5. IS-IS Flexible Algorithm Exclude Reverse Admin Group Sub-TLV

This section preserves the RFC text for IGP Flex-Algorithm reverse affinity constraints, including FAERAG, FAD, IS-IS and OSPF Sub-TLVs, reverse Administrative Groups, IANA registrations, and path pruning rules.

Original RFC Text

5.  IS-IS Flexible Algorithm Exclude Reverse Admin Group Sub-TLV

   The IS-IS Flexible Algorithm Exclude Reverse Admin Group (FAERAG)
   Sub-TLV is used to advertise the exclude rule that is used during the
   Flex-Algorithm path calculation as specified in Section 11.

   The IS-IS FAERAG Sub-TLV is a sub-TLV of the IS-IS FAD Sub-TLV.  It
   has the following format:

    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     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Extended Admin Group                     |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   Type (1 octet):  10

   Length (1 octet):  Variable, dependent on the size of the Extended
      Admin Group.  The length MUST be a multiple of 4 octets.  If the
      length is not a multiple of 4 octets, the entire sub-TLV MUST be
      ignored by the receiver.

   Extended Administrative Group:  Extended Administrative Group as
      defined in [RFC7308].

   The IS-IS FAERAG Sub-TLV MUST NOT appear more than once in a single
   IS-IS FAD Sub-TLV.  If it appears more than once, the IS-IS FAD Sub-
   TLV MUST be ignored by the receiver.

   The IS-IS FAERAG Sub-TLV MUST NOT appear more than once in the set of
   FAD Sub-TLVs for a given Flex-Algorithm from a given IS.  If it
   appears more than once in such set, the IS-IS FAERAG Sub-TLV in the
   first occurrence in the lowest-numbered LSP from a given IS MUST be
   used and any other occurrences MUST be ignored by the receiver.