Re: [secdir] SecDir review of draft-ietf-pim-hello-intid-01

[Chris Lonvick <[e-mail]>]

Hi Stig,

On Tue, 9 Aug 2011, Stig Venaas wrote:
<some elided>
>> > 
>> >  While PIM is certainly not my strong suit the document is
>> >  understandable except for the following paragraph from Section 2.1:
>> > 
>> >  The Local Interface Identifier MUST be non-zero. The reason for
>> >  this, is that some protocols may want to only optionally refer to an
>> >  Interface using the Interface Identifier Hello option, and use the
>> >  value of 0 to show that it is not referred to. Note that the value
>> >  of 0 is not a valid ifIndex as defined in [RFC1213].
>> > 
>> >  This seems to be saying that the Local Interface Identifier must not
>> >  be 0, except when some protocol wants to use the Interface Identifier
>> >  Hello to not refer to any actual interface. Which leaves me confused.
>
> Perhaps there is a better way to explain it. To see what I'm talking
> about, please have a look at section 3.6.2 of
> http://tools.ietf.org/html/draft-hou-pim-ecmp-01
>
> The message format includes both Neighbor address and Interface ID,
> but use of the Interface ID is optional. If the Neighbor address is
> sufficient for uniqueness, then Interface ID 0 is sent. Basically,
> the idea is that instead of using some TLV format, it is easier to
> always have an Interface ID field, and use the value 0 as saying
> not in use, or unspecified.
>
> I'm happy if you can think of a better way of phrasing it.

How about:

    The Local Interface Identifier is normally non-zero.  Since the value
    of 0 is not a valid ifIndex as defined in [RFC1213], it's use in
    this field has special meaning.  A Local Interface Identifier of 0 will
    indicate that the Router Identifier is sufficiently unique for
    identification for the protocol using it.  For example, this field is
    non-zero when used in IPv4 when one or more RPF neighbors in the ECMP
    bundle are unnumbered.  For other IPv4 usage, this field is zero'ed
    when sent, and ignored when received.  If the "Router ID" part of the
    "Interface ID" is zero, the field MUST be ignored, regardless of its
    value.

Does that work?

Thanks,
Chris