Flexible Algorithm Definition Advertisement with BGP Link-State
draft-ietf-idr-bgp-ls-flex-algo-08
Inter-Domain Routing K. Talaulikar, Ed.
Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems
Expires: May 14, 2022 S. Zandi
G. Dawra
LinkedIn
November 10, 2021
Flexible Algorithm Definition Advertisement with BGP Link-State
draft-ietf-idr-bgp-ls-flex-algo-08
Abstract
Flexible Algorithm is a solution that allows routing protocols (viz.
OSPF and IS-IS) to compute paths over a network based on user-defined
(and hence, flexible) constraints and metrics. The computation is
performed by routers participating in the specific network in a
distribute manner using a Flex Algorithm definition. This definition
provisioned on one or more routers and propagated (viz. OSPF and IS-
IS flooding) through the network.
BGP Link-State (BGP-LS) enables the collection of various topology
information from the network. This draft defines extensions to BGP-
LS address-family to advertise the Flexible Algorithm Definition as a
part of the topology information from the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 14, 2022.
Talaulikar, et al. Expires May 14, 2022 [Page 1]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. BGP-LS Extensions for Flex Algo . . . . . . . . . . . . . . . 4
3. Flexible Algorithm Definition . . . . . . . . . . . . . . . . 5
3.1. Flex Algo Exclude Any Affinity . . . . . . . . . . . . . 6
3.2. Flex Algo Include Any Affinity . . . . . . . . . . . . . 7
3.3. Flex Algo Include All Affinity . . . . . . . . . . . . . 7
3.4. Flex Algo Definition Flags . . . . . . . . . . . . . . . 8
3.5. Flex Algo Exclude SRLG . . . . . . . . . . . . . . . . . 9
3.6. Flex Algo Unknown . . . . . . . . . . . . . . . . . . . . 9
4. Flex Algorithm Prefix Metric . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Manageability Considerations . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
IGP protocols (OSPF and IS-IS) traditionally compute best paths over
the network based on the IGP metric assigned to the links. Many
network deployments use RSVP-TE [RFC3209] based or Segment Routing
(SR) Policy [RFC8402] based solutions to enforce traffic over a path
that is computed using different metrics or constraints than the
shortest IGP path. [I-D.ietf-lsr-flex-algo] defines the Flexible
Algorithm solution that allows IGPs themselves to compute constraint
based paths over the network.
Talaulikar, et al. Expires May 14, 2022 [Page 2]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
Flexible Algorithm is called so as it allows a user the flexibility
to define
o the type of calculation to be used (e.g. shortest path)
o the metric type to be used (e.g. IGP metric or TE metric)
o the set of constraints to be used (e.g. inclusion or exclusion of
certain links using affinities)
The operations of the flexible algorithm solution are described in
detail in [I-D.ietf-lsr-flex-algo] and a high-level summary of the
same is described here for clarity. The network operator enables the
participation of specific nodes in the network for a specific
algorithm and then provisions the definition of that flexible
algorithm on one or more of these nodes. The nodes where the
flexible algorithm definition (FAD) is advertised then flood these
definitions via respective IGP (IS-IS and OSPFv2/v3) mechanisms to
all other nodes in the network. The nodes select the definition for
each algorithm based on the flooded information in a deterministic
manner and thus all nodes participating in a flexible algorithm
computation arrive at a common understanding of the type of
calculation that they need to use.
When using Segment Routing (SR) [RFC8402] MPLS forwarding plane
[RFC8660], the result of a flex algorithm computation is the
provisioning of the Prefix SIDs associated with that algorithm with
paths based on the topology computed based on that algorithm's
definition. When using SR over IPv6 (SRv6) [RFC8986], the result of
a flex algorithm computation is the provisioning of the SRv6 Locators
associated with that algorithm with paths based on the topology
computed based on that algorithm. This flex algorithm computation is
within an IGP area or level similar to the default shortest path tree
(SPT) algorithm.
A flex algorithm specific metric MAY be advertised along with the
prefix as described in [I-D.ietf-lsr-flex-algo] to enable end-to-end
optimal path computation for prefixes across multiple areas/domains
in the flex algorithm computation for the SR-MPLS forwarding plane.
The BGP-LS extensions for SR are defined in [RFC9085] and
[I-D.ietf-idr-bgpls-srv6-ext]. They include the
o SR Algorithm TLV to indicate the participation of a node in a flex
algorithm computation
o Prefix SID TLV to indicate the association of the Prefix-SIDs to a
specific flex algorithm for SR-MPLS forwarding
Talaulikar, et al. Expires May 14, 2022 [Page 3]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
o SRv6 Locator TLV to indicate the Locator for specific flex
algorithm for SRv6 forwarding
Thus a controller or a Path Computation Engine (PCE) is aware of the
IGP topology across multiple domains which includes the above
information related to the flexible algorithm. This draft defines
extensions to BGP-LS for carrying the FAD information so that it
enables the controller/PCE to learn the mapping of the flex algorithm
number to its definition in each area/domain of the underlying IGP.
The controller/PCE also learns the type of computation used and the
constraints for the same. This information can then be leveraged by
it for setting up SR Policy paths end to end across domains by
leveraging the appropriate Flex Algorithm specific SIDs in its
Segment List [I-D.ietf-spring-segment-routing-policy]. e.g. picking
the Flex Algorithm Prefix SID (in case of SR-MPLS) or End SID (in
case of SRv6) of ABRs/ASBRs corresponding to a definition that
optimizes on the delay metric enables the PCE/controller to build an
end to end low latency path across IGP domains with minimal SIDs in
the SID list.
1.1. Requirements Language
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.
2. BGP-LS Extensions for Flex Algo
The BGP-LS [RFC7752] specifies the Node NLRI for the advertisement of
nodes along with their attributes using the BGP-LS Attribute, the
Link NLRI for the advertisement of links along with their attributes
using the BGP-LS Attribute and the Prefix NLRI for the advertisement
of prefixes along with their attributes using the BGP-LS Attribute.
The FAD advertised by a node is considered as its node level
attributes and advertised as such.
Various link attributes like affinities and SRLGs used during the
Flex-Algorithm path calculations in IS-IS and OSPF are advertised in
those protocols using the Application Specific Link Attribute (ASLA)
advertisements as described in [I-D.ietf-lsr-flex-algo]. The BGP-LS
extensions for ASLA advertisements
[I-D.ietf-idr-bgp-ls-app-specific-attr] MUST be used for the
advertisement of these Flex-Algorithm application-specific link
attributes from the underlying IGP protocols using the Flexible
Talaulikar, et al. Expires May 14, 2022 [Page 4]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
Algorithm application specific bit defined in
[I-D.ietf-lsr-flex-algo].
The Flexible Algorithm Prefix Metric (FAPM) are considered as prefix
attributes and advertised as such.
3. Flexible Algorithm Definition
This document defines a new optional BGP-LS Attribute TLV associated
with the Node NLRI called the Flexible Algorithm Definition (FAD) TLV
and its format is as follows:
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-Type | Calc-Type | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs ... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Flex Algorithm Definition TLV
where:
o Type: 1039
o Length: variable. Minimum of 4 octets.
o Flex-Algorithm : 1 octet value in the range between 128 and 255
inclusive which is the range defined for Flexible Algorithms in
the IANA "IGP Parameters" registries under the "IGP Algorithm
Types" registry [I-D.ietf-lsr-flex-algo].
o Metric-Type : 1 octet value indicating the type of metric used in
the computation. Values allowed come from the IANA "IGP
Parameters" registries under the "Flexible Algorithm Definition
Metric-Type" registry [I-D.ietf-lsr-flex-algo].
o Calculation-Type : 1 octet value in the range between 0 and 127
inclusive which is the range defined for the standard algorithms
in the IANA "IGP Parameters" registries under the "IGP Algorithm
Types" registry [I-D.ietf-lsr-flex-algo].
o Priority : 1 octet value between 0 and 255 inclusive that
specifies the priority of the FAD.
Talaulikar, et al. Expires May 14, 2022 [Page 5]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
o sub-TLVs : zero or more sub-TLVs may be included as described
further in this section.
The FAD TLV can only be added to the BGP-LS Attribute of the Node
NLRI if the corresponding node originates the underlying IGP TLV/sub-
TLV as described below. This information is derived from the
protocol specific advertisements as below.
o IS-IS, as defined by the ISIS Flexible Algorithm Definition sub-
TLV in [I-D.ietf-lsr-flex-algo].
o OSPFv2/OSPFv3, as defined by the OSPF Flexible Algorithm
Definition TLV in [I-D.ietf-lsr-flex-algo].
The BGP-LS Attribute associated with a Node NLRI MAY include one or
more FAD TLVs corresponding to the FAD for each algorithm that the
particular node is advertising.
The following sub-sections define the sub-TLVs for the FAD TLV.
3.1. Flex Algo Exclude Any Affinity
The Flex Algo Exclude Any Affinity sub-TLV is an optional sub-TLV
that is used to carry the affinity constraints [RFC2702] associated
with the FAD and enable the exclusion of links carrying any of the
specified affinities from the computation of the specific algorithm
as described in [I-D.ietf-lsr-flex-algo]. The affinity is expressed
in terms of Extended Admin Group (EAG) as defined in [RFC7308].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-Any EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1040
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Exclude-Any EAG : the bitmask used to represent the affinities to
be excluded.
Talaulikar, et al. Expires May 14, 2022 [Page 6]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
The information in the Flex Algo Exclude Any Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Exclude Admin Group sub-TLV as defined in [I-D.ietf-lsr-flex-algo].
3.2. Flex Algo Include Any Affinity
The Flex Algo Include Any Affinity sub-TLV is an optional sub-TLV
that is used to carry the affinity constraints [RFC2702] associated
with the FAD and enable the inclusion of links carrying any of the
specified affinities in the computation of the specific algorithm as
described in [I-D.ietf-lsr-flex-algo]. The affinity is expressed in
terms of Extended Admin Group (EAG) as defined in [RFC7308].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-Any EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1041
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Include-Any EAG : the bitmask used to represent the affinities to
be included.
The information in the Flex Algo Include Any Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Include-Any Admin Group sub-TLV as defined in
[I-D.ietf-lsr-flex-algo].
3.3. Flex Algo Include All Affinity
The Flex Algo Include All Affinity sub-TLV is an optional sub-TLV
that is used to carry the affinity constraints [RFC2702] associated
with the FAD and enable the inclusion of links carrying all of the
specified affinities in the computation of the specific algorithm as
described in [I-D.ietf-lsr-flex-algo]. The affinity is expressed in
terms of Extended Admin Group (EAG) as defined in [RFC7308].
The sub-TLV has the following format:
Talaulikar, et al. Expires May 14, 2022 [Page 7]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-All EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1042
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Include-All EAG : the bitmask used to represent the affinities to
be included.
The information in the Flex Algo Include All Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Include-All Admin Group sub-TLV as defined in
[I-D.ietf-lsr-flex-algo].
3.4. Flex Algo Definition Flags
The Flex Algo Definition Flags sub-TLV is an optional sub-TLV that is
used to carry the flags associated with the FAD that are used in the
computation of the specific algorithm as described in
[I-D.ietf-lsr-flex-algo].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1043
o Length: variable. MUST be a multiple of 4 octets.
o Flags : the bitmask used to represent the flags for the FAD as
introduced by [I-D.ietf-lsr-flex-algo] and listed in the "Flex-
Talaulikar, et al. Expires May 14, 2022 [Page 8]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
Algorithm Definition Flags" registry under the "Interior Gateway
Protocol (IGP) Parameters" IANA registry.
The information in the Flex Algo Definition Flags sub-TLV is derived
from the IS-IS and OSPF protocol specific Flexible Algorithm
Definition Flags sub-TLV as defined in [I-D.ietf-lsr-flex-algo].
3.5. Flex Algo Exclude SRLG
The Flex Algo Exclude SRLG sub-TLV is an optional sub-TLV that is
used to carry the shared risk link group (SRLG) [RFC4202] information
associated with the FAD and enable the exclusion of links that are
associated with any of the specified SRLG in the computation of the
specific algorithm as described in [I-D.ietf-lsr-flex-algo]. The
SRLGs associated with a link are carried in the BGP-LS Shared Link
Risk Group (TLV 1096) [RFC7752].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Values (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1045
o Length: variable, dependent on the number of SRLG values. MUST be
a multiple of 4 octets.
o SRLG Values : One or more SRLG values, each of 4 octet size, as
defined in [RFC4202].
The information in the Flex Algo SRLG Exclude sub-TLV is derived from
the IS-IS and OSPF protocol specific Flexible Algorithm Exclude SRLG
sub-TLV as defined in [I-D.ietf-lsr-flex-algo].
3.6. Flex Algo Unknown
The OSPF and ISIS signaling for FAD allows for extensions via new
sub-TLVs under the respective IGP's Flex Algorithm Definition TLV.
As specified in section 5.3 of [I-D.ietf-lsr-flex-algo], it is
important that the entire FAD be understood by anyone using it for
computation purposes. Therefore the FAD is different from most other
Talaulikar, et al. Expires May 14, 2022 [Page 9]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
protocol extensions where the skipping or ignoring of unknown or
unsupported sub-TLV information does not affect the base behavior.
The Flex Algo Unknown sub-TLV is an optional sub-TLV that is used to
indicate the presence of unknown or unsupported FAD sub-TLVs. The
need for this sub-TLV arises when the BGP-LS implementation on the
advertising node does not support one or more of the FAD sub-TLVs
present in the IGP advertisement.
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-ID | sub-TLV types (variable) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD
o Length: variable
o Protocol-ID: Indicates the BGP-LS Protocol-ID of the protocol from
which the FAD is being advertised via BGP-LS. The values are from
the "BGP-LS Protocol-IDs" registry under the IANA BGP-LS
Parameters registry.
o Sub-TLV Types : Zero or more sub-TLV types that are unknown or
unsupported by the node originating the BGP-LS advertisement. The
size of each sub-TLV type depends on the protocol indicated by the
Protocol-ID field e.g., for ISIS each sub-TLV type would be of
size 1 byte while for OSPF each sub-TLV type would be of size 2
bytes.
The discussion on the use of the FAD information by the consumers of
the BGP-LS information is beyond the scope of this document.
However, it is RECOMMENDED that the choice of the node used for
originating the IGP topology information into BGP-LS be made such
that the advertising node supports all the FAD extensions in use in
its part of the network. This avoids the scenario where an
incomplete FAD gets advertised via BGP-LS.
The node originating the advertisement SHOULD include the Flex Algo
Unknown sub-TLV when it comes across an unsupported or unknown sub-
TLV in the corresponding FAD in the IS-IS and OSPF advertisement.
Talaulikar, et al. Expires May 14, 2022 [Page 10]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
This serves as an indication that the FAD information in BGP-LS is
incomplete and is not usable for computation purposes. When
advertising the Flex Algo Unknown sub-TLV, the protocol specific sub-
TLV types that are unsupported or unknown SHOULD be included. This
information serves as a diagnostic aid.
4. Flex Algorithm Prefix Metric
This document defines a new optional BGP-LS Attribute TLV associated
with the Prefix NLRI called the Flexible Algorithm Prefix Metric
(FAPM) TLV and its format is as follows:
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 | Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: 1044
o Length: 8 octets.
o Flex-Algorithm : 1 octet value in the range between 128 and 255
inclusive which is the range defined for Flexible Algorithms in
the IANA "IGP Parameters" registries under the "IGP Algorithm
Types" registry [I-D.ietf-lsr-flex-algo].
o Flags: single octet value and only applicable for OSPF as defined
in [I-D.ietf-lsr-flex-algo]. The value MUST be set to 0 for ISIS
and ignored by the receiver.
o Reserved : 2 octet value that SHOULD be set to 0 by the originator
and MUST be ignored by the receiver.
o Metric : 4 octets field to carry the metric information.
The FAPM TLV can be added to the BGP-LS Attribute of the Prefix NLRI
originated by a node, only if the corresponding node originates the
Prefix in along with the underlying IGP TLV/sub-TLV as described
below. This information is derived from the protocol specific
advertisements as below.
Talaulikar, et al. Expires May 14, 2022 [Page 11]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
o IS-IS, as defined by the ISIS Flexible Algorithm Prefix Metric
sub-TLV in [I-D.ietf-lsr-flex-algo].
o OSPFv2/OSPFv3, as defined by the OSPF Flexible Algorithm Prefix
Metric sub-TLV in [I-D.ietf-lsr-flex-algo].
The BGP-LS Attribute associated with a Prefix NLRI MAY include one or
more FAPM TLVs corresponding to the Flexible Algorithm Prefix Metric
for each algorithm associated with that particular prefix.
5. IANA Considerations
This document requests assigning code-points from the registry "BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" <https://www.iana.org/assignments/bgp-ls-parameters/bgp-ls-
parameters.xhtml#node-descriptor-link-descriptor-prefix-descriptor-
attribute-tlv> based on the table below which reflects the values
assigned via the early allocation process. The column "IS-IS TLV/
Sub-TLV" defined in the registry does not require any value and
should be left empty.
+------------+----------------------------------------+----------+
| Code Point | Description | Length |
+------------+----------------------------------------+----------+
| 1039 | Flex Algorithm Definition TLV | variable |
| 1040 | Flex Algo Exclude Any Affinity sub-TLV | variable |
| 1041 | Flex Algo Include Any Affinity sub-TLV | variable |
| 1042 | Flex Algo Include All Affinity sub-TLV | variable |
| 1043 | Flex Algo Definition Flags sub-TLV | variable |
| 1044 | Flex Algorithm Prefix Metric TLV | variable |
| 1045 | Flex Algorithm Exclude SRLG sub-TLV | variable |
| TBD | Flex Algorithm Unknown sub-TLV | variable |
+------------+----------------------------------------+----------+
6. Manageability Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [RFC7752].
Procedures and protocol extensions defined in this document do not
affect the BGP protocol operations and management other than as
discussed in the Manageability Considerations section of [RFC7752].
Specifically, the malformed NLRIs attribute tests in the Fault
Management section of [RFC7752] now encompass the new TLVs for the
BGP-LS NLRI in this document.
The extensions specified in this document do not specify any new
configuration or monitoring aspects in BGP or BGP-LS. The
Talaulikar, et al. Expires May 14, 2022 [Page 12]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
specification of BGP models is an ongoing work based on
[I-D.ietf-idr-bgp-model].
7. Security Considerations
The procedures and protocol extensions defined in this document do
not affect the BGP security model. See the "Security Considerations"
section of [RFC4271] for a discussion of BGP security. Also, refer
to [RFC4272] and [RFC6952] for analyses of security issues for BGP.
Security considerations for acquiring and distributing BGP-LS
information are discussed in [RFC7752]. The TLVs introduced in this
document are used to propagate the IGP Flexible Algorithm extensions
defined in [I-D.ietf-lsr-flex-algo]. It is assumed that the IGP
instances originating these TLVs will support all the required
security (as described in [I-D.ietf-lsr-flex-algo]) in order to
prevent any security issues when propagating the TLVs into BGP-LS.
The advertisement of the node and prefix attribute information
defined in this document presents no significant additional risk
beyond that associated with the existing node and prefix attribute
information already supported in [RFC7752].
8. Acknowledgements
The authors would like to thank Les Ginsberg, Amalesh Maity and Y F
Siu for their reviews and contributions to this work. The authors
would also like to thanks Jie Dong for his shepherd review.
9. References
9.1. Normative References
[I-D.ietf-idr-bgp-ls-app-specific-attr]
Talaulikar, K., Psenak, P., and J. Tantsura, "Application-
Specific Attributes Advertisement with BGP Link-State",
draft-ietf-idr-bgp-ls-app-specific-attr-08 (work in
progress), November 2021.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-18 (work in progress), October 2021.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Talaulikar, et al. Expires May 14, 2022 [Page 13]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
<https://www.rfc-editor.org/info/rfc4202>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[I-D.ietf-idr-bgp-model]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
YANG Model for Service Provider Networks", draft-ietf-idr-
bgp-model-12 (work in progress), October 2021.
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
Bernier, D., and B. Decraene, "BGP Link State Extensions
for SRv6", draft-ietf-idr-bgpls-srv6-ext-09 (work in
progress), November 2021.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-14 (work in progress),
October 2021.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<https://www.rfc-editor.org/info/rfc2702>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
Talaulikar, et al. Expires May 14, 2022 [Page 14]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
Authors' Addresses
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
Talaulikar, et al. Expires May 14, 2022 [Page 15]
Internet-Draft BGP-LS Extensions for Flex Algo November 2021
Peter Psenak
Cisco Systems
Slovakia
Email: ppsenak@cisco.com
Shawn Zandi
LinkedIn
USA
Email: szandi@linkedin.com
Gaurav Dawra
LinkedIn
USA
Email: gdawra.ietf@gmail.com
Talaulikar, et al. Expires May 14, 2022 [Page 16]