Re: Node Requirements: Elevating DHCPv6 from MAY to SHOULD

[Markus Hanauska <[e-mail]>]

On 2011-05-31, at 13:38 , Mohacsi Janos wrote:

> I disagree with introduction of another flags. This requires substantial changes in the codes.... Which will take ages....

I took a look at the IPv6 implementations of Mac OS X (which comes from the BSD world) and Linux a couple of weeks ago. Introducing such a second flag can be done with only a hand full of code lines and those can be written in about 30 minutes. Basically this flag only needs to be set for all SLAAC addresses, that's all there is to be done. We call this flag A, for automatically assigned, and keep the existing U flag, for globally unique. Then we have the following cases:

Manual (Static) Address: U = 0, A = 0
DHCP Address: U = 0, A = 0
SLAAC: U = 1, A = 1
SLAAC + Priv Ext: U = 0, A = 1

Now only DHCP and Static Addresses can collide and this would happen in case of a misconfiguration; it is impossible to prevent misconfigurations, so you shouldn't even try.

Right now SLAAC + Priv Ext can collide with Static/DHCP addresses (e.g. while the host is offline, ND will not detect such a collision and when the host goes online, it cannot get its address any longer, since it is taken by a SLAAC host). If we would define SLAAC + Priv Ext to set the U bit (which would be wrong, since these addresses are not globally unique), then it could collide with SLAAC addresses of hosts currently offline (again, ND will not work here and those host cannot go online later because their interface ID collides with an address already in use).

> We need M/O bits to give some sort of consistency.

May I ask what kind of consistency are you referring to?

> Nothing prevent you the suggest an draft document for multicast or anycast resolving DNS.

I consider it way too late to start such a project as of today. This should have been standardized already when the other well known multicast/anycast addresses were standardized.

> There is environment where SLAAC more acceptable - e.g. less adminisration

My home DSL router supports IPv6 and the difference between SLAAC and DHCPv6 is one checkbox; check it, and it runs a DHCPv6 server. There is nothing else you have to configure - you can configure address pools, static assignments, which DNS servers to hand out and other options, but you don't have to, if you don't feel like it. So I cannot really comprehend what is so hard about DHCP administration. Most routers/firewalls as of today have a build in DHCPv4 server and in the worst case, you'll have to enter a DNS server, create an address pool and enable it - not really a lot of administration work - in the best case, it will configure all of that automatically for you and you only have to customize settings if you feel like doing so (most home routers have DHCPv4 enabled and pre-configured, so for most users it means, plug your computer into the router or connect to the WLAN and it works out of the box, nothing to configure at all, except for internet access).


Regards,
Markus