draft-ietf-ospf-ospfv3-segment-routing-extensions-12.txt   draft-ietf-ospf-ospfv3-segment-routing-extensions-13.txt 
Open Shortest Path First IGP P. Psenak, Ed. Open Shortest Path First IGP P. Psenak, Ed.
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: October 22, 2018 S. Previdi, Ed. Expires: November 24, 2018 S. Previdi, Ed.
Individual Individual
H. Gredler H. Gredler
RtBrick Inc. RtBrick Inc.
R. Shakir R. Shakir
Google, Inc. Google, Inc.
W. Henderickx W. Henderickx
Nokia Nokia
J. Tantsura J. Tantsura
Nuage Networks Nuage Networks
April 20, 2018 May 23, 2018
OSPFv3 Extensions for Segment Routing OSPFv3 Extensions for Segment Routing
draft-ietf-ospf-ospfv3-segment-routing-extensions-12 draft-ietf-ospf-ospfv3-segment-routing-extensions-13
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. Routing.
skipping to change at page 2, line 7 skipping to change at page 2, line 7
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 October 22, 2018. This Internet-Draft will expire on November 24, 2018.
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 47 skipping to change at page 2, line 47
6.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 17 6.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 17
6.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 19 6.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 19
7. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 20 7. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 20
7.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 20 7.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 20
7.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 22 7.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 22
7.3. Segment Routing for External Prefixes . . . . . . . . . . 23 7.3. Segment Routing for External Prefixes . . . . . . . . . . 23
7.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 23 7.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 23
7.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 23 7.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 23
7.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 23 7.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8.1. OSPFv3 Extend-LSA TLV Registry . . . . . . . . . . . . . 24 8.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 24
8.2. OSPFv3 Extend-LSA Sub-TLV registry . . . . . . . . . . . 24 8.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 24
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25 12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 26 12.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
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
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The SR-Algorithm TLV is a top-level TLV of the OSPFv3 Router The SR-Algorithm TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]). Information Opaque LSA (defined in [RFC7770]).
The SR-Algorithm TLV is optional. It SHOULD only be advertised once The SR-Algorithm TLV is optional. It SHOULD only be advertised once
in the OSPFv3 Router Information Opaque LSA. If the SR-Algorithm TLV 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 is not advertised by the node, such node is considered as not being
segment routing capable. segment routing capable.
An SR router can use various algorithms when calculating reachability An SR router can use various algorithms when calculating reachability
to OSPFv3 routers or prefixes in an OSPFv3 area. Examples of these to OSPFv3 routers or prefixes in an OSPFv3 area. Examples of these
algorithms are metric based Shortest Path First (SPF), various algorithms are metric-based Shortest Path First (SPF), various
flavors of Constrained SPF, etc. The SR-Algorithm TLV allows a flavors of Constrained SPF, etc. The SR-Algorithm TLV allows a
router to advertise the algorithms currently used by the router to router to advertise the algorithms currently used by the router to
other routers in an OSPFv3 area. The SR-Algorithm TLV has following other routers in an OSPFv3 area. The SR-Algorithm TLV has following
format: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm n | | | Algorithm 1 | Algorithm... | Algorithm n | |
+- -+ +- -+
| | | |
+ + + +
where: where:
Type: 8 Type: 8
Length: Variable, in octets, dependent on number of algorithms Length: Variable, in octets, dependent on number of algorithms
advertised. advertised.
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included. included.
1: Strict Shortest Path First (SPF) algorithm based on link 1: Strict Shortest Path First (SPF) algorithm based on link
metric. The algorithm is identical to Algorithm 0 but metric. The algorithm is identical to Algorithm 0 but
Algorithm 1 requires that all nodes along the path will honor Algorithm 1 requires that all nodes along the path will honor
the SPF routing decision. Local policy at the node claiming the SPF routing decision. Local policy at the node claiming
support for Algorithm 1 MUST NOT alter the SPF paths computed support for Algorithm 1 MUST NOT alter the SPF paths computed
by Algorithm 1. by Algorithm 1.
When multiple SR-Algorithm TLVs are received from a given router, the When multiple SR-Algorithm TLVs are received from a given router, the
receiver MUST use the first occurrence of the TLV in the OSPFV3 receiver MUST use the first occurrence of the TLV in the OSPFv3
Router Information Opaque LSA. If the SR-Algorithm TLV appears in Router Information Opaque LSA. If the SR-Algorithm TLV appears in
multiple OSPFv3 Router Information Opaque LSAs that have different multiple OSPFv3 Router Information Opaque LSAs that have different
flooding scopes, the SR-Algorithm TLV in the OSPFv3 Router flooding scopes, the SR-Algorithm TLV in the OSPFv3 Router
Information Opaque LSA with the area-scoped flooding scope MUST be Information Opaque LSA with the area-scoped flooding scope MUST be
used. If the SR-Algorithm TLV appears in multiple OSPFv3 Router used. If the SR-Algorithm TLV appears in multiple OSPFv3 Router
Information Opaque LSAs that have the same flooding scope, the SR- Information Opaque LSAs that have the same flooding scope, the SR-
Algorithm TLV in the OSPFv3 Router Information Opaque LSA with the Algorithm TLV in the OSPFv3 Router Information Opaque LSA with the
numerically smallest Instance ID MUST be used and subsequent numerically smallest Instance ID MUST be used and subsequent
instances of the SR-Algorithm TLV MUST be ignored. instances of the SR-Algorithm TLV MUST be ignored.
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The SID/Label Range TLV is a top-level TLV of the OSPFv3 Router The SID/Label Range TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]). Information Opaque LSA (defined in [RFC7770]).
The SID/Label Range TLV MAY appear multiple times and has the The SID/Label Range TLV MAY appear multiple times and has the
following format: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved | | Range Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) | | Sub-TLVs (variable) |
+- -+ +- -+
| | | |
+ + + +
where: where:
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the SRLB. the SRLB.
The OSPFv3 Router Information Opaque LSA can be advertised at any of The OSPFv3 Router Information Opaque LSA can be advertised at any of
the defined flooding scopes (link, area, or autonomous system (AS)). the defined flooding scopes (link, area, or autonomous system (AS)).
For the purpose of SRLB TLV advertisement, area-scoped flooding is For the purpose of SRLB TLV advertisement, area-scoped flooding is
REQUIRED. REQUIRED.
3.4. SRMS Preference TLV 3.4. SRMS Preference TLV
The Segment Routing Mapping Server Preference TLV (SRMS Preference The Segment Routing Mapping Server Preference TLV (SRMS Preference
TLV) is used to advertise a preference associated with the node that 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 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 [I-D.ietf-spring-segment-routing-ldp-interop]. SRMS preference is
defined in [I-D.ietf-spring-segment-routing-ldp-interop]. defined in [I-D.ietf-spring-segment-routing-ldp-interop].
The SRMS Preference TLV is a top-level TLV of the OSPFv3 Router The SRMS Preference TLV is a top-level TLV of the OSPFv3 Router
Information Opaque LSA (defined in [RFC7770]). Information Opaque LSA (defined in [RFC7770]).
The SRMS Preference TLV MAY only be advertised once in the OSPFv3 The SRMS Preference TLV MAY only be advertised once in the OSPFv3
Router Information Opaque LSA and has the following format: Router Information Opaque LSA and 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference | Reserved | | Preference | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 15 Type: 15
Length: 4 octets Length: 4 octets
Preference: 1 octet. SRMS preference value from 0 to 255. Preference: 1 octet. SRMS preference value from 0 to 255.
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SRMS server's area, area-scoped flooding MAY be used. SRMS server's area, area-scoped flooding MAY be used.
4. OSPFv3 Extended Prefix Range TLV 4. 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 where we [I-D.ietf-spring-segment-routing-ldp-interop], is an example where we
need a single advertisement to advertise SIDs for multiple prefixes need a single advertisement to advertise SIDs for multiple prefixes
from a contiguous address range. 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 [I-D.ietf-ospf-ospfv3-lsa-extend]: following LSAs defined in [I-D.ietf-ospf-ospfv3-lsa-extend]:
E-Intra-Area-Prefix-LSA E-Intra-Area-Prefix-LSA
E-Inter-Area-Prefix-LSA E-Inter-Area-Prefix-LSA
E-AS-External-LSA E-AS-External-LSA
E-Type-7-LSA E-Type-7-LSA
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AF: 1 - IPv6 unicast AF: 1 - IPv6 unicast
Range size: Represents the number of prefixes that are covered by Range size: Represents the number of prefixes that are covered by
the advertisement. The Range Size MUST NOT exceed the number of the advertisement. The Range Size MUST NOT exceed the number of
prefixes that could be satisfied by the prefix length without prefixes that could be satisfied by the prefix length without
including: including:
IPv4 multicast address range (224.0.0.0/3), if the AF is IPv4 IPv4 multicast address range (224.0.0.0/3), if the AF is IPv4
unicast unicast
addresses from other than the IPv6 unicast address class, if Addresses from other than the IPv6 unicast address class, if
the AF is IPv6 unicast the AF is IPv6 unicast
Flags: Single octet field. The following flags are defined: Flags: Single octet field. The following flags are defined:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+
|IA| | | | | | | | |IA| | | | | | | |
+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+
where: where:
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OSPFv3 Extended Prefix Range TLV OSPFv3 Extended Prefix Range TLV
It MAY appear more than once in the parent TLV and has the following It MAY appear more than once in the parent TLV and has the following
format: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm | Reserved | | Flags | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) | | SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 4 Type: 4
Length: 7 or 8 octets, dependent on the V-flag Length: 7 or 8 octets, dependent on the V-flag
Flags: Single octet field. The following flags are defined: Flags: Single octet field. The following flags are defined:
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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.
When calculating the outgoing label for the prefix, the router MUST When calculating the outgoing label for the prefix, the router MUST
take into account, as described below, the E, NP and M flags take into account, as described below, the E, NP, and M flags
advertised by the next-hop router if that router advertised the SID advertised by the next-hop router if that router advertised the SID
for the prefix. This MUST be done regardless of whether the next-hop for the prefix. This MUST be done regardless of whether the next-hop
router contributes to the best path to the prefix. router contributes to the best path to the prefix.
The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for
Prefix-SIDs allocated to inter-area prefixes that are originated by Prefix-SIDs allocated to prefixes that are propagated between areas
the ABR based on intra-area or inter-area reachability between areas, by an ABR based on intra-area or inter-area reachability, unless the
unless the advertised prefix is directly attached to the ABR. advertised prefix is directly attached to such ABR.
The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for
Prefix-SIDs allocated to redistributed prefixes, unless the Prefix-SIDs allocated to redistributed prefixes, unless the
redistributed prefix is directly attached to the ASBR. redistributed prefix is directly attached to the advertising ASBR.
If the NP-Flag is not set, then any upstream neighbor of the Prefix- If the NP-Flag is not set, then any upstream neighbor of the Prefix-
SID originator MUST pop the Prefix-SID. This is equivalent to the SID originator MUST pop the Prefix-SID. This is equivalent to the
penultimate hop popping mechanism used in the MPLS dataplane. If the penultimate hop popping mechanism used in the MPLS dataplane. If the
NP-flag is not set, then the received E-flag is ignored. NP-flag is not set, then the received E-flag is ignored.
If the NP-flag is set then: If the NP-flag is set then:
If the E-flag is not set, then any upstream neighbor of the If the E-flag is not set, then any upstream neighbor of the
Prefix-SID originator MUST keep the Prefix-SID on top of the Prefix-SID originator MUST keep the Prefix-SID on top of the
stack. This is useful when the originator of the Prefix-SID need stack. This is useful when the originator of the Prefix-SID needs
to stitch the incoming packet into a continuing MPLS LSP to the to stitch the incoming packet into a continuing MPLS LSP to the
final destination. This could occur at an Area Border Router final destination. This could occur at an Area Border Router
(prefix propagation from one area to another) or at an AS Boundary (prefix propagation from one area to another) or at an AS Boundary
Router (prefix propagation from one domain to another). Router (prefix propagation from one domain to another).
If the E-flag is set, then any upstream neighbor of the Prefix-SID If the E-flag is set, then any upstream neighbor of the Prefix-SID
originator MUST replace the Prefix-SID with an Explicit-NULL originator MUST replace the Prefix-SID with an Explicit-NULL
label. This is useful, e.g., when the originator of the Prefix- label. This is useful, e.g., when the originator of the Prefix-
SID is the final destination for the related prefix and the SID is the final destination for the related prefix and the
originator wishes to receive the packet with the original EXP originator wishes to receive the packet with the original EXP
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reception. reception.
As the Mapping Server does not specify the originator of a prefix As the Mapping Server does not specify the originator of a prefix
advertisement, it is not possible to determine PHP behavior solely advertisement, it is not possible to determine PHP behavior solely
based on the Mapping Server advertisement. However, PHP behavior based on the Mapping Server advertisement. However, PHP behavior
SHOULD be done in following cases: SHOULD be done in following cases:
The Prefix is intra-area type and the downstream neighbor is the The Prefix is intra-area type and the downstream neighbor is the
originator of the prefix. originator of the prefix.
The Prefix is inter-area type and downstream neighbor is an ABR, The Prefix is inter-area type and the downstream neighbor is an
which is advertising prefix reachability and is setting LA-bit in ABR, which is advertising prefix reachability and is setting the
the Prefix Options as described in LA-bit in the Prefix Options as described in
[I-D.ietf-ospf-ospfv3-lsa-extend]. [I-D.ietf-ospf-ospfv3-lsa-extend].
The Prefix is external type and downstream neighbor is an ASBR, The Prefix is external type and the downstream neighbor is an
which is advertising prefix reachability and is setting LA-bit in ASBR, which is advertising prefix reachability and is setting the
the Prefix Options as described in LA-bit in the Prefix Options as described in
[I-D.ietf-ospf-ospfv3-lsa-extend]. [I-D.ietf-ospf-ospfv3-lsa-extend].
When a Prefix-SID is advertised in the OSPFv3 Extended Prefix Range When a Prefix-SID is advertised in the OSPFv3 Extended Prefix Range
TLV, then the value advertised in the Prefix SID Sub-TLV is TLV, then the value advertised in the Prefix SID Sub-TLV is
interpreted as a starting SID/Label value. interpreted as a starting SID/Label value.
Example 1: If the following router addresses (loopback addresses) Example 1: If the following router addresses (loopback addresses)
need to be mapped into the corresponding Prefix SID indexes: need to be mapped into the corresponding Prefix SID indexes:
Router-A: 2001:DB8::1/128, Prefix-SID: Index 1 Router-A: 2001:DB8::1/128, Prefix-SID: Index 1
Router-B: 2001:DB8::2/128, Prefix-SID: Index 2 Router-B: 2001:DB8::2/128, Prefix-SID: Index 2
Router-C: 2001:DB8::3/128, Prefix-SID: Index 3 Router-C: 2001:DB8::3/128, Prefix-SID: Index 3
Router-D: 2001:DB8::4/128, Prefix-SID: Index 4 Router-D: 2001:DB8::4/128, Prefix-SID: Index 4
then the Address Prefix field in the OSPFv3 Extended Prefix Range TLV then the Address Prefix field in the OSPFv3 Extended Prefix Range TLV
would be set to 2001:DB8::1, Prefix Length would be set to 128, Range would be set to 2001:DB8::1, the Prefix Length would be set to 128,
Size would be set to 4, and the Index value in the Prefix-SID Sub-TLV the Range Size would be set to 4, and the Index value in the Prefix-
would be set to 1. SID Sub-TLV would be set to 1.
Example 2: If the following prefixes need to be mapped into the Example 2: If the following prefixes need to be mapped into the
corresponding Prefix-SID indexes: corresponding Prefix-SID indexes:
2001:DB8:1::0/120, Prefix-SID: Index 51 2001:DB8:1::0/120, Prefix-SID: Index 51
2001:DB8:1::100/120, Prefix-SID: Index 52 2001:DB8:1::100/120, Prefix-SID: Index 52
2001:DB8:1::200/120, Prefix-SID: Index 53 2001:DB8:1::200/120, Prefix-SID: Index 53
2001:DB8:1::300/120, Prefix-SID: Index 54 2001:DB8:1::300/120, Prefix-SID: Index 54
2001:DB8:1::400/120, Prefix-SID: Index 55 2001:DB8:1::400/120, Prefix-SID: Index 55
2001:DB8:1::500/120, Prefix-SID: Index 56 2001:DB8:1::500/120, Prefix-SID: Index 56
2001:DB8:1::600/120, Prefix-SID: Index 57 2001:DB8:1::600/120, Prefix-SID: Index 57
then the Prefix field in the OSPFv3 Extended Prefix Range TLV would then the Prefix field in the OSPFv3 Extended Prefix Range TLV would
be set to 2001:DB8:1::0, Prefix Length would be set to 120, Range be set to 2001:DB8:1::0, the Prefix Length would be set to 120, the
Size would be set to 7, and the Index value in the Prefix-SID Sub-TLV Range Size would be set to 7, and the Index value in the Prefix-SID
would be set to 51. Sub-TLV would be set to 51.
6. Adjacency Segment Identifier (Adj-SID) 6. Adjacency Segment Identifier (Adj-SID)
An Adjacency Segment Identifier (Adj-SID) represents a router An Adjacency Segment Identifier (Adj-SID) represents a router
adjacency in Segment Routing. adjacency in Segment Routing.
6.1. Adj-SID Sub-TLV 6.1. Adj-SID Sub-TLV
Adj-SID is an optional Sub-TLV of the Router-Link TLV as defined in Adj-SID is an optional Sub-TLV of the Router-Link TLV as defined in
[I-D.ietf-ospf-ospfv3-lsa-extend]. It MAY appear multiple times in [I-D.ietf-ospf-ospfv3-lsa-extend]. It MAY appear multiple times in
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SID/Index/Label: According to the V and L flags, it contains SID/Index/Label: According to the V and L flags, 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.
An SR capable router MAY allocate an Adj-SID for each of its An SR-capable router MAY allocate an Adj-SID for each of its
adjacencies and set the B-Flag when the adjacency is eligible for adjacencies and set the B-Flag when the adjacency is eligible for
protection by an FRR mechanism (IP or MPLS) as described in protection by an FRR mechanism (IP or MPLS) as described in
[I-D.ietf-spring-segment-routing]. [I-D.ietf-spring-segment-routing].
An SR capable router MAY allocate more than one Adj-SID to an An SR-capable router MAY allocate more than one Adj-SID to an
adjacency adjacency
An SR capable router MAY allocate the same Adj-SID to different An SR-capable router MAY allocate the same Adj-SID to different
adjacencies adjacencies
When the P-flag is not set, the Adj-SID MAY be persistent. When the When the P-flag is not set, the Adj-SID MAY be persistent. When the
P-flag is set, the Adj-SID MUST be persistent. P-flag is set, the Adj-SID MUST be persistent.
6.2. LAN Adj-SID Sub-TLV 6.2. LAN Adj-SID Sub-TLV
LAN Adj-SID is an optional Sub-TLV of the Router-Link TLV. It MAY LAN Adj-SID is an optional Sub-TLV of the Router-Link TLV. It MAY
appear multiple times in the Router-Link TLV. It is used to appear multiple times in the Router-Link TLV. It is used to
advertise a SID/Label for an adjacency to a non-DR router on a advertise a SID/Label for an adjacency to a non-DR router on a
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the P-flag is set, the Adj-SID MUST be persistent. the P-flag is set, the Adj-SID MUST be persistent.
7. Elements of Procedure 7. Elements of Procedure
7.1. Intra-area Segment routing in OSPFv3 7.1. Intra-area Segment routing in OSPFv3
An OSPFv3 router that supports segment routing MAY advertise Prefix- An OSPFv3 router that supports segment routing MAY advertise Prefix-
SIDs for any prefix to which it is advertising reachability (e.g., a SIDs for any prefix to which it is advertising reachability (e.g., a
loopback IP address as described in Section 5). loopback IP address as described in Section 5).
A Prefix-SID can also be advertised by the SR Mapping Servers (as A Prefix-SID can also be advertised by SR Mapping Servers (as
described in [I-D.ietf-spring-segment-routing-ldp-interop]). A described in [I-D.ietf-spring-segment-routing-ldp-interop]). A
Mapping Server advertises Prefix-SIDs for remote prefixes that exist Mapping Server advertises Prefix-SIDs for remote prefixes that exist
in the OSPFv3 routing domain. Multiple Mapping Servers can advertise in the OSPFv3 routing domain. Multiple Mapping Servers can advertise
Prefix-SIDs for the same prefix, in which case the same Prefix-SID Prefix-SIDs for the same prefix, in which case the same Prefix-SID
MUST be advertised by all of them. The SR Mapping Server could use MUST be advertised by all of them. The SR Mapping Server could use
either area scope or autonomous system flooding scope when either area flooding scope or autonomous system flooding scope when
advertising Prefix SID for prefixes, based on the configuration of advertising Prefix SID for prefixes, based on the configuration of
the SR Mapping Server. Depending on the flooding scope used, the SR the SR Mapping Server. Depending on the flooding scope used, the SR
Mapping Server chooses the OSPFv3 LSA type that will be used. If the Mapping Server chooses the OSPFv3 LSA type that will be used. If the
area flooding scope is needed, E-Intra-Area-Prefix-LSA area flooding scope is needed, an E-Intra-Area-Prefix-LSA
([I-D.ietf-ospf-ospfv3-lsa-extend]) is used. If autonomous system ([I-D.ietf-ospf-ospfv3-lsa-extend]) is used. If autonomous system
flooding scope is needed, E-AS-External-LSA flooding scope is needed, an E-AS-External-LSA
([I-D.ietf-ospf-ospfv3-lsa-extend]) is used. ([I-D.ietf-ospf-ospfv3-lsa-extend]) is used.
When a Prefix-SID is advertised by the Mapping Server, which is When a Prefix-SID is advertised by the Mapping Server, which is
indicated by the M-flag in the Prefix-SID Sub-TLV (Section 5), the indicated by the M-flag in the Prefix-SID Sub-TLV (Section 5), the
route type as implied by the LSA type is ignored and the Prefix-SID route type as implied by the LSA type is ignored and the Prefix-SID
is bound to the corresponding prefix independent of the route type. is bound to the corresponding prefix independent of the route type.
Advertisement of the Prefix-SID by the Mapping Server using Inter- Advertisement of the Prefix-SID by the Mapping Server using an Inter-
Area Prefix TLV, External-Prefix TLV or Intra-Area-Prefix TLV Area Prefix TLV, External-Prefix TLV, or Intra-Area-Prefix TLV
([I-D.ietf-ospf-ospfv3-lsa-extend]) does not itself contribute to the ([I-D.ietf-ospf-ospfv3-lsa-extend]) does not itself contribute to the
prefix reachability. The NU-bit MUST be set in the PrefixOptions prefix reachability. The NU-bit MUST be set in the PrefixOptions
field of the LSA which is used by the Mapping Server to advertise SID field of the LSA which is used by the Mapping Server to advertise SID
or SID Range, which prevents the advertisement to contribute to the or SID Range, which prevents the advertisement from contributing to
prefix reachability. prefix reachability.
An SR Mapping Server MUST use the OSPFv3 Extended Prefix Range TLVs An SR Mapping Server MUST use the OSPFv3 Extended Prefix Range TLVs
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
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ABRs MUST set the IA-Flag, that is used to prevent redundant flooding 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 of the OSPFv3 Extended Prefix Range TLV between areas as described in
Section 4. Section 4.
7.2. Inter-area Segment routing in OSPFv3 7.2. 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 a 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 Prefix- area prefix to all its connected areas, it will also include Prefix-
SID Sub-TLV, as described in Section 5. The Prefix-SID value will be SID Sub-TLV, as described in Section 5. The Prefix-SID value will be
set as follows: set as follows:
The ABR will look at its best path to the prefix in the source The ABR will look at its best path to the prefix in the source
area and find the advertising router associated with the best path area and find the advertising router associated with the best path
to that prefix. to that prefix.
The ABR will then determine if such router advertised a Prefix-SID The ABR will then determine if such router advertised a Prefix-SID
for the prefix and use it when advertising the Prefix-SID to other for the prefix and use it when advertising the Prefix-SID to other
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If no Prefix-SID was advertised for the prefix in the backbone If no Prefix-SID was advertised for the prefix in the backbone
area by the ABR that contributes to the best path to the prefix, area by the ABR that contributes to the best path to the prefix,
the originating ABR will use the Prefix-SID advertised by any the originating ABR will use the Prefix-SID advertised by any
other router when propagating the Prefix-SID for the prefix to other router when propagating the Prefix-SID for the prefix to
other areas. other areas.
7.3. Segment Routing for External Prefixes 7.3. Segment Routing for External Prefixes
AS-External-LSAs are flooded domain wide. When an ASBR, which AS-External-LSAs are flooded domain wide. When an ASBR, which
supports SR, generates E-AS-External-LSA, it SHOULD also include supports SR, originates an E-AS-External-LSA, it SHOULD also include
Prefix-SID Sub-TLV, as described in Section 5. The Prefix-SID value a Prefix-SID Sub-TLV, as described in Section 5. The Prefix-SID
will be set to the SID that has been reserved for that prefix. value will be set to the SID that has been reserved for that prefix.
When an NSSA [RFC3101] ABR translates an E-NSSA-LSA into an E-AS- When an NSSA [RFC3101] ABR translates an E-NSSA-LSA into an E-AS-
External-LSA, it SHOULD also advertise the Prefix-SID for the prefix. External-LSA, it SHOULD also advertise the Prefix-SID for the prefix.
The NSSA ABR determines its best path to the prefix advertised in the The NSSA ABR determines its best path to the prefix advertised in the
translated E-NSSA-LSA and finds the advertising router associated translated E-NSSA-LSA and finds the advertising router associated
with that path. If the advertising router has advertised a Prefix- with that path. If the advertising router has advertised a Prefix-
SID for the prefix, then the NSSA ABR uses it when advertising the SID for the prefix, then the NSSA ABR uses it when advertising the
Prefix-SID for the E-AS-External-LSA. Otherwise, the Prefix-SID Prefix-SID for the E-AS-External-LSA. Otherwise, the Prefix-SID
advertised by any other router will be used. advertised by any other router will be used.
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or hybrid network connect. As a result, routers on the broadcast, or hybrid network connect. As a result, routers on the broadcast,
NBMA, or hybrid network advertise only their adjacency to the DR. NBMA, or hybrid network advertise only their adjacency to the DR.
Routers that do not act as DR do not form or advertise adjacencies Routers that do not act as DR do not form or advertise adjacencies
with each other. They do, however, maintain 2-Way adjacency state with each other. They do, however, maintain 2-Way adjacency state
with each other and are directly reachable. with each other and are directly reachable.
When Segment Routing is used, each router on the broadcast, NBMA, or When Segment Routing is used, each router on the broadcast, NBMA, or
hybrid network MAY advertise the Adj-SID for its adjacency to the DR hybrid network MAY advertise the Adj-SID for its adjacency to the DR
using the Adj-SID Sub-TLV as described in Section 6.1. using the Adj-SID Sub-TLV as described in Section 6.1.
SR capable routers MAY also advertise a LAN-Adj-SID for other SR-capable routers MAY also advertise a LAN-Adj-SID for other
neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid
network using the LAN-Adj-SID Sub-TLV as described in Section 6.2. network using the LAN-Adj-SID Sub-TLV as described in Section 6.2.
8. IANA Considerations 8. IANA Considerations
This specification updates several existing OSPFv3 registries. This specification updates several existing OSPFv3 registries.
8.1. OSPFv3 Extend-LSA TLV Registry 8.1. OSPFv3 Extended-LSA TLV Registry
Following values are allocated: Following values are allocated:
o suggested value 9 - OSPFv3 Extended Prefix Range TLV o suggested value 9 - OSPFv3 Extended Prefix Range TLV
8.2. OSPFv3 Extend-LSA Sub-TLV registry 8.2. OSPFv3 Extended-LSA Sub-TLV registry
o 4 - Prefix SID Sub-TLV o 4 - Prefix SID Sub-TLV
o 5 - Adj-SID Sub-TLV o 5 - Adj-SID Sub-TLV
o 6 - LAN Adj-SID Sub-TLV o 6 - LAN Adj-SID Sub-TLV
o 7 - SID/Label Sub-TLV o 7 - SID/Label Sub-TLV
9. Security Considerations 9. Security Considerations
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IP control plane can be carried out on the MPLS control plane IP control plane can be carried out on the MPLS control plane
resulting in traffic being misrouted in the respective data planes. resulting in traffic being misrouted in the respective data planes.
However, the latter can be more difficult to detect and isolate. However, the latter can be more difficult to detect and isolate.
Existing security extensions as described in [RFC5340] and Existing security extensions as described in [RFC5340] and
[I-D.ietf-ospf-ospfv3-lsa-extend] apply to these segment routing [I-D.ietf-ospf-ospfv3-lsa-extend] apply to these segment routing
extensions. While OSPFv3 is under a single administrative domain, extensions. While OSPFv3 is under a single administrative domain,
there can be deployments where potential attackers have access to one there can be deployments where potential attackers have access to one
or more networks in the OSPFv3 routing domain. In these deployments, or more networks in the OSPFv3 routing domain. In these deployments,
stronger authentication mechanisms such as those specified in stronger authentication mechanisms such as those specified in
[RFC4552] SHOULD be used. [RFC4552] or [RFC7166] SHOULD be used.
Implementations MUST assure that malformed TLV and Sub-TLV defined in Implementations MUST assure that malformed TLV and Sub-TLV defined in
this document are detected and do not provide a vulnerability for this document are detected and do not provide a vulnerability for
attackers to crash the OSPFv3 router or routing process. Reception attackers to crash the OSPFv3 router or routing process. Reception
of malformed TLV or Sub-TLV SHOULD be counted and/or logged for of a malformed TLV or Sub-TLV SHOULD be counted and/or logged for
further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be
rate-limited to prevent a Denial of Service (DoS) attack (distributed rate-limited to prevent a Denial of Service (DoS) attack (distributed
or otherwise) from overloading the OSPFv3 control plane. or otherwise) from overloading the OSPFv3 control plane.
10. Contributors 10. Contributors
Acee Lindem gave a substantial contribution to the content of this Acee Lindem gave a substantial contribution to the content of this
document. document.
11. Acknowledgements 11. Acknowledgements
skipping to change at page 26, line 38 skipping to change at page 26, line 38
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
12.2. Informative References 12.2. Informative References
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>. <https://www.rfc-editor.org/info/rfc4552>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B., [RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>. 2016, <https://www.rfc-editor.org/info/rfc7855>.
Authors' Addresses Authors' Addresses
Peter Psenak (editor) Peter Psenak (editor)
Cisco Systems, Inc. Cisco Systems, Inc.
Eurovea Centre, Central 3 Eurovea Centre, Central 3
Pribinova Street 10 Pribinova Street 10
Bratislava 81109 Bratislava 81109
Slovakia Slovakia
Email: ppsenak@cisco.com Email: ppsenak@cisco.com
Clarence Filsfils Clarence Filsfils
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