RFC7580: OSPF-TE Extensions for General Network Element Constraints
Download in PDF format Download in text format
Related keywords:
(Optical Routing)
(WSON)
Internet Engineering Task Force (IETF) F. Zhang
Request for Comments: 7580 Y. Lee
Category: Standards Track J. Han
ISSN: 2070-1721 Huawei
G. Bernstein
Grotto Networking
Y. Xu
CATR
June 2015
OSPF-TE Extensions for General Network Element Constraints
Abstract
Generalized Multiprotocol Label Switching (GMPLS) can be used to
control a wide variety of technologies including packet switching
(e.g., MPLS), time division (e.g., Synchronous Optical Network /
Synchronous Digital Hierarchy (SONET/SDH) and Optical Transport
Network (OTN)), wavelength (lambdas), and spatial switching (e.g.,
incoming port or fiber to outgoing port or fiber). In some of these
technologies, network elements and links may impose additional
routing constraints such as asymmetric switch connectivity, non-
local label assignment, and label range limitations on links. This
document describes Open Shortest Path First (OSPF) routing protocol
extensions to support these kinds of constraints under the control of
GMPLS.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7580.
Zhang, et al. Standards Track [Page 1]
RFC 7580 Generic Constraint OSPF-TE June 2015
Copyright Notice
Copyright (c) 2015 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
1.1. Conventions Used in This Document ..........................3
2. Node Information ................................................3
2.1. Connectivity Matrix ........................................4
3. Link Information ................................................4
3.1. Port Label Restrictions ....................................5
4. Routing Procedures ..............................................5
5. Scalability and Timeliness ......................................6
5.1. Different Sub-TLVs into Multiple LSAs ......................6
5.2. Decomposing a Connectivity Matrix into Multiple Matrices ...6
6. Security Considerations .........................................7
7. Manageability ...................................................7
8. IANA Considerations .............................................8
8.1. Node Information ...........................................8
8.2. Link Information ...........................................8
9. References ......................................................9
9.1. Normative References .......................................9
9.2. Informative References ....................................10
Acknowledgments ...................................................11
Contributors ......................................................11
Authors' Addresses ................................................12
Zhang, et al. Standards Track [Page 2]
RFC 7580 Generic Constraint OSPF-TE June 2015
1. Introduction
Some data-plane technologies that require the use of a GMPLS control
plane impose additional constraints on switching capability and label
assignment. In addition, some of these technologies should be
capable of performing non-local label assignment based on the nature
of the technology, e.g., wavelength continuity constraint in
Wavelength Switched Optical Networks (WSONs) [RFC6163]. Such
constraints can lead to the requirement for link-by-link label
availability in path computation and label assignment.
[RFC7579] provides efficient encodings of information needed by the
routing and label assignment process in technologies such as WSON.
These encodings are potentially applicable to a wider range of
technologies as well. The encoding provided in [RFC7579] is
protocol-neutral and can be used in routing, signaling, and/or Path
Computation Element communication protocol extensions.
This document defines extensions to the OSPF routing protocol based
on [RFC7579] to enhance the Traffic Engineering (TE) properties of
GMPLS TE that are defined in [RFC3630], [RFC4202], and [RFC4203].
The enhancements to the TE properties of GMPLS TE links can be
advertised in OSPF-TE Link State Advertisements (LSAs). The TE LSA,
which is an opaque LSA with area flooding scope [RFC3630], has only
one top-level Type-Length-Value (TLV) triplet and has one or more
nested sub-TLVs for extensibility. The top-level TLV can take one of
three values: Router Address [RFC3630], Link [RFC3630], or Node
Attribute [RFC5786]. In this document, we enhance the sub-TLVs for
the Link TLV in support of the general network element constraints
under the control of GMPLS.
The detailed encoding of OSPF extensions is not defined in this
document. [RFC7579] provides encoding details.
1.1. Conventions Used in This Document
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].
2. Node Information
According to [RFC7579], the additional node information representing
node switching asymmetry constraints includes device type and
connectivity matrix. Except for the device type, which is defined in
[RFC7579], the other pieces of information are defined in this
document.
Zhang, et al. Standards Track [Page 3]
RFC 7580 Generic Constraint OSPF-TE June 2015
Per [RFC7579], this document defines the Connectivity Matrix sub-TLV
of the Node Attribute TLV defined in [RFC5786]. The new sub-TLV has
Type 14.
Depending on the control-plane implementation being used, the
Connectivity Matrix sub-TLV may be optional in some specific
technologies, e.g., WSON networks. Usually, for example, in WSON
networks, the Connectivity Matrix sub-TLV may be advertised in the
LSAs since WSON switches are currently asymmetric. If no
Connectivity Matrix sub-TLV is included, it is assumed that the
switches support symmetric switching.
2.1. Connectivity Matrix
If the switching devices supporting certain data-plane technology are
asymmetric, it is necessary to identify which input ports and labels
can be switched to some specific labels on a specific output port.
The connectivity matrix, which can represent either the potential
connectivity matrix for asymmetric switches (e.g., Reconfigurable
Optical Add/Drop Multiplexers (ROADMs) and such) or fixed
connectivity for an asymmetric device such as a multiplexer as
defined in [RFC7446], is used to identify these restrictions.
The Connectivity Matrix is a sub-TLV of the Node Attribute TLV. The
length is the length of the value field in octets. The meaning and
format of this sub-TLV value field are defined in Section 2.1 of
[RFC7579]. One sub-TLV contains one matrix. The Connectivity Matrix
sub-TLV may occur more than once to contain multiple matrices within
the Node Attribute TLV. In addition, a large connectivity matrix can
be decomposed into smaller sub-matrices for transmission in multiple
LSAs as described in Section 5.
3. Link Information
The most common link sub-TLVs nested in the top-level Link TLV are
already defined in [RFC3630] and [RFC4203]. For example, Link ID,
Administrative Group, Interface Switching Capability Descriptor
(ISCD), Link Protection Type, Shared Risk Link Group (SRLG), and
Traffic Engineering Metric are among the typical link sub-TLVs.
Per [RFC7579], this document defines the Port Label Restrictions sub-
TLV of the Link TLV defined in [RFC3630]. The new sub-TLV has Type
34.
Zhang, et al. Standards Track [Page 4]
RFC 7580 Generic Constraint OSPF-TE June 2015
Generally, all the sub-TLVs above are optional, depending on control-
plane implementations being used. The Port Label Restrictions sub-
TLV will not be advertised when there are no restrictions on label
assignment.
3.1. Port Label Restrictions
Port label restrictions describe the label restrictions that the
network element (node) and link may impose on a port. These
restrictions represent what labels may or may not be used on a link
and are intended to be relatively static. For increased modeling
flexibility, port label restrictions may be specified relative to the
port in general or to a specific connectivity matrix.
For example, the port label restrictions describe the wavelength
restrictions that the link and various optical devices such as
Optical Cross-Connects (OXCs), ROADMs, and waveband multiplexers may
impose on a port in WSON. These restrictions represent which
wavelengths may or may not be used on a link and are relatively
static. Detailed information about port label restrictions is
provided in [RFC7446].
The Port Label Restrictions sub-TLV is a sub-TLV of the Link TLV.
The length is the length of value field in octets. The meaning and
format of this sub-TLV value field are defined in Section 2.2 of
[RFC7579]. The Port Label Restrictions sub-TLV may occur more than
once to specify a complex port constraint within the Link TLV.
4. Routing Procedures
All sub-TLVs are nested in top-level TLV(s) and contained in Opaque
LSAs. The flooding rules of Opaque LSAs are specified in [RFC2328],
[RFC5250], [RFC3630], and [RFC4203].
Considering the routing scalability issues in some cases, the routing
protocol should be capable of supporting the separation of dynamic
information from relatively static information to avoid unnecessary
updates of static information when dynamic information is changed. A
standards-compliant approach is to separate the dynamic information
sub-TLVs from the static information sub-TLVs, each nested in a
separate top-level TLV (see [RFC3630] and [RFC5786]), and advertise
them in the separate OSPF-TE LSAs.
For node information, since the connectivity matrix information is
static, the LSA containing the Node Attribute TLV can be updated with
a lower frequency to avoid unnecessary updates.
Zhang, et al. Standards Track [Page 5]
RFC 7580 Generic Constraint OSPF-TE June 2015
For link information, a mechanism MAY be applied such that static
information and dynamic information of one TE link are contained in
separate Opaque LSAs. For example, the Port Label Restrictions sub-
TLV could be nested in separate top-level Link TLVs and advertised in
the separate LSAs.
As with other TE information, an implementation typically takes
measures to avoid rapid and frequent updates of routing information
that could cause the routing network to become swamped. See
Section 3 of [RFC3630] for related details.
5. Scalability and Timeliness
This document defines two sub-TLVs for describing generic routing
constraints. The examples given in [RFC7579] show that very large
systems, in terms of label count or ports, can be very efficiently
encoded. However, because there has been concern expressed that some
possible systems may produce LSAs that exceed the IP Maximum
Transmission Unit (MTU), methods should be given to allow for the
splitting of general constraint LSAs into smaller LSAs that are under
the MTU limit. This section presents a set of techniques that can be
used for this purpose.
5.1. Different Sub-TLVs into Multiple LSAs
Two sub-TLVs are defined in this document:
1. Connectivity Matrix (carried in the Node Attribute TLV)
2. Port Label Restrictions (carried in the Link TLV)
The Connectivity Matrix sub-TLV can be carried in the Node Attribute
TLV (as defined in [RFC5786]), whereas the Port Label Restrictions
sub-TLV can be carried in a Link TLV, of which there can be at most
one in an LSA (as defined in [RFC3630]). Note that the port label
restrictions are relatively static, i.e., only would change with
hardware changes or significant system reconfiguration.
5.2. Decomposing a Connectivity Matrix into Multiple Matrices
In the highly unlikely event that a Connectivity Matrix sub-TLV by
itself would result in an LSA exceeding the MTU, a single large
matrix can be decomposed into sub-matrices. Per [RFC7579], a
connectivity matrix just consists of pairs of input and output ports
that can reach each other; hence, this decomposition would be
straightforward. Each of these sub-matrices would get a unique
matrix identifier per [RFC7579].
Zhang, et al. Standards Track [Page 6]
RFC 7580 Generic Constraint OSPF-TE June 2015
From the point of view of a path computation process, prior to
receiving an LSA with a Connectivity Matrix sub-TLV, no connectivity
restrictions are assumed, i.e., the standard GMPLS assumption of any
port to any port reachability holds. Once a Connectivity Matrix sub-
TLV is received, path computation would know that connectivity is
restricted and use the information from all Connectivity Matrix sub-
TLVs received to understand the complete connectivity potential of
the system. Prior to receiving any Connectivity Matrix sub-TLVs,
path computation may compute a path through the system when, in fact,
no path exists. In between the reception of an additional
Connectivity Matrix sub-TLV, path computation may not be able to find
a path through the system when one actually exists. Both cases are
currently encountered and handled with existing GMPLS mechanisms.
Due to the reliability mechanisms in OSPF, the phenomena of late or
missing Connectivity Matrix sub-TLVs would be relatively rare.
In the case where the new sub-TLVs or their attendant encodings are
malformed, the proper action would be to log the problem and ignore
just the sub-TLVs in GMPLS path computations rather than ignoring the
entire LSA.
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC3630], [RFC4203], and [RFC5250].
For general security aspects relevant to GMPLS-controlled networks,
please refer to [RFC5920].
7. Manageability
No existing management tools handle the additional TE parameters as
defined in this document and distributed in OSPF-TE. The existing
MIB module contained in [RFC6825] allows the TE information
distributed by OSPF-TE to be read from a network node; this MIB
module could be augmented (possibly by a sparse augmentation) to
report this new information.
The current environment in the IETF favors the Network Configuration
Protocol (NETCONF) [RFC6241] and YANG [RFC6020] over SNMP and MIB
modules. Work is in progress in the TEAS working group to develop a
YANG module to represent the generic TE information that may be
present in a Traffic Engineering Database (TED). This model may be
extended to handle the additional information described in this
document to allow that information to be read from network devices or
exchanged between consumers of the TED. Furthermore, links state
Zhang, et al. Standards Track [Page 7]
RFC 7580 Generic Constraint OSPF-TE June 2015
export using BGP [BGP-LS] enables the export of TE information from a
network using BGP. Work could realistically be done to extend BGP-LS
to also carry the information defined in this document.
It is not envisaged that the extensions defined in this document will
place substantial additional requirements on Operations,
Administration, and Maintenance (OAM) mechanisms currently used to
diagnose and debug OSPF systems. However, tools that examine the
contents of opaque LSAs will need to be enhanced to handle these new
sub-TLVs.
8. IANA Considerations
IANA has allocated new sub-TLVs as defined in Sections 2 and 3 as
follows:
8.1. Node Information
IANA maintains the "Open Shortest Path First (OSPF) Traffic
Engineering TLVs" registry with a sub-registry called "Types for sub-
TLVs of TE Node Attribute TLV (Value 5)". IANA has assigned a new
code point as follows:
Type | Sub-TLV | Reference
-------+-------------------------------+------------
14 | Connectivity Matrix | [RFC7580]
8.2. Link Information
IANA maintains the "Open Shortest Path First (OSPF) Traffic
Engineering TLVs" registry with a sub-registry called "Types for sub-
TLVs of TE Link TLV (Value 2)". IANA has assigned a new code point
as follows:
Type | Sub-TLV | Reference
-------+-------------------------------+------------
34 | Port Label Restrictions | [RFC7580]
Zhang, et al. Standards Track [Page 8]
RFC 7580 Generic Constraint OSPF-TE June 2015
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC4202,
October 2005, <http://www.rfc-editor.org/info/rfc4202>.
[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<http://www.rfc-editor.org/info/rfc4203>.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
July 2008, <http://www.rfc-editor.org/info/rfc5250>.
[RFC5786] Aggarwal, R. and K. Kompella, "Advertising a Router's
Local Addresses in OSPF Traffic Engineering (TE)
Extensions", RFC 5786, DOI 10.17487/RFC5786, March 2010,
<http://www.rfc-editor.org/info/rfc5786>.
[RFC7579] Bernstein, G., Ed., Lee, Y., Ed., Li, D., Imajuku, W., and
J. Han, "General Network Element Constraint Encoding for
GMPLS-Controlled Networks", RFC 7579,
DOI 10.17487/RFC7579, June 2015,
<http://www.rfc-editor.org/info/rfc7579>.
Zhang, et al. Standards Track [Page 9]
RFC 7580 Generic Constraint OSPF-TE June 2015
9.2. Informative References
[BGP-LS] Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
Ray, "North-Bound Distribution of Link-State and TE
Information using BGP", Work in Progress,
draft-ietf-idr-ls-distribution-11, June 2015.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
"Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, DOI 10.17487/RFC6163, April 2011,
<http://www.rfc-editor.org/info/rfc6163>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6825] Miyazawa, M., Otani, T., Kumaki, K., and T. Nadeau,
"Traffic Engineering Database Management Information Base
in Support of MPLS-TE/GMPLS", RFC 6825,
DOI 10.17487/RFC6825, January 2013,
<http://www.rfc-editor.org/info/rfc6825>.
[RFC7446] Lee, Y., Ed., Bernstein, G., Ed., Li, D., and W. Imajuku,
"Routing and Wavelength Assignment Information Model for
Wavelength Switched Optical Networks", RFC 7446,
DOI 10.17487/RFC7446, February 2015,
<http://www.rfc-editor.org/info/rfc7446>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
Zhang, et al. Standards Track [Page 10]
RFC 7580 Generic Constraint OSPF-TE June 2015
Acknowledgments
We thank Ming Chen and Yabin Ye from DICONNET Project who provided
valuable information for this document.
Contributors
Guoying Zhang
China Academy of Telecommunication Research of MII
11 Yue Tan Nan Jie
Beijing
China
Phone: +86-10-68094272
EMail: zhangguoying@mail.ritt.com.cn
Dan Li
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
China
Phone: +86-755-28973237
EMail: danli@huawei.com
Ming Chen
European Research Center
Huawei Technologies
Riesstr. 25, 80992
Munchen
Germany
Phone: 0049-89158834072
EMail: minc@huawei.com
Yabin Ye
European Research Center
Huawei Technologies
Riesstr. 25, 80992
Munchen
Germany
Phone: 0049-89158834074
EMail: yabin.ye@huawei.com
Zhang, et al. Standards Track [Page 11]
RFC 7580 Generic Constraint OSPF-TE June 2015
Authors' Addresses
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
China
Phone: +86-755-28972912
EMail: zhangfatai@huawei.com
Young Lee
Huawei Technologies
5360 Legacy Drive, Building 3
Plano, TX 75023
United States
Phone: (469)277-5838
EMail: leeyoung@huawei.com
Jianrui Han
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
China
Phone: +86-755-28977943
EMail: hanjianrui@huawei.com
Greg Bernstein
Grotto Networking
Fremont, CA
United States
Phone: (510) 573-2237
EMail: gregb@grotto-networking.com
Yunbin Xu
China Academy of Telecommunication Research of MII
11 Yue Tan Nan Jie
Beijing
China
Phone: +86-10-68094134
EMail: xuyunbin@mail.ritt.com.cn
Zhang, et al. Standards Track [Page 12]