Internet DRAFT - draft-ietf-ospf-ospfv3-segment-routing-extensions
draft-ietf-ospf-ospfv3-segment-routing-extensions
Open Shortest Path First IGP P. Psenak, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Previdi, Ed.
Expires: July 13, 2019 Individual
January 9, 2019
OSPFv3 Extensions for Segment Routing
draft-ietf-ospf-ospfv3-segment-routing-extensions-23
Abstract
Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological
sub-paths, called "segments". These segments are advertised by the
link-state routing protocols (IS-IS and OSPF).
This draft describes the OSPFv3 extensions required for Segment
Routing with MPLS data plane.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 13, 2019.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 4
3.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4
4. Segment Routing Capabilities . . . . . . . . . . . . . . . . 5
5. OSPFv3 Extended Prefix Range TLV . . . . . . . . . . . . . . 5
6. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 7
7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 11
7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 11
7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 13
8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 14
8.1. Intra-area Segment routing in OSPFv3 . . . . . . . . . . 14
8.2. Inter-area Segment routing in OSPFv3 . . . . . . . . . . 15
8.3. Segment Routing for External Prefixes . . . . . . . . . . 16
8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 16
8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 16
8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9.1. OSPFv3 Extended-LSA TLV Registry . . . . . . . . . . . . 17
9.2. OSPFv3 Extended-LSA Sub-TLV registry . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 17
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
Segment Routing (SR) allows a flexible definition of end-to-end paths
within IGP topologies by encoding paths as sequences of topological
sub-paths, 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 does not require any additional
signalling (other than IGP extensions). The IPv6 data plane is out
of the scope of this specification - OSPFv3 extension for SR with
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
signalling. However, SR can interoperate in the presence of LSPs
established with RSVP or LDP.
This draft describes the OSPFv3 extensions required for Segment
Routing with 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 - Multi Protocol Label Switching
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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
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
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: Either 3 or 4 octets
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
represents a 32-bit SID.
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The receiving router MUST ignore the SID/Label Sub-TLV if the
length is other than 3 or 4.
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
[I-D.ietf-ospf-segment-routing-extensions].
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 Segment Routing Mapping
Server, which is described in
[I-D.ietf-spring-segment-routing-ldp-interop], 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:
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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, dependent on 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:
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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, encoded as an
even multiple of 32-bit words, 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 the future standard-track IETF
specifications.
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:
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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, dependent 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 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
a Segment Routing Mapping Server as described in
[I-D.ietf-spring-segment-routing-ldp-interop].
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.
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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
[I-D.ietf-ospf-segment-routing-extensions].
A router receiving a Prefix-SID from a remote node and with an
algorithm value that such remote node has not advertised in the
SR-Algorithm Sub-TLV [I-D.ietf-ospf-segment-routing-extensions]
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 dataplane. If the
NP-flag is not set, then the received E-flag is ignored.
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If the NP-flag is set then:
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
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 the E-flag is 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 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
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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, dependent on the V flag.
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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 IPFRR or
MPLS-FRR) as described in section 3.5 of [RFC8402].
The 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.
The 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.
The 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.
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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 Adj-SID Sub-TLV 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, 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, dependent on 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-Adj-
SID is advertised.
SID/Index/Label: as described in Section 6.
When the P-flag is not set, the LAN Adj-SID MAY be persistent.
When the P-flag is set, the LAN Adj-SID MUST be persistent.
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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 [I-D.ietf-spring-segment-routing-ldp-interop]). 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.
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8.2. Inter-area Segment routing in OSPFv3
In order to support SR in a multi-area 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 such 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 Inter-Area-Prefix-LSA LSAs 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 such 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.
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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 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.
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 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-Adj-SID for other
neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid
network using the LAN-Adj-SID Sub-TLV as described in Section 7.2.
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9. IANA Considerations
This specification updates several existing OSPFv3 registries.
9.1. OSPFv3 Extended-LSA TLV Registry
Following values are allocated:
o 9 - OSPFv3 Extended Prefix Range TLV
9.2. OSPFv3 Extended-LSA Sub-TLV registry
o 4 - Prefix SID Sub-TLV
o 5 - Adj-SID Sub-TLV
o 6 - LAN Adj-SID Sub-TLV
o 7 - SID/Label Sub-TLV
10. 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 assure that malformed TLV and Sub-TLV defined in
this document are detected and 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.
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11. Contributors
The following people gave a substantial contribution to the content
of this document and should be considered as co-authors:
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Hannes Gredler
RtBrick Inc.
Austria
Email: hannes@rtbrick.com
Rob Shakir
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: robjs@google.com
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018
BE
Email: wim.henderickx@nokia.com
Jeff Tantsura
Nuage Networks
US
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.
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12. References
12.1. Normative References
[ALGOREG] "IGP Algorithm Types", <https://www.iana.org/assignments/
igp-parameters/igp-parameters.xhtml#igp-algorithm-types>.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-27 (work in progress), December 2018.
[I-D.ietf-spring-segment-routing-ldp-interop]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., and
S. Litkowski, "Segment Routing interworking with LDP",
draft-ietf-spring-segment-routing-ldp-interop-15 (work in
progress), September 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-18
(work in progress), December 2018.
[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>.
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[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>.
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>.
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Authors' Addresses
Peter Psenak (editor)
Cisco Systems, Inc.
Eurovea Centre, Central 3
Pribinova Street 10
Bratislava 81109
Slovakia
Email: ppsenak@cisco.com
Stefano Previdi (editor)
Individual
Email: stefano.previdi@net
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