< draft-ietf-lsr-flex-algo-02.txt   draft-ietf-lsr-flex-algo-03.txt >
Network Working Group P. Psenak, Ed. Network Working Group P. Psenak, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Intended status: Standards Track S. Hegde Intended status: Standards Track S. Hegde
Expires: November 14, 2019 Juniper Networks, Inc. Expires: January 5, 2020 Juniper Networks, Inc.
C. Filsfils C. Filsfils
K. Talaulikar K. Talaulikar
Cisco Systems, Inc. Cisco Systems, Inc.
A. Gulko A. Gulko
Thomson Reuters Thomson Reuters
May 13, 2019 July 4, 2019
IGP Flexible Algorithm IGP Flexible Algorithm
draft-ietf-lsr-flex-algo-02.txt draft-ietf-lsr-flex-algo-03.txt
Abstract Abstract
IGP protocols traditionally compute best paths over the network based IGP protocols traditionally compute best paths over the network based
on the IGP metric assigned to the links. Many network deployments on the IGP metric assigned to the links. Many network deployments
use RSVP-TE based or Segment Routing based Traffic Engineering to use RSVP-TE based or Segment Routing based Traffic Engineering to
enforce traffic over a path that is computed using different metrics enforce traffic over a path that is computed using different metrics
or constraints than the shortest IGP path. This document proposes a or constraints than the shortest IGP path. This document proposes a
solution that allows IGPs themselves to compute constraint based solution that allows IGPs themselves to compute constraint based
paths over the network. This document also specifies a way of using paths over the network. This document also specifies a way of using
Segment Routing Prefix-SIDs to steer packets along the constraint- Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets
based paths. along the constraint-based paths.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 14, 2019. This Internet-Draft will expire on January 5, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 25 skipping to change at page 2, line 25
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 4 4. Flexible Algorithm . . . . . . . . . . . . . . . . . . . . . 5
5. Flexible Algorithm Definition Advertisement . . . . . . . . . 5 5. Flexible Algorithm Definition Advertisement . . . . . . . . . 5
5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 5 5.1. ISIS Flexible Algorithm Definition Sub-TLV . . . . . . . 5
5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 7 5.2. OSPF Flexible Algorithm Definition TLV . . . . . . . . . 7
5.3. Common Handling of Flexible Algorithm Definition TLV . . 8 5.3. Common Handling of Flexible Algorithm Definition TLV . . 8
6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 9 6. Sub-TLVs of ISIS FAD Sub-TLV . . . . . . . . . . . . . . . . 9
6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 9 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV . . . 9
6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 10 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV . 10
6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 10 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV . 10
7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 11 6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV . . . . 11
7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 11 7. Sub-TLVs of OSPF FAD TLV . . . . . . . . . . . . . . . . . . 12
7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 11 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV . . . 12
7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 12 7.2. OSPF Flexible Algorithm Include-Any Admin Group Sub-TLV . 13
8. Advertisement of Node Participation in a Flex-Algorithm . . . 12 7.3. OSPF Flexible Algorithm Include-All Admin Group Sub-TLV . 13
8.1. Advertisement of Node Participation for Segment Routing . 12 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV . . . . 13
8.2. Advertisement of Node Participation for Other 8. ISIS Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 14
Applications . . . . . . . . . . . . . . . . . . . . . . 13 9. OSPF Flex-Algorithm Prefix Metric Sub-TLV . . . . . . . . . . 15
9. Advertisement of Link Attributes for Flex-Algorithm . . . . . 13 10. Advertisement of Node Participation in a Flex-Algorithm . . . 16
10. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 13 10.1. Advertisement of Node Participation for Segment Routing 16
11. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 15 10.2. Advertisement of Node Participation for Other
11.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 15 Applications . . . . . . . . . . . . . . . . . . . . . . 17
11.2. Other Applications' Forwarding for Flex-Algorithm . . . 16 11. Advertisement of Link Attributes for Flex-Algorithm . . . . . 17
12. Backward Compatibility . . . . . . . . . . . . . . . . . . . 16 12. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 18
13. Security Considerations . . . . . . . . . . . . . . . . . . . 16 12.1. Multi-area and Multi-domain Considerations . . . . . . . 19
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 13. Flex-Algorithm and Forwarding Plane . . . . . . . . . . . . . 20
14.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 16 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm . . . 20
14.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 16 13.2. SRv6 Forwarding for Flex-Algorithm . . . . . . . . . . . 21
14.1.2. Flexible Algorithm Definition Metric-Type Registry . 17 13.3. Other Applications' Forwarding for Flex-Algorithm . . . 21
14.2. ISIS IANA Considerations . . . . . . . . . . . . . . . . 17 14. Backward Compatibility . . . . . . . . . . . . . . . . . . . 22
14.2.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 17 15. Security Considerations . . . . . . . . . . . . . . . . . . . 22
14.2.2. Sub-Sub-TLVs for Flexible Algorithm Definition Sub- 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
TLV . . . . . . . . . . . . . . . . . . . . . . . . 17 16.1. IGP IANA Considerations . . . . . . . . . . . . . . . . 22
14.3. OSPF IANA Considerations . . . . . . . . . . . . . . . . 18 16.1.1. IGP Algorithm Types Registry . . . . . . . . . . . . 22
14.3.1. OSPF Router Information (RI) TLVs Registry . . . . . 18 16.1.2. Flexible Algorithm Definition Metric-Type Registry . 22
14.3.2. OSPF Flexible Algorithm Definition TLV Sub-TLV 16.2. Flex-Algorithm Definition Flags Registry . . . . . . . . 23
Registry . . . . . . . . . . . . . . . . . . . . . . 18 16.3. ISIS IANA Considerations . . . . . . . . . . . . . . . . 23
15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19 16.3.1. Sub TLVs for Type 242 . . . . . . . . . . . . . . . 23
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237 . . . . 24
16.1. Normative References . . . . . . . . . . . . . . . . . . 20 16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-
16.2. Informative References . . . . . . . . . . . . . . . . . 21 TLV . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 16.4. OSPF IANA Considerations . . . . . . . . . . . . . . . . 25
16.4.1. OSPF Router Information (RI) TLVs Registry . . . . . 25
16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs . . . . . . . . 25
16.4.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . 25
16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV
Registry . . . . . . . . . . . . . . . . . . . . . . 25
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
18.1. Normative References . . . . . . . . . . . . . . . . . . 27
18.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
An IGP computed path based on the shortest IGP metric must often be An IGP computed path based on the shortest IGP metric must often be
replaced by traffic engineered path due to the traffic requirements replaced by a traffic engineered path due to the traffic requirements
which are not reflected by the IGP metric. Some networks engineer which are not reflected by the IGP metric. Some networks engineer
the IGP metric assignments in a way that the IGP Metric reflects the the IGP metric assignments in a way that the IGP Metric reflects the
link bandwidth or delay. If, for example, the IGP metric is link bandwidth or delay. If, for example, the IGP metric is
reflecting the bandwidth on the link and the application traffic is reflecting the bandwidth on the link and the application traffic is
delay sensitive, the best IGP path may not reflect the best path from delay sensitive, the best IGP path may not reflect the best path from
such application's perspective. such an application's perspective.
To overcome this limitation, various sorts of traffic engineering To overcome this limitation, various sorts of traffic engineering
have been deployed, including RSVP-TE and SR-TE, in which case the TE have been deployed, including RSVP-TE and SR-TE, in which case the TE
component is responsible for computing the path based on additional component is responsible for computing paths based on additional
metrics and/or constraints. Such paths need to be installed in the metrics and/or constraints. Such paths need to be installed in the
forwarding tables in addition to, or as a replacement for the forwarding tables in addition to, or as a replacement for, the
original paths computed by IGPs. Tunnels are often used to represent original paths computed by IGPs. Tunnels are often used to represent
the engineered paths and mechanisms like one described in [RFC3906] the engineered paths and mechanisms like one described in [RFC3906]
are used to replace the native IGP paths with such tunnel paths. are used to replace the native IGP paths with such tunnel paths.
This document specifies a set of extensions to ISIS, OSPFv2 and This document specifies a set of extensions to ISIS, OSPFv2 and
OSPFv3 that enable a router to send TLVs that (a) describe a set of OSPFv3 that enable a router to send TLVs that identify (a)
constraints on the topology, (b) identify calculation-type, and (c) calculation-type, (b) specify a metric-type, and (c )describe a set
metric-type that are to be used to compute the best paths along the of constraints on the topology, that are to be used to compute the
constrained topology. A given combination of calculation-type, best paths along the constrained topology. A given combination of
metric-type and constraints is known as a "Flexible Algorithm calculation-type, metric-type, and constraints is known as a
Definition". A router that sends such a set of TLVs also assigns a "Flexible Algorithm Definition". A router that sends such a set of
specific value, Flex-Algorithm, to the specified combination of TLVs also assigns a Flex-Algorithm value, to the specified
calculation-type, metric-type and constraints. combination of calculation-type, metric-type, and constraints.
This document also specifies a way for a router to use IGPs to This document also specifies a way for a router to use IGPs to
associate one or more Segment Routing Prefix-SIDs with a particular associate one or more SR Prefix-SIDs or SRv6 locators with a
Flex-Algorithm. Each such Prefix-SID then represents a path that is particular Flex-Algorithm. Each such Prefix-SID or SRv6 locator then
computed according to the identified Flex-Algorithm. represents a path that is computed according to the identified Flex-
Algorithm.
2. Requirements notation 2. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Terminology 3. Terminology
This section defines terms that are often used in this document. This section defines terms that are often used in this document.
Flexible Algorithm Definition - the set consisting of (a) Flexible Algorithm Definition - the set consisting of (a)
calculation-type, (b) metric-type and (c) a set of constraints. calculation-type, (b) metric-type, and (c) a set of constraints,.
Flexible Algorithm - a numeric identifier in the range 128-255 that Flexible Algorithm - a numeric identifier in the range 128-255 that
is associated via provisioning with the Flexible-Algorithm is associated via provisioning with the Flexible-Algorithm
Definition. Definition.
Local Flexible Algorithm Definition - Flexible Algorithm Definition Local Flexible Algorithm Definition - Flexible Algorithm Definition
defined locally on the node. defined locally on the node.
Remote Flexible Algorithm Definition - Flexible Algorithm Definition Remote Flexible Algorithm Definition - Flexible Algorithm Definition
received from other nodes via IGP flooding. received from other nodes via IGP flooding.
skipping to change at page 6, line 51 skipping to change at page 7, line 7
Calculation Type defined for the specified IGP Algorithm is used. Calculation Type defined for the specified IGP Algorithm is used.
The Metric/Constraints MUST NOT be inherited. If the required The Metric/Constraints MUST NOT be inherited. If the required
calculation type is Shortest Path First, the value 0 SHOULD appear calculation type is Shortest Path First, the value 0 SHOULD appear
in this field. in this field.
Priority: Value between 0 and 255 inclusive that specifies the Priority: Value between 0 and 255 inclusive that specifies the
priority of the advertisement. priority of the advertisement.
Sub-TLVs - optional sub-TLVs. Sub-TLVs - optional sub-TLVs.
The ISIS FAD Sub-TLV MAY be advertised in an LSP of any number, but a
router MUST NOT advertise more than one ISIS FAD Sub-TLV for a given
Flexible-Algorithm. A router receiving multiple ISIS FAD Sub-TLVs
for a given Flexible-Algorithm from the same originator SHOULD select
the first advertisement in the lowest numbered LSP.
The ISIS FAD Sub-TLV MAY be flooded only in a given level or The ISIS FAD Sub-TLV MAY be flooded only in a given level or
throughout the domain. In the latter case the S-flag is set as throughout the domain. In the latter case the S-flag is set as
described in [RFC7981]. It is recommended that domain-wide flooding described in [RFC7981]. It is recommended that domain-wide flooding
NOT be the default behavior. NOT be the default behavior.
5.2. OSPF Flexible Algorithm Definition TLV 5.2. OSPF Flexible Algorithm Definition TLV
OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is OSPF FAD TLV is advertised as a top-level TLV of the RI LSA that is
defined in [RFC7770]. defined in [RFC7770].
skipping to change at page 8, line 26 skipping to change at page 8, line 36
5.3. Common Handling of Flexible Algorithm Definition TLV 5.3. Common Handling of Flexible Algorithm Definition TLV
This section describes the protocol independent handling of the FAD This section describes the protocol independent handling of the FAD
TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in TLV (OSPF) or FAD Sub-TLV (ISIS). We will refer to it as FAD TLV in
this section, even though in case of ISIS it is a Sub-TLV. this section, even though in case of ISIS it is a Sub-TLV.
The value of the Flex-Algorithm MUST be between 128 and 255 The value of the Flex-Algorithm MUST be between 128 and 255
inclusive. If it is not, the FAD TLV MUST be ignored. inclusive. If it is not, the FAD TLV MUST be ignored.
Not every router configured to participate in a particular Flex- Only a subset of the routers participating in the particular Flex-
Algorithm need a local definition of such Flex-Algorithm. Only a Algorithm need to advertise the definition of the Flex-Algorithm.
subset of the routers participating in the particular Flex-Algorithm
need the local definition of the Flex-Algorithm.
Every router, that is configured to participate in a particular Flex- Every router, that is configured to participate in a particular Flex-
Algorithm, MUST select the Flex-Algorithm definition based on the Algorithm, MUST select the Flex-Algorithm definition based on the
following ordered rules. This allows for the consistent Flex- following ordered rules. This allows for the consistent Flex-
Algorithm definition selection in cases where different routers Algorithm definition selection in cases where different routers
advertise different definitions for a given Flex-Algorithm: advertise different definitions for a given Flex-Algorithm:
1. From the advertisements of the FAD in the area (including both 1. From the advertisements of the FAD in the area (including both
locally generated advertisements and received advertisements) locally generated advertisements and received advertisements)
select the one(s) with the highest priority. select the one(s) with the highest priority value.
2. If there are multiple advertisements of the FAD with the same 2. If there are multiple advertisements of the FAD with the same
highest priority, select the one that is originated from the highest priority, select the one that is originated from the
router with the highest System-ID in case of ISIS or Router ID in router with the highest System-ID in case of ISIS or Router ID in
case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in case of OSPFv2 and OSPFv3. For ISIS the System-ID is described in
[ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described [ISO10589]. For OSPFv2 and OSPFv3 standard Router ID is described
in [RFC2328] and [RFC5340] respectively. in [RFC2328] and [RFC5340] respectively.
A router that is not configured to participate in a particular Flex- A router that is not configured to participate in a particular Flex-
Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex- Algorithm MUST ignore FAD Sub-TLVs advertisements for such Flex-
Algorithm. Algorithm.
A router that is not participating in a particular Flex-Algorithm is
allowed to advertise FAD for such Flex-Algorithm. Receiving routers
MUST consider FAD advertisement regardless of the Flex-Algorithm
participation of the FAD originator.
Any change in the Flex-Algorithm definition may result in temporary Any change in the Flex-Algorithm definition may result in temporary
disruption of traffic that is forwarded based on such Flex-Algorithm disruption of traffic that is forwarded based on such Flex-Algorithm
paths. The impact is similar to any other event that requires paths. The impact is similar to any other event that requires
network wide convergence. network wide convergence.
If a node is configured to participate in a particular Flexible- If a node is configured to participate in a particular Flexible-
Algorithm, but the selected Flex-Algorithm definition includes Algorithm, but the selected Flex-Algorithm definition includes
calculation-type, metric-type or constraint that is not supported by calculation-type, metric-type, constraint, flag or Sub-TLV that is
the node, it MUST stop participating in such Flexible-Algorithm. not supported by the node, it MUST stop participating in such
That implies that it MUST NOT announce participation for such Flexible-Algorithm. That implies that it MUST NOT announce
Flexible-Algorithm and it MUST remove any forwarding state associated participation for such Flexible-Algorithm as specified in Section 10
with it. and it MUST remove any forwarding state associated with it.
Flex-Algorithm definition is topology independent. It applies to all Flex-Algorithm definition is topology independent. It applies to all
topologies that a router participates in. topologies that a router participates in.
6. Sub-TLVs of ISIS FAD Sub-TLV 6. Sub-TLVs of ISIS FAD Sub-TLV
6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV 6.1. ISIS Flexible Algorithm Exclude Admin Group Sub-TLV
The Flexible-Algorithm definition can specify 'colors' that are used The Flexible-Algorithm definition can specify 'colors' that are used
by the operator to exclude links during the Flex-Algorithm path by the operator to exclude links during the Flex-Algorithm path
computation. computation.
ISIS Flexible Algorithm Exclude Admin Group Sub-TLV is used to
advertise the exclude rule that is used during the Flex-Algorithm
path calculation as specified in Section 12.
Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a
Sub-TLV of the ISIS FAD Sub-TLV. It has the following format: Sub-TLV of the ISIS FAD Sub-TLV. It has the following format:
0 1 2 3 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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Admin Group | | Extended Admin Group |
+- -+ +- -+
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Extended Administrative Group: Extended Administrative Group as Extended Administrative Group: Extended Administrative Group as
defined in [RFC7308]. defined in [RFC7308].
ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub- ISIS FAEAG Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-
TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be
ignored by the receiver. ignored by the receiver.
6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV 6.2. ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV
The Flexible-Algorithm definition can specify 'colors' that are used The Flexible-Algorithm definition can specify 'colors' that are used
by the operator to include link during the Flex-Algorithm path by the operator to include links during the Flex-Algorithm path
computation. computation.
ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV is used to
advertise include-any rule that is used during the Flex-Algorithm advertise include-any rule that is used during the Flex-Algorithm
path calculation as specified in Section Section 10. path calculation as specified in Section 12.
The format of the ISIS Flexible Algorithm Include-Any Admin Group The format of the ISIS Flexible Algorithm Include-Any Admin Group
Sub-TLV is identical to the format of the FAEAG Sub-TLV in Sub-TLV is identical to the format of the FAEAG Sub-TLV in
Section 6.1. Section 6.1.
Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2. Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 2.
ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT ISIS Flexible Algorithm Include-Any Admin Group Sub-TLV MAY NOT
appear more then once in an ISIS FAD Sub-TLV. If it appears more appear more then once in an ISIS FAD Sub-TLV. If it appears more
then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver.
6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV 6.3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV
The Flexible-Algorithm definition can specify 'colors' that are used The Flexible-Algorithm definition can specify 'colors' that are used
by the operator to include link during the Flex-Algorithm path by the operator to include link during the Flex-Algorithm path
computation. computation.
ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to ISIS Flexible Algorithm Include-All Admin Group Sub-TLV is used to
advertise include-all rule that is used during the Flex-Algorithm advertise include-all rule that is used during the Flex-Algorithm
path calculation as specified in Section Section 10. path calculation as specified in Section 12.
The format of the ISIS Flexible Algorithm Include-All Admin Group The format of the ISIS Flexible Algorithm Include-All Admin Group
Sub-TLV is identical to the format of the FAEAG Sub-TLV in Sub-TLV is identical to the format of the FAEAG Sub-TLV in
Section 6.1. Section 6.1.
ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3. ISIS Flexible Algorithm Include-All Admin Group Sub-TLV Type is 3.
ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT ISIS Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT
appear more then once in an ISIS FAD Sub-TLV. If it appears more appear more then once in an ISIS FAD Sub-TLV. If it appears more
then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver. then once, the ISIS FAD Sub-TLV MUST be ignored by the receiver.
6.4. ISIS Flexible Algorithm Definition Flags Sub-TLV
ISIS Flexible Algorithm Definition Flags Sub-TLV (FADF Sub-TLV) is a
Sub-TLV of the ISIS 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+- -+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 4
Length: variable, non-zero number of octets of the Flags field
Flags:
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|M| | | ...
+-+-+-+-+-+-+-+-+...
M-flag: when set, Flex-Algorithm specific prefix metric MUST be
used, if advertised with the prefix. This flag is not
applicable to prefixes advertised as SRv6 locators.
Bits are defined/sent starting with Bit 0 defined above. Additional
bit definitions that may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits that will
need to be transmitted.
Undefined bits MUST be transmitted as 0.
Bits that are NOT transmitted MUST be treated as if they are set to 0
on receipt.
ISIS FADF Sub-TLV MAY NOT appear more then once in an ISIS FAD Sub-
TLV. If it appears more then once, the ISIS FAD Sub-TLV MUST be
ignored by the receiver.
If the ISIS FADF Sub-TLV is not present inside the ISIS FAD Sub-TLV,
all the bits are assumed to be set to 0.
7. Sub-TLVs of OSPF FAD TLV 7. Sub-TLVs of OSPF FAD TLV
7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV 7.1. OSPF Flexible Algorithm Exclude Admin Group Sub-TLV
Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a Flexible Algorithm Exclude Admin Group Sub-TLV (FAEAG Sub-TLV) is a
Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1. Sub-TLV of the OSPF FAD TLV. It's usage is described in Section 6.1.
It has the following format: It has the following format:
0 1 2 3 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 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
skipping to change at page 12, line 19 skipping to change at page 13, line 33
The format of the OSPF Flexible Algorithm Include-Any Admin Group The format of the OSPF Flexible Algorithm Include-Any Admin Group
Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in Sub-TLV is identical to the format of the OSPF FAEAG Sub-TLV in
Section 7.1. Section 7.1.
Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3. Flexible Algorithm Include-Any Admin Group Sub-TLV Type is 3.
OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT OSPF Flexible Algorithm Include-All Admin Group Sub-TLV MAY NOT
appear more then once in an OPSF FAD TLV. If it appears more then appear more then once in an OPSF FAD TLV. If it appears more then
once, the OSPF FAD TLV MUST be ignored by the receiver. once, the OSPF FAD TLV MUST be ignored by the receiver.
8. Advertisement of Node Participation in a Flex-Algorithm 7.4. OSPF Flexible Algorithm Definition Flags Sub-TLV
OSPF Flexible Algorithm Definition Flags Sub-TLV (FADF 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+- -+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 4
Length: variable, dependent on the size of the Flags field. MUST
be a multiple of 4 octets.
Flags:
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|M| | | ...
+-+-+-+-+-+-+-+-+...
M-flag: when set, Flex-Algorithm specific prefix metric MUST be
used, if advertised with the prefix. This flag is not
applicable to prefixes advertised as SRv6 locators.
Bits are defined/sent starting with Bit 0 defined above. Additional
bit definitions that may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits that will
need to be transmitted.
Undefined bits MUST be transmitted as 0.
Bits that are NOT transmitted MUST be treated as if they are set to 0
on receipt.
OSPF FADF Sub-TLV MAY NOT appear more then once in an OSPF FAD TLV.
If it appears more then once, the OSPF FAD TLV MUST be ignored by the
receiver.
If the OSPF FADF Sub-TLV is not present inside the OSPF FAD TLV, all
the bits are assumed to be set to 0.
8. ISIS Flex-Algorithm Prefix Metric Sub-TLV
ISIS Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the
advertisement of a Flex-Algorithm specific prefix metric associated
with a given prefix advertisement.
ISIS FAPM Sub-TLV is a sub-TLV of TLVs 135, 235, 236, and 237 and 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 |Flex-Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD, suggested value 5
Length: 5 octets
Flex-Algorithm: Single octet value between 128 and 255 inclusive.
Metric: 4 octets of metric information
ISIS FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it
appears more then once with the same Flex-Algorithm value, the first
appearance MUST be used and any subsequent ones MUST be ignored.
If a prefix is advertised with a Flex-Algorithm prefix metric larger
then MAX_PATH_METRIC as defined in [RFC5305] this prefix MUST NOT be
considered during the Flexible-Algorithm computation.
The usage of the Flex-Algorithm prefix metric is described in
Section 12.
ISIS FAPM Sub-TLV MUST NOT be advertised as sub-TLV of the ISIS SRv6
Locator TLV [I-D.ietf-lsr-isis-srv6-extensions]. ISIS SRv6 Locator
TLV includes the Algorithm and Metric fields which MUST be used
instead. If FAPM Sub-TLV is present as sub-TLV of the ISIS SRv6
Locator TLV in the received LSP, such FAPM Sub-TLV MUST be ignored.
9. OSPF Flex-Algorithm Prefix Metric Sub-TLV
OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLV supports the
advertisement of a Flex-Algorithm specific prefix metric associated
with a given prefix advertisement.
The OSPF Flex-Algorithm Prefix Metric (FAPM) Sub-TLVis a Sub-TLV of
the:
- OSPFv2 Extended Prefix TLV [RFC7684]
- Following OSPFv3 TLVs as defined in [RFC8362]:
Intra-Area Prefix TLV
Inter-Area Prefix TLV
External Prefix TLV
OSPF FAPM Sub-TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flex-Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD, suggested value for OSPFv2 is 3, for OSPFv3 is 10
Length: 8 octets
Flex-Algorithm: Single octet value between 128 and 255 inclusive.
Reserved: Must be set to 0, ignored at reception.
Metric: 4 octets of metric information
OSPF FAPM Sub-TLV MAY appear multiple times in its parent TLV. If it
appears more then once with the same Flex-Algorithm value, the first
appearance MUST be used and any subsequent ones MUST be ignored.
The usage of the Flex-Algorithm prefix metric is described in
Section 12.
10. Advertisement of Node Participation in a Flex-Algorithm
When a router is configured to support a particular Flex-Algorithm, When a router is configured to support a particular Flex-Algorithm,
we say it is participating in that Flex-Algorithm. we say it is participating in that Flex-Algorithm.
Paths computed for a specific Flex-Algorithm MAY be used by various Paths computed for a specific Flex-Algorithm MAY be used by various
applications, each potentially using its own specific data plane for applications, each potentially using its own specific data plane for
forwarding the data over such paths. To guarantee the presence of forwarding the data over such paths. To guarantee the presence of
the application specific forwarding state associated with a the application specific forwarding state associated with a
particular Flex-Algorithm, a router MUST advertise its participation particular Flex-Algorithm, a router MUST advertise its participation
for a particular Flex-Algorithm for each application specifically. for a particular Flex-Algorithm for each application specifically.
8.1. Advertisement of Node Participation for Segment Routing 10.1. Advertisement of Node Participation for Segment Routing
[I-D.ietf-isis-segment-routing-extensions], [I-D.ietf-isis-segment-routing-extensions],
[I-D.ietf-ospf-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions] and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions] (IGP Segment [I-D.ietf-ospf-ospfv3-segment-routing-extensions] (IGP Segment
Routing extensions) describe how SR-Algorithm is used to define how Routing extensions) describe how SR-Algorithm is used to define how
the best path is computed by the IGP. the best path is computed by the IGP.
Routers advertise the support for the SR-Algorithm as a node Routers advertise the support for the SR-Algorithm as a node
capability as described in the above mentioned IGP Segment Routing capability as described in the above mentioned IGP Segment Routing
extensions. To advertise participation for a particular Flex- extensions. To advertise participation for a particular Flex-
Algorithm for Segment Routing, the Flex-Algorithm value MUST be Algorithm for Segment Routing, including both SR MPLS and SRv6, the
advertised in the SR-Algorithm TLV (OSPF) or sub-TLV (ISIS). Flex-Algorithm value MUST be advertised in the SR-Algorithm TLV
(OSPF) or sub-TLV (ISIS).
Segment Routing Flex-Algorithm participation advertisement is Segment Routing Flex-Algorithm participation advertisement is
topology independent. When a router advertises participation in an topology independent. When a router advertises participation in an
SR-Algorithm, the participation applies to all topologies in which SR-Algorithm, the participation applies to all topologies in which
the advertising node participates. the advertising node participates.
8.2. Advertisement of Node Participation for Other Applications 10.2. Advertisement of Node Participation for Other Applications
This section describes considerations related to how other This section describes considerations related to how other
applications can advertise its participation in a specific Flex- applications can advertise its participation in a specific Flex-
Algorithm. Algorithm.
Application specific Flex-Algorithm participation advertisements MAY Application specific Flex-Algorithm participation advertisements MAY
be topology specific or MAY be topology independent, depending on the be topology specific or MAY be topology independent, depending on the
application itself. application itself.
Application specific advertisement for Flex-Algorithm participation Application specific advertisement for Flex-Algorithm participation
MUST be defined for each application and is outside of the scope of MUST be defined for each application and is outside of the scope of
this document. this document.
9. Advertisement of Link Attributes for Flex-Algorithm 11. Advertisement of Link Attributes for Flex-Algorithm
Various link include or exclude rules can be part of the Flex- Various link include or exclude rules can be part of the Flex-
Algorithm definition. These rules use Admin Groups (AG) as defined Algorithm definition. These rules use Admin Groups (AG) as defined
in [RFC7308] and [RFC5305], or Extended Administrative Groups (EAG) in [RFC5305], or Extended Administrative Groups (EAG) as defined in
as defined in [RFC7308]. [RFC7308].
To advertise a link affinity in a form of the AG or EAG that is used To advertise a link affinity in a form of the AG or EAG that is used
during Flex-Algorithm calculation, an Application Specific Link during Flex-Algorithm calculation, an Application Specific Link
Attributes sub-TLV as described in [I-D.ietf-isis-te-app], or sub-TLV Attributes sub-TLV as described in [I-D.ietf-isis-te-app], or sub-TLV
of Extended Link TLV as described in of Extended Link TLV as described in
[I-D.ietf-ospf-te-link-attr-reuse] MUST be used. The advertisement [I-D.ietf-ospf-te-link-attr-reuse] MUST be used. The advertisement
MUST indicate that it is usable by the Flex-Algorithm application. MUST indicate that it is usable by the Flex-Algorithm application.
10. Calculation of Flexible Algorithm Paths If the link Flex-Algorithm application affinities are advertised in a
form of the AG inside the Application Specific Link Attributes sub-
TLV, these are mapped to the affinities specified in the FAD Sub-TLVs
as defined in [RFC7308].
A router MUST be configured to participate in a given Flex-Algorithm 12. Calculation of Flexible Algorithm Paths
K before it can compute any path for that Flex-Algorithm.
A router which participates in a given Flex Algorithm MUST use the A router MUST be configured to participate in a given Flex-Algorithm
FAD selected based on the rules defined in Section Section 5.3. K and MUST use the FAD selected based on the rules defined in
Section 5.3 before it can compute any path for that Flex-Algorithm.
As described in Section 8, participation for any particular Flex- As described in Section 10, participation for any particular Flex-
Algorithm MUST be advertised on a per application basis. Calculation Algorithm MUST be advertised on a per application basis. Calculation
of the paths for any particular Flex-Algorithm MUST be application of the paths for any particular Flex-Algorithm MUST be application
specific. specific.
The way applications handle nodes that do not participate in The way applications handle nodes that do not participate in
Flexible-Algorithm is application specific. If the application only Flexible-Algorithm is application specific. If the application only
wants to consider participating nodes during the Flex-Algorithm wants to consider participating nodes during the Flex-Algorithm
calculation, then when computing paths for a given Flex-Algorithm, calculation, then when computing paths for a given Flex-Algorithm,
all nodes that do not advertise participation for that Flex-Algorithm all nodes that do not advertise participation for that Flex-Algorithm
in the application specific advertisements MUST be pruned from the in the application specific advertisements MUST be pruned from the
topology. MPLS Segment Routing is an application that MUST use such topology. Segment Routing, including both SR MPLS and SRv6, are
pruning when computing Flex-Algorithm paths. applications that MUST use such pruning when computing Flex-Algorithm
paths.
When computing the path for a give Flex-Algorithm, the metric-type When computing the path for a given Flex-Algorithm, the metric-type
that is part of the Flex-Algorithm definition (Section 5) MUST be that is part of the Flex-Algorithm definition (Section 5) MUST be
used. used.
When computing the path for a given Flex-Algorithm, the calculation- When computing the path for a given Flex-Algorithm, the calculation-
type that is part of the Flex-Algorithm definition (Section 5) MUST type that is part of the Flex-Algorithm definition (Section 5) MUST
be used. be used.
Various link include or exclude rules can be part of the Flex- Various link include or exclude rules can be part of the Flex-
Algorithm definition. To refer to particular bit within an AG or EAG Algorithm definition. To refer to a particular bit within an AG or
we uses term 'color'. EAG we uses term 'color'.
Rules, in the order as specified below, MUST be used to prune link Rules, in the order as specified below, MUST be used to prune links
from the topology during the Flex-Algorithm computation. from the topology during the Flex-Algorithm computation.
For all links in the topology: For all links in the topology:
1. Check if any exclude rule is part of the Flex-Algorithm 1. Check if any exclude rule is part of the Flex-Algorithm
definition. If such exclude rule exists, check if any color that definition. If such exclude rule exists, check if any color that
is part of the exclude rule is also set on the link. If such a is part of the exclude rule is also set on the link. If such a
color exist, the link MUST be pruned from the computation. color is set, the link MUST be pruned from the computation.
2. Check if any include-any rule is part of the Flex-Algorithm 2. Check if any include-any rule is part of the Flex-Algorithm
definition. if such include-any rule exists, check if any color definition. If such include-any rule exists, check if any color
that is part of the include-any rule is also set on the link. If that is part of the include-any rule is also set on the link. If
such color does not exist, the link MUST be pruned from the no such color is set, the link MUST be pruned from the
computation. computation.
3. Check if any include-all rule is part of the Flex-Algorithm 3. Check if any include-all rule is part of the Flex-Algorithm
definition. If such include-all rule exists, check if all colors definition. If such include-all rule exists, check if all colors
that are part of the include-all rule are also set on the link. that are part of the include-all rule are also set on the link.
If not all such colors are set on the link, the link MUST be If all such colors are not set on the link, the link MUST be
pruned from the computation. pruned from the computation.
4. If the Flex-Algorithm definition uses other than IGP metric 4. If the Flex-Algorithm definition uses other than IGP metric
(Section 5), and such metric is not advertised for the particular (Section 5), and such metric is not advertised for the particular
link in a topology for which the computation is done, such link 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 MUST be pruned from the computation. A metric of value 0 MUST NOT
be assumed in such case. be assumed in such case.
12.1. Multi-area and Multi-domain Considerations
Any IGP Shortest Path Tree calculation is limited to a single area. Any IGP Shortest Path Tree calculation is limited to a single area.
Same applies to Flex-Algorithm calculations. Given that the Same applies to Flex-Algorithm calculations. Given that the
computing router may not have the visibility to the topology of computing router may not have the visibility to the topology of
remote areas, the Flex-Algorithm specific path to an inter-area remote areas, the Flex-Algorithm specific path to an inter-area or
prefix will only be computed for the local area only. The egress L1/ inter-domain prefix will be computed for the local area only. The
L2 router (ABR in OSPF) will be selected based on the best path for egress L1/L2 router (ABR in OSPF), or ASBR for inter-domain case,
the given Flex-Algorithm in the local area and such egress L1/L2 (ABR will be selected based on the best path for the given Flex-Algorithm
in OSPF) router will be responsible to compute the best Flex- in the local area and such egress ABR or ASBR router will be
Algorithm specific path over the next area. This may produce an end- responsible to compute the best Flex-Algorithm specific path over the
to-end path, which is sub-optimal based on Flex-Algorithm next area or domain. This may produce an end-to-end path, which is
constraints. If the best end-to-end path for a given Flex-Algorithm sub-optimal based on Flex-Algorithm constraints.
needs to be used for inter-area destinations, paths for such
destinations need to be computed by the entity that has the
topological information about all areas.
11. Flex-Algorithm and Forwarding Plane To allow the best end-to-end path for a prefix for a given Flex-
Algorithm to be computed, an ABR or ASBR MAY set the Flex-Algorithm
prefix metric (Section 8, Section 9) when advertising the prefix
between areas or domains. Such metric will be equal to the metric to
reach the prefix for a given Flex-Algorithm in a source area or
domain. This is similar in nature to how the metric is set when
prefixes are advertised between areas or domains for default
algorithm.
This section describes how Flex-Algorithm paths are used with Flex-Algorithm prefix metrics MUST NOT be used during the Flex-
Algorithm computation unless the FAD selected based on the rules
defined in Section 5.3 includes the M-Flag, as described in
(Section 6.4 or Section 7.4).
If the FAD selected based on the rules defined in Section 5.3
includes the M-flag, Flex-Algorithm prefix metrics MUST be used
during calculation when advertised with the prefix. If the Flex-
Algorithm prefix metric is not advertised with the prefix, the
standard IGP metric advertised with the prefix MUST be used.
M-flag in FAD is not applicable to prefixes advertised as SRv6
locators. ISIS SRv6 Locator TLV includes the Algorithm and Metric
fields [I-D.ietf-lsr-isis-srv6-extensions]. When the ISIS SRv6
Locator is advertised between areas or domains, the metric field in
the Locator TLV MUST be used irrespective of the M flag in the FAD
advertisement.
13. Flex-Algorithm and Forwarding Plane
This section describes how Flex-Algorithm paths are used in
forwarding. forwarding.
11.1. Segment Routing MPLS Forwarding for Flex-Algorithm 13.1. Segment Routing MPLS Forwarding for Flex-Algorithm
This section describes how Flex-Algorithm paths are used with SR MPLS This section describes how Flex-Algorithm paths are used with SR MPLS
forwarding. forwarding.
Prefix SID advertisements include an SR-Algorithm value and as such Prefix SID advertisements include an SR-Algorithm value and as such
are associated with the specified SR-Algorithm. Prefix-SIDs are also are associated with the specified SR-Algorithm. Prefix-SIDs are also
associated with a specific topology which is inherited from the associated with a specific topology which is inherited from the
associated prefix reachability advertisement. When the algorithm associated prefix reachability advertisement. When the algorithm
value advertised is a Flex-Algorithm value, the Prefix SID is value advertised is a Flex-Algorithm value, the Prefix SID is
associated with paths calculated using that Flex-Algorithm in the associated with paths calculated using that Flex-Algorithm in the
skipping to change at page 16, line 7 skipping to change at page 21, line 5
advertised specifically for the given algorithm. LFA paths MUST NOT advertised specifically for the given algorithm. LFA paths MUST NOT
use an Adjacency-SID that belongs to a link that has been pruned from use an Adjacency-SID that belongs to a link that has been pruned from
the Flex-Algorithm computation. the Flex-Algorithm computation.
If LFA protection is being used to protect a given Flex-Algorithm If LFA protection is being used to protect a given Flex-Algorithm
paths, all routers in the area participating in the given Flex- paths, all routers in the area participating in the given Flex-
Algorithm SHOULD advertise at least one Flex-Algorithm specific Node- Algorithm SHOULD advertise at least one Flex-Algorithm specific Node-
SID. These Node-SIDs are used to enforce traffic over the LFA SID. These Node-SIDs are used to enforce traffic over the LFA
computed backup path. computed backup path.
11.2. Other Applications' Forwarding for Flex-Algorithm 13.2. SRv6 Forwarding for Flex-Algorithm
This section describes how Flex-Algorithm paths are used with SRv6
forwarding.
In SRv6 a node is provisioned with topology/algorithm specific
locators for each of the topology/algorithm pairs supported by that
node. Each locator is a covering prefix for all SIDs provisioned on
that node which have the matching topology/algorithm.
SRv6 locator advertisement in IGPs
([I-D.ietf-lsr-isis-srv6-extensions]
[I-D.li-ospf-ospfv3-srv6-extensions]) includes the MTID value that
associates the locator with a specific topology. SRv6 locator
advertisements also includes an Algorithm value that explicitly
associates the locator with a specific algorithm. When the algorithm
value advertised with a locator represents a Flex-Algorithm, the
paths to the locator prefix MUST be calculated using the specified
Flex-Algorithm in the associated topology.
Forwarding entries for the locator prefixes advertised in IGPs MUST
be installed in the forwarding plane of the receiving SRv6 capable
routers when the associated topology/algorithm is participating in
them. Forwarding entries for locators associated with Flex-
Algorithms in which the node is not participating MUST NOT be
installed in the forwarding.
When the locator is associated with the Flex-Algorithm, LFA paths to
the locator prefix MUST be calculated using such Flex-Algorithm in
the associated topology, to guarantee that they follow the same
constraints as the calculation of the primary paths. LFA paths MUST
only use SRv6 SIDs advertised specifically for the given Flex-
Algorithm.
If LFA protection is being used to protect locators associated with a
given Flex-Algorithm, all routers in the area participating in the
given Flex-Algorithm SHOULD advertise at least one Flex-Algorithm
specific locator and END SID per node and one END.X SID for every
link that has not been pruned from such Flex-Algorithm computation.
These locators and SIDs are used to enforce traffic over the LFA
computed backup path.
13.3. Other Applications' Forwarding for Flex-Algorithm
Any application that wants to use Flex-Algorithm specific forwarding Any application that wants to use Flex-Algorithm specific forwarding
need to install some form of Flex-Algorithm specific forwarding needs to install some form of Flex-Algorithm specific forwarding
entries. entries.
Application specific forwarding for Flex-Algorithm MUST be defined Application specific forwarding for Flex-Algorithm MUST be defined
for each application and is outside of the scope of this document. for each application and is outside of the scope of this document.
12. Backward Compatibility 14. Backward Compatibility
This extension brings no new backward compatibility issues. This extension brings no new backward compatibility issues.
13. Security Considerations 15. Security Considerations
This draft adds a two new ways to disrupt the IGP networks: This draft adds two new ways to disrupt the IGP networks:
An attacker can hijack a particular Flex-Algorithm by advertising An attacker can hijack a particular Flex-Algorithm by advertising
a FAD with a priority of 255 (or any priority higher than that of a FAD with a priority of 255 (or any priority higher than that of
the legitimate nodes). the legitimate nodes).
An attacker could make it look like a router supports a particular An attacker could make it look like a router supports a particular
Flex-Algorithm when it actually doesn't, or vice versa. Flex-Algorithm when it actually doesn't, or vice versa.
Both of these attacks can be addressed by the existing security Both of these attacks can be addressed by the existing security
extensions as described in [RFC5304] and [RFC5310] for ISIS, in extensions as described in [RFC5304] and [RFC5310] for ISIS, in
[RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for [RFC2328] and [RFC7474] for OSPFv2 and in [RFC5340] and [RFC4552] for
OSPFv3. OSPFv3.
14. IANA Considerations 16. IANA Considerations
14.1. IGP IANA Considerations 16.1. IGP IANA Considerations
14.1.1. IGP Algorithm Types Registry 16.1.1. IGP Algorithm Types Registry
This document makes the following registrations in the "IGP Algorithm This document makes the following registrations in the "IGP Algorithm
Types" registry: Types" registry:
Type: 128-255. Type: 128-255.
Description: Flexible Algorithms. Description: Flexible Algorithms.
Reference: This document (Section 4). Reference: This document (Section 4).
14.1.2. Flexible Algorithm Definition Metric-Type Registry 16.1.2. Flexible Algorithm Definition Metric-Type Registry
IANA is requested to set up a registry called "Flexible Algorithm IANA is requested to set up a registry called "Flexible Algorithm
Definition Metric-Type Registry" under a "Interior Gateway Protocol Definition Metric-Type Registry" under a "Interior Gateway Protocol
(IGP) Parameters" IANA registries. The registration policy for this (IGP) Parameters" IANA registries. The registration policy for this
registry is "Standards Action" ([RFC8126] and [RFC7120]). registry is "Standards Action" ([RFC8126] and [RFC7120]).
Values in this registry come from the range 0-255. Values in this registry come from the range 0-255.
This document registers following values in the "Flexible Algorithm This document registers following values in the "Flexible Algorithm
Definition Metric-Type Registry": Definition Metric-Type Registry":
skipping to change at page 17, line 35 skipping to change at page 23, line 26
Description: Min Unidirectional Link Delay [RFC7810] Description: Min Unidirectional Link Delay [RFC7810]
Reference: This document (Section 5.1) Reference: This document (Section 5.1)
Type: 2 Type: 2
Description: TE Default Metric [RFC5305] Description: TE Default Metric [RFC5305]
Reference: This document (Section 5.1) Reference: This document (Section 5.1)
14.2. ISIS IANA Considerations 16.2. Flex-Algorithm Definition Flags Registry
14.2.1. Sub TLVs for Type 242 IANA is requested to set up a registry called "ISIS Flex-Algorithm
Definition Flags Registry" under a "Interior Gateway Protocol (IGP)
Parameters" IANA registries. The registration policy for this
registry is "Standards Action" ([RFC8126] and [RFC7120]).
This document defines the following single bit in Flex-Algorithm
Definition Flags registry:
Bit # Name
----- ------------------------------
0 Prefix Metric Flag (M-flag)
Reference: This document (Section 6.4, Section 7.4).
16.3. ISIS IANA Considerations
16.3.1. Sub TLVs for Type 242
This document makes the following registrations in the "sub-TLVs for This document makes the following registrations in the "sub-TLVs for
TLV 242" registry. TLV 242" registry.
Type: TBD (suggested value 26). Type: TBD (suggested value 26).
Description: Flexible Algorithm Definition Sub-TLV. Description: Flexible Algorithm Definition.
Reference: This document (Section 5.1). Reference: This document (Section 5.1).
14.2.2. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 16.3.2. Sub TLVs for for TLVs 135, 235, 236, and 237
This document makes the following registrations in the "Sub-TLVs for
for TLVs 135, 235, 236, and 237" registry.
Type: TBD (suggested value 5).
Description: Flex-Algorithm Prefix Metric.
Reference: This document (Section 8).
16.3.3. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
This document creates the following Sub-Sub-TLV Registry: This document creates the following Sub-Sub-TLV Registry:
Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV Registry: Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
Registration Procedure: Expert review Registration Procedure: Expert review
Reference: This document (Section 5.1) Reference: This document (Section 5.1)
This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs
for Flexible Algorithm Definition Sub-TLV" registry: for Flexible Algorithm Definition Sub-TLV" registry:
Type: 1 Type: 1
Description: Flexible Algorithm Exclude Admin Group Sub-TLV Description: Flexible Algorithm Exclude Admin Group
Reference: This document (Section 6.1). Reference: This document (Section 6.1).
Type: 2 Type: 2
Description: Flexible Algorithm Include-Any Admin Group Sub-TLV Description: Flexible Algorithm Include-Any Admin Group
Reference: This document (Section 6.2). Reference: This document (Section 6.2).
Type: 3 Type: 3
Description: Flexible Algorithm Include-All Admin Group Sub-TLV Description: Flexible Algorithm Include-All Admin Group
Reference: This document (Section 6.3). Reference: This document (Section 6.3).
14.3. OSPF IANA Considerations Type: 4
14.3.1. OSPF Router Information (RI) TLVs Registry Description: Flexible Algorithm Definition Flags
Reference: This document (Section 6.4).
16.4. OSPF IANA Considerations
16.4.1. OSPF Router Information (RI) TLVs Registry
This specification updates the OSPF Router Information (RI) TLVs This specification updates the OSPF Router Information (RI) TLVs
Registry with the following value: Registry with the following value:
o TBD (suggested value 16) - Flexible Algorithm Definition TLV o TBD (suggested value 16) - Flexible Algorithm Definition TLV
14.3.2. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 16.4.2. OSPFv2 Extended Prefix TLV Sub-TLVs
This document makes the following registrations in the "OSPFv2
Extended Prefix TLV Sub-TLVs" registry.
Type: TBD (suggested value 3).
Description: Flex-Algorithm Prefix Metric.
Reference: This document (Section 9).
16.4.3. OSPFv3 Extended-LSA Sub-TLVs
This document makes the following registrations in the "OSPFv3
Extended-LSA Sub-TLVs" registry.
Type: TBD (suggested value 10).
Description: Flex-Algorithm Prefix Metric.
Reference: This document (Section 9).
16.4.4. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry
This document creates the following registry: This document creates the following registry:
Registry: OSPF Flexible Algorithm Definition TLV sub-TLV Registry: OSPF Flexible Algorithm Definition TLV sub-TLV
Registration Procedure: Expert review Registration Procedure: Expert review
Reference: This document (Section 5.2) Reference: This document (Section 5.2)
The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will The "OSPF Flexible Algorithm Definition TLV sub-TLV" registry will
define sub-TLVs at any level of nesting for Flexible Algorithm TLV define sub-TLVs at any level of nesting for Flexible Algorithm TLV
and should be added to the "Open Shortest Path First (OSPF) and should be added to the "Open Shortest Path First (OSPF)
Parameters" registries group. New values can be allocated via IETF Parameters" registries group. New values can be allocated via IETF
Review or IESG Approval. Review or IESG Approval.
This document resisters following Sub-TLVs in the "TLVs for Flexible This document registers following Sub-TLVs in the "TLVs for Flexible
Algorithm Definition TLV" registry: Algorithm Definition TLV" registry:
Type: 1 Type: 1
Description: Flexible Algorithm Exclude Admin Group Sub-TLV Description: Flexible Algorithm Exclude Admin Group
Reference: This document (Section 7.1). Reference: This document (Section 7.1).
Type: 2 Type: 2
Description: Flexible Algorithm Include-Any Admin Group Sub-TLV Description: Flexible Algorithm Include-Any Admin Group
Reference: This document (Section 7.2). Reference: This document (Section 7.2).
Type: 3 Type: 3
Description: Flexible Algorithm Include-All Admin Group Sub-TLV Description: Flexible Algorithm Include-All Admin Group
Reference: This document (Section 7.3). Reference: This document (Section 7.3).
Type: 4
Description: Flexible Algorithm Definition Flags
Reference: This document (Section 7.4).
Types in the range 32768-33023 are for experimental use; these will Types in the range 32768-33023 are for experimental use; these will
not be registered with IANA, and MUST NOT be mentioned by RFCs. not be registered with IANA, and MUST NOT be mentioned by RFCs.
Types in the range 33024-65535 are not to be assigned at this time. Types in the range 33024-65535 are not to be assigned at this time.
Before any assignments can be made in the 33024-65535 range, there Before any assignments can be made in the 33024-65535 range, there
MUST be an IETF specification that specifies IANA Considerations that MUST be an IETF specification that specifies IANA Considerations that
covers the range being assigned. covers the range being assigned.
15. Contributors 17. Acknowledgements
This draft, among other things, is also addressing the problem that This draft, among other things, is also addressing the problem that
the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve. the [I-D.gulkohegde-routing-planes-using-sr] was trying to solve.
All authors of that draft agreed to join this draft. All authors of that draft agreed to join this draft.
Thanks to Eric Rosen, Les Ginsberg and Tony Przygienda for their Thanks to Eric Rosen, Tony Przygienda for their detailed review and
detailed review and excellent comments. excellent comments.
Thanks to Cengiz Halit for his review and feedback during initial Thanks to Cengiz Halit for his review and feedback during initial
phase of the solution definition. phase of the solution definition.
Thanks to Kenji Kumaki for his comments. Thanks to Kenji Kumaki for his comments.
16. References 18. References
16.1. Normative References 18.1. Normative References
[BCP14] , <https://tools.ietf.org/html/bcp14>. [BCP14] , <https://tools.ietf.org/html/bcp14>.
[I-D.ietf-isis-segment-routing-extensions] [I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., and B. Decraene, "IS-IS Extensions for Gredler, H., and B. Decraene, "IS-IS Extensions for
Segment Routing", draft-ietf-isis-segment-routing- Segment Routing", draft-ietf-isis-segment-routing-
extensions-24 (work in progress), April 2019. extensions-25 (work in progress), May 2019.
[I-D.ietf-isis-te-app] [I-D.ietf-isis-te-app]
Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS TE Attributes per application", draft- J. Drake, "IS-IS TE Attributes per application", draft-
ietf-isis-te-app-06 (work in progress), April 2019. ietf-isis-te-app-06 (work in progress), April 2019.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Routing over IPv6
Dataplane", draft-ietf-lsr-isis-srv6-extensions-00 (work
in progress), May 2019.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions] [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment
Routing", draft-ietf-ospf-ospfv3-segment-routing- Routing", draft-ietf-ospf-ospfv3-segment-routing-
extensions-23 (work in progress), January 2019. extensions-23 (work in progress), January 2019.
[I-D.ietf-ospf-segment-routing-extensions] [I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment- Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-27 (work in progress), December 2018. routing-extensions-27 (work in progress), December 2018.
[I-D.ietf-ospf-te-link-attr-reuse] [I-D.ietf-ospf-te-link-attr-reuse]
Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J., Psenak, P., Ginsberg, L., Henderickx, W., Tantsura, J.,
and J. Drake, "OSPF Link Traffic Engineering (TE) and J. Drake, "OSPF Link Traffic Engineering (TE)
Attribute Reuse", draft-ietf-ospf-te-link-attr-reuse-07 Attribute Reuse", draft-ietf-ospf-te-link-attr-reuse-07
(work in progress), April 2019. (work in progress), April 2019.
[I-D.li-ospf-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-li-ospf-
ospfv3-srv6-extensions-03 (work in progress), March 2019.
[ISO10589] [ISO10589]
International Organization for Standardization, International Organization for Standardization,
"Intermediate system to Intermediate system intra-domain "Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in routeing information exchange protocol for use in
conjunction with the protocol for providing the conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", ISO/ connectionless-mode Network Service (ISO 8473)", ISO/
IEC 10589:2002, Second Edition, Nov 2002. IEC 10589:2002, Second Edition, Nov 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS [RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308, Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014, DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>. <https://www.rfc-editor.org/info/rfc7308>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>. February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981, for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016, DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>. <https://www.rfc-editor.org/info/rfc7981>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
16.2. Informative References [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
18.2. Informative References
[I-D.gulkohegde-routing-planes-using-sr] [I-D.gulkohegde-routing-planes-using-sr]
Hegde, S. and a. arkadiy.gulko@thomsonreuters.com, Hegde, S. and a. arkadiy.gulko@thomsonreuters.com,
"Separating Routing Planes using Segment Routing", draft- "Separating Routing Planes using Segment Routing", draft-
gulkohegde-routing-planes-using-sr-00 (work in progress), gulkohegde-routing-planes-using-sr-00 (work in progress),
March 2017. March 2017.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
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