Subject: Home network topology

From: Rémi Denis-Courmont <[email-masked]>
Date: Tue, 11 Mar 2008 21:48:16 +0200

Hello,

I recall Iljitsch raising the question a while ago (I could be wrong), but I 
don't recall any conclusive answer. So...

As new layer-2 technologies show up, and as ISP are more and more commonly 
provisioning the CPE, we see more and more nested routers within the home. In 
IPv4, this is usually resolved using nested NATting (which is quite bad). If 
the Microsoft Vista requirements are followed, we would have bridging instead 
(which is not perfect but much better).

So how do we expect to chain network boxes in the home when IPv6 comes to the 
picture? Is it so that we expect some recursive usage of DHCPv6-PD? I believe 
we need some kind of answer, as this may affects a bunch of current I-Ds, as 
well as requirements for v6-capable CPEs.

For instance, 6to4rd is now proposing that only a /64 be assigned to a given 
customer. If we expect the home to be fully bridged, that's fine. Otherwise, 
there's going to be an interesting problem.

-- 
Rémi Denis-Courmont

---

From: Brian E Carpenter <[email-masked]>
Date: Wed, 12 Mar 2008 16:11:24 +1300

On 2008-03-12 08:48, Rémi Denis-Courmont wrote:
...
> there's going to be an interesting problem.

Why do you think we originally recommended /48 for all SOHO customers,
with some recent pressure to accept /56 as well? Clearly prefix delegation
has to be automated, though.

Bridging is bound to fail, if we see non-802 networks in the home.

   Brian

---

From: Mark Smith <[email-masked]>
Date: Wed, 12 Mar 2008 18:44:07 +1030

On Wed, 12 Mar 2008 16:11:24 +1300

> Bridging is bound to fail, if we see non-802 networks in the home.

To add a datapoint to this, the fairly recently formed Routing Over Low
power and Lossy networks (roll) working group seem to be focusing some
of these and similar issues for what would typically be non-802
networks in the home and other environments. 

http://www.ietf.org/html.charters/roll-charter.html

Regards,
Mark.

---

From: james woodyatt <[email-masked]>
Date: Wed, 12 Mar 2008 08:41:13 -0400

> there's going to be an interesting problem.

I expect that most home networks for the foreseeable future will be  
well-served by just a single bridged 802.1 network.  A significant,  
and non-ignorable fraction of them will need to run an interior  
routing protocol behind the residential Internet gateway.  One  
scenario is the remote worker whose office network is required by  
policy [or tax law] to be firewalled from their personal network.   
Other potentially more common scenarios spring to mind, but sadly, I'm  
unable to offer a disquisition on them at this time.

--
james woodyatt <[email-masked]>
member of technical staff, communications engineering

---

From: Rémi Denis-Courmont <[email-masked]>
Date: Wed, 12 Mar 2008 14:57:51 +0200

Le Wednesday 12 March 2008 05:11:24 Brian E Carpenter, vous avez écrit :
> > For instance, 6to4rd is now proposing that only a /64 be assigned to a
> > given customer. If we expect the home to be fully bridged, that's fine.
> > Otherwise, there's going to be an interesting problem.
>
> with some recent pressure to accept /56 as well?

Well, for subnetting, obviously, but I don't remember seeing a document that 
said how to do that subnetting in an unmanaged network.

> Clearly prefix delegation has to be automated, though.

Precisely. And there will also be interesting problems when people try to do 
link-local multicast discovery. There has to be a reason why 802.11 is pretty 
much designed to be bridged with 802.3.

If CPEs needs to be not only PD "clients" but also PD "servers", and if they 
need some basic form of in-site multicast routing/bridging, this may need to 
be specified. Even if we mandate /56, without standard way to use more 
than /64, people will resort to bridging and... address translation.

> Bridging is bound to fail, if we see non-802 networks in the home.

Right. Then I'm afraid 64rd is a non-starter in its /64 form.

-- 
Rémi Denis-Courmont

---

From: Ralph Droms <[email-masked]>
Date: Wed, 12 Mar 2008 09:43:01 -0400

Rémi - Configuring a single-level multi-link/multi-prefix SOHO network  
is easy; we have implementations.

The subscriber gateway device can use a /56 or /48 (or anything  
shorter than a /64) prefix, and assign separate /64s from that prefix  
to each of the links in the subscriber network to which it is attached.

There are a couple of details; perhaps most important is to devise a  
way for consistent numbering of the links if interfaces are added or  
taken away from the subscriber gateway.  The subscriber gateway has to  
derive RA configuration, etc., from the prefix numbering.

As you point out, more complex network topologies in the subscriber  
network might require a DHCPv6-PD server in the subscriber gateway.

- Ralph

---

From: Fred Baker <[email-masked]>
Date: Wed, 12 Mar 2008 11:01:57 -0400

I would be very careful in making sweeping statements about home  
networks.

I have four "home" networks that come quickly to mind. Two are the  
networks in my daughter's and one of my son's apartments; they each  
use a typical low end router with combined 10/100 Ethernet and  
802.11g wireless capabilities; they wire things that stand still and  
use wireless for things that move around. The third is my eldest  
son's fraternity house, which is best described as a piece of work.  
The fourth is my own home, a map-of-sorts for which is at

     ftp://ftpeng.cisco.com/fred/v6ops/Fred_home_network.pdf

The reason for the internal addressing behind Linksys routers in that  
configuration has to do with the configuration of those routers and  
the bugs in our Nokia and Samsung phones, which only seem to do the  
802.11 hotspot service correctly if the routers are in a firewall  
configuration. Apart from the special configuration for low rate  
beaconing, which results in longer battery life on the phones, I  
would happily replace the Linksys routers with access points.

The distinction between wired and wireless uses is important with the  
industry trends in the direction of the "connected home". While my  
marketing people tell me that everyone that installs a router in  
their home uses wireless for everything and can be expected to try to  
run HDTV over it along with everything else, my kids (who are not  
networking experts in any sense) pragmatically reply that they have  
tried it and it doesn't work. Those of us who understand the  
pragmatic aspects of networking could write treatises on why, but the  
fact is that we don't have to. Picking one, when I moved my UCSD son  
to an apartment last summer, he specified to me that he wanted  
wireless in the living room, but for the five student desks he wanted  
wired service (we installed 10/100/1000 switches). He wanted the  
desks wired because that configuration had worked well in his prior  
apartment, and wireless didn't. As I say, in general, wiring things  
that stand still (like TVs and people's desks) and using wireless for  
more flexible purposes trades off signaling characteristics in a  
pretty sensible way, and sensible people do so.

In general, I would encourage the folks who manage address space to  
enable different options for different users depending on their needs  
and willingness to pay; I might find useful options for /64, /60,  
and /56 addressing for a typical home, SOHO, or SMB. /48 is  
appropriate for larger installations, and for truly large companies  
(my own, with 60,000 employees each of whom has a remote corporate  
LAN in their home in addition to labs and workspaces at work, comes  
to mind), even an addressing plan that gives 65,000 routable prefixes  
might be too small if there are more than 65,000 separately routable  
endpoints. The /44 available in a ULA makes sense in that context.

In short, one size doesn't fit all, and giving folks the ability to  
do sensible things for a budget trade-off makes sense.

On Mar 12, 2008, at 8:41 AM, james woodyatt wrote:

> Other potentially more common scenarios spring to mind, but sadly,  
> I'm unable to offer a disquisition on them at this time.
>
>
> --

---

From: james woodyatt <[email-masked]>
Date: Wed, 12 Mar 2008 13:42:19 -0400

On Mar 12, 2008, at 11:01, Fred Baker wrote:
>> well-served by just a single bridged 802.1 network.  [...]
>
> networks. [...]

Just to be clear, that wasn't a typo in my previous message.  I did  
not mean 802.11.  I meant IEEE 802.1D.

> The third is my eldest son's fraternity house, which is best  
> described as a piece of work.

Yeah, that's another scenario I think is worth bearing in mind.   
Thanks you for reminding me.  Srsly.

---

From: Bob Hinden <[email-masked]>
Date: Thu, 13 Mar 2008 18:36:29 -0400

> Bridging is bound to fail, if we see non-802 networks in the home.

I agree.

I think our ability to predict what will be needed in the future home  
networks 5, 10, 15,... years from now is very limited.  It's not so  
long ago that the home consisted of a single dialup host.  Many of  
the early DSL and cable modem tried to replicate that with things  
like PPPoverEthernet.  Now many homes have a one or two networks  
bridged or routed/NATed together.  Some mix of wired Ethernet or  
WLAN.  Note, that some cable and DSL operators still seem to want to  
lock a customer to a single machine.  Many customers work around this  
with a NAT.

Is it likely that this will be the model going forward?  I doubt it  
and think we need to make architectural and policy decisions today  
that don't lock us into what is common today and allows for future  
flexibility.  There is a lot of things happening in home networking  
today including video, home automation, home security, VoIP, home  
servers, etc., etc.  I suspect that some of these like video will  
work better with distinct IP subnets.  This is today.

I think in five to ten years the future home network will end up  
looking like today's small enterprise.  This means there will be  
multiple subnets, different technologies, different administrative  
domains, and different speeds.   One big difference between the  
enterprise and home network won't be size, but will be that the home  
network will be auto-configured.  The enterprise will be managed, the  
home network will be unmanaged.  This will require enough address  
space to permit multiple subnets with room left for future growth.

Bob

---

From: Fred Baker <[email-masked]>
Date: Thu, 13 Mar 2008 19:02:41 -0400

On Mar 12, 2008, at 1:42 PM, james woodyatt wrote:

>>> I expect that most home networks for the foreseeable future will  
>>> be well-served by just a single bridged 802.1 network.  [...]
>>

Yes, and I am pointing out that there is a significant set of  
networks, mine being an example, which are not one 802.1d network.

I come back to the substance of my remark. I think there are sets of  
users that can very reasonably use various prefix lengths - one size  
does not fit all, even in a SOHO CPE. Building such an assumption  
into base specifications that are expected to guide implementations  
from multiple vendors seems like a very bad idea. If Apple wants to  
do that in a very low end single-subnet CPE, that's Apple's choice,  
but that doesn't make that the canonical product.

---

From: Rémi Denis-Courmont <[email-masked]>
Date: Fri, 14 Mar 2008 01:30:37 +0200

Bob, Brian, Ralph, and all, hello,

> space to permit multiple subnets with room left for future growth.

What I am concerned about is, should this need for "subnetting" the unmanaged 
networks actually substantiate (and I agree it is not unlikely), what is the 
solution? Anything that requires a manual setting of some home appliances 
(beyond plugging cables) is probably dead on arrival by definition of 
an "unmanaged" network.

If there is no clear guidance on how home routers ought to handle this, I 
suspect vendors would have to resort to IPv6 NATting :(
That is why I was not very comfortable with the /64-per-home option of, e.g. 
the 6to4rd proposal.

If I am just being totally confused and it is obvious to everyone else what 
the solution is (RIPng? "recursive" DHCPv6-PD? ...?), then please accept my 
apologies.

-- 
Rémi Denis-Courmont

---

From: james woodyatt <[email-masked]>
Date: Thu, 13 Mar 2008 21:26:54 -0400

> networks, mine being an example, which are not one 802.1d network.

I don't think I'm in disagreement.  Am I?

---

From: Fred Baker <[email-masked]>
Date: Sat, 15 Mar 2008 06:04:40 -0400

On Mar 13, 2008, at 9:26 PM, james woodyatt wrote:

>>>>> I expect that most home networks for the foreseeable future  
>>>>> will be well-served by just a single bridged 802.1 network.  [...]
>>>>
>>> Just to be clear, that wasn't a typo in my previous message.  I  
>>> did not mean 802.11.  I meant IEEE 802.1D.
>>

Maybe not, but our statements appear to be diametrically opposed. You  
appear to be saying that "most home networks for the foreseeable  
future will be well-served by just a single bridged 802.1 network"  
while I am saying "there is a significant set of networks which are  
not one 802.1d network".

Maybe you can help me understand in what way we are saying the same  
thing? :-)

---

From: james woodyatt <[email-masked]>
Date: Sat, 15 Mar 2008 11:26:56 -0400

> Maybe you can help me understand in what way we are saying the same  

I would ask for my statement to be evaluated in its original context,  
i.e. the one where the next two sentences were as follows:

>> A significant, and non-ignorable fraction of them will need to run  
>> an interior routing protocol behind the residential Internet  
>> gateway.  One scenario is the remote worker whose office network is  
>> required by policy [or tax law] to be firewalled from their  
>> personal network.

I was thinking of precisely your home network when I wrote that.

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Mon, 24 Mar 2008 17:05:18 +0100

On 15 mrt 2008, at 16:26, james woodyatt wrote:

>>> gateway.  One scenario is the remote worker whose office network  
>>> is required by policy [or tax law] to be firewalled from their  
>>> personal network.

That's not a good idea.

A routing protocol allows one router to tell another router which  
prefixes are attached to it. Although permutations where this is  
needed in a home network are conceivable, this is not the problem at  
hand. That would be how to get a router to discover which prefixes it  
should use on its interfaces.

Currently we only have DHCPv6 prefix delegation for this. If you have  
a hierarchy of routers that act as DHCPv6 PD clients in the upstream  
direction and as DHCPv6 PD servers in the downstream direction, this  
is a solved problem.

It gets more complex if there are routers in the middle that aren't  
involved in the DHCP PD process but which do need to know which prefix  
goes where. I think dhc is working on this but they haven't quite  
figured it out. In this case, it would be possible for a central  
DHCPv6 server to delegate a prefix and then have the router that got  
the prefix announce in using a routing protocol but this is a security  
and debugging nightmare even in an ISP network, let alone when the  
routing protocol needs to cross the ISP/customer demarcation point in  
the customer-to-ISP direction.

I tried to tackle a bunch of these issues in my "CPEs" message of  
january 4, but this didn't get much attention. I still think it would  
be best to try to come up with an integrated CPE / ISP service model  
for IPv6 but that can only work if there is a modicum of interest from  
service providers and CPE builders.