12. IANA Considerations
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
12. IANA Considerations
12.1. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
IANA has registered the following in the "IS-IS Sub-Sub-TLVs for
Flexible Algorithm Definition Sub-TLV" registry under the "IS-IS TLV
Codepoints" registry group:
Type: 10
Description: Flexible Algorithm Exclude Reverse Admin Group
MP: n
Reference: RFC 9917, Section 5
Type: 11
Description: Flexible Algorithm Include-Any Reverse Admin Group
MP: n
Reference: RFC 9917, Section 6
Type: 12
Description: Flexible Algorithm Include-All Reverse Admin Group
MP: n
Reference: RFC 9917, Section 7
12.2. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry
This document makes the following registration in the "OSPF Flexible
Algorithm Definition TLV Sub-TLVs" registry under the "Open Shortest
Path First (OSPF) Parameters" registry group:
Type: 10
Description: Flexible Algorithm Exclude Reverse Admin Group
Reference: RFC 9917, Section 8
Type: 11
Description: Flexible Algorithm Include-Any Reverse Admin Group
Reference: RFC 9917, Section 9
Type: 12
Description: Flexible Algorithm Include-All Reverse Admin Group
Reference: RFC 9917, Section 10
12.3. IGP Flex-Algorithm Path Computation Rules Registry
IANA has created a new registry called "IGP Flex-Algorithm Path
Computation Rules" within the "Interior Gateway Protocol (IGP)
Parameters" registry group. The registration procedure for the new
registry is Expert Review [RFC8126]. Section 12.3.1 provides
guidance for designated experts.
The "IGP Flex-Algorithm Path Computation Rules" registry specifies
the ordered set of rules that are used to prune links from the
topology during the Flex-Algorithm path computation.
There is no upper bound on the number of rules that the registry
supports.
In Table 1, "FAEMB" means "Flex-Algorithm Exclude Minimum Bandwidth",
and "FAEMD" means "Flex-Algorithm Exclude Maximum Delay".
+==========+===========================================+===========+
| Sequence | Description | Reference |
| Number | | |
+==========+===========================================+===========+
| 1 | Check if any exclude Administrative Group | Section |
| | rule is part of the Flex-Algorithm | 13 of |
| | Definition. If such exclude rule exists, | [RFC9350] |
| | check if any color that is part of the | |
| | exclude rule is also set on the link. If | |
| | such a color is set, the link MUST be | |
| | pruned from the computation. | |
+----------+-------------------------------------------+-----------+
| 2 | Check if any exclude SRLG rule is part of | Section |
| | the Flex-Algorithm Definition. If such | 13 of |
| | exclude rule exists, check if the link is | [RFC9350] |
| | part of any SRLG that is also part of the | |
| | SRLG exclude rule. If the link is part | |
| | of such SRLG, the link MUST be pruned | |
| | from the computation. | |
+----------+-------------------------------------------+-----------+
| 3 | Check if any include-any Administrative | Section |
| | Group rule is part of the Flex-Algorithm | 13 of |
| | Definition. If such include-any rule | [RFC9350] |
| | exists, check if any color that is part | |
| | of the include-any rule is also set on | |
| | the link. If no such color is set, the | |
| | link MUST be pruned from the computation. | |
+----------+-------------------------------------------+-----------+
| 4 | Check if any include-all Administrative | Section |
| | Group rule is part of the Flex-Algorithm | 13 of |
| | Definition. If such include-all rule | [RFC9350] |
| | exists, check if all colors that are part | |
| | of the include-all rule are also set on | |
| | the link. If all such colors are not set | |
| | on the link, the link MUST be pruned from | |
| | the computation. | |
+----------+-------------------------------------------+-----------+
| 5 | If the Flex-Algorithm Definition uses | Section |
| | something other than the IGP metric | 13 of |
| | (Section 5 of [RFC9350]), and such metric | [RFC9350] |
| | is not advertised for the particular link | |
| | in a topology for which the computation | |
| | is done, such link MUST be pruned from | |
| | the computation. A metric of value 0 | |
| | MUST NOT be assumed in such a case. | |
+----------+-------------------------------------------+-----------+
| 6 | Check if any exclude FAEMB rule is part | Section 6 |
| | of the Flex-Algorithm definition. If | of |
| | such exclude rule exists and the link has | [RFC9843] |
| | Maximum Link Bandwidth advertised, check | |
| | if the link bandwidth satisfies the FAEMB | |
| | rule. If the link does not satisfy the | |
| | FAEMB rule, the link MUST be pruned from | |
| | the Flex-Algorithm computation. | |
+----------+-------------------------------------------+-----------+
| 7 | Check if any exclude FAEMD rule is part | Section 6 |
| | of the Flex-Algorithm definition. If | of |
| | such exclude rule exists and the link has | [RFC9843] |
| | Min Unidirectional link delay advertised, | |
| | check if the link delay satisfies the | |
| | FAEMD rule. If the link does not satisfy | |
| | the FAEMD rule, the link MUST be pruned | |
| | from the Flex-Algorithm computation. | |
+----------+-------------------------------------------+-----------+
| 8 | Check if any exclude reverse Admin Group | Section |
| | rule is part of the Flex-Algorithm | 11 of RFC |
| | definition. If such exclude rule exists, | 9917 |
| | check if any Admin Group that is part of | |
| | the exclude rule is also set on the link | |
| | in the reverse direction. If such Admin | |
| | Group is set on the link in the reverse | |
| | direction, the link MUST be pruned from | |
| | the computation. | |
+----------+-------------------------------------------+-----------+
| 9 | Check if any include-any reverse Admin | Section |
| | Group rule is part of the Flex-Algorithm | 11 of RFC |
| | definition. If such include-any rule | 9917 |
| | exists, check if any Admin Group that is | |
| | part of the include-any rule is also set | |
| | on the link in the reverse direction. If | |
| | no such Admin Group is set on the link in | |
| | the reverse direction, the link MUST be | |
| | pruned from the computation. | |
+----------+-------------------------------------------+-----------+
| 10 | Check if any include-all reverse Admin | Section |
| | Group rule is part of the Flex-Algorithm | 11 of RFC |
| | definition. If such include-all rule | 9917 |
| | exists, check if all Admin Groups that | |
| | are part of the include-all rule are also | |
| | set on the link in the reverse direction. | |
| | If all such Admin Groups are not set on | |
| | the link in the reverse direction, the | |
| | link MUST be pruned from the computation. | |
+----------+-------------------------------------------+-----------+
Table 1: IGP Flex-Algorithm Path Calculation Rules
12.3.1. Guidance for Designated Experts
Since the original Flex-Algorithm specification [RFC9350], many Flex-
Algorithm extensions have been proposed and standardized. Many of
them added additional rules to the Flex-Algorithm path computation.
Maintaining an IANA registry for these rules allows specification
across multiple documents progressing independently. The new "IGP
Flex-Algorithm Path Computation Rules" registry has been created and
is specified in Section 12.3.
This section provides the guidance for designated experts on
evaluating new registrations in the "IGP Flex-Algorithm Path
Computation Rules" registry:
1. When a new constraint is defined, the rule associated with that
constraint MAY be inserted at any position. Backwards
compatibility is guaranteed because nodes that don't support the
new constraint will not participate in an algorithm where the FAD
specifies a constraint they don't support.
2. The relative ordering of existing rules MUST NOT be altered.
Doing so has the potential to create backwards compatibility
issues.
3. Deletion of the rules MUST NOT be done. Given that the rules are
only used conditionally based on the information carried in the
winning FAD, deletion of the rule is not necessary.
4. Merging or repeating of the rules MUST NOT be done.