[Idr] draft-jiang-idr-sr-policy-composite-path-03 - Question on precedence of Color setting

[Susan Hares <[e-mail]>]

Jeffrey Haas12:04 (chat)- statement
I think this is a broader concern with sr policy as a
mechanism rather than this extension in particular?

Sue's specific Question:
What is the precedence (and interaction) of possible ways
To specify color in the Tunnel Encapsulation Attribute.

See the different ways you can specify color that could
Impact a segment that is part of a segment list.


References
==============
Way 1: draft-jiang-idr-sr-policy-composite-path-03
defines Constituent SR Policy with Color Sub-TLV in the following manner:

      SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
          Attributes:
              Tunnel Encaps Attribute (23)
                  Tunnel Type: SR Policy
                      Binding SID
                      SRv6 Binding SID
                      Preference
                      Priority
                      Policy Name
                      Policy Candidate Path Name
                      Explicit NULL Label Policy (ENLP)
                      Segment List
                          Weight
                          Segment
                          Segment
                          ...
                      Constituent SR Policy
                          Color
                          Weight
                          Forwarding Class


Way 2: RFC 9012 - Tunnel Encapsulation Attribute carries:

3.4.2.  Color Sub-TLV (Type Code 4)

   The Color sub-TLV MAY be used as a way to "color" the corresponding
   Tunnel TLV.  The Value field of the sub-TLV is eight octets long and
   consists of a Color Extended Community, as defined in Section 4.3.
   For the use of this sub-TLV and extended community, please see
   Section 8.

   The format of the Value field is depicted in Figure 15.

   If the Length field of a Color sub-TLV has a value other than 8, or
   the first two octets of its Value field are not 0x030b, the sub-TLV
   MUST be treated as if it were an unrecognized sub-TLV (see
   Section 13).

Way 3: In addition, RFC9012 defines interactions with the Color Extended Community.

4.3.  Color Extended Community

   The Color Extended Community is a Transitive Opaque Extended
   Community with the encoding shown in Figure 15.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | 0x03 (1 octet)| 0x0b (1 octet)|        Flags (2 octets)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Color Value (4 octets)                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+