RE: Glen's proposal for Attribute Extension

["Nelson, David" <dnelson@enterasys.com>]

Uggh!  Let me try again, to get the ASCII art aligned.  I really dislike
the line-wrap behavior of my current e-mail client, when it comes to
plain text messages, with ">" quoting characters inserted.

Glen has also suggested, as have others, that a fixed tag field
could/should be used to address issues of attribute grouping.  The tag
does not show up in this layout.

>     0                   1                   2                   3
>     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |     Type      |  Length       |            Vendor-Id
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         Vendor-Id (cont)           | Extended type |    Length2    |
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |    Data...
>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

If we were to add it, would the format look like this?

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |  Length       |            Vendor-Id
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Vendor-Id (cont)           | Extended type |    Length2    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Tag      |     Data...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

An additional question -- are we suggesting that this format is a MUST
for the Extended RADIUS Attributes, as opposed to the merely suggested
format for VSAs?  I think we should do so.

I also think that maybe we want to not use the VSA attribute type (26)
for this purpose.  

> 
>    Type
> 
>       26 for Vendor-Specific.
> 
>    Length
> 
>       >= 7
> 
>    Vendor-Id
> 
>       0 (for Extended Attributes)
> 
>    Extended Type
> 
>       0:       Reserved
>       1-250:   Allocated by IANA
>       250-255: Reserved
> 
>    Length2
> 
>       >=0
> 
>       Multiple subattributes MAY be encoded within a single Extended
>       Attribute, although they do not have to be.

     Tag

        0:        Not Used (i.e. attribute is untagged)
        1-255:    Tag value used to aggregate attributes into groups

The value of the Tag field MAY be limited to printable ASCII values, for
ease of human entry and interpretation.
 
> For Diameter compatibility, the RADIUS Extended Type attributes would
need
> to be allocated within the Diameter AVP space.



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