[kea-dev] IA_NA + IA_PD

Sebastián Fritz sfritz at stechs.com.ar
Thu Sep 25 19:06:37 UTC 2014

Hi Tomek,
We are considering to support several CMTSs, so as you recommend us,  we’re
going to start assigning IA_NA as management address (side WAN) and
IAPREFIX at the side LAN within the  same subnet. Additionally, below I’m
presenting another scenario where I found a problem and I would like to
know your opinion:

- Knowing that CMTS already supports route injection to update the prefixes
assigned to eRouters according to RFC 4779  (Section ), it could be
possible to keep the prefix to a client which I need moving from one to
other CMTS. In this case, if I have associated relay-agent, IA_NA pool and
pd-pools altogether at the same subnet,  it’s impossible to keep the same
IAPREFIX because the subnet and the relay-agent  changes when the client is
moved to another CMTS. In this way, personally I think  that  I would be
great,  if Kea can support associate a same pd-pool with different subnets.

What do you think?


2014-09-24 15:08 GMT-03:00 Tomek Mrugalski <tomasz at isc.org>:

> 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,
> Tomek
> p.s.
> 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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