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

Nathan Ward nanog at daork.net
Tue Feb 10 22:38:59 UTC 2009

On 11/02/2009, at 10:41 AM, Ricky Beam wrote:

> It's useless.  It does NOT provide enough information alone for a  
> host to function.  In your own words, you need a DNS server.  That  
> is NOT provided by RA thus requires yet another system to get that  
> bit of configuration to the host -- either entered manually, DHCPv6,  
> or from IPv4 network configuration (ie. DHCP!)  Forcing this BS on  
> the world is a colossal waste.  We've had a system to provide *ALL*  
> the information a host needs or wants in the IPv4 world for years.   
> Why it's not good enough for IPv6 is beyond me.

You are correct, alone RA does not provide enough for a host to  

We have two mechanisms of providing addressing information to hosts -  

How do you, as a network manager, tell hosts which one to use? RA  
performs this function. Without RA you need to go around all the  
machines and manually configure how they will discover what addresses  
to use. That seems a bit silly, and going around every machine is  
something you have already indicated you don't want to do.

RA has two functions - telling your hosts which of SLAAC and DHCPv6 to  
use for addressing information, and providing addressing information  
in the case of SLAAC. Also, in the case of SLAAC, it might hint to the  
client to get additional information from DHCPv6 - DNS servers and so  
on - in this case it will not get addressing information.

Perhaps you have a problem with SLAAC? That is fine, you might not  
want to use it. Other people *do* want to use it, and RA is the best  
place to signal which of SLAAC and DHCPv6 a host should use for  

Please do not use blanket comments that RA is bad if you actually mean  
SLAAC. Yes, if we do not have SLAAC then we don't need RA, because  
hosts will always know to use DHCPv6. However, many people do want  
SLAAC, so we need RA.

If you have an idea for alternative to RA for indicating whether to  
use SLAAC or DHCPv6 then I encourage you to get involved in the IETF  
and get your idea written up. If you would like to deprecate/fix SLAAC  
because you have a problem with it then again, I encourage you to get  
involved in the IETF.

Nathan Ward

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