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

[Ralph Droms]

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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