| Internet-Draft | Flex-Algorithm Reverse Affinity | July 2023 |
| Psenak, et al. | Expires 25 January 2024 | [Page] |
An IGP Flexible Algorithm (Flex-Algorithm) allows IGPs to compute constraint-based paths.¶
This document extends IGP Flex-Algorithm with additional constraints.¶
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An IGP Flex-Algorithm as specified in [I-D.ietf-lsr-flex-algo] computes a constraint-based path.¶
This document extends IGP Flex-Algorithm with additional constraints.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The Flexible Algorithm definition can specify 'colors' that are used by the operator to include or exclude links during the Flex-Algorithm path computation. These link 'colors' are checked in the forwarding direction of the SPF computation - e.g. in the direction from the parent to the child.¶
In some cases, it is beneficial to check the 'colors' of the link from the reverse direction of the traffic flow. For example, on a point-to-point link between endpoints A and B and for the traffic flowing in a direction from A to B, the input errors can only be detected at node B. An operator may measure the rate of such input errors and set certain 'color' on a link locally on node B when the input error rate crosses a certain threshold. When Flex-Algorithm calculation processes the link A to B, it may look at the 'colors' of the link in the reverse direction, e.g., link B to A. This would allow the operator to exclude such link from the Flex-Algorithm topology.¶
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 10.¶
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:¶
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.¶
The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is used to advertise include-any rule that is used during the Flex-Algorithm path calculation as specified in Section 10.¶
The format of the IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in Section 4.¶
The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV Type is 11.¶
The IS-IS Flexible Algorithm Include-Any Reverse Admin Group 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 Flexible Algorithm Include-Any Reverse Admin Group 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 Flexible Algorithm Include-Any Reverse Admin Group 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.¶
The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is used to advertise include-any rule that is used during the Flex-Algorithm path calculation as specified in Section 10.¶
The format of the IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in Section 4.¶
The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV Type is 12.¶
The IS-IS Flexible Algorithm Include-All Reverse Admin Group 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 Flexible Algorithm Include-All Reverse Admin Group 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 Flexible Algorithm Include-All Reverse Admin Group 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.¶
The OSPF 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 10.¶
The OSPF FAERAG Sub-TLV is a Sub-TLV of the OSPF FAD 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:¶
The OSPF FAERAG Sub-TLV MUST NOT appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored by the receiver.¶
The usage of this Sub-TLVs is described in Section 5.¶
The format of the OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV in Section 7.¶
The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV Type is 11.¶
The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV MUST NOT appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored by the receiver.¶
The usage of this Sub-TLVs is described in Section 6.¶
The format of the OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV in Section 7.¶
The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV Type is 12.¶
The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV MUST NOT appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLV MUST be ignored by the receiver.¶
Three new rules are added to the existing rules specified in sec 13 of [I-D.ietf-lsr-flex-algo].¶
This document defines the following Sub-Sub-TLVs in the "ISIS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV" registry:¶
Above code points represent suggested values. The final code points allocation is subject to the allocations made by [I-D.ietf-lsr-flex-algo] and [I-D.ietf-lsr-flex-algo-bw-con].¶
This document registers following Sub-TLVs in the "OSPF TLVs for Flexible Algorithm Definition TLV" registry:¶
Above code points represent suggested values. The final code points allocation is subject to the allocations made by [I-D.ietf-lsr-flex-algo] and [I-D.ietf-lsr-flex-algo-bw-con].¶
This document inherits security considerations from [I-D.ietf-lsr-flex-algo].¶
TBD¶