v6 subnet size for DSL & leased line customers

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21

As I see it, one of the big benefits IPv4 provided was logical addresssing in an easy-to-understand and easy-to-aggregate manner, with small layer-2 networks divided by routers. What we've gone to with IPv6 is a gigantic layer-2 network (the flat autoconfiguration space).

I think we got here when "site-local" went away - we've effectively redefined link-local to mean "site-local," while using globally unique addressing.

Personally, I don't relish the idea of millions of hosts participating in spanning-tree, so I'd rather see us move back toward the direction of using layer-3 addresses to break up layer-2 islands.

How about this for a modest proposal for a capability:
Allow autoconfigured generation of IPv6 interface addresses to use this format:

(one byte VLAN ID) (48 bit MAC address)

instead of:

(24 bit half-mac) (FFFE) (24 bit half-MAC)

This would allow a CPE router to serve as the gateway for up to 64K VLANs, and wouldn't waste a byte in the middle of the address space.

How about it?

David Barak
Need Geek Rock? Try The Franchise:
http://www.listentothefranchise.com

22

> 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.

Ahhh, thanks - that is the only thing I have ever seen that gives any
reason for the /64 prefix. Sadly, the document contains no
compelling technical reasons for it - looks like it's done just so
things are easy when generating interface IDs from ethernet addresses.

If operational simplicity of fixed length node addressing is a
technical reason, then I think it is a compelling one. If you've ever
done any reasonable amount of work with Novell's IPX (or other fixed
length node addressing layer 3 protocols (mainly all of them except
IPv4!)) you'll know what I mean.

I think Ethernet is also another example of the benefits of
spending/"wasting" address space on operational convenience - who needs
46/47 bits for unicast addressing on a single layer 2 network!? If I
recall correctly from bits and pieces I've read about early Ethernet,
the very first versions of Ethernet only had 16 bit node addressing.
They then decided to spend/"waste" bits on addressing to get
operational convenience - "plug and play" layer 2 networking.

If IPv6 can have the same operational simplicity as Ethernet,
and addressing bits can afford to be spent on it, then I think those
bits are well worth spending.

The /64 for all subnets idea is probably an example of "worse is
better" principle. It's not ideal for everything, but because it's
general enough, it works with everything, and is simpler and a
*single* solution to everything, and that's what makes it better.

Regarding where the /64 boundary came from, from what I understand, the
following Internet Drafts are it's origin:

"8+8 - An Alternate Addressing Architecture for IPv6"
http://arneill-py.sacramento.ca.us/ipv6mh/draft-odell-8+8-00.txt

"GSE - An Alternate Addressing Architecture for IPv6"
http://arneill-py.sacramento.ca.us/ipv6mh/draft-ipng-gseaddr-00.txt

23

Or possibly maybe Peter M. Gleitz's and Steven M. Bellovin's idea of

"Transient Addressing for Related Processes: Improved Firewalling by Using IPV6 and Multiple Addresses per Host"

http://www.cs.columbia.edu/~smb/papers/tarp/tarp.html

A /64 per host is probably not necessary, however if an end-site has
a /48, that's 65K hosts so it wouldn't likely be much of a problem for
most sites ... certainly not my house currently or in the forseeable
future or my current employer, or most employers I've worked for in the
past.

24

I think we got here when "site-local" went away - we've effectively
redefined link-local to mean "site-local," while using globally unique
addressing.

  site-local was replaced with ULA. Have you got your ULA yet? :slight_smile:

  ULA gives you /48's.
  6to4 gives you /48's.

  Your customers already have /48's whether they know it or not
  (and some do).

  Mark

25

There's a tendency to move away from (simulated) shared media networks.
"One host per subnet" might become the norm.

and, with multiple addresses per interface, the home user surely _might_
need a /32.

<sigh>

might does not make right

randy

26

> There's a tendency to move away from (simulated) shared media networks.
> "One host per subnet" might become the norm.

and, with multiple addresses per interface, the home user surely _might_
need a /32.

What prompted you to suggest that? Trolling maybe?

might does not make right

Neither does being ridiculous.

27

Christopher Morrow wrote:

28

Actually we are using stateless form of DHCPv6 to announce DNS servers with autoconf + static address comfiguration for servers. This is satisfactory for a small organisation like us (less than 40 persons). We are testing DHCPv6 also. For a larger organisation (>1000 computer) I will ask my colleagues about their DHCPv6 experiences....

Best Regards,
     Janos Mohacsi