is fine.

> Does that address your need?

The concern I have is this part:

        > # That doesn't really matter. Kea will be unhappy if there's no
        > # subnet parameter.
        >       "subnet": "2001:db8::/64",

That is what I mean by "burning a prefix". I don't want to have to
associate any global IPv6 prefix with the eth0 interface in any way;
I want it to be purely link-local just like for "ping6 -I eth0 fe80::1',
So, I would like to have a "no subnet" model where the only
guidance to kea is the interface name itself.

Thanks - Fred
fred.l.templin at boeing.com

> Tomek
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