Subject: Re: IPv6 Addr/Prefix clarification

From: Philip Homburg <[email-masked]>
Date: Fri, 01 Feb 2002 13:04:48 +0100

In your letter dated Thu, 31 Jan 2002 20:55:16 +0100 you wrote:
>--On Thursday, January 31, 2002 03:09:08 PM +0700 Robert Elz
><[email-masked]> wrote:
>> I probably wouldn't either, though we don't want to totally forget
>> allocation efficiency - the way we make sure that IPv6 never runs
>> out is to always make sure we justify every allocation (which
>> doesn't mean organisations need to justify their need for a /48 -
>
>> but I'd certainly be making any organisation asking for a 2nd one
>> (in the same aggregatable block,
>
>If this will happen, which organisation would this be? Compared with
>current IPv4 /48 with the 16 bits for SLA is similar to a IPv4 Class
>A network.

What happens if an organization has a modem bank for dail-in? Do you hand
out /64s or something larger? Suppose that you want to give each 'modem user'
a fixed prefix, how soon do you run out of prefixes?

					Philip Homburg
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From: "Tony Hain" <[email-masked]>
Date: Fri, 1 Feb 2002 09:50:58 -0800

Philip Homburg wrote:
> out /64s or something larger?

Hand out a /64 or shorter depending on the customer.

> Suppose that you want to give each 'modem user'

If you assign a /48 to the pop and allocate /64's to the customers, you
will run out when you exceed 65536 active users. If the pop has more
ports than that, assign a /47.

Tony

---

From: Pekka Savola <[email-masked]>
Date: Fri, 1 Feb 2002 20:00:28 +0200 (EET)

> ports than that, assign a /47.

I'm broadening the topic to include all kinds of home users, e.g.
xDSL, Cable etc. in addition to dial-in.

This is in conflict with IAB/IESG recommendations for address assignments
(draft-iesg-ipv6-addressing-recommendations-03.txt).  A RIR policy issue, 
though.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

---

From: Peter Bieringer <[email-masked]>
Date: Fri, 01 Feb 2002 19:57:36 +0100

--On Friday, February 01, 2002 01:04:48 PM +0100 Philip Homburg
<[email-masked]> wrote:

>> If this will happen, which organisation would this be? Compared
>> with current IPv4 /48 with the 16 bits for SLA is similar to a
>> IPv4 Class A network.
> 
> What happens if an organization has a modem bank for dail-in? Do
> you hand out /64s or something larger? Suppose that you want to
> give each 'modem user' a fixed prefix, how soon do you run out of
> prefixes?

Where is the problem? 

Today they got *one* *dynamic* IPv4 address and have to be happy with
it. Connection of additional internal hosts requires masquerading,
causing perhaps problems and had (without dedicated port forwarding)
no capability to direct traffic from outside to inside.

In IPv6 future, they will get one /64 prefix and can connect a lot of
toasters, VCRs, TVs, battery chargers, light switches and so on. All
devices get a *global* IPv6 address.
And in case of no IPv6 firewalling, all this devices can be connected
directly from outside.

--> normally a big advantage
not mention any potential security issues in network-connected
toasters here now ;-)

People have only to think that they do no longer need to take care
about Layer 3 routing and addresses in their home networks, they only
need a Layer 2 switch and the "IPv6 access device".

Your described scenario only cause a problem if someone really wants
to Layer 3 route in his home network - but how many really want to do
this or need this?

Conclusion: people have to think about network redesigning from
dedicated small IPv4 network islands to bigger full switched IPv6
networks.

Note: broadcast traffic is reduced/eliminated in IPv6 because of
Layer 3 multicast mechanism, which should be also mapped into Layer 2
multicast addresses.

        Peter

---

From: "Tony Hain" <[email-masked]>
Date: Fri, 1 Feb 2002 11:24:57 -0800

> xDSL, Cable etc. in addition to dial-in.

No problem as the actual implementation at the consumer end is probably
similar. There will be some device between the provider network and the
consumer network, be that dial or always-on. The device needs either a
/48 so it can provide subnet based routing, or a /64 so it can provide a
bridged subnet capability.

> (draft-iesg-ipv6-addressing-recommendations-03.txt).  A RIR

I assume you mean RFC3177... but the point is that it is aligned. Except
in the private network context, there is never a reason to believe that
only a single device is connected, even a cell phone might be a
router/bridge.

Tony

---

From: "Tony Hain" <[email-masked]>
Date: Fri, 1 Feb 2002 12:00:47 -0800

> not mention any potential security issues in network-connected

All sites have a /64 and a /48 prefix available to them *before* they
make any global connection; link-local & site-local. For those devices
where global connectivity may cause undue security concerns (like a
light switch) there is absolutely no reason they need to pay attention
to any global prefixes that may be in the RA. They will still be
perfectly functional auto-configuring IPv6 devices, they just won't have
global access. If privacy is the intended policy, it is easier to
implement and more secure to have only the nodes that need global
addresses listen to them in the RA, than to rely on a NAT/filter which
is most likely confused because its state updates take longer than the
dynamics of connections.

> need a Layer 2 switch and the "IPv6 access device".

We have an allocation mechanism for the simple layer-2 network, a /64,
and a mechansim for those who want a complex layer-3, a /48.

> to Layer 3 route in his home network - but how many really want to do

It doesn't matter, the mechansim exists and is sufficient for all but a
handful of multi-national corporations.

> dedicated small IPv4 network islands to bigger full switched IPv6

To be precise, people should think about designing the network topology
to meet the functional requirements.

> Layer 3 multicast mechanism, which should be also mapped into Layer 2

Layer-2 broadcasts are still appropriate for some uses, so don't assume
that just because we can do without them at layer-3 that we should get
rid of them at layer-2 as well.

Tony

---

From: Antonio Querubin <[email-masked]>
Date: Sat, 2 Feb 2002 00:26:15 -1000 (HST)

> handful of multi-national corporations.

I suspect the practice of assigning a /48 for every complex layer-3
network isn't scalable for many medium and large service providers.  The
number of service providers with more than 65536 clients or customers is
not just a handful.  I would also suggest that many of them aren't even
multi-national.  The ISP stats at Boardwatch for example suggest the
existance of many providers that might find this allocation mechanism to
be impractical or wasteful of address space based on the size of their
customer base.

---

From: Antonio Querubin <[email-masked]>
Date: Sat, 2 Feb 2002 00:40:04 -1000 (HST)

> number of service providers with more than 65536 clients or customers is
                                             ^^^^^

Oops!  What am I thinking?  Change that to 8192 as we're really butting up
against the size of the space between /35 and /48, Reality is probably
somewhere between 8192 and 65536.

---

From: "Tony Hain" <[email-masked]>
Date: Mon, 4 Feb 2002 12:39:58 -0800

> somewhere between 8192 and 65536.

Reality is that any provider with customers will get more than a /35,
that is only the starting point and even that number is likely to
change. If a provider doesn't allocate a /48 to its customers with
complex networks, the customers will simply tunnel over them because
they already have a /48 by using 6to4.

Tony