[kea-dev] IA_NA + IA_PD

Tomek Mrugalski tomasz at isc.org
Wed Sep 24 18:08:50 UTC 2014

On 23.09.2014 22:26, Sebastián Fritz wrote:
> Hi Tomek, 
>                   Thank you for your help. I believe that,  there is not
> any problem in assign an IA_NA  at the DOCSIS eRouter’s WAN side and a
> different range prefix IAPREFIX at the DOCSIS eRouter’s LAN side. In
> this way, I could have  an  smaller prefix to only assign IA_NA at the
> WAN side and a bigger subnet to assign IAPREFIX at the LAN side.
In a typical network, you would put both addresses (IA_NA + IAADDR) and
prefixes (IA_PD + IAPREFIX) in the same subnet. That is important,
because otherwise you can't aggregate routing configuration and for X
clients you'd have to have X routing entries.

Does that scale if you X goes into thousands clients? I honestly don't
know. And I have very limited experience with cable modems.

>                    Knowing  that DOCSIS Spec suggests to do the
> assignment (IA_NA) and DHCPv6 prefix delegation (IA_PD) in a single
> DHCPv6 session. Do you plan to support it in the future?.
Yes, we support responding to IA_NA and IA_PD in a single session already.

>  Below, there
> is the references with this recommendation.
> “CM-SP-eRouter-I13-140729” -( Section 8.3 - Obtain IPv6 address and
> other configuration parameters),
>  (http://www.cablelabs.com/wp-content/uploads/specdocs/CM-SP-eRouter-I13-140729.pdf):
> “...DHCPv6 address assignment (IA_NA) and DHCPv6 prefix delegation
> (IA_PD) SHOULD be done as a single DHCPv6 session....” 
As stated above, we fully support that. I just read the whole section
8.3. There is nothing in there that says that addresses and prefixes
should belong to different subnets.

What we don't support is the ability you are requesting: to send
prefixes and addresses that belong to disjoint subnets.

How many CTMSes you need to support? Here's something you may consider.
If you need to provide arbitrary addresses and arbitrary prefixes, maybe
subnet ::/0 would work for you?

Hope that helps,

Oh, and we don't support SOLMAXRT option mentioned in the docsis specs
you linked. Fortunately, you can define custom option format and start
sending this particular option. See section 6.2.7 of Kea ARM.

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