draft-ietf-ospf-ospfv3-segment-routing-extensions-18.txt   draft-ietf-ospf-ospfv3-segment-routing-extensions-19.txt 
Open Shortest Path First IGP P. Psenak, Ed. Open Shortest Path First IGP P. Psenak, Ed.
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Previdi, Ed. Intended status: Standards Track S. Previdi, Ed.
Expires: May 20, 2019 Individual Expires: May 24, 2019 Individual
November 16, 2018 November 20, 2018
OSPFv3 Extensions for Segment Routing OSPFv3 Extensions for Segment Routing
draft-ietf-ospf-ospfv3-segment-routing-extensions-18 draft-ietf-ospf-ospfv3-segment-routing-extensions-19
Abstract Abstract
Segment Routing (SR) allows a flexible definition of end-to-end paths Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological within IGP topologies by encoding paths as sequences of topological
sub-paths, called "segments". These segments are advertised by the sub-paths, called "segments". These segments are advertised by the
link-state routing protocols (IS-IS and OSPF). link-state routing protocols (IS-IS and OSPF).
This draft describes the OSPFv3 extensions required for Segment This draft describes the OSPFv3 extensions required for Segment
Routing with MPLS data plane. Routing with MPLS data plane.
skipping to change at page 1, line 43 skipping to change at page 1, line 43
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 May 20, 2019. This Internet-Draft will expire on May 24, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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 21 skipping to change at page 2, line 21
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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 4 3. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 4
3.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4 3.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4
4. Segment Routing Capabilities . . . . . . . . . . . . . . . . 5 4. Segment Routing Capabilities . . . . . . . . . . . . . . . . 4
4.1. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 5 5. OSPFv3 Extended Prefix Range TLV . . . . . . . . . . . . . . 5
4.2. SID/Label Range TLV . . . . . . . . . . . . . . . . . . . 6 6. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7
4.3. SR Local Block TLV . . . . . . . . . . . . . . . . . . . 8 7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 10
4.4. SRMS Preference TLV . . . . . . . . . . . . . . . . . . . 10 7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 10
5. OSPFv3 Extended Prefix Range TLV . . . . . . . . . . . . . . 11 7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 12
6. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 13 8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 13
7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 17 8.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 13
7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 17 8.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 14
7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 19 8.3. Segment Routing for External Prefixes . . . . . . . . . . 15
8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 20 8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 15
8.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 20 8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 15
8.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 21 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 16
8.3. Segment Routing for External Prefixes . . . . . . . . . . 22 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 22 9.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 16
8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 22 9.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 16
8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 22 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 23 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 23 12.1. Normative References . . . . . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 23 12.2. Informative References . . . . . . . . . . . . . . . . . 20
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction 1. Introduction
Segment Routing (SR) allows a flexible definition of end-to-end paths Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological within IGP topologies by encoding paths as sequences of topological
sub-paths, called "segments". These segments are advertised by the sub-paths, called "segments". These segments are advertised by the
link-state routing protocols (IS-IS and OSPF). Prefix segments link-state routing protocols (IS-IS and OSPF). Prefix segments
represent an ECMP-aware shortest-path to a prefix (or a node), as per represent an ECMP-aware shortest-path to a prefix (or a node), as per
the state of the IGP topology. Adjacency segments represent a hop the state of the IGP topology. Adjacency segments represent a hop
over a specific adjacency between two nodes in the IGP. A prefix over a specific adjacency between two nodes in the IGP. A prefix
skipping to change at page 4, line 42 skipping to change at page 4, line 38
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) | | SID/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 7 Type: 7
Length: Variable, 3 or 4 octets Length: Either 3 or 4 octets
SID/Label: If length is set to 3, then the 20 rightmost bits SID/Label: If length is set to 3, then the 20 rightmost bits
represent a label. If length is set to 4, then the value represent a label. If length is set to 4, then the value
represents a 32-bit SID. represents a 32-bit SID.
The receiving router MUST ignore the SID/Label Sub-TLV if the The receiving router MUST ignore the SID/Label Sub-TLV if the
length is other than 3 or 4. length is other than 3 or 4.
4. Segment Routing Capabilities 4. Segment Routing Capabilities
Segment Routing requires some additional router capabilities to be Segment Routing requires some additional router capabilities to be
advertised to other routers in the area. advertised to other routers in the area.
These SR capabilities are advertised in the OSPFv3 Router Information These SR capabilities are advertised in the OSPFv3 Router Information
Opaque LSA (defined in [RFC7770]). Opaque LSA (defined in [RFC7770]) and specified in
[I-D.ietf-ospf-segment-routing-extensions].
4.1. SR-Algorithm TLV
The SR-Algorithm TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]).
The SR-Algorithm TLV is optional. It SHOULD only be advertised once
in the OSPFv3 Router Information Opaque LSA. If the SR-Algorithm TLV
is not advertised by the node, such node is considered as not being
segment routing capable.
An SR router can use various algorithms when calculating reachability
to OSPFv3 routers or prefixes in an OSPFv3 area. Examples of these
algorithms are metric-based Shortest Path First (SPF), various
flavors of Constrained SPF, etc. The SR-Algorithm TLV allows a
router to advertise the algorithms currently used by the router to
other routers in an OSPFv3 area. The SR-Algorithm TLV has 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm n | |
+- -+
| |
+ +
where:
Type: 8 as defined in [I-D.ietf-ospf-segment-routing-extensions]
and applicable to OSPFv3.
Length: Variable, in octets, dependent on number of algorithms
advertised.
Algorithm: Single octet identifying the algorithm. Algorithms are
defined in "IGP Algorithm Type" registry under "Interior Gateway
Protocol (IGP) Parameters" [ALGOREG], defined in
[I-D.ietf-ospf-segment-routing-extensions].
When multiple SR-Algorithm TLVs are received from a given router, the
receiver MUST use the first occurrence of the TLV in the OSPFv3
Router Information Opaque LSA. If the SR-Algorithm TLV appears in
multiple OSPFv3 Router Information Opaque LSAs that have different
flooding scopes, the SR-Algorithm TLV in the OSPFv3 Router
Information Opaque LSA with the area-scoped flooding scope MUST be
used. If the SR-Algorithm TLV appears in multiple OSPFv3 Router
Information Opaque LSAs that have the same flooding scope, the SR-
Algorithm TLV in the OSPFv3 Router Information Opaque LSA with the
numerically smallest Instance ID MUST be used and subsequent
instances of the SR-Algorithm TLV MUST be ignored.
The OSPFv3 Router Information Opaque LSA can be advertised at any of
the defined opaque flooding scopes (link, area, or Autonomous System
(AS)). For the purpose of SR-Algorithm TLV advertisement, at least
area-scoped flooding is REQUIRED.
4.2. SID/Label Range TLV
Prefix SIDs MAY be advertised in a form of an index as described in
Section 6. Such index defines the offset in the SID/Label space
advertised by the router. The SID/Label Range TLV is used to
advertise such SID/Label space.
The SID/Label Range TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]).
The SID/Label Range TLV MAY appear multiple times 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
+ +
where:
Type: 9 as defined in [I-D.ietf-ospf-segment-routing-extensions]
and applicable to OSPFv3.
Length: Variable, in octets, dependent on Sub-TLVs.
Range Size: 3-octet SID/label range size (i.e., the number of SIDs
or labels in the range including the first SID/label). It MUST be
greater than 0.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Initially, the only supported Sub-TLV is the SID/Label Sub-TLV as
defined in Section 3.1. The SID/Label Sub-TLV MUST be included in
the SID/Label Range TLV. The SID/Label advertised in the SID/Label
Sub-TLV represents the first SID/Label in the advertised range.
Only a single SID/Label Sub-TLV MAY be advertised in SID/Label Range
TLV. If more than one SID/Label Sub-TLVs are present, the SID/Label
Range TLV MUST be ignored.
Multiple occurrences of the SID/Label Range TLV MAY be advertised, in
order to advertise multiple ranges. In such case:
o The originating router MUST encode each range into a different
SID/Label Range TLV.
o The originating router decides the order in which the set of SID/
Label Range TLVs are advertised inside the Router Information
Opaque LSA. The originating router MUST ensure the order is the
same after a graceful restart (using checkpointing, non-volatile
storage, or any other mechanism) in order to assure the SID/label
range and SID index correspondence is preserved across graceful
restarts.
o The receiving router MUST adhere to the order in which the ranges
are advertised when calculating a SID/label from a SID index.
o The originating router MUST NOT advertise overlapping ranges.
o When a router receives multiple overlapping ranges, it MUST
conform to the procedures defined in section 2.3 of
[I-D.ietf-spring-segment-routing-mpls].
The following example illustrates the advertisement of multiple
ranges:
The originating router advertises the following ranges:
Range 1: Range Size: 100 SID/Label Sub-TLV: 100
Range 1: Range Size: 100 SID/Label Sub-TLV: 1000
Range 1: Range Size: 100 SID/Label Sub-TLV: 500
The receiving routers concatenate the ranges and build the Segment
Routing Global Block (SRGB) as follows:
SRGB = [100, 199]
[1000, 1099]
[500, 599]
The indexes span multiple ranges:
index=0 means label 100
...
index 99 means label 199
index 100 means label 1000
index 199 means label 1099
...
index 200 means label 500
...
The OSPFv3 Router Information Opaque LSA can be advertised at any of
the defined flooding scopes (link, area, or autonomous system (AS)).
For the purpose of SID/Label Range TLV advertisement, at least area-
scoped flooding is REQUIRED.
4.3. SR Local Block TLV
The SR Local Block TLV (SRLB TLV) contains the range of labels the
node has reserved for local SIDs. SIDs from the SRLB MAY be used for
Adjacency-SIDs, but also by components other than the OSPFv3
protocol. As an example, an application or a controller can instruct
the router to allocate a specific local SID. Some controllers or
applications can use the control plane to discover the available set
of local SIDs on a particular router. In such cases, the SRLB is
advertised in the control plane. The requirement to advertise the
SRLB is further described in [I-D.ietf-spring-segment-routing-mpls].
The SRLB TLV is used to advertise the SRLB.
The SRLB TLV is a top-level TLV of the OSPFv3 Router Information
Opaque LSA (defined in [RFC7770]).
The SRLB TLV MAY appear multiple times in the OSPFv3 Router
Information Opaque LSA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
+ +
where:
Type: 14 as defined in [I-D.ietf-ospf-segment-routing-extensions]
and applicable to OSPFv3.
Length: Variable, in octets, dependent on Sub-TLVs.
Range Size: 3-octet SID/label range size (i.e., the number of SIDs
or labels in the range including the first SID/label). It MUST be
greater than 0.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Initially, the only supported Sub-TLV is the SID/Label Sub-TLV as
defined in Section 3.1. The SID/Label Sub-TLV MUST be included in
the SRLB TLV. The SID/Label advertised in the SID/Label Sub-TLV
represents the first SID/Label in the advertised range.
Only a single SID/Label Sub-TLV MAY be advertised in the SRLB TLV.
If more than one SID/Label Sub-TLVs are present, the SRLB TLV MUST be
ignored.
The originating router MUST NOT advertise overlapping ranges.
When a router receives multiple overlapping ranges, it MUST conform
to the procedures defined in section 2.3 of
[I-D.ietf-spring-segment-routing-mpls].
Each time a SID from the SRLB is allocated, it SHOULD also be
reported to all components (e.g., controller or applications) in
order for these components to have an up-to-date view of the current
SRLB allocation. This is required to avoid collisions between
allocation instructions.
Within the context of OSPFv3, the reporting of local SIDs is done
through OSPFv3 Sub-TLVs such as the Adjacency-SID (Section 7).
However, the reporting of allocated local SIDs can also be done
through other means and protocols which are outside the scope of this
document.
A router advertising the SRLB TLV MAY also have other label ranges,
outside of the SRLB, used for its local allocation purposes which are
not advertised in the SRLB TLV. For example, it is possible that an
Adjacency-SID is allocated using a local label that is not part of
the SRLB.
The OSPFv3 Router Information Opaque LSA can be advertised at any of
the defined flooding scopes (link, area, or autonomous system (AS)).
For the purpose of SRLB TLV advertisement, at least area-scoped
flooding is REQUIRED.
4.4. SRMS Preference TLV
The Segment Routing Mapping Server Preference TLV (SRMS Preference
TLV) is used to advertise a preference associated with a node that
acts as an SR Mapping Server. The role of an SRMS is described in
[I-D.ietf-spring-segment-routing-ldp-interop]. SRMS preference is
defined in [I-D.ietf-spring-segment-routing-ldp-interop].
The SRMS Preference TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]).
The SRMS Preference TLV MAY only be advertised once in the OSPFv3
Router Information Opaque LSA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 15 as defined in [I-D.ietf-ospf-segment-routing-extensions]
and applicable to OSPFv3.
Length: 4 octets
Preference: 1 octet. SRMS preference value from 0 to 255.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
When multiple SRMS Preference TLVs are received from a given router,
the receiver MUST use the first occurrence of the TLV in the OSPFv3
Router Information Opaque LSA. If the SRMS Preference TLV appears in
multiple OSPFv3 Router Information Opaque LSAs that have different
flooding scopes, the SRMS Preference TLV in the OSPFv3 Router
Information Opaque LSA with the narrowest flooding scope MUST be
used. If the SRMS Preference TLV appears in multiple OSPFv3 Router
Information Opaque LSAs that have the same flooding scope, the SRMS
Preference TLV in the OSPFv3 Router Information Opaque LSA with the
numerically smallest Instance ID MUST be used and subsequent
instances of the SRMS Preference TLV MUST be ignored.
The OSPFv3 Router Information Opaque LSA can be advertised at any of
the defined flooding scopes (link, area, or autonomous system (AS)).
For the purpose of the SRMS Preference TLV advertisement, AS-scoped
flooding SHOULD be used. This is because SRMS servers can be located
in different areas than consumers of the SRMS advertisements. If
SRMS advertisements from an SRMS server are only used inside the SRMS
server's area, area-scoped flooding MAY be used.
5. OSPFv3 Extended Prefix Range TLV 5. OSPFv3 Extended Prefix Range TLV
In some cases it is useful to advertise attributes for a range of In some cases it is useful to advertise attributes for a range of
prefixes. The Segment Routing Mapping Server, which is described in prefixes. The Segment Routing Mapping Server, which is described in
[I-D.ietf-spring-segment-routing-ldp-interop], is an example of where [I-D.ietf-spring-segment-routing-ldp-interop], is an example of where
we need a single advertisement to advertise SIDs for multiple a single advertisement is needed to advertise SIDs for multiple
prefixes from a contiguous address range. prefixes from a contiguous address range.
The OSPFv3 Extended Prefix Range TLV is defined for this purpose. The OSPFv3 Extended Prefix Range TLV is defined for this purpose.
The OSPFv3 Extended Prefix Range TLV is a top-level TLV of the The OSPFv3 Extended Prefix Range TLV is a top-level TLV of the
following LSAs defined in [RFC8362]: following LSAs defined in [RFC8362]:
E-Intra-Area-Prefix-LSA E-Intra-Area-Prefix-LSA
E-Inter-Area-Prefix-LSA E-Inter-Area-Prefix-LSA
skipping to change at page 14, line 41 skipping to change at page 8, line 26
then the value/index carried by this Sub-TLV has global then the value/index carried by this Sub-TLV has global
significance. significance.
Other bits: Reserved. These MUST be zero when sent and are Other bits: Reserved. These MUST be zero when sent and are
ignored when received. ignored when received.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception. on reception.
Algorithm: Single octet identifying the algorithm the Prefix-SID Algorithm: Single octet identifying the algorithm the Prefix-SID
is associated with as defined in Section 4.1. is associated with as defined in
[I-D.ietf-ospf-segment-routing-extensions].
A router receiving a Prefix-SID from a remote node and with an A router receiving a Prefix-SID from a remote node and with an
algorithm value that such remote node has not advertised in the algorithm value that such remote node has not advertised in the
SR-Algorithm Sub-TLV (Section 4.1) MUST ignore the Prefix-SID Sub- SR-Algorithm Sub-TLV [I-D.ietf-ospf-segment-routing-extensions]
TLV. MUST ignore the Prefix-SID Sub-TLV.
SID/Index/Label: According to the V and L flags, it contains SID/Index/Label: According to the V-Fag, it contains either:
either:
A 32-bit index defining the offset in the SID/Label space A 32-bit index defining the offset in the SID/Label space
advertised by this router. advertised by this router.
A 24-bit label where the 20 rightmost bits are used for A 24-bit label where the 20 rightmost bits are used for
encoding the label value. encoding the label value.
If an OSPFv3 router advertises multiple Prefix-SIDs for the same If an OSPFv3 router advertises multiple Prefix-SIDs for the same
prefix, topology, and algorithm, all of them MUST be ignored. prefix, topology, and algorithm, all of them MUST be ignored.
skipping to change at page 20, line 50 skipping to change at page 14, line 28
when advertising SIDs for prefixes. Prefixes of different route- when advertising SIDs for prefixes. Prefixes of different route-
types can be combined in a single OSPFv3 Extended Prefix Range TLV types can be combined in a single OSPFv3 Extended Prefix Range TLV
advertised by an SR Mapping Server. advertised by an SR Mapping Server.
Area-scoped OSPFv3 Extended Prefix Range TLVs are propagated between Area-scoped OSPFv3 Extended Prefix Range TLVs are propagated between
areas. Similar to propagation of prefixes between areas, an ABR only areas. Similar to propagation of prefixes between areas, an ABR only
propagates the OSPFv3 Extended Prefix Range TLV that it considers to propagates the OSPFv3 Extended Prefix Range TLV that it considers to
be the best from the set it received. The rules used to pick the be the best from the set it received. The rules used to pick the
best OSPFv3 Extended Prefix Range TLV are described in Section 5. best OSPFv3 Extended Prefix Range TLV are described in Section 5.
When propagating an OSPFv3 Extended Prefix Range TLV between areas,
ABRs MUST set the IA-Flag, that is used to prevent redundant flooding
of the OSPFv3 Extended Prefix Range TLV between areas as described in
Section 5.
8.2. Inter-area Segment routing in OSPFv3 8.2. Inter-area Segment routing in OSPFv3
In order to support SR in a multi-area environment, OSPFv3 MUST In order to support SR in a multi-area environment, OSPFv3 MUST
propagate Prefix-SID information between areas. The following propagate Prefix-SID information between areas. The following
procedure is used to propagate Prefix SIDs between areas. procedure is used to propagate Prefix SIDs between areas.
When an OSPFv3 ABR advertises an Inter-Area-Prefix-LSA from an intra- When an OSPFv3 ABR advertises an Inter-Area-Prefix-LSA from an intra-
area prefix to all its connected areas, it will also include the area prefix to all its connected areas, it will also include the
Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value Prefix-SID Sub-TLV, as described in Section 6. The Prefix-SID value
will be set as follows: will be set as follows:
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