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

Iljitsch van Beijnum iljitsch at muada.com
Fri Feb 6 14:48:53 UTC 2009

On 6 feb 2009, at 0:55, David W. Hankins wrote:

>>> Exhibit A: With IPv6 Address Autoconfiguration (tm) (patent  
>>> pending), you
>>> don't need DHCP. *face plant*  The IPv4 mistake you've NOT learned  
>>> from
>>> here is "rarp".  DCHP does far more than tell a host was address  
>>> it should
>>> use.

> Actually it goes further back than rarp; IPv6 RA is actually more
> closely related to IPv4 ICMP Router Advertisements

It makes more sense to look at it like this. In the 1990s we had:

- IPv4: manual configuration
- IPv4: DHCP
- IPX: router advertised network prefix + MAC address
- AppleTalk: router advertised network prefix + random number

IPv6 gives us all of these.

> Let's just say it's a slightly restricted (feature-limited?) RIP.

RIP is a routing protocol, not an address configuration protocol.

> But yeah, in that the static->RARP->BOOTP->DHCP progression was a
> dialogue between operators and IETF, IPv6 has basically thrown that
> dialogue out with the bathwater, and we're having it all over again.

The problem is that DHCP seemed like a good idea at the time but it  
doesn't make any sense today. We know that parsing complex binary data  
formats is asking for security problems. Also, whenever you want to  
put something new in DHCP you must update the client and server  
SOFTWARE. Because on the clients, address configuration is a very  
fundamental thing, this is something buried deep inside the system  
where it's hard to make changes by anyone other than the OS vendor.

What we need is a simple, fast, efficient way to distribute the basic  
information that a host needs to start sending and receiving packets  
and a pointer to a place where additional location dependent  
configuration information can be found. That would be: address+prefix,  
gateway and (arguably) DNS and then something like a URL for a server  
that has the config info. The system and applications can then load  
information from the config server over HTTP in XML format or some such.

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