OSPF Extensions for Segment Routing
draft-psenak-ospf-segment-routing-extensions-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Peter Psenak , Stefano Previdi , Clarence Filsfils , Hannes Gredler , Rob Shakir | ||
| Last updated | 2013-07-12 | ||
| Replaced by | draft-ietf-ospf-segment-routing-extensions, RFC 8665 | ||
| RFC stream | (None) | ||
| Formats | |||
| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-psenak-ospf-segment-routing-extensions-02
Open Shortest Path First IGP P. Psenak, Ed.
Internet-Draft S. Previdi, Ed.
Intended status: Standards Track C. Filsfils
Expires: January 13, 2014 Cisco Systems, Inc.
H. Gredler
Juniper Networks, Inc.
R. Shakir
British Telecom
July 12, 2013
OSPF Extensions for Segment Routing
draft-psenak-ospf-segment-routing-extensions-02
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."
This Internet-Draft will expire on January 13, 2014.
Copyright Notice
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Internet-Draft OSPF Extensions for Segment Routing July 2013
Copyright (c) 2013 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
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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 3
2.1. SID/Label TLV . . . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . 6
4.1. OSPF Extended Prefix TLV . . . . . . . . . . . . . . . . . 7
4.2. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . 8
4.3. SID/Label Binding TLV . . . . . . . . . . . . . . . . . . 9
4.3.1. ERO TLVs . . . . . . . . . . . . . . . . . . . . . . . 11
5. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . . 15
5.1. OSPFv2 Extended Link Opaque LSA . . . . . . . . . . . . . 15
5.2. OSPFv2 Extended Link TLV . . . . . . . . . . . . . . . . . 16
5.3. Adj-SID sub-TLV . . . . . . . . . . . . . . . . . . . . . 17
5.4. LAN Adj-SID/Label Sub-TLV . . . . . . . . . . . . . . . . 18
6. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 19
6.1. Intra-area Segment routing in OSPFv2 . . . . . . . . . . . 19
6.2. Inter-area Segment routing in OSPFv2 . . . . . . . . . . . 20
6.3. SID for External Prefixes . . . . . . . . . . . . . . . . 21
6.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . . 21
6.4.1. Advertisement of Adj-SID on Point-to-Point Links . . . 21
6.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8. Manageability Considerations . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
12.1. Normative References . . . . . . . . . . . . . . . . . . . 22
12.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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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.
2.1. SID/Label TLV
SID/Label TLV appears as Sub-TLV 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/Lable 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBA
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.
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]).
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),
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:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm 1 | Algorithm... | Algorithm n | |
+- -+
| |
+ +
where:
Type: TBA
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:
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:
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Type: TBA
Length: variable
Range Size: size 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.
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:
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 TBA.
The format of the TLVs within the body of the LSA is the same as the
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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:
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 is TBA.
Length is variable
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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:
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 | MT-ID | Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBA.
Length: A 16-bit field that indicates the length of the value
portion in octets. Set to 8.
Flags: 1 octet field. The following flags are defined:
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0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|N|P|M| |
+-+-+-+-+-+-+-+-+
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].
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.
Index: 32 bits representing the offset to the advertised SID/Label
range.
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.
PHP flag MUST NOT be set on the Prefix-SIDs allocated to inter- area
prefixes that are originated by the router based on intra-area or
inter-area reachability between areas.
4.3. SID/Label Binding TLV
SID/Label Binding TLV is used to advertise SID/Label mapping for a
prefix or a path to the prefix. SID/Label value advertised in this
TLV has local significance (to the router).
SID/Label Binding TLV is a Sub-TLV of the OSPF Extended Prefix TLV.
Multiple SID/Label Binding TLVs can be present in OSPF Extended
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Prefix TLV. SID/Label Binding 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | MT-ID | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: TBA
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].
SID/Label Binding TLV currently supports following Sub-TLVs:
SID/Lable TLV as described in Section 2.1. This TLV MUST appear
in the SID/Label Binding Sub-TLV and it MUST only appear once.
ERO TLVs as defined in Section 4.3.1.
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4.3.1. ERO TLVs
All 'ERO' information represents an ordered set which describes the
segments of a path. The last ERO TLV describes the segment closest
to the egress point, contrary the first ERO 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 ERO TLVs must immediately follow last ERO Sub-TLV.
4.3.1.1. IPv4 ERO TLV
IPv4 ERO TLV is a Sub-TLV of the SID/Lable Binding TLV.
The IPv4 ERO 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 TLV format
where:
Type: TBA
Length: 8 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
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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.
4.3.1.2. Unnumbered Interface ID ERO TLV
Unnumbered Interface ID ERO TLV is a Sub-TLV of the SID/Lable Binding
TLV.
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from [RFC3477].
The Unnumbered Interface-ID ERO 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 TLV format
Type: TBA
Length: 12 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
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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.
4.3.1.3. IPv4 Backup ERO TLV
IPv4 Prefix Backup ERO TLV is a Sub-TLV of the SID/Lable Binding TLV.
The IPv4 Backup ERO 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 TLV format
where:
Type: TBA
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.'
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IPv4 Address - the address of the explicit route hop.
4.3.1.4. Unnumbered Interface ID Backup ERO TLV
Unnumbered Interface ID Backup TLV is a Sub-TLV of the SID/Lable
Binding TLV.
The appearance and semantics of the 'Unnumbered Interface ID' have
been borrowed from [RFC3477].
The Unnumbered Interface-ID ERO 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 TLV format
where:
Type: TBA
Length: 12 bytes
Flags: 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
+-+-+-+-+-+-+-+-+
where:
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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.
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 TBA
The format of the TLVs within the body of LSA is the same as the
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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.
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 TBA.
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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].
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 | MT-ID | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: TBA.
Length: variable.
Flags. 1 octet field of following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B| |
+-+-+-+-+-+-+-+-+
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].
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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].
Adj-SID Sub-TLV supports following Sub-TLVs:
SID/Label TLV as described in Section 2.1. This TLV MUST
appear in the Adj-SID Sub-TLV and it MUST only appear once.
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/Label 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 | MT-ID | Weight | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) |
+- -+
| |
where:
Type: TBA.
Length: variable.
Flags. 1 octet field of following flags:
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|B| |
+-+-+-+-+-+-+-+-+
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].
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].
LAN Adj-SID Sub-TLV supports following Sub-TLVs:
SID/Label TLV as described in Section 2.1. This TLV MUST
appear in the Adj-SID Sub-TLV and it MUST only appear once.
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.
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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.
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.
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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]).
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.
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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
TBD
8. Manageability Considerations
TBD
9. Security Considerations
TBD
10. 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, Saku Ytti and Wim
Henderickx.
11. 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].
12. References
12.1. 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
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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.
[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.
12.2. 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-00 (work in
progress), June 2013.
[I-D.filsfils-rtgwg-segment-routing-use-cases]
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 Use Cases",
draft-filsfils-rtgwg-segment-routing-use-cases-00 (work in
progress), June 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",
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draft-minto-rsvp-lsp-egress-fast-protection-02 (work in
progress), April 2013.
Authors' Addresses
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
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Rob Shakir
British Telecom
London
UK
Email: rob.shakir@bt.com
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