Subject: RE: M & O Bits was: draft-ietf-ipv6-node-requirements-01.txt

From: Ralph Droms <[email-masked]>
Date: Wed, 05 Feb 2003 07:34:08 -0500

John,

I've reviewed the text in draft-ietf-ipv6-node-requirements-02.txt, and I 
have some comments about the text concerning DHCP.

Regarding the use of DHCP for address assignment...RFC2462 is somewhat 
vague about the requirement - there are no RFC2119 words guiding the ues of 
DHCP in section 5.5.3, and no warnings about the consequences of not using 
DHCP when the 'M' bit is set.  I think we should assume that DHCP is the 
stateful address assignment protocol at this point (esp. now that the spec 
has been accepted as a PS).  Also, RFC2462 does not explicitly explain that 
stateless address autoconfiguration and the use of DHCP are independent - 
if the 'M' bit is set and there are prefix options in the RA, the host will 
obtain both SAAC and DHCP addresses.  I propose the following text :

   4.5.5 Stateful Address Autoconfiguration

   Stateful Address Autoconfiguration SHOULD be supported.  DHCP
   [DHCPv6] is the standard stateful address configuration protocol. An
   IPv6 node that does not include an implementation of DHCP will be
   unable to obtain any IPv6 addresses aside from link-local addresses
   when it is connected to a link over which it receives a router
   advertisement with the 'M' flag (Managed address configuration) set
   and which contains no prefixes advertised for Stateless Address
   Autoconfiguration (see section 4.5.2). An IPv6 node that receives
   a router advertisement with the 'M' flag set and that contains
   advertised prefixes will configure interfaces with both stateless
   autoconfiguration addresses and addresses obtained through DHCP.

   For those IPv6 Nodes that implement DHCP, those nodes MUST use DHCP
   upon the receipt of a Router Advertisement with the 'M' flag set
   (see section 5.5.3 of RFC2462).  In addition, in the absence of a
   router, IPv6 Nodes that implement DHCP MUST attempt to use DHCP.

   For IPv6 Nodes that do not implement DHCP, the 'M' flag
   of a Router Advertisement can be ignored.  Furthermore, in the
   absence of a router, this type of node is not required to initiate
   DHCP.

Regarding the 'O' flag...RFC2462 uses about the same (non-RFC2119) words 
here as for the 'M' flag.  Again, there is no mention of the consequences 
of not implementing the "stateful autoconfiguration protocol", and it's 
appropriate to assume DHCP will be stateful autoconfiguration 
protocol.  So, I think section 5.3 should look a lot like 4.5.5:

5.3 Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

   Stateful Autoconfiguration SHOULD be supported.  DHCP [DHCPv6] is
   the standard stateful configuration protocol. An IPv6 node that does
   not include an implementation of DHCP will be unable to obtain other
   configuration information such as the addresses of DNS servers when
   it is connected to a link over which the node receives a router
   advertisement in which the 'O' flag ("Other stateful configuration")
   is set.

   For those IPv6 Nodes that implement DHCP, those nodes MUST use DHCP
   upon the receipt of a Router Advertisement with the 'O' flag set
   (see section 5.5.3 of RFC2462).  In addition, in the absence of a
   router, hosts that implement DHCP MUST attempt to use DHCP.

   For IPv6 Nodes that do not implement DHCP, the 'O' flag
   of a Router Advertisement can be ignored.  Furthermore, in the
   absence of a router, this type of node is not required to initiate
   DHCP.

- Ralph

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From: Jari Arkko <[email-masked]>
Date: Wed, 05 Feb 2003 15:24:41 +0200

Ralph Droms wrote:
> John,
> 
> I've reviewed the text in draft-ietf-ipv6-node-requirements-02.txt, and 
> I have some comments about the text concerning DHCP.
> 
> vague about the requirement - there are no RFC2119 words guiding the ues 
> of DHCP in section 5.5.3, and no warnings about the consequences of not 
> using DHCP when the 'M' bit is set.  I think we should assume that DHCP 

Yes (though in defense of 2462 this is probably some "weasel wording"
to get around the fact that at the time 2462 was written there was no
RFC for DHCPv6).

> is the stateful address assignment protocol at this point (esp. now that 
> the spec has been accepted as a PS).  Also, RFC2462 does not explicitly 
> explain that stateless address autoconfiguration and the use of DHCP are 
> independent - if the 'M' bit is set and there are prefix options in the 
> RA, the host will obtain both SAAC and DHCP addresses.  I propose the 

Yes.

> following text :

SHOULD or MAY?

>   autoconfiguration addresses and addresses obtained through DHCP.

Looks good.

>   router, IPv6 Nodes that implement DHCP MUST attempt to use DHCP.

Ok.

> here as for the 'M' flag.  Again, there is no mention of the 
> consequences of not implementing the "stateful autoconfiguration 
> protocol", and it's appropriate to assume DHCP will be stateful 
> autoconfiguration protocol.  So, I think section 5.3 should look a lot 
> like 4.5.5:
> 

Looks good.

Jari

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From: Francis Dupont <[email-masked]>
Date: Wed, 05 Feb 2003 16:10:06 +0100

SHOULD or MAY?
   
=> I agree, a MAY is enough.

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