Internet DRAFT - draft-psenak-ospf-segment-routing-extensions
draft-psenak-ospf-segment-routing-extensions
Open Shortest Path First IGP P. Psenak, Ed.
Internet-Draft S. Previdi, Ed.
Intended status: Standards Track C. Filsfils
Expires: December 7, 2014 Cisco Systems, Inc.
H. Gredler
Juniper Networks, Inc.
R. Shakir
British Telecom
W. Henderickx
Alcatel-Lucent
J. Tantsura
Ericsson
June 5, 2014
OSPF Extensions for Segment Routing
draft-psenak-ospf-segment-routing-extensions-05
Abstract
Segment Routing (SR) allows for 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 necessary OSPF extensions that need to be
introduced for Segment Routing.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 http://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."
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This Internet-Draft will expire on December 7, 2014.
Copyright Notice
Copyright (c) 2014 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
(http://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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 3
2.1. SID/Label sub-TLV . . . . . . . . . . . . . . . . . . . . 4
3. Segment Routing Capabilities . . . . . . . . . . . . . . . . 4
3.1. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 4
3.2. SID/Label Range TLV . . . . . . . . . . . . . . . . . . . 5
4. OSPFv2 Extended Prefix Opaque LSA type . . . . . . . . . . . 7
4.1. OSPF Extended Prefix TLV . . . . . . . . . . . . . . . . 8
4.2. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . 9
4.3. SID/Label Binding sub-TLV . . . . . . . . . . . . . . . . 13
4.3.1. ERO Metric sub-TLV . . . . . . . . . . . . . . . . . 15
4.3.2. ERO sub-TLVs . . . . . . . . . . . . . . . . . . . . 15
5. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 20
5.1. OSPFv2 Extended Link Opaque LSA . . . . . . . . . . . . . 20
5.2. OSPFv2 Extended Link TLV . . . . . . . . . . . . . . . . 21
5.3. Adj-SID sub-TLV . . . . . . . . . . . . . . . . . . . . . 22
5.4. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 23
6. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 25
6.1. Intra-area Segment routing in OSPFv2 . . . . . . . . . . 25
6.2. Inter-area Segment routing in OSPFv2 . . . . . . . . . . 25
6.3. SID for External Prefixes . . . . . . . . . . . . . . . . 26
6.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 27
6.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 27
6.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 27
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
7.1. OSPF Extend Prefix LSA TLV Registry . . . . . . . . . . . 28
7.2. OSPF Extend Prefix LSA sub-TLV Registry . . . . . . . . . 28
7.3. OSPF Extend Link LSA TLV Registry . . . . . . . . . . . . 29
7.4. OSPF Extend Link LSA sub-TLV Registry . . . . . . . . . . 29
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 30
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1. Normative References . . . . . . . . . . . . . . . . . . 30
11.2. Informative References . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
Segment Routing (SR) allows for 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 of the cases, is a one-hop path. SR's
control-plane can be applied to both IPv6 and MPLS data-planes, and
do not require any additional signaling (other than the regular IGP).
For example, when used in MPLS networks, SR paths do not require any
LDP or RSVP-TE signaling. Still, SR can interoperate in the presence
of LSPs established with RSVP or LDP .
This draft describes the necessary OSPF extensions that need to be
introduced for Segment Routing.
Segment Routing architecture is described in
[I-D.filsfils-rtgwg-segment-routing].
Segment Routing use cases are described in
[I-D.filsfils-rtgwg-segment-routing-use-cases].
2. Segment Routing Identifiers
Segment Routing defines various types of Segment Identifiers (SIDs):
Prefix-SID, Adjacency-SID, LAN Adjacency SID and Binding SID.
For the purpose of the advertisements of various SID values new
Opaque LSAs (defined in [RFC5250]) are defined. These new LSAs are
defined as generic containers that can be used in order to advertise
any additional attributes associated with the prefix or link. These
new Opaque LSAs are complementary to the existing LSAs and are not
aimed to replace any of the existing LSAs.
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2.1. SID/Label sub-TLV
SID/Label sub-TLV appears in multiple TLVs or sub-TLVs defined later
in this document. It is used to advertise SID or label associated
with the prefix or adjacency. SID/Label 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: TBD, suggested value 1
Length: variable, 3 or 4 bytes
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.
The receiving router MUST ignore SID/Label sub-TLV if the length
is other then 3 or 4.
3. Segment Routing Capabilities
Segment Routing requires some additional capabilities of the router
to be advertised to other routers in the area.
These SR capabilities are advertised in Router Information Opaque LSA
(defined in [RFC4970]).
3.1. SR-Algorithm TLV
SR-Algorithm TLV is a TLV of Router Information Opaque LSA (defined
in [RFC4970]).
The SR-Algorithm Sub-TLV is optional, it MAY only appear once inside
the Router Informational Opaque LSA. If the SID/Label Range TLV, as
defined in Section 3.2, is advertised, then SR-Algorithm TLV MUST
also be advertised.
Router may use various algorithms when calculating reachability to
other nodes in area or to prefixes attached to these nodes. Examples
of these algorithms are metric based Shortest Path First (SPF),
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various sorts of Constrained SPF, etc. SR-Algorithm TLV allows a
router to advertise algorithms that router is currently using to
other routers in an area. SR-Algorithm TLV has following structure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm n | |
+- -+
| |
+ +
where:
Type: TBD, suggested value 8
Length: variable
Algorithm: one octet identifying the algorithm. The following
value has been defined:
0: IGP metric based SPT.
RI LSA can be advertised at any of the defined flooding scopes (link,
area, or autonomous system (AS)). For the purpose of the SR-
Algorithm TLV propagation area scope flooding is required.
3.2. SID/Label Range TLV
The SID/Label Range TLV is a TLV of Router Information Opaque LSA
(defined in [RFC4970]).
SID/Label Sub-TLV MAY appear multiple times and has 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
+ +
where:
Type: TBD, suggested value 9
Length: variable
Range Size: 3 octet of the SID/label range
Currently the only supported Sub-TLV is the SID/Label TLV as defined
in Section 2.1. SID/Label advertised in SID/Label TLV represents the
first SID/Label from the advertised range.
Multiple occurrence of the SID/Label Range TLV MAY be advertised, in
order to advertise multiple ranges. In such case:
o The originating router MUST encode each range into a different
SID/Label Range TLV.
o The originating router decides in which order the set of SID/Label
Range TLVs are advertised inside Router Information Opaque LSA.
The originating router MUST ensure the order is same after a
graceful restart (using checkpointing, non-volatile storage or any
other mechanism) in order to guarantee the same order before and
after graceful restart.
o Receiving router must adhere to the order in which the ranges are
advertised when calculating a SID/label from the SID index.
Here follows an example of advertisement of multiple ranges:
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The originating router advertises following ranges:
Range 1: [100, 199]
Range 2: [1000, 1099]
Range 3: [500, 599]
The receiving routers concatenate the ranges and build the SRGB
is as follows:
SRGB = [100, 199]
[1000, 1099]
[500, 599]
The indexes span multiple ranges:
index=0 means label 100
...
index 99 means label 199
index 100 means label 1000
index 199 means label 1099
...
index 200 means label 500
...
RI LSA can be advertised at any of the defined flooding scopes (link,
area, or autonomous system (AS)). For the purpose of the SR-
Capability TLV propagation area scope flooding is required.
4. OSPFv2 Extended Prefix Opaque LSA type
A new Opaque LSA (defined in [RFC5250]) is defined in OSPFv2 in order
to advertise additional prefix attributes: OSPFv2 Extended Prefix
Opaque LSA.
Multiple OSPFv2 Extended Prefix Opaque LSAs can be advertised by a
single router. Flooding scope of the OSPFv2 Extended Prefix Opaque
LSA depends on the content inside the LSA and is in control of the
originating router.
The format of the OSPFv2 Extended Prefix Opaque LSA is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 9, 10, or 11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque type | Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |
Opaque type used by OSPFv2 Extended Prefix Opaque LSA is 7.
The format of the TLVs within the body of the LSA is the same as the
format used by the Traffic Engineering Extensions to OSPF defined in
[RFC3630]. The LSA payload consists of one or more nested
Type/Length/Value (TLV) triplets. The format of each TLV is:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Length field defines the length of the value portion in octets.
The TLV is padded to 4-octet alignment; padding is not included in
the length field. Nested TLVs are also 32-bit aligned. Unrecognized
types are ignored.
4.1. OSPF Extended Prefix TLV
The OSPF Extended Prefix TLV is used in order to advertise additional
attributes associated with the prefix. Multiple OSPF Extended Prefix
TLVs MAY be carried in each OSPFv2 Extended Prefix Opaque LSA,
however all prefixes included in the single OSPFv2 Extended Prefix
Opaque LSA MUST have the same flooding scope. The structure of the
OSPF Extended Prefix TLV is as follows:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Type | Prefix Length | AF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: TBD, suggested value 1.
Length: variable
Route type: type of the OSPF route. Supported types are:
0 - unspecified
1 - intra-area
3 - inter-area
5 - external
7 - NSSA external
If the route type is 0 (unspecified) the information inside the
OSPF External Prefix TLV applies to the prefix regardless of what
route-type it is. This is useful when some prefix specific
attributes are advertised by some external entity, which is not
aware of the route-type associated with the prefix.
Prefix length: length of the prefix
AF: 0 - IPv4 unicast
Address Prefix: the prefix itself encoded as an even multiple of
32-bit words, padded with zeroed bits as necessary. This encoding
consumes ((PrefixLength + 31) / 32) 32-bit words. The default
route is represented by a prefix of length 0.
4.2. Prefix SID Sub-TLV
The Prefix SID Sub-TLV is a Sub-TLV of the OSPF Extended Prefix TLV.
It MAY appear more than once and has 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 | Reserved | MT-ID | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD, suggested value 2.
Length: variable
Flags: 1 octet field. The following flags are defined:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|N|P|M|E|V|L| |
+-+-+-+-+-+-+-+-+
where:
N-Flag: Node-SID flag. If set, then the Prefix-SID refers to
the router identified by the prefix. Typically, the N-Flag is
set on Prefix-SIDs attached to a router loopback address. The
N-Flag is set when the Prefix-SID is a Node- SID as described
in [I-D.filsfils-rtgwg-segment-routing].
P-Flag: no-PHP flag. If set, then the penultimate hop MUST NOT
pop the Prefix-SID before delivering the packet to the node
that advertised the Prefix-SID.
M-Flag: Mapping Server Flag. If set, the SID is advertised
from the Segment Routing Mapping Server functionality as
described in [I-D.filsfils-rtgwg-segment-routing-use-cases].
E-Flag: Explicit-Null Flag. If set, any upstream neighbor of
the Prefix-SID originator MUST replace the Prefix-SID with a
Prefix-SID having an Explicit-NULL value (0 for IPv4) before
forwarding the packet.
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The 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.
The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set,
then the value/index carried by this subTLV has global
significance.
Other bits: MUST be zero when sent and ignored when received.
MT-ID: Multi-Topology ID (as defined in [RFC4915]).
Algorithm: one octet identifying the algorithm the Prefix-SID is
associated with as defined in Section 3.1.
Range size: this field provides the ability to specify a range of
addresses and their associated Prefix SIDs. It represents a
compression scheme to distribute a continuous Prefix and their
continuous, corresponding SID/Label Block. If a single SID is
advertised then the Range Size field MUST be set to one. For
range advertisements > 1, Range Size represents the number of
addresses that need to be mapped into a Prefix-SID.
SID/Index/Label: according to the V and L flags, it contains
either:
A 32 bit index defining the offset in the SID/Label space
advertised by this router.
A 24 bit label where the 20 rightmost bits are used for
encoding the label value.
If multiple Prefix-SIDs are advertised for the same prefix, the
receiving router MUST use the first encoded SID and MAY use the
subsequent ones.
When calculating the outgoing label for the prefix, the router MUST
take into account E and P flags advertised by the next-hop router, if
next-hop router advertised the SID for the prefix. This MUST be done
regardless of next-hop router contributing to the best path to the
prefix or not.
P-Flag (no-PHP) MUST be set on the Prefix-SIDs allocated to inter-
area prefixes that are originated by the ABR based on intra-area or
inter-area reachability between areas. In case the inter-area prefix
is generated based on the prefix which is directly attached to the
ABR, P-Flag SHOULD NOT be set
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P-Flag (no-PHP) MUST NOT be set on the Prefix-SIDs allocated to
redistributed prefixes, unless the redistributed prefix is directly
attached to ASBR, in which case the P-Flag SHOULD NOT be set.
If the P-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. In
such case MPLS EXP bits of the Prefix-SID are not preserved to the
ultimate hop (the Prefix-SID being removed). If the P-flag is unset
the received E-flag is ignored.
If the P-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 must stitch the
incoming packet into a continuing MPLS LSP to the final
destination. This could occur at an inter-area border router
(prefix propagation from one area to another) or at an inter-
domain border router (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 PrefixSID with a Prefix-SID having an
Explicit-NULL value. 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 EXP
bits.
When M-Flag is set, P-flag MUST be set and E-bit MUST NOT be set.
Example 1: if the following router addresses (loopback addresses)
need to be mapped into the corresponding Prefix SID indexes:
Router-A: 192.0.2.1/32, Prefix-SID: Index 1
Router-B: 192.0.2.2/32, Prefix-SID: Index 2
Router-C: 192.0.2.3/32, Prefix-SID: Index 3
Router-D: 192.0.2.4/32, Prefix-SID: Index 4
then the Prefix field in Extended Prefix TLV would be set to
192.0.2.1, Prefix Length would be set to 32, Range Size in Prefix SID
sub-TLV would be 4 and Index value would be set to 1.
Example 2: If the following prefixes need to be mapped into the
corresponding Prefix-SID indexes:
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10.1.1/24, Prefix-SID: Index 51
10.1.2/24, Prefix-SID: Index 52
10.1.3/24, Prefix-SID: Index 53
10.1.4/24, Prefix-SID: Index 54
10.1.5/24, Prefix-SID: Index 55
10.1.6/24, Prefix-SID: Index 56
10.1.7/24, Prefix-SID: Index 57
then the Prefix field in Extended Prefix TLV would be set to
10.1.1.0, Prefix Length would be set to 24, Range Size in Prefix SID
sub-TLV would be 7 and Index value would be set to 51.
4.3. SID/Label Binding sub-TLV
SID/Label Binding sub-TLV is used to advertise SID/Label mapping for
a path to the prefix.
The SID/Label Binding TLV MAY be originated by any router in an OSPF
domain. The router may advertise a SID/Label binding to a FEC along
with at least a single 'nexthop style' anchor. The protocol supports
more than one 'nexthop style' anchor to be attached to a SID/Label
binding, which results into a simple path description language. In
analogy to RSVP the terminology for this is called an 'Explicit Route
Object' (ERO). Since ERO style path notation allows to anchor SID/
label bindings to both link and node IP addresses any label switched
path, can be described. Furthermore also SID/Label Bindings from
external protocols can get easily re-advertised.
The SID/Label Binding TLV may be used for advertising SID/Label
Bindings and their associated Primary and Backup paths. In one
single TLV either a primary ERO Path, a backup ERO Path or both are
advertised. If a router wants to advertise multiple parallel paths
then it can generate several TLVs for the same Prefix/FEC. Each
occurrence of a Binding TLV with respect with a given FEC Prefix has
accumulating and not canceling semantics.
SID/Label Binding sub-TLV is as sub-TLV of the OSPF Extended Prefix
TLV. Multiple SID/Label Binding TLVs can be present in OSPF Extended
Prefix TLV. SID/Label Binding sub-TLV has 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 | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Range Size | Reserved +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: TBD, suggested value 3
Length: variable
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M| |
+-+-+-+-+-+-+-+-+
where:
M-bit - When the bit is set the binding represents the
mirroring context as defined in
[I-D.minto-rsvp-lsp-egress-fast-protection].
MT-ID: Multi-Topology ID (as defined in [RFC4915]).
Weight: weight used for load-balancing purposes. The use of the
weight is defined in [I-D.filsfils-rtgwg-segment-routing].
Range Size: usage is the same as described in Section 4.2.
SID/Label Binding TLV currently supports following Sub-TLVs:
SID/Label sub-TLV as described in Section 2.1. This sub-TLV MUST
appear in the SID/Label Binding Sub-TLV and it MUST only appear
once.
ERO Metric sub-TLV as defined in Section 4.3.1.
ERO sub-TLVs as defined in Section 4.3.2.
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4.3.1. ERO Metric sub-TLV
ERO Metric sub-TLV is a Sub-TLV of the SID/Label Binding TLV.
The ERO Metric sub-TLV carries the cost of an ERO path. It is used
to compare the cost of a given source/destination path. A router
SHOULD advertise the ERO Metric sub-TLV. The cost of the ERO Metric
sub-TLV SHOULD be set to the cumulative IGP or TE path cost of the
advertised ERO. Since manipulation of the Metric field may attract
or distract traffic from and to the advertised segment it MAY be
manually overridden.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ERO Metric sub-TLV format
where:
Type: TBD, suggested value 8
Length: 4 bytes
Metric: 4 bytes
4.3.2. ERO sub-TLVs
All 'ERO' information represents an ordered set which describes the
segments of a path. The last ERO sub-TLV describes the segment
closest to the egress point, contrary the first ERO sub-TLV describes
the first segment of a path. If a router extends or stitches a path
it MUST prepend the new segments path information to the ERO list.
The above similarly applies to backup EROs.
All ERO Sub-TLVs must immediately follow the (SID)/Label Sub-TLV.
All Backup sub-ERO TLVs must immediately follow last ERO Sub-TLV.
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4.3.2.1. IPv4 ERO subTLV
IPv4 ERO sub-TLV is a Sub-TLV of the SID/Label Binding sub-TLV.
The IPv4 ERO sub-TLV describes a path segment using IPv4 Address
style of encoding. Its semantics have been borrowed from [RFC3209].
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 ERO sub-TLV format
where:
Type: TBD, suggested value 4
Length: 8 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
L-bit - If the L bit is set, then the value of the attribute is
'loose.' Otherwise, the value of the attribute is 'strict.'
IPv4 Address - the address of the explicit route hop.
4.3.2.2. Unnumbered Interface ID ERO sub-TLV
Unnumbered Interface ID ERO sub-TLV is a Sub-TLV of the SID/Label
Binding sub-TLV.
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from [RFC3477].
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The Unnumbered Interface-ID ERO sub-TLV describes a path segment that
spans over an unnumbered interface. Unnumbered interfaces are
referenced using the interface index. Interface indices are assigned
local to the router and therefore not unique within a domain. All
elements in an ERO path need to be unique within a domain and hence
need to be disambiguated using a domain unique Router-ID.
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Unnumbered Interface ID ERO sub-TLV format
Type: TBD, suggested value 5
Length: 12 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
L-bit - If the L bit is set, then the value of the attribute is
'loose.' Otherwise, the value of the attribute is 'strict.'
Router-ID: Router-ID of the next-hop.
Interface ID: is the identifier assigned to the link by the router
specified by the Router-ID.
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4.3.2.3. IPv4 Backup ERO sub-TLV
IPv4 Prefix Backup ERO sub-TLV is a Sub-TLV of the SID/Label Binding
sub-TLV.
The IPv4 Backup ERO sub-TLV describes a path segment using IPv4
Address style of encoding. Its semantics have been borrowed from
[RFC3209].
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 Backup ERO sub-TLV format
where:
Type: TBD, suggested value 6
Length: 8 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
L-bit - If the L bit is set, then the value of the attribute is
'loose.' Otherwise, the value of the attribute is 'strict.'
IPv4 Address - the address of the explicit route hop.
4.3.2.4. Unnumbered Interface ID Backup ERO sub-TLV
Unnumbered Interface ID Backup -sub-TLV is a sub-TLV of the SID/Label
Binding sub-TLV.
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from [RFC3477].
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The Unnumbered Interface-ID ERO sub-TLV describes a path segment that
spans over an unnumbered interface. Unnumbered interfaces are
referenced using the interface index. Interface indices are assigned
local to the router and therefore not unique within a domain. All
elements in an ERO path need to be unique within a domain and hence
need to be disambiguated using a domain unique Router-ID.
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unnumbered Interface ID Backup ERO sub-TLV format
where:
Type: TBD, suggested value 7
Length: 12 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
L-bit - If the L bit is set, then the value of the attribute is
'loose.' Otherwise, the value of the attribute is 'strict.'
Router-ID: Router-ID of the next-hop.
Interface ID: is the identifier assigned to the link by the router
specified by the Router-ID.
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5. Adjacency Segment Identifier (Adj-SID)
An Adjacency Segment Identifier (Adj-SID) represents a router
adjacency in Segment Routing. At the current stage of Segment
Routing architecture it is assumed that the Adj-SID value has local
significance (to the router).
5.1. OSPFv2 Extended Link Opaque LSA
A new Opaque LSA (defined in [RFC5250] is defined in OSPFv2 in order
to advertise additional link attributes: the OSPFv2 Extended Link
Opaque LSA.
The OSPFv2 Extended Link Opaque LSA has an area flooding scope.
Multiple OSPFv2 Extended Link Opaque LSAs can be advertised by a
single router in an area.
The format of the OSPFv2 Extended Link Opaque LSA is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque type | Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |
Opaque type used by OSPFv2 Extended Link Opaque LSA is 8.
The format of the TLVs within the body of LSA is the same as the
format used by the Traffic Engineering Extensions to OSPF defined in
[RFC3630]. The LSA payload consists of one or more nested
Type/Length/Value (TLV) triplets. The format of each TLV is:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Length field defines the length of the value portion in octets.
The TLV is padded to 4-octet alignment; padding is not included in
the length field. Nested TLVs are also 32-bit aligned. Unrecognized
types are ignored.
5.2. OSPFv2 Extended Link TLV
OSPFv2 Extended Link TLV is used in order to advertise various
attributes of the link. It describes a single link and is
constructed of a set of Sub-TLVs. There are no ordering requirements
for the Sub-TLVs. Only one Extended Link TLV SHALL be carried in
each Extended Link Opaque LSA, allowing for fine granularity changes
in the topology.
The Extended Link 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type is 1.
Length is variable.
Link-Type: as defined in section A.4.2 of [RFC2328].
Link-ID: as defined in section A.4.2 of [RFC2328].
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Link Data: as defined in section A.4.2 of [RFC2328].
5.3. Adj-SID sub-TLV
Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY
appear multiple times in Extended Link TLV. Examples where more than
one Adj-SID may be used per neighbor are described in
[I-D.filsfils-rtgwg-segment-routing-use-cases]. The structure of the
Adj-SID Sub-TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:
Type: TBD, suggested value 2.
Length: variable.
Flags. 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B|V|L|S| |
+-+-+-+-+-+-+-+-+
where:
B-Flag: Backup-flag: set if the Adj-SID refer to an adjacency
being protected (e.g.: using IPFRR or MPLS-FRR) as described in
[I-D.filsfils-rtgwg-segment-routing-use-cases].
The 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.
The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set,
then the value/index carried by this subTLV has global
significance.
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The S-Flag. Set Flag. When set, the S-Flag indicates that the
Adj-SID refers to a set of adjacencies (and therefore MAY be
assigned to other adjacencies as well).
Other bits: MUST be zero when originated and ignored when
received.
MT-ID: Multi-Topology ID (as defined in [RFC4915].
Weight: weight used for load-balancing purposes. The use of the
weight is defined in [I-D.filsfils-rtgwg-segment-routing].
SID/Index/Label: according to the V and L flags, it contains
either:
A 32 bit index defining the offset in the SID/Label space
advertised by this router.
A 24 bit label where the 20 rightmost bits are used for
encoding the label value.
A SR capable router MAY allocate an Adj-SID for each of its
adjacencies and set the B-Flag when the adjacency is protected by a
FRR mechanism (IP or MPLS) as described in
[I-D.filsfils-rtgwg-segment-routing-use-cases].
5.4. LAN Adj-SID Sub-TLV
LAN Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY
appear multiple times in Extended Link TLV. It is used to advertise
SID/Label for adjacency to non-DR node on broadcast or NBMA 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 | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
where:
Type: TBD, suggested value 3.
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Length: variable.
Flags. 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B|V|L|S| |
+-+-+-+-+-+-+-+-+
where:
B-Flag: Backup-flag: set if the LAN-Adj-SID refer to an
adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as
described in [I-D.filsfils-rtgwg-segment-routing-use-cases].
The 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.
The L-Flag: Local/Global Flag. If set, then the value/index
carried by the PrefixSID has local significance. If not set,
then the value/index carried by this subTLV has global
significance.
The S-Flag. Set Flag. When set, the S-Flag indicates that the
Adj-SID refers to a set of adjacencies (and therefore MAY be
assigned to other adjacencies as well).
Other bits: MUST be zero when originated and ignored when
received.
MT-ID: Multi-Topology ID (as defined in [RFC4915].
Weight: weight used for load-balancing purposes. The use of the
weight is defined in [I-D.filsfils-rtgwg-segment-routing].
SID/Index/Label: according to the V and L flags, it contains
either:
A 32 bit index defining the offset in the SID/Label space
advertised by this router.
A 24 bit label where the 20 rightmost bits are used for
encoding the label value.
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6. Elements of Procedure
6.1. Intra-area Segment routing in OSPFv2
The OSPFv2 node that supports segment routing MAY advertise Prefix-
SIDs for any prefix that it is advertising reachability for (e.g.
loopback IP address) as described in Section 4.2.
If multiple routers advertise Prefix-SID for the same prefix, then
the Prefix-SID MUST be the same. This is required in order to allow
traffic load-balancing if multiple equal cost paths to the
destination exist in the network.
Prefix-SID can also be advertised by the SR Mapping Servers (as
described in [I-D.filsfils-rtgwg-segment-routing-use-cases]). The
Mapping Server advertise Prefix-SID for remote prefixes that exist in
the network. Multiple Mapping Servers can advertise Prefix-SID for
the same prefix, in which case the same Prefix-SID MUST be advertised
by all of them. Flooding scope of the OSPF Extended Prefix Opaque
LSA that is generated by the SR Mapping Server could be either area
scope or autonomous system scope and is decided based on the
configuration of the SR Mapping Server.
6.2. Inter-area Segment routing in OSPFv2
In order to support SR in a multi-area environment, OSPFv2 must
propagate Prefix-SID information between areas. The following
procedure is used in order to propagate Prefix SIDs between areas.
When an OSPF ABR advertises a Type-3 Summary LSA from an intra-area
prefix to all its connected areas, it will also originate an Extended
Prefix Opaque LSA, as described in Section 4. The flooding scope of
the Extended Prefix Opaque LSA type will be set to area-scope. The
route-type in OSPF Extended Prefix TLV is set to inter-area. The
Prefix-SID Sub-TLV will be included in this LSA and 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 out the advertising router associated with its best
path to that prefix.
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,
then the ABR will use the Prefix-SID advertised by any other
router (e.g.: a Prefix-SID coming from an SR Mapping Server as
defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when
propagating Prefix-SID for the prefix to other areas.
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When an OSPF ABR advertises Type-3 Summary LSAs from an inter-area
route to all its connected areas it will also originate an Extended
Prefix Opaque LSA, as described in Section 4. The flooding scope of
the Extended Prefix Opaque LSA type will be set to area-scope. The
route-type in OSPF Extended Prefix TLV is set to inter-area. The
Prefix-SID Sub-TLV will be included in this LSA and the Prefix-SID
will be set as follows:
The ABR will look at its best path to the prefix in the source
area and find out the advertising router associated with its best
path to that prefix.
The ABR will then look 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 ABR that contributes to the best path to the prefix, the
originating ABR will use the Prefix-SID advertised by any other
router (e.g.: a Prefix-SID coming from an SR Mapping Server as
defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when
propagating Prefix-SID for the prefix to other areas.
6.3. SID for External Prefixes
Type-5 LSAs are flooded domain wide. When an ASBR, which supports
SR, generates Type-5 LSAs, it should also originate Extended Prefix
Opaque LSAs, as described in Section 4. The flooding scope of the
Extended Prefix Opaque LSA type is set to AS-scope. The route-type
in OSPF Extended Prefix TLV is set to external. Prefix-SID Sub-TLV
is included in this LSA and the Prefix-SID value will be set to the
SID that has been reserved for that prefix.
When a NSSA ASBR translates Type-7 LSAs into Type-5 LSAs, it should
also advertise the Prefix-SID for the prefix. The NSSA ABR
determines its best path to the prefix advertised in the translated
Type-7 LSA and finds the advertising router associated with such
path. If such advertising router has advertised a Prefix-SID for the
prefix, then the NSSA ASBR uses it when advertising the Prefix-SID
for the Type-5 prefix. Otherwise the Prefix-SID advertised by any
other router will be used (e.g.: a Prefix-SID coming from an SR
Mapping Server as defined in
[I-D.filsfils-rtgwg-segment-routing-use-cases]).
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6.4. Advertisement of Adj-SID
The Adjacency Segment Routing Identifier (Adj-SID) is advertised
using the Adj-SID Sub-TLV as described in Section 5.
6.4.1. Advertisement of Adj-SID on Point-to-Point Links
Adj-SID MAY be advertised for any adjacency on p2p link that is in a
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
then 2-Way, then the Adj-SID MUST be removed from the area.
6.4.2. Adjacency SID on Broadcast or NBMA Interfaces
Broadcast or NBMA networks in OSPF are represented by a star topology
where the Designated Router (DR) is the central point all other
routers on the broadcast or NBMA network connect to. As a result,
routers on the broadcast or NBMA network advertise only their
adjacency to DR and BDR. Routers that are neither DR nor BDR do not
form and do not advertise adjacencies between them. They, however,
maintain a 2-Way adjacency state between them.
When Segment Routing is used, each router on the broadcast or NBMA
network MAY advertise the Adj-SID for its adjacency to DR using Adj-
SID Sub-TLV as described in Section 5.3.
SR capable router MAY also advertise Adj-SID for other neighbors
(e.g. BDR, DR-OTHER) on broadcast or NBMA network using the LAN ADJ-
SID Sub-TLV as described in section 5.1.1.2. Section 5.4.
7. IANA Considerations
This specification updates two existing OSPF registries.
Opaque Link-State Advertisements (LSA) Option Types:
o suggested value 7 - OSPFv2 Extended Prefix Opaque LSA
o suggested value 8 - OSPFv2 Extended Link Opaque LSA
OSPF Router Information (RI) TLVs:
o suggested value 8 - SR-Algorithm TLV
o suggested value 9 - SID/Label Range TLV
This specification also creates four new registries:
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- OSPF Extended Prefix LSA TLVs and sub-TLVs
- OSPF Extended Link LSA TLVs and sub-TLVs
7.1. OSPF Extend Prefix LSA TLV Registry
The OSPF Extend Prefix LSA TLV registry will define top-level TLVs
for Extended Prefix LSAs and should be placed in the existing OSPF
IANA registry. New values can be allocated via IETF Consensus or
IESG Approval.
Following initial values are allocated:
o 0 - Reserved
o 1 - OSPF Extended Prefix TLV
Types in the range 32768-32023 are for experimental use; these will
not be registered with IANA, and MUST NOT be mentioned by RFCs.
Types in the range 32023-65535 are not to be assigned at this time.
Before any assignments can be made in this range, there MUST be a
Standards Track RFC that specifies IANA Considerations that covers
the range being assigned.
7.2. OSPF Extend Prefix LSA sub-TLV Registry
The OSPF Extended Prefix sub-TLV registry will define will define
sub-TLVs at any level of nesting for Extended Prefix LSAs and should
be placed in the existing OSPF IANA registry. New values can be
allocated via IETF Consensus or IESG Approval.
Following initial values are allocated:
o 0 - Reserved
o 1 - SID/Label sub-TLV
o 2 - Prefix SID sub-TLV
o 3 - SID/Label Binding sub-TLV
o 4 - IPv4 ERO sub-TLV
o 5 - Unnumbered Interface ID ERO sub-TLV
o 6 - IPv4 Backup ERO sub-TLV
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o 7 - Unnumbered Interface ID Backup ERO sub-TLV
o 8 - ERO Metric sub-TLV
Types in the range 32768-32023 are for experimental use; these will
not be registered with IANA, and MUST NOT be mentioned by RFCs.
Types in the range 32023-65535 are not to be assigned at this time.
Before any assignments can be made in this range, there MUST be a
Standards Track RFC that specifies IANA Considerations that covers
the range being assigned.
7.3. OSPF Extend Link LSA TLV Registry
The OSPF Extend Link LSA TLV registry will define top-level TLVs for
Extended Link LSAs and should be placed in the existing OSPF IANA
registry. New values can be allocated via IETF Consensus or IESG
Approval.
Following initial values are allocated:
o 0 - Reserved
o 1 - OSPFv2 Extended Link TLV
Types in the range 32768-32023 are for experimental use; these will
not be registered with IANA, and MUST NOT be mentioned by RFCs.
Types in the range 32023-65535 are not to be assigned at this time.
Before any assignments can be made in this range, there MUST be a
Standards Track RFC that specifies IANA Considerations that covers
the range being assigned.
7.4. OSPF Extend Link LSA sub-TLV Registry
The OSPF Extended Link LSA sub-TLV registry will define will define
sub-TLVs at any level of nesting for Extended Link LSAs and should be
placed in the existing OSPF IANA registry. New values can be
allocated via IETF Consensus or IESG Approval.
Following initial values are allocated:
o 1 - SID/Label sub-TLV
o 2 - Adj-SID sub-TLV
o 3 - LAN Adj-SID/Label Sub-TLV
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Types in the range 32768-32023 are for experimental use; these will
not be registered with IANA, and MUST NOT be mentioned by RFCs.
Types in the range 32023-65535 are not to be assigned at this time.
Before any assignments can be made in this range, there MUST be a
Standards Track RFC that specifies IANA Considerations that covers
the range being assigned.
8. Security Considerations
In general, new LSAs defined in this document are subject to the same
security concerns as those described in [RFC2328]. Additionally,
implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard OSPF failures.
9. Contributors
The following people gave a substantial contribution to the content
of this document: Ahmed Bashandy, Martin Horneffer, Bruno Decraene,
Stephane Litkowski, Igor Milojevic, Rob Shakir and Saku Ytti.
10. Acknowledgements
We would like to thank Anton Smirnov for his contribution.
Many thanks to Yakov Rekhter, John Drake and Shraddha Hedge for their
contribution on earlier incarnations of the "Binding / MPLS Label
TLV" in [I-D.gredler-ospf-label-advertisement].
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
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Internet-Draft OSPF Extensions for Segment Routing June 2014
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC
4915, June 2007.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, July 2008.
11.2. Informative References
[I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-rtgwg-
segment-routing-01 (work in progress), October 2013.
[I-D.filsfils-rtgwg-segment-routing-use-cases]
Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
Crabbe, "Segment Routing Use Cases", draft-filsfils-rtgwg-
segment-routing-use-cases-02 (work in progress), October
2013.
[I-D.gredler-ospf-label-advertisement]
Gredler, H., Amante, S., Scholl, T., and L. Jalil,
"Advertising MPLS labels in OSPF", draft-gredler-ospf-
label-advertisement-03 (work in progress), May 2013.
[I-D.minto-rsvp-lsp-egress-fast-protection]
Jeganathan, J., Gredler, H., and Y. Shen, "RSVP-TE LSP
egress fast-protection", draft-minto-rsvp-lsp-egress-fast-
protection-03 (work in progress), November 2013.
Authors' Addresses
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Peter Psenak (editor)
Cisco Systems, Inc.
Apollo Business Center
Mlynske nivy 43
Bratislava 821 09
Slovakia
Email: ppsenak@cisco.com
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Rob Shakir
British Telecom
London
UK
Email: rob.shakir@bt.com
Psenak, et al. Expires December 7, 2014 [Page 32]
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Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
Antwerp 2018
BE
Email: wim.henderickx@alcatel-lucent.com
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
US
Email: Jeff.Tantsura@ericsson.com
Psenak, et al. Expires December 7, 2014 [Page 33]
