RFC 8666 PROPOSED STANDARD ROUTING · OSPFV3 · SEGMENT ROUTING
OSPFv3 SR extensions: OSPFv3 Extensions for Segment Routing
How OSPFv3 routers advertise Segment Routing identifiers so IPv6 networks can steer MPLS traffic along paths built from segments.
RFC EDITOR
Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, December 2019, <https://www.rfc-editor.org/info/rfc8666>.
BIBTEX
@misc{rfc8666,
series = {Request for Comments},
number = 8666,
howpublished = {RFC 8666},
publisher = {RFC Editor},
doi = {10.17487/RFC8666},
url = {https://www.rfc-editor.org/info/rfc8666},
author = {P. Psenak and S. Previdi},
title = {{OSPFv3 Extensions for Segment Routing}},
pagetotal = 18,
year = 2019,
month = dec,
} RFC text
Contents
Internet Engineering Task Force (IETF) P. Psenak, Ed.
Request for Comments: 8666 S. Previdi, Ed.
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 December 2019
OSPFv3 Extensions for Segment Routing
Abstract
Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological
subpaths called "segments". These segments are advertised by the
link-state routing protocols (IS-IS and OSPF).
This document describes the OSPFv3 extensions required for Segment
Routing with the MPLS data plane.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8666.
Copyright Notice
Copyright (c) 2019 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. Terminology
3. Segment Routing Identifiers
3.1. SID/Label Sub-TLV
4. Segment Routing Capabilities
5. OSPFv3 Extended Prefix Range TLV
6. Prefix-SID Sub-TLV
7. Adjacency Segment Identifier (Adj-SID)
7.1. Adj-SID Sub-TLV
7.2. LAN Adj-SID Sub-TLV
8. Elements of Procedure
8.1. Intra-area Segment Routing in OSPFv3
8.2. Inter-area Segment Routing in OSPFv3
8.3. Segment Routing for External Prefixes
8.4. Advertisement of Adj-SID
8.4.1. Advertisement of Adj-SID on Point-to-Point Links
8.4.2. Adjacency SID on Broadcast or NBMA Interfaces
9. IANA Considerations
9.1. "OSPFv3 Extended-LSA TLVs" Registry
9.2. "OSPFv3 Extended-LSA Sub-TLVs" Registry
10. TLV/Sub-TLV Error Handling
11. Security Considerations
12. References
12.1. Normative References
12.2. Informative References
Contributors
Authors' Addresses
1. Introduction
Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological
subpaths called "segments". These segments are advertised by the
link-state routing protocols (IS-IS and OSPF). Prefix segments
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
over a specific adjacency between two nodes in the IGP. A prefix
segment is typically a multi-hop path while an adjacency segment, in
most cases, is a one-hop path. SR's control plane can be applied to
both IPv6 and MPLS data planes, and it does not require any
additional signaling (other than IGP extensions). The IPv6 data
plane is out of the scope of this specification; the OSPFv3 extension
for SR with the IPv6 data plane will be specified in a separate
document. When used in MPLS networks, SR paths do not require any
LDP or RSVP-TE signaling. However, SR can interoperate in the
presence of Label Switched Paths (LSPs) established with RSVP or LDP.
This document describes the OSPFv3 extensions required for Segment
Routing with the MPLS data plane.
Segment Routing architecture is described in [RFC8402].
Segment Routing use cases are described in [RFC7855].
2. Terminology
This section lists some of the terminology used in this document:
ABR: Area Border Router
Adj-SID: Adjacency Segment Identifier
AS: Autonomous System
ASBR: Autonomous System Boundary Router
DR: Designated Router
IS-IS: Intermediate System to Intermediate System
LDP: Label Distribution Protocol
LSP: Label Switched Path
MPLS: Multiprotocol Label Switching
OSPF: Open Shortest Path First
SPF: Shortest Path First
RSVP: Resource Reservation Protocol
SID: Segment Identifier
SR: Segment Routing
SRGB: Segment Routing Global Block
SRLB: Segment Routing Local Block
SRMS: Segment Routing Mapping Server
TLV: Type Length Value
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.
3. Segment Routing Identifiers
Segment Routing defines various types of Segment Identifiers (SIDs):
Prefix-SID, Adjacency SID, and LAN Adjacency SID.
3.1. SID/Label Sub-TLV
The SID/Label sub-TLV appears in multiple TLVs or sub-TLVs defined
later in this document. It is used to advertise the SID or label
associated with a prefix or adjacency. The SID/Label 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 7
Length: 3 or 4 octets.
SID/Label: If the length is set to 3, then the 20 rightmost bits
represent a label. If the length is set to 4, then the value
represents a 32-bit SID.
4. Segment Routing Capabilities
Segment Routing requires some additional router capabilities to be
advertised to other routers in the area.
These SR capabilities are advertised in the OSPFv3 Router Information
Opaque LSA (defined in [RFC7770]) and specified in [RFC8665].
5. OSPFv3 Extended Prefix Range TLV
In some cases, it is useful to advertise attributes for a range of
prefixes in a single advertisement. The SR Mapping Server, which is
described in [RFC8661], is an example of where SIDs for multiple
prefixes can be advertised. To optimize such advertisement in case
of multiple prefixes from a contiguous address range, OSPFv3 Extended
Prefix Range TLV is defined.
The OSPFv3 Extended Prefix Range TLV is a top-level TLV of the
following LSAs defined in [RFC8362]:
E-Intra-Area-Prefix-LSA
E-Inter-Area-Prefix-LSA
E-AS-External-LSA
E-Type-7-LSA
Multiple OSPFv3 Extended Prefix Range TLVs MAY be advertised in each
LSA mentioned above. The OSPFv3 Extended Prefix Range 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | AF | Range Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: 9
Length: Variable, in octets, depending on the sub-TLVs.
Prefix Length: Length of prefix in bits.
AF: Address family for the prefix.
AF: 0 - IPv4 unicast
AF: 1 - IPv6 unicast
Range Size: Represents the number of prefixes that are covered by
the advertisement. The Range Size MUST NOT exceed the number
of prefixes that could be satisfied by the Prefix Length
without including:
Addresses from the IPv4 multicast address range
(224.0.0.0/3), if the AF is IPv4 unicast.
Addresses other than the IPv6 unicast addresses, if the AF
is IPv6 unicast.
Flags: Reserved. MUST be zero when sent and are ignored when
received.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Address Prefix: For the address family IPv4 unicast, the
prefix itself is encoded as a 32-bit value. The default
route is represented by a prefix of length 0.
For the address family IPv6 unicast, the
prefix is encoded as an even multiple of 32-bit words and
padded with zeroed bits as necessary. This encoding
consumes ((PrefixLength + 31) / 32) 32-bit words.
Prefix encoding for other address families is
beyond the scope of this specification. Prefix encoding for
other address families can be defined in future Standards
Track specifications from the IETF stream.
The range represents the contiguous set of prefixes with the same
prefix length as specified by the Prefix Length field. The set
starts with the prefix that is specified by the Address Prefix field.
The number of prefixes in the range is equal to the Range Size.
If the OSPFv3 Extended Prefix Range TLVs advertising the exact same
range appears in multiple LSAs of the same type, originated by the
same OSPFv3 router, the LSA with the numerically smallest Instance ID
MUST be used, and subsequent instances of the OSPFv3 Extended Prefix
Range TLVs MUST be ignored.
6. Prefix-SID Sub-TLV
The Prefix-SID sub-TLV is a sub-TLV of the following OSPFv3 TLVs as
defined in [RFC8362] and in Section 5:
Intra-Area Prefix TLV
Inter-Area Prefix TLV
External Prefix TLV
OSPFv3 Extended Prefix Range TLV
It MAY appear more than once in the parent TLV 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: 4
Length: 7 or 8 octets, depending on the V-Flag.
Flags: Single-octet field. The following flags are defined:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| |NP|M |E |V |L | | |
+--+--+--+--+--+--+--+--+
where:
NP-Flag: No-PHP (Penultimate Hop Popping) Flag. If set, then
the penultimate hop MUST NOT pop the Prefix-SID before
delivering packets to the node that advertised the Prefix-
SID.
M-Flag: Mapping Server Flag. If set, the SID was advertised
by an SR Mapping Server as described in [RFC8661].
E-Flag: Explicit Null Flag. If set, any upstream neighbor of
the Prefix-SID originator MUST replace the Prefix-SID with
the Explicit NULL label (0 for IPv4, 2 for IPv6) before
forwarding the packet.
V-Flag: Value/Index Flag. If set, then the Prefix-SID carries
an absolute value. If not set, then the Prefix-SID carries
an index.
L-Flag: Local/Global Flag. If set, then the value/index
carried by the Prefix-SID has local significance. If not
set, then the value/index carried by this sub-TLV has global
significance.
Other bits: Reserved. These MUST be zero when sent and are
ignored when received.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Algorithm: Single octet identifying the algorithm the Prefix-SID
is associated with as defined in the IGP Algorithm Types
registry [ALGOREG].
A router receiving a Prefix-SID from a remote node and with an
algorithm value that the remote node has not advertised in the
SR-Algorithm TLV [RFC8665] MUST ignore the Prefix-SID sub-TLV.
SID/Index/Label: According to the V-Flag and L-Flag, it contains:
V-Flag is set to 0 and L-Flag is set to 0: The SID/Index/
Label field is a 4-octet index defining the offset in the
SID/Label space advertised by this router.
V-Flag is set to 1 and L-Flag is set to 1: The SID/Index/
Label field is a 3-octet local label where the 20 rightmost
bits are used for encoding the label value.
All other combinations of V-Flag and L-Flag are invalid and
any SID Advertisement received with an invalid setting for
V- and L-Flags MUST be ignored.
If an OSPFv3 router advertises multiple Prefix-SIDs for the same
prefix, topology, and algorithm, all of them MUST be ignored.
When calculating the outgoing label for the prefix, the router MUST
take into account, as described below, the E-, NP-, and M-Flags
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
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
Prefix-SIDs allocated to prefixes that are propagated between areas
by an ABR based on intra-area or inter-area reachability, unless the
advertised prefix is directly attached to such ABR.
The NP-Flag (No-PHP) MUST be set and the E-Flag MUST be clear for
Prefix-SIDs allocated to redistributed prefixes, unless the
redistributed prefix is directly attached to the advertising ASBR.
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 penultimate hop-popping
mechanism used in the MPLS data plane.
The received E-Flag is ignored.
If the NP-Flag is set and the E-Flag is not set, then:
Any upstream neighbor 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 needs to stitch the incoming packet
into a continuing MPLS LSP to the final destination. This could
occur at an ABR (prefix propagation from one area to another) or
at an ASBR (prefix propagation from one domain to another).
If both the NP-Flag and E-Flag are set, then:
Any upstream neighbor of the Prefix-SID originator MUST replace
the Prefix-SID with an Explicit NULL label. This is useful, e.g.,
when the originator of the Prefix-SID is the final destination for
the related prefix and the originator wishes to receive the packet
with the original Traffic Class field [RFC5462].
When the M-Flag is set, the NP-Flag and the E-Flag MUST be ignored on
reception.
As the Mapping Server does not specify the originator of a prefix
advertisement, it is not possible to determine PHP behavior solely
based on the Mapping Server Advertisement. However, PHP behavior
SHOULD be done in the following cases:
The Prefix is intra-area type and the downstream neighbor is the
originator of the prefix.
The Prefix is inter-area type and the downstream neighbor is an
ABR, which is advertising prefix reachability and is setting the
LA-bit in the Prefix Options as described in [RFC8362].
The Prefix is external type and the downstream neighbor is an
ASBR, which is advertising prefix reachability and is setting the
LA-bit in the Prefix Options as described in [RFC8362].
When a Prefix-SID is advertised in the OSPFv3 Extended Prefix Range
TLV, then the value advertised in the Prefix-SID sub-TLV is
interpreted as a starting SID/Label value.
Example 1: If the following router addresses (loopback addresses)
need to be mapped into the corresponding Prefix-SID indexes:
Router-A: 2001:DB8::1/128, Prefix-SID: Index 1
Router-B: 2001:DB8::2/128, Prefix-SID: Index 2
Router-C: 2001:DB8::3/128, Prefix-SID: Index 3
Router-D: 2001:DB8::4/128, Prefix-SID: Index 4
then the Address Prefix field in the OSPFv3 Extended Prefix Range TLV
would be set to 2001:DB8::1, the Prefix Length would be set to 128,
the Range Size would be set to 4, and the Index value in the Prefix-
SID sub-TLV would be set to 1.
Example 2: If the following prefixes need to be mapped into the
corresponding Prefix-SID indexes:
2001:DB8:1::0/120, Prefix-SID: Index 51
2001:DB8:1::100/120, Prefix-SID: Index 52
2001:DB8:1::200/120, Prefix-SID: Index 53
2001:DB8:1::300/120, Prefix-SID: Index 54
2001:DB8:1::400/120, Prefix-SID: Index 55
2001:DB8:1::500/120, Prefix-SID: Index 56
2001:DB8:1::600/120, Prefix-SID: Index 57
then the Prefix field in the OSPFv3 Extended Prefix Range TLV would
be set to 2001:DB8:1::0, the Prefix Length would be set to 120, the
Range Size would be set to 7, and the Index value in the Prefix-SID
sub-TLV would be set to 51.
7. Adjacency Segment Identifier (Adj-SID)
An Adjacency Segment Identifier (Adj-SID) represents a router
adjacency in Segment Routing.
7.1. Adj-SID Sub-TLV
The Adj-SID sub-TLV is an optional sub-TLV of the Router-Link TLV as
defined in [RFC8362]. It MAY appear multiple times in the Router-
Link TLV. The Adj-SID 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 | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:
Type: 5
Length: 7 or 8 octets, depending on the V-Flag.
Flags: Single-octet field containing the following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B|V|L|G|P| |
+-+-+-+-+-+-+-+-+
where:
B-Flag: Backup Flag. If set, the Adj-SID refers to an
adjacency that is eligible for protection (e.g., using IP
Fast Reroute (IPFRR) or MPLS-FRR (MPLS Fast Reroute)) as
described in Section 3.4 of [RFC8402].
V-Flag: Value/Index Flag. If set, then the Adj-SID carries an
absolute value. If not set, then the Adj-SID carries an
index.
L-Flag: Local/Global Flag. If set, then the value/index
carried by the Adj-SID has local significance. If not set,
then the value/index carried by this sub-TLV has global
significance.
G-Flag: Group Flag. When set, the G-Flag indicates that the
Adj-SID refers to a group of adjacencies (and therefore MAY
be assigned to other adjacencies as well).
P-Flag. Persistent Flag. When set, the P-Flag indicates that
the Adj-SID is persistently allocated, i.e., the Adj-SID
value remains the same across router restart and/or
interface flap.
Other bits: Reserved. These MUST be zero when sent and are
ignored when received.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Weight: Weight used for load-balancing purposes. The use of the
weight is defined in [RFC8402].
SID/Index/Label: As described in Section 6.
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
protection by an FRR mechanism (IP or MPLS) as described in
[RFC8402].
An SR-capable router MAY allocate more than one Adj-SID to an
adjacency.
An SR-capable router MAY allocate the same Adj-SID to different
adjacencies.
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.
7.2. LAN Adj-SID Sub-TLV
The LAN Adjacency 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
advertise a SID/Label for an adjacency to a non-DR router on a
broadcast, Non-Broadcast Multi-Access (NBMA), or hybrid [RFC6845]
network.
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 | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:
Type: 6
Length: 11 or 12 octets, depending on the V-Flag.
Flags: Same as in Section 7.1.
Weight: Weight used for load-balancing purposes. The use of the
weight is defined in [RFC8402].
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception.
Neighbor ID: The Router ID of the neighbor for which the LAN
Adjacency SID is advertised.
SID/Index/Label: As described in Section 6.
When the P-Flag is not set, the LAN Adjacency SID MAY be
persistent. When the P-Flag is set, the LAN Adjacency SID MUST
be persistent.
8. Elements of Procedure
8.1. Intra-area Segment Routing in OSPFv3
An OSPFv3 router that supports Segment Routing MAY advertise Prefix-
SIDs for any prefix to which it is advertising reachability (e.g., a
loopback IP address as described in Section 6).
A Prefix-SID can also be advertised by SR Mapping Servers (as
described in [RFC8661]). A Mapping Server advertises Prefix-SIDs for
remote prefixes that exist in the OSPFv3 routing domain. Multiple
Mapping Servers can advertise 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 either area flooding scope or
autonomous system flooding scope when advertising Prefix-SIDs for
prefixes, based on the configuration of 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 area flooding scope is
needed, an E-Intra-Area-Prefix-LSA [RFC8362] is used. If autonomous
system flooding scope is needed, an E-AS-External-LSA [RFC8362] is
used.
When a Prefix-SID is advertised by the Mapping Server, which is
indicated by the M-Flag in the Prefix-SID sub-TLV (Section 6), the
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.
Advertisement of the Prefix-SID by the Mapping Server using an Inter-
Area Prefix TLV, External-Prefix TLV, or Intra-Area-Prefix TLV
[RFC8362] does not itself contribute to the prefix reachability. The
NU-bit [RFC5340] MUST be set in the PrefixOptions field of the LSA,
which is used by the Mapping Server to advertise SID or SID Range,
which prevents the advertisement from contributing to prefix
reachability.
An SR Mapping Server MUST use the OSPFv3 Extended Prefix Range TLVs
when advertising SIDs for prefixes. Prefixes of different route
types can be combined in a single OSPFv3 Extended Prefix Range TLV
advertised by an SR Mapping Server.
Area-scoped OSPFv3 Extended Prefix Range TLVs are propagated between
areas, similar to propagation of prefixes between areas. Same rules
that are used for propagating prefixes between areas [RFC5340] are
used for the propagation of the prefix ranges.
8.2. Inter-area Segment Routing in OSPFv3
In order to support SR in a multiarea environment, OSPFv3 MUST
propagate Prefix-SID information between areas. The following
procedure is used to propagate Prefix-SIDs between areas.
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
Prefix-SID sub-TLV as described in Section 6. The Prefix-SID value
will be set as follows:
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
to that prefix.
The ABR will then determine if this router advertised a Prefix-SID
for the prefix and use it when advertising the Prefix-SID to other
connected areas.
If no Prefix-SID was advertised for the prefix in the source area
by the router that contributes to the best path to the prefix, the
originating ABR will use the Prefix-SID advertised by any other
router when propagating the Prefix-SID for the prefix to other
areas.
When an OSPFv3 ABR advertises an Inter-Area-Prefix-LSA from an inter-
area route to all its connected areas, it will also include the
Prefix-SID sub-TLV as described in Section 6. The Prefix-SID value
will be set as follows:
The ABR will look at its best path to the prefix in the backbone
area and find the advertising router associated with the best path
to that prefix.
The ABR will then determine if this router advertised a Prefix-SID
for the prefix and use it when advertising the Prefix-SID to other
connected areas.
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,
the originating ABR will use the Prefix-SID advertised by any
other router when propagating the Prefix-SID for the prefix to
other areas.
8.3. Segment Routing for External Prefixes
AS-External-LSAs are flooded domain wide. When an ASBR, which
supports SR, originates an E-AS-External-LSA, it SHOULD also include
a Prefix-SID sub-TLV as described in Section 6. The Prefix-SID value
will be set to the SID that has been reserved for that prefix.
When a Not-So-Stubby Area (NSSA) [RFC3101] ABR translates an E-NSSA-
LSA into an E-AS-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 translated E-NSSA-LSA and finds the
advertising router associated with that path. If the advertising
router has advertised a Prefix-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 advertised by any other router will be
used.
8.4. Advertisement of Adj-SID
The Adjacency Segment Routing Identifier (Adj-SID) is advertised
using the Adj-SID sub-TLV as described in Section 7.
8.4.1. Advertisement of Adj-SID on Point-to-Point Links
An Adj-SID MAY be advertised for any adjacency on a point-to-point
(P2P) link that is in neighbor state 2-Way or higher. If the
adjacency on a P2P link transitions from the FULL state, then the
Adj-SID for that adjacency MAY be removed from the area. If the
adjacency transitions to a state lower than 2-Way, then the Adj-SID
Advertisement MUST be withdrawn from the area.
8.4.2. Adjacency SID on Broadcast or NBMA Interfaces
Broadcast, NBMA, or hybrid [RFC6845] networks in OSPFv3 are
represented by a star topology where the DR is the central point to
which all other routers on the broadcast, NBMA, or hybrid network
connect. As a result, routers on the broadcast, NBMA, or hybrid
network advertise only their adjacency to the DR. 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 and
are directly reachable.
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
using the Adj-SID sub-TLV as described in Section 7.1.
SR-capable routers MAY also advertise a LAN Adjacency SID for other
neighbors (e.g., Backup Designated Router (BDR), DR-OTHER, etc.) on
the broadcast, NBMA, or hybrid network using the LAN Adj-SID sub-TLV
as described in Section 7.2.
9. IANA Considerations
This specification updates two existing OSPFv3 registries.
9.1. "OSPFv3 Extended-LSA TLVs" Registry
The following values have been allocated:
+-------+----------------------------------+---------------+
| Value | Description | Reference |
+=======+==================================+===============+
| 9 | OSPFv3 Extended Prefix Range TLV | This document |
+-------+----------------------------------+---------------+
Table 1: OSPFv3 Extended-LSA TLVs
9.2. "OSPFv3 Extended-LSA Sub-TLVs" Registry
The following values have been allocated:
+-------+---------------------+---------------+
| Value | Description | Reference |
+=======+=====================+===============+
| 4 | Prefix-SID sub-TLV | This document |
+-------+---------------------+---------------+
| 5 | Adj-SID sub-TLV | This document |
+-------+---------------------+---------------+
| 6 | LAN Adj-SID sub-TLV | This document |
+-------+---------------------+---------------+
| 7 | SID/Label sub-TLV | This document |
+-------+---------------------+---------------+
Table 2: OSPFv3 Extended-LSA Sub-TLVs
10. TLV/Sub-TLV Error Handling
For any new TLVs/sub-TLVs defined in this document, if the length is
invalid, the LSA in which it is advertised is considered malformed
and MUST be ignored. Errors SHOULD be logged subject to rate
limiting.
11. Security Considerations
With the OSPFv3 Segment Routing extensions defined herein, OSPFv3
will now program the MPLS data plane [RFC3031]. Previously, LDP
[RFC5036] or another label distribution mechanism was required to
advertise MPLS labels and program the MPLS data plane.
In general, the same types of attacks that can be carried out on the
IP control plane can be carried out on the MPLS control plane
resulting in traffic being misrouted in the respective data planes.
However, the latter can be more difficult to detect and isolate.
Existing security extensions, as described in [RFC5340] and
[RFC8362], apply to these Segment Routing extensions. While OSPFv3
is under a single administrative domain, there can be deployments
where potential attackers have access to one or more networks in the
OSPFv3 routing domain. In these deployments, stronger authentication
mechanisms, such as those specified in [RFC4552] or [RFC7166], SHOULD
be used.
Implementations MUST ensure that malformed TLVs and sub-TLVs defined
in this document are detected and that they do not provide a
vulnerability for attackers to crash the OSPFv3 router or routing
process. Reception 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 rate limited to prevent a Denial-of-Service (DoS)
attack (distributed or otherwise) from overloading the OSPFv3 control
plane.
12. References
12.1. Normative References
[ALGOREG] IANA, "Interior Gateway Protocol (IGP) Parameters",
<https://www.iana.org/assignments/igp-parameters>.
[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>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc3101>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <https://www.rfc-editor.org/info/rfc5036>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013,
<https://www.rfc-editor.org/info/rfc6845>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[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>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
[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>.
[RFC8661] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., and S. Litkowski, "Segment Routing MPLS
Interworking with LDP", RFC 8661, DOI 10.17487/RFC8661,
December 2019, <https://www.rfc-editor.org/info/rfc8661>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
12.2. Informative References
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<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.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>.
Contributors
The following people gave a substantial contribution to the content
of this document and should be considered coauthors:
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Hannes Gredler
RtBrick Inc.
Austria
Email: hannes@rtbrick.com
Rob Shakir
Google, Inc.
United States of America
Email: robjs@google.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
Jeff Tantsura
Apstra, Inc.
United States of America
Email: jefftant.ietf@gmail.com
Thanks to Acee Lindem for his substantial contribution to the content
of this document.
We would like to thank Anton Smirnov for his contribution as well.
Authors' Addresses
Peter Psenak (editor)
Cisco Systems, Inc.
Eurovea Centre, Central 3, Pribinova Street 10
81109 Bratislava
Slovakia
Email: ppsenak@cisco.com
Stefano Previdi (editor)
Cisco Systems, Inc.
Email: stefano@previdi.net
AI ELI5
On this page
PROBLEMSegment Routing encodes an end-to-end path as a sequence of segments, and the link-state routing protocols must advertise those segments. OSPFv3 had no way to carry them.
MECHANISMThe RFC defines a Prefix-SID sub-TLV, Adj-SID and LAN Adj-SID sub-TLVs, an SID/Label sub-TLV and an Extended Prefix Range TLV, plus rules for flooding them within an area, between areas and for external prefixes.
WHY IT MATTERSOSPFv3 can now program the MPLS data plane with Segment Routing, with no LDP or RSVP-TE signaling needed. The IPv6 data plane is out of scope and left to a separate document.
§1Segment Routing in OSPFv3
Segment Routing (SR) lets a network define flexible end-to-end paths inside an IGP topology by encoding a path as a sequence of topological subpaths called segments. The link-state protocols IS-IS and OSPF advertise these segments. A prefix segment stands for an ECMP-aware shortest path to a prefix or node, and is typically a multi-hop path. An adjacency segment stands for a hop over a specific adjacency between two nodes and is, in most cases, a one-hop path.
The SR control plane can be applied to both IPv6 and MPLS data planes, and it needs no extra signaling beyond the IGP extensions. In MPLS networks, SR paths need no LDP or RSVP-TE signaling, although SR can interoperate with LSPs set up by LDP or RSVP. This RFC covers only the MPLS data plane; the OSPFv3 extension for the IPv6 data plane is left to a separate document. The architecture itself is in RFC 8402.
A path is built from pieces: some pieces are long stretches to a faraway place, and some are a single step to the next neighbor. Routers announce the names of these pieces so anyone can chain them together.
§2Segment Identifiers and Capabilities
Segment Routing defines several kinds of Segment Identifiers (SIDs): the Prefix-SID, the Adjacency SID and the LAN Adjacency SID. Whenever one of them is advertised, the actual SID or label is carried in a SID/Label sub-TLV, which has Type 7. Its Length is 3 or 4 octets. With length 3, the 20 rightmost bits are an MPLS label; with length 4, the value is a 32-bit SID.
SR also needs some router capabilities to be advertised to the other routers in the area. These go in the OSPFv3 Router Information Opaque LSA (from RFC 7770) and are specified in RFC 8665, not here.
Each road sign has a number on it. The number can be a small label or a bigger identifier, and the sign says which kind it is.
§3The Extended Prefix Range TLV
Sometimes it helps to advertise attributes for a whole range of prefixes in one message. A Segment Routing Mapping Server (RFC 8661) is an example, since it advertises SIDs for many prefixes. The OSPFv3 Extended Prefix Range TLV (Type 9) handles contiguous prefixes of the same length. It is a top-level TLV of the E-Intra-Area-Prefix-LSA, E-Inter-Area-Prefix-LSA, E-AS-External-LSA and E-Type-7-LSA defined in RFC 8362, and several may appear in each LSA.
Its fields are Prefix Length, AF (0 for IPv4 unicast, 1 for IPv6 unicast), Range Size, Flags, a reserved field, the Address Prefix and optional sub-TLVs. The range starts at the given prefix, and the number of prefixes equals the Range Size. The Range Size MUST NOT exceed what the Prefix Length allows without including IPv4 multicast addresses (224.0.0.0/3) or, for IPv6, anything other than unicast addresses.
If the same range appears in several LSAs of the same type from the same router, the LSA with the numerically smallest Instance ID is used and the others MUST be ignored.
Instead of writing one sign for each house on a street, you write one sign that says "starting at this house, the next seven houses". It saves a lot of writing.
§4The Prefix-SID Sub-TLV
The Prefix-SID sub-TLV (Type 4) attaches a segment to a prefix. It is a sub-TLV of the Intra-Area Prefix, Inter-Area Prefix, External Prefix and Extended Prefix Range TLVs, and may appear more than once in its parent. Its Length is 7 or 8 octets depending on the V-Flag. After the flags come an Algorithm octet, a reserved field and the SID/Index/Label value.
The flags are NP (no penultimate hop popping), M (advertised by a Mapping Server), E (explicit null), V (value or index) and L (local or global). The V and L flags must be set together or clear together: both 0 means a 4-octet index into the SID/label space advertised by the router, and both 1 means a 3-octet local label. Any other combination is invalid and the advertisement MUST be ignored. A router that receives a Prefix-SID whose algorithm the remote node has not advertised in the SR-Algorithm TLV MUST ignore it, and if a router advertises several Prefix-SIDs for the same prefix, topology and algorithm, all of them MUST be ignored.
The NP and E flags control what upstream neighbors do with the label:
- NP clear: the upstream neighbor MUST pop the Prefix-SID, like penultimate hop popping in MPLS. The E flag is ignored.
- NP set and E clear: the neighbor MUST keep the Prefix-SID on top of the stack. This suits an ABR or ASBR that stitches the packet into a continuing LSP.
- NP and E both set: the neighbor MUST replace the Prefix-SID with an Explicit NULL label (0 for IPv4, 2 for IPv6).
NP MUST be set and E MUST be clear for Prefix-SIDs of prefixes propagated between areas by an ABR, or redistributed by an ASBR, unless the prefix is directly attached to that router. When M is set, NP and E MUST be ignored on reception.
A prefix sign says which place it points to and how to treat the sign when you get near. Either take it off one step early, leave it on, or swap it for a plain sign.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 2 bytes | 4 | Sub-TLV type. |
LENGTH | Length | 2 bytes | 7 or 8 octets, depending on the V-Flag. | |
FLAGS | Flags | 1 byte | NP, M, E, V and L flags. | |
ALGORITHM | Algorithm | 1 byte | Algorithm the Prefix-SID is associated with. | |
RESERVED | Reserved | 2 bytes | Set to 0 on transmission, ignored on reception. | |
SID | SID/Index/Label | 4 bytes | Variable: a 4-octet index or a 3-octet local label. |
- NPNo-PHP — If set, the penultimate hop MUST NOT pop the Prefix-SID.
- MMapping Server — The SID was advertised by an SR Mapping Server.
- EExplicit Null — Upstream neighbor replaces the Prefix-SID with Explicit NULL.
- VValue/Index — Set: absolute value. Clear: an index.
- LLocal/Global — Set: local significance. Clear: global significance.
§5Adjacency Segments
An Adj-SID identifies a router's adjacency. The Adj-SID sub-TLV (Type 5) is an optional sub-TLV of the Router-Link TLV and may appear several times. Its flags are B (backup: the adjacency is eligible for protection such as IP or MPLS fast reroute), V, L, G (group: the Adj-SID refers to a group of adjacencies) and P (persistent: the value stays the same across router restart or interface flap). A Weight field is used for load balancing, as defined in RFC 8402.
A router MAY allocate an Adj-SID to each adjacency, MAY allocate more than one to an adjacency, and MAY give the same Adj-SID to different adjacencies. When P is set, the Adj-SID MUST be persistent.
The LAN Adj-SID sub-TLV (Type 6) is for adjacencies to non-DR routers on broadcast, NBMA or hybrid networks. It adds a Neighbor ID field holding the Router ID of the neighbor, and its Length is 11 or 12 octets.
An adjacency sign points at one specific neighbor, like "take the door to the next room". On a busy shared hallway, the sign also names which neighbor it means.
§6Procedures Within and Between Areas
Inside an area, an SR-capable OSPFv3 router MAY advertise Prefix-SIDs for any prefix it advertises reachability to, such as a loopback address. A Mapping Server can advertise Prefix-SIDs for remote prefixes; several Mapping Servers advertising the same prefix MUST advertise the same Prefix-SID. A Mapping Server MUST use Extended Prefix Range TLVs, with an E-Intra-Area-Prefix-LSA for area flooding scope or an E-AS-External-LSA for AS flooding scope. It MUST set the NU-bit in PrefixOptions so the advertisement does not itself create prefix reachability.
Across areas, OSPFv3 MUST propagate Prefix-SID information. When an ABR advertises an Inter-Area-Prefix-LSA, it includes a Prefix-SID sub-TLV taken from the router on its best path to the prefix. If that router advertised none, the ABR uses a Prefix-SID advertised by any other router.
For external prefixes, an ASBR that originates an E-AS-External-LSA SHOULD include a Prefix-SID sub-TLV. An NSSA ABR translating an E-NSSA-LSA into an E-AS-External-LSA SHOULD also advertise the Prefix-SID, following the same best-path rule.
Adj-SIDs on point-to-point links MAY be advertised for neighbors in state 2-Way or higher, and MUST be withdrawn if the adjacency drops below 2-Way. On broadcast, NBMA or hybrid networks, routers advertise an Adj-SID for the adjacency to the DR with the Adj-SID sub-TLV, and MAY advertise LAN Adj-SIDs for other neighbors such as the BDR or DR-OTHER routers.
Signs are posted in the home town. When a sign is passed to the next town, the border guard copies the sign from whoever knows the best way, so people there can use it too.
§7Error Handling and IANA Registrations
For any new TLV or sub-TLV, if the length is invalid, the LSA carrying it is considered malformed and MUST be ignored. Errors SHOULD be logged, subject to rate limiting.
The RFC updates two OSPFv3 registries: the Extended-LSA TLVs registry gets value 9 (OSPFv3 Extended Prefix Range TLV), and the Extended-LSA Sub-TLVs registry gets 4 (Prefix-SID), 5 (Adj-SID), 6 (LAN Adj-SID) and 7 (SID/Label).
If a sign is the wrong size, it is thrown away, and the problem is written down, but not too often. The new sign kinds get official numbers in a master list.
- 9Extended Prefix Range TLV — Top-level TLV for a range of prefixes.
- 4Prefix-SID sub-TLV — Segment for a prefix.
- 5Adj-SID sub-TLV — Segment for an adjacency.
- 6LAN Adj-SID sub-TLV — Segment for an adjacency to a non-DR router on a LAN.
- 7SID/Label sub-TLV — Carries a SID or label.
§8Security Considerations
With these extensions OSPFv3 programs the MPLS data plane. Previously LDP or another label distribution mechanism was required to advertise MPLS labels. The same types of attacks possible on the IP control plane are possible on the MPLS control plane and can misroute traffic, though the latter can be harder to detect and isolate.
The existing OSPFv3 security extensions from RFC 5340 and RFC 8362 apply. Where attackers might have access to the routing domain, stronger authentication such as that in RFC 4552 or RFC 7166 SHOULD be used. Implementations MUST ensure malformed TLVs and sub-TLVs cannot crash the router or routing process, and logging of them SHOULD be rate limited to avoid a denial-of-service attack on the control plane.
Because routers now hand out the road signs themselves, a bad guy who tricks them could send traffic the wrong way. So the routers should check who is talking, and not fall over when they see a broken sign.
§9References
[RFC8402]RFC 8402Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, July 2018.July 2018[RFC8665]RFC 8665Psenak, P., Ed., Previdi, S., Ed., Filfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", RFC 8665, December 2019.December 2019[RFC8362]RFC 8362Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, April 2018.April 2018[RFC8661]RFC 8661Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., Decraene, B., and S. Litkowski, "Segment Routing MPLS Interworking with LDP", RFC 8661, December 2019.December 2019[RFC5340]RFC 5340Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008.July 2008[RFC7770]RFC 7770Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, February 2016.February 2016