v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space (IPv6-MW)]

Iljitsch van Beijnum iljitsch at muada.com
Fri Feb 6 14:39:01 UTC 2009

On 6 feb 2009, at 1:15, Ricky Beam wrote:

> I see IPv6 address space being carved out in huge chunks for reasons  
> that equate to little more than because the total space is  
> "inexhaustable".  This is the exact same type of mis-management that  
> plagues us from IPv4's early allocations.

Think of it this way: if addresses are going to be wasted, I'll be  
happy to take my share an un-waste as required. For instance, there  
have been suggestions to move the /64 subnet boundary to /80 because  
64-bit MAC addresses never took off. I'll take my /64s now and then  
move the boundary to /80 later so I can multiply the number of subnets  
that I have by 65536. This is a whole lot more pleasant that slicing  
and dicing that single IPv4 address in ever tinier parts as I get more  
stuff that runs IP in my house. (And there is a real risk that I won't  
even have that single IPv4 address anymore in the future but have to  
share one with my neighbors.)

IPv6 is a whole new way of doing things. It doesn't make sense to  
apply IPv4 sensitivities here, just like in the middle of the ocean,  
water management is a different game than in the desert. You could  
make a fair case that 48 bits would have been sufficient for IPv6  
(6/4th of 32 bits after all) and then we'd have to manage that space  
pretty much the same as today's IPv4 space. But it's almost three  
times that.

>> you get to generate an address from a prefix through a function  
>> that gives you the same address without requiring anyone to  
>> remember that address, which is also useful.

> Well, it is extremely wasteful.

Not really. The waste started and ended with the decison to make IPv6  
addresses 128 bits. Now that you have to carry those 128 bits in all  
your packets, there is no additional penalty for actually using them.

> If you want the machine to always have the same address, either  
> enter it manually or set your DHCP server to always give it the same  
> address.

Manual configuration doesn't scale. With IPv4, it's quite hard to make  
this work with DHCP, but mostly because of a lack of IPv4 addresses.  
With IPv6 it's easier, but you're still limiting the uptime of your  
system to that of the DHCPv6 server. Router advertisements is much  
more robust.

> And face reality, many people have enough trouble remembering IPv4  
> addresses -- even when it's simplified to a /24 prefix plus 3 digit  
> number.  They will have an even harder time remembering a 48bit or  
> 64bit MAC.  Do you remember the MAC addresses of ANY of the NICs on  
> your lan(s)?

Isn't remembering stuff what we have computers for?

> It's not even that.  Had they simply not ignored, and out-right  
> dismissed as "wrong", the way networks were being run, then we  
> wouldn't have the mess we have today.  I pick on autoconfig because  
> it's the simplest bit of stupid on their part... we have Stateless  
> Autoconfiguration, *jedi hand wave*, you don't need DHCP.  It was  
> bull the instant they said it.

I have a lot of problems with DHCP and most people don't _need_ it.  
Still, very many people _want_ it and some people do in fact need it.  
I have no problem with that, as long as it doesn't lead to the  
situation where I have to run it.

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