Re: [secdir] secdir review of draft-ietf-6man-addr-select-opt

[Arifumi Matsumoto <[e-mail]>]

Hi Dan,
I appreciate your review.

Comments below.

2013/5/22 Dan Harkins <[e-mail]>

>
>   Hello,
>
>   I have reviewed draft-ietf-6man-addr-select-opt as part of the
> security directorate's  ongoing effort to review all IETF documents
> being processed by the IESG.  These comments were written primarily
> for the benefit of the  security area directors.  Document editors and
> WG chairs should treat these comments just like any other last call
> comments.
>
>   draft-ietf-6man-addr-select-opt defines address selection options
> for DHCPv6 that allow a network administrator to effect some
> control over address selection behavior of nodes on their sites.
>
>   This sounds like a reasonably straightforward problem but as I
> read the draft it seemed like it might be have interoperability issues.
> I don't believe this draft is ready for advancement until these issues
> are resolved.
>
>   For instance, while I think I understand the policy override of RFC
> 6724, having the Automatic Row Additions Flag be part of the address
> selection options seems problematic. If it is set to zero, then what are
> the semantics of such a message? "Here's an address selection option
> but don't you dare use it!"? What is the point? Me, as a node, can have
> this as part of my policy state which would allow me to ignore such
> an update but to have the bit be part of the option to update does
> not seem to make much sense. The semantics of the message needs
> to be explained much more clearly, or the bit needs to be removed
> from the message.
>

If A flag is zero, it means Automatic Row Addition is indicated not to
perform.
If A flag is 1, it means it is up to the node.

Even in the latter case, the Address Selection Option may contain other
information to the node, such as the policy table and other flags.

Make sense ?

If not, splitting the flag into another new sub-option makes sense to you ?


>
>   Section 3.3 says, "Even if the received policy from one source is
> merged with one from another source, the effect of both policy are
> more or less changed." I don't understand how both policies are
> changed. And what does "more or less" mean?


I think that a policy table has its own unique meaning. Even single
insertion/deletion from the table makes the table different.

For example, when adding a line, from one source, to the default policy
table below,

      Prefix        Precedence Label
      ::1/128               50     0
      ::/0                  40     1
      ::ffff:0:0/96         35     4
      2002::/16             30     2
      2001::/32              5     5
      fc00::/7               3    13
      ::/96                  1     3
      fec0::/10              1    11
      3ffe::/16              1    12

makes

      Prefix        Precedence Label
      ::1/128               50     0
      ::/0                  40     1
      ::ffff:0:0/96         35     4
      2002::/16             30     2
+     2003::/16             10    6
      2001::/32              5     5
      fc00::/7               3    13
      ::/96                  1     3
      fec0::/10              1    11
      3ffe::/16              1    12

In this case, the prefix 2003::/16 has lower precendence than the default
policy table. And, the table contains a lot of policy that is not intended
by
the source who deliver single line of policy.



> 3.3 also says,
> "It also should be noted that absence of the distributed policy from a
> certain network interface should not be treated as absence of policy
> itself, because it may mean preference for the default address
> selection policy." So I use the default address selection policy then,
> is that it?


I mean, there is no way to tell the network with no policy distribution
prefers default policy, or does not care about it.
The conclusion is "using the default policy should be safe", though.


> This whole section (3.3) screams out for some normative
> language since it sounds like it refers to behavioral changes on the
> node.
>

Do you mean this section should have more SHOULDs and MUSTs ?
If so, on which part do you think should we put ?


>
>   There is an "Implementation Consideration" mentioning that the
> label is passed as an unsigned integer. But it then goes on to say,
> "DHCPv6 clients SHOULD convert this label to a representation
> appropriate for the local implementation (e.g., string)." This has
> interoperability implications because it is not solely a local matter.
> The node may represent these things differently than the network
> administrator and the preference will not be done properly. RFC 6724
> does not really define what the label is from what I can tell. It's
> used to just allow for policies to prefer a particular source address,
> S, with a particular destination address, D, if "Label(S) = Label(D)".
> But to pass a value over a network, and have it be used by the
> recipient, means that a canonical representation of "label" has to
> be defined.
>

Maybe, I don't understand your point quite well.
As far as the one-to-one mapping in a node is performed between an
unsinged integer and representation format, I think there will not arise
interoperability issue, such that a policy has different meaning depending
on a receiving host.


>   An appendix with examples would be most helpful!
>

RFC 6724 has a lot of examples for policy table.
Do you think we need other examples, or just same ones ?


>
>   Spelling nit: section 3.1 "The choice a SHOULD be default, as far as
> the policy table is not configured by the user." There's an extra
> word in there somewhere, or maybe there's some words missing,
> it's hard to understand what is being implied.
>

It means the choice called "a" below should be default.
Maybe using parenthesis (a) makes it clearer ?

Best regards,


>
>   regards,
>
>   Dan.
>
>
>