Network Working Group P. Psenak
Internet-Draft A. Lindem
Intended status: Standards Track Cisco Systems
Expires: July 25, 2016 W. Henderickx
Alcatel-Lucent
J. Tantsura
Ericsson
H. Gredler
Individual
January 22, 2016
OSPFv2 Link Traffic Engineering (TE) Attribute Reuse
draft-ppsenak-ospf-te-link-attr-reuse-01.txt
Abstract
Various link attributes have been defined in OSPFv2 in the context of
the MPLS Traffic Engineering (TE) and GMPLS. Many of these link
attributes can be used for purposes other than MPLS Traffic
Engineering or GMPLS. This documents defines how to distribute such
attributes in OSPFv2 for applications other than MPLS Traffic
Engineering or GMPLS purposes.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 25, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Link attributes examples . . . . . . . . . . . . . . . . . . 3
3. Advertising Link Attributes . . . . . . . . . . . . . . . . . 3
3.1. TE Opaque LSA . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Extended Link Opaque LSA . . . . . . . . . . . . . . . . 4
3.3. Proposed solution . . . . . . . . . . . . . . . . . . . . 5
4. Reused TE link attributes . . . . . . . . . . . . . . . . . . 5
4.1. Remote interface IP address . . . . . . . . . . . . . . . 5
4.2. Link Local/Remote Identifiers . . . . . . . . . . . . . . 6
4.3. Shared Risk Link Group (SRLG) . . . . . . . . . . . . . . 6
4.4. Extended Metrics . . . . . . . . . . . . . . . . . . . . 6
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Various link attributes have been defined in OSPFv2 [RFC2328] in the
context of the MPLS traffic engineering and GMPLS. All these
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attributes are distributed by OSPFv2 as a sub-TLVs of the Link-TLV
advertised in the OSPFv2 TE Opaque LSA [RFC3630].
Many of these link attributes are useful outside of the traditional
MLPLS Traffic Engineering or GMPLS. This brings its own set of
problems, in particular how to distribute these link attributes in
OSPFv2 when MPLS TE or GMPLS are not deployed or are deployed in
parallel with other applications that use these link attributes.
1.1. Requirements notation
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 [RFC2119].
2. Link attributes examples
This section lists some of the link attributes originally defined for
MPLS Traffic Engineering that can be used for other purposes in
OSPFv2. The list doesn't necessarily contain all the required
attributes.
1. Remote Interface IP address [RFC3630] - OSPFv2 currently cannot
distinguish between parallel set of links between two remote
OSPFv2 routers. As a result, the two-way connectivity check
performed during SPF may succeed when the two routers disagree on
which of the links to use for data traffic.
2. Link Local/Remote Identifiers - [RFC4203] - Used for the two-way
connectivity check for parallel unnumbered links. Also used for
identifying adjacencies for unnumbered links in Segment Routing
traffic engineering.
3. Shared Risk Link Group (SRLG) [RFC4203] - In IPFRR, the SRLG is
used to compute diverse backup paths [RFC5714].
4. Unidirectional Link Delay/Loss Metrics [RFC7471] - Could be used
for the shortest path first (SPF) computation using alternate
metrics within an OSPF area.
3. Advertising Link Attributes
This section outlines possible approaches for advertising link
attributes originally defined for MPLS Traffic Engineering purposes
or GMPLS when they are used for other applications.
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3.1. TE Opaque LSA
One approach for advertising link attributes is to continue to use TE
Opaque LSA ([RFC3630]). There are several problems with this
approach:
1. Whenever the link is advertised in a TE Opaque LSA, the link
becomes a part of the TE topology, which may not match IP routed
topology. By making the link part of the TE topology, remote
nodes may mistakenly believe that the link is available for MPLS
TE or GMPLS, when, in fact, MPLS is not enabled on the link.
2. The TE Opaque LSA carries link attributes that are not used or
required by MPLS TE or GMPLS. There is no mechanism in TE Opaque
LSA to indicate which of the link attributes should be passed to
MPLS TE application and which should be used by OSPFv2 and other
applications.
3. Link attributes used for non-TE purposes is partitioned across
multiple LSAs - the TE Opaque LSA and the Extended Link Opaque
LSA. This partitioning will require implementations to lookup
multiple LSAs to extract link attributes for a single link,
bringing needless complexity to the OSPFv2 implementations.
The advantage of this approach is that there is no additional
standardization requirement to advertise the TE/GMPL attributes for
other applications. Additionally, link attributes are only
advertised once when both OSPF TE and other applications are deployed
on the same link. This is not expected to be a common deployment
scenario.
3.2. Extended Link Opaque LSA
An alternative approach for advertising link attributes is to use
Extended Link Opaque LSAs as defined in [RFC7684]. This LSA was
defined as a generic container for distribution of the extended link
attributes. There are several advantages in using Extended Link LSA:
1. Advertisement of the link attributes does not make the link part
of the TE topology. It avoids any conflicts and is fully
compatible with the [RFC3630].
2. The TE Opaque LSA remains truly opaque to OSPFv2 as originally
defined in [RFC3630]. Its content is not inspected by OSPFv2 and
OSPFv2 acts as a pure transport.
3. There is clear distinction between link attributes used by TE and
link attributes used by other OSPFv2 applications.
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4. All link attributes that are used by OSPFv2 applications are
advertised in a single LSA, the Extended Link Opaque LSA.
The disadvantage of this approach is that in rare cases, the same
link attribute is advertised in both the TE Opaque and Extended Link
Attribute LSAs. Additionally, there will be additional
standardization effort. However, this could also be viewed as an
advantage as the non-TE use cases for the TE link attributes are
documented and validated by the OSPF working group.
3.3. Proposed solution
It is RECOMMENDED to use the Extended Link Opaque LSA ([RFC7684] to
advertise any link attributes used for non-TE purposes in OSPFv2,
including those that have been originally defined for TE purposes.
TE link attributes used for TE purposes continue to use TE Opaque LSA
([RFC3630]).
Is is also RECOMMENDED to keep the format of the link attribute TLVs
that have been defined for TE purposes unchanged even when they are
used for non-TE purposes.
Finally, it is RECOMMENDED to allocate unique code points for link
attribute TLVs that have been defined for TE purposes for the OSPFv2
Extended Link TLV Sub-TLV Registry as defined in [RFC7684]. For each
reused TLV, the code point will be defined in an IETF document along
with the expected usecase(s).
4. Reused TE link attributes
This section defines the use case and code points for the OSPFv2
Extended Link TLV Sub-TLV Registry for some of the link attributes
that have been originally defined for TE or GMPLS purposes.
4.1. Remote interface IP address
The OSPFv2 description of an IP numbered point-to-point adjacency
does not include remote IP address. As described in Section 2, this
makes the two-way connectivity check ambiguous in the presence of the
parallel point-to-point links between two OSPFv2 routers.
The Remote IP address of the link can also be used for Segment
Routing traffic engineering to identify the link in a set of parallel
links between two OSPFv2 routers
[I-D.ietf-ospf-segment-routing-extensions]. Similarly, the remote IP
address is useful in identifying individual parallel OSPF links
advertised in BGP Link-State as described in
[I-D.ietf-idr-ls-distribution].
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To advertise the Remote interface IP address in the OSPFv2 Extended
Link TLV, the same format of the sub-TLV as defined in section 2.5.4.
of [RFC3630] is used and TLV type 4 is used.
4.2. Link Local/Remote Identifiers
The OSPFv2 description of an IP unnumbered point-to-point adjacency
does not include remote link identifier. As described in Section 2,
this makes the two-way connectivity check ambiguous in the presence
of the parallel point-to-point IP unnumbered links between two OSPFv2
routers.
The local and remote link identifiers can also be used for Segment
Routing traffic engineering to identify the link in a set of parallel
IP unnumbered links between two OSPFv2 routers
[I-D.ietf-ospf-segment-routing-extensions]. Similarly, these
identifiers are useful in identifying individual parallel OSPF links
advertised in BGP Link-State as described in
[I-D.ietf-idr-ls-distribution].
To advertise the link Local/Remote identifiers in the OSPFv2 Extended
Link TLV, the same format of the sub-TLV as defined in section 1.1.
of [RFC4203] is used and TLV type 5 is used.
4.3. Shared Risk Link Group (SRLG)
The SRLG of a link can be used in IPFRR to compute a backup path that
does not share any SRLG group with the protected link.
To advertise the SRLG of the link in the OSPFv2 Extended Link TLV,
the same format of the sub-TLV as defined in section 1.3. of
[RFC4203] is used and TLV type 6 is used.
4.4. Extended Metrics
[RFC3630] defines several link bandwidth types. [RFC7471] defines
extended link metrics that are based on link bandwidth, delay and
loss characteristics. All these can be used to compute best paths
within an OSPF area to satisfy requirements for bandwidth, delay
(nominal or worst case) or loss.
To advertise extended link metrics in the OSPFv2 Extended Link TLV,
the same format of the sub-TLVs as defined in [RFC7471] is used with
following TLV types:
7 - Unidirectional Link Delay
8 - Min/Max Unidirectional Link Delay
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9 - Unidirectional Delay Variation
10 - Unidirectional Link Loss
11 - Unidirectional Residual Bandwidth
12 - Unidirectional Available Bandwidth
13 - Unidirectional Utilized Bandwidth
To advertise link maximum bandwidth, maximum reservable bandwidth an
unreserved bandwidth in the OSPFv2 Extended Link TLV, the same format
of the sub-TLVs as defined in [RFC3630] is used with following TLV
types:
7 - Maximum bandwidth
8 - Maximum reservable bandwidth
9 - Unreserved bandwidth
5. Backward Compatibility
It is allowed to advertise the same link attribute in TE Opaque LSA
[RFC3630] as well as in the Extended Link Opaque LSA [RFC7684] at the
same time. If the same link attribute is advertised in both LSAs, it
is expected that the information in these LSA would be identical. If
they are different, TE will use the information in the TE Opaque LSA
and the non-TE applications will use the information in the OSPFv2
Extended Link Opaque LSA.
Even though there is no IETF specification documenting the usage of
TE link attributes beyond the traffic engineering, some deployments
may rely on link attributes being carried in the TE Opaque LSA. For
example, some implementations of LFA and remote LFA currently rely on
link attributes such as SRLG and admin groups to be carried in the TE
Opaque LSA. These applications are described in [RFC5286],
[RFC7490], [I-D.ietf-rtgwg-lfa-manageability] and
[I-D.psarkar-rtgwg-rlfa-node-protection].
When a network is using an application that relies on link attributes
being carried in the TE Opaque LSA, care should be taken to continue
to advertise the appropriate link attributes in the TE Opaque LSA.
Note that by doing so, the link will continue to be considered part
of the traffic engineering topology as defined in [RFC3630].
Note that a node that does not directly participate in remote LFA by
originating repair tunnels itself may still need to continue
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originating link attributes in the TE Opaque LSA for use by other
nodes in the network. Therefore, when evaluating software upgrades
or configuration changes which may result in changes to which link
attributes are being advertised in the TE Opaque LSA, even for a
subset of routers in the network, care should be taken to evaluate
the impact of that change across the entire network.
6. Security Considerations
Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors that cause hard OSPFv2 failures.
7. IANA Considerations
This specification updates the OSPFv2 Extended Link TLV sub-TLV
registry that is defined in [RFC7684] with the following TLV types:
4 - Remote interface IP address
5 - Link Local/Remote Identifiers
6 - Shared Risk Link Group
7 - Unidirectional Link Delay
8 - Min/Max Unidirectional Link Delay
9 - Unidirectional Delay Variation
10 - Unidirectional Link Loss
11 - Unidirectional Residual Bandwidth
12 - Unidirectional Available Bandwidth
13 - Unidirectional Utilized Bandwidth
8. Acknowledgments
Thanks to Chris Bowers for his review and comments.
9. References
9.1. Normative References
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[I-D.ietf-idr-ls-distribution]
Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
Ray, "North-Bound Distribution of Link-State and TE
Information using BGP", draft-ietf-idr-ls-distribution-13
(work in progress), October 2015.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-06 (work in progress), December 2015.
[I-D.ietf-rtgwg-lfa-manageability]
Litkowski, S., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and P. Sarkar, "Operational management of
Loop Free Alternates", draft-ietf-rtgwg-lfa-
manageability-11 (work in progress), June 2015.
[I-D.psarkar-rtgwg-rlfa-node-protection]
psarkar@juniper.net, p., Gredler, H., Hegde, S., Bowers,
C., Litkowski, S., and H. Raghuveer, "Remote-LFA Node
Protection and Manageability", draft-psarkar-rtgwg-rlfa-
node-protection-05 (work in progress), June 2014.
[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>.
[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>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<http://www.rfc-editor.org/info/rfc5286>.
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[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<http://www.rfc-editor.org/info/rfc5714>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<http://www.rfc-editor.org/info/rfc7490>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <http://www.rfc-editor.org/info/rfc7684>.
9.2. Informative References
[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>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<http://www.rfc-editor.org/info/rfc7471>.
Authors' Addresses
Peter Psenak
Cisco Systems
Apollo Business Center
Mlynske nivy 43
Bratislava, 821 09
Slovakia
Email: ppsenak@cisco.com
Acee Lindem
Cisco Systems
301 Midenhall Way
Cary, NC 27513
USA
Email: acee@cisco.com
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Wim Henderickx
Alcatel-Lucent
Copernicuslaan
Antwerp, 2018 94089
Belgium
Email: wim.henderickx@alcatel-lucent.com
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: jeff.tantsura@ericsson.com
Hannes Gredler
Individual
Austria
Email: hannes@gredler.at
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