[101212] in North American Network Operators' Group
Re: v6 subnet size for DSL & leased line customers
daemon@ATHENA.MIT.EDU (Mohacsi Janos)
Sun Dec 23 03:53:37 2007
Date: Sun, 23 Dec 2007 09:49:04 +0100 (CET)
From: Mohacsi Janos <mohacsi@niif.hu>
To: Iljitsch van Beijnum <iljitsch@muada.com>
cc: Ross Vandegrift <ross@kallisti.us>, Deepak Jain <deepak@ai.net>,
Joe Greco <jgreco@ns.sol.net>, nanog@merit.edu
In-Reply-To: <BE49A4CF-E726-4009-9995-713C35714DC7@muada.com>
Errors-To: owner-nanog@merit.edu
On Sun, 23 Dec 2007, Iljitsch van Beijnum wrote:
>
> On 22 dec 2007, at 21:23, Ross Vandegrift wrote:
>
>> IPv6 documents seem to assume
>> that because auto-discovery on a LAN uses a /64, you always have to
>> use a /64 global-scope subnet. I don't see any technical issues that
>> require this though. ICMPv6 is capable of passing info on prefixes of
>> any length - prefix length is a plain old 8bit field.
>
>> In fact, until I read the ARIN documents to receive an assignment at
>> work, I assumed this would be how people would operate. So what's the
>> concern? Give all end users a /64 and let them subnet that as they
>> see fit. If DHCPv6 would take care of it automatically with shorter
>> prefixes, that's fine
>
> First of all, there's RFC 3513:
>
> For all unicast addresses, except those that start with binary value 000,
> Interface IDs are required to be 64 bits long and to be constructed in
> Modified EUI-64 format.
>
> Second, we currently have two mechanisms to configure IPv6 hosts with an
> address: router advertisements and DHCPv6. The former has been implemented in
> ALL IPv6 stacks but doesn't work if your subnet isn't a /64. The latter is (I
> think) available on the client side in Windows Vista. There are a few DHCPv6
> server implementations, but the ones I tested 2 years ago wouldn't do address
> assignment. (You still need the router advertisements to learn your default
> gateway and prefix length as DHCPv6 can't tell you those.) So although many
> people want to stick to the DHCP model they know from IPv4, that's extremely
> hard to do with IPv6 the way things currently are.
Actually we tested DHCv6 implementation 2-3 years ago.
http://www.6net.org/publications/deliverables/D3.2.3v3.pdf
The dibbler seemed to be rather complete DHCPv6 implementation. I think
default gateway and prefix length distribution via DHCPv6 will be quite
problematical any many situation. There plenty of organisation who has a
dedicated team/person for network management (routers, switches etc.),
while another team/person for system management (dhcp, servers etc.). So
configuring DHCPv6 requires cooperation which takes time, but users are
complaining....
Best Regards,
Janos Mohacsi
