Internet DRAFT - draft-ietf-ospf-te-link-attr-reuse
draft-ietf-ospf-te-link-attr-reuse
LSR Working Group P. Psenak, Ed.
Internet-Draft L. Ginsberg
Intended status: Standards Track Cisco Systems
Expires: January 1, 2021 W. Henderickx
Nokia
J. Tantsura
Apstra
J. Drake
Juniper Networks
June 30, 2020
OSPF Application-Specific Link Attributes
draft-ietf-ospf-te-link-attr-reuse-16.txt
Abstract
Existing traffic engineering related link attribute advertisements
have been defined and are used in RSVP-TE deployments. Since the
original RSVP-TE use case was defined, additional applications (e.g.,
Segment Routing Policy, Loop Free Alternate) have been defined that
also make use of the link attribute advertisements. In cases where
multiple applications wish to make use of these link attributes the
current advertisements do not support application specific values for
a given attribute nor do they support indication of which
applications are using the advertised value for a given link. This
document introduces new link attribute advertisements in OSPFv2 and
OSPFv3 that address both of these shortcomings.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 1, 2021.
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Copyright Notice
Copyright (c) 2020 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
(https://trustee.ietf.org/license-info) in effect on the date of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Discussion . . . . . . . . . . . . . . . . . . . 4
4. Existing Advertisement of Link Attributes . . . . . . . . . . 5
5. Advertisement of Link Attributes . . . . . . . . . . . . . . 5
5.1. OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA . 5
6. Advertisement of Application-Specific Values . . . . . . . . 6
7. Reused TE link attributes . . . . . . . . . . . . . . . . . . 9
7.1. Shared Risk Link Group (SRLG) . . . . . . . . . . . . . . 10
7.2. Extended Metrics . . . . . . . . . . . . . . . . . . . . 10
7.3. Administrative Group . . . . . . . . . . . . . . . . . . 11
7.4. Traffic Engineering Metric . . . . . . . . . . . . . . . 11
8. Maximum Link Bandwidth . . . . . . . . . . . . . . . . . . . 11
9. Considerations for Extended TE Metrics . . . . . . . . . . . 12
10. Local Interface IPv6 Address Sub-TLV . . . . . . . . . . . . 12
11. Remote Interface IPv6 Address Sub-TLV . . . . . . . . . . . . 12
12. Attribute Advertisements and Enablement . . . . . . . . . . . 13
13. Deployment Considerations . . . . . . . . . . . . . . . . . . 14
13.1. Use of Legacy RSVP-TE LSA Advertisements . . . . . . . . 14
13.2. Interoperability, Backwards Compatibility and Migration
Concerns . . . . . . . . . . . . . . . . . . . . . . . . 15
13.2.1. Multiple Applications: Common Attributes with RSVP-
TE . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.2.2. Multiple Applications: Some Attributes Not Shared
with RSVP-TE . . . . . . . . . . . . . . . . . . . . 15
13.2.3. Interoperability with Legacy Routers . . . . . . . . 15
13.2.4. Use of Application-Specific Advertisements for RSVP-
TE . . . . . . . . . . . . . . . . . . . . . . . . . 16
14. Security Considerations . . . . . . . . . . . . . . . . . . . 16
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
15.1. OSPFv2 . . . . . . . . . . . . . . . . . . . . . . . . . 17
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15.2. OSPFv3 . . . . . . . . . . . . . . . . . . . . . . . . . 18
16. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
18.1. Normative References . . . . . . . . . . . . . . . . . . 19
18.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Advertisement of link attributes by the OSPFv2 [RFC2328] and OSPFv3
[RFC5340] protocols in support of traffic engineering (TE) was
introduced by [RFC3630] and [RFC5329] respectively. It has been
extended by [RFC4203], [RFC7308] and [RFC7471]. Use of these
extensions has been associated with deployments supporting Traffic
Engineering over Multiprotocol Label Switching (MPLS) in the presence
of the Resource Reservation Protocol (RSVP) - more succinctly
referred to as RSVP-TE [RFC3209].
For the purposes of this document an application is a technology that
makes use of link attribute advertisements, examples of which are
listed in Section 6.
In recent years new applications have been introduced that have use
cases for many of the link attributes historically used by RSVP-TE.
Such applications include Segment Routing (SR) Policy
[I-D.ietf-spring-segment-routing-policy] and Loop Free Alternates
(LFA) [RFC5286]. This has introduced ambiguity in that if a
deployment includes a mix of RSVP-TE support and SR Policy support
(for example) it is not possible to unambiguously indicate which
advertisements are to be used by RSVP-TE and which advertisements are
to be used by SR Policy. If the topologies are fully congruent this
may not be an issue, but any incongruence leads to ambiguity.
An example where this ambiguity causes a problem is a network in that
RSVP-TE is enabled only on a subset of its links. A link attribute
is advertised for the purpose of another application (e.g. SR
Policy) for a link that is not enabled for RSVP-TE. As soon as the
router that is an RSVP-TE head-end sees the link attribute being
advertised for that link, it assumes RSVP-TE is enabled on that link,
even though it is not. If such RSVP-TE head-end router tries to
setup an RSVP-TE path via that link, it will result in the path setup
failure.
An additional issue arises in cases where both applications are
supported on a link but the link attribute values associated with
each application differ. Current advertisements do not support
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advertising application-specific values for the same attribute on a
specific link.
This document defines extensions that address these issues. Also, as
evolution of use cases for link attributes can be expected to
continue in the years to come, this document defines a solution that
is easily extensible for the introduction of new applications and new
use cases.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Requirements Discussion
As stated previously, evolution of use cases for link attributes can
be expected to continue. Therefore, any discussion of existing use
cases is limited to requirements that are known at the time of this
writing. However, in order to determine the functionality required
beyond what already exists in OSPF, it is only necessary to discuss
use cases that justify the key points identified in the introduction,
which are:
1. Support for indicating which applications are using the link
attribute advertisements on a link
2. Support for advertising application-specific values for the same
attribute on a link
[RFC7855] discusses use cases/requirements for Segment Routing (SR).
Included among these use cases is SR Policy which is defined in
[I-D.ietf-spring-segment-routing-policy]. If both RSVP-TE and SR
Policy are deployed in a network, link attribute advertisements can
be used by one or both of these applications. As there is no
requirement for the link attributes advertised on a given link used
by SR Policy to be identical to the link attributes advertised on
that same link used by RSVP-TE, there is a clear requirement to
indicate independently which link attribute advertisements are to be
used by each application.
As the number of applications that may wish to utilize link
attributes may grow in the future, an additional requirement is that
the extensions defined allow the association of additional
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applications to link attributes without altering the format of the
advertisements or introducing new backwards compatibility issues.
Finally, there may still be many cases where a single attribute value
can be shared among multiple applications, so the solution must
minimize advertising duplicate link/attribute pairs whenever
possible.
4. Existing Advertisement of Link Attributes
There are existing advertisements used in support of RSVP-TE. These
advertisements are carried in the OSPFv2 TE Opaque LSA [RFC3630] and
OSPFv3 Intra-Area-TE-LSA [RFC5329]. Additional RSVP-TE link
attributes have been defined by [RFC4203], [RFC7308] and [RFC7471].
Extended Link Opaque LSAs as defined in [RFC7684] for OSPFv2 and
Extended Router-LSAs [RFC8362] for OSPFv3 are used to advertise link
attributes that are used by applications other than RSVP-TE or GMPLS
[RFC4203]. These LSAs were defined as a generic containers for
distribution of the extended link attributes.
5. Advertisement of Link Attributes
This section outlines the solution for advertising link attributes
originally defined for RSVP-TE or GMPLS when they are used for other
applications.
5.1. OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA
Advantages of Extended Link Opaque LSAs as defined in [RFC7684] for
OSPFv2 and Extended Router-LSAs [RFC8362] for OSPFv3 with respect to
advertisement of link attributes originally defined for RSVP-TE when
used in packet networks and in GMPLS:
1. Advertisement of the link attributes does not make the link part
of the RSVP-TE topology. It avoids any conflicts and is fully
compatible with [RFC3630] and [RFC5329].
2. The OSPFv2 TE Opaque LSA and OSPFv3 Intra-Area-TE-LSA remains
truly opaque to OSPFv2 and OSPFv3 as originally defined in
[RFC3630] and [RFC5329] respectively. Their contents are not
inspected by OSPF, which instead acts as a pure transport.
3. There is a clear distinction between link attributes used by
RSVP-TE and link attributes used by other OSPFv2 or OSPFv3
applications.
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4. All link attributes that are used by other applications are
advertised in a single LSA, the Extended Link Opaque LSA in
OSPFv2 or the OSPFv3 E-Router-LSA [RFC8362] in OSPFv3.
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 in OSPFv2 or the Intra-Area-TE-LSA and E-Router-LSA in
OSPFv3.
Extended Link Opaque LSA [RFC7684] and E-Router-LSA [RFC8362] are
used to advertise any link attributes used for non-RSVP-TE
applications in OSPFv2 or OSPFv3 respectively, including those that
have been originally defined for RSVP-TE applications (See
Section 7).
TE link attributes used for RSVP-TE/GMPLS continue to use OSPFv2 TE
Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329].
The format of the link attribute TLVs that have been defined for
RSVP-TE applications will be kept unchanged even when they are used
for non-RSVP-TE applications. Unique code points are allocated for
these link attribute TLVs from the OSPFv2 Extended Link TLV Sub-TLV
Registry [RFC7684] and from the OSPFv3 Extended-LSA Sub-TLV Registry
[RFC8362], as specified in Section 15.
6. Advertisement of Application-Specific Values
To allow advertisement of the application-specific values of the link
attribute, a new Application-Specific Link Attributes (ASLA) sub-TLV
is defined. The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended
Link TLV [RFC7684] and OSPFv3 Router-Link TLV [RFC8362].
On top of advertising the link attributes for standardized
applications, link attributes can be advertised for the purpose of
applications that are not standardized. We call such an application
a "User Defined Application" or "UDA". These applications are not
subject to standardization and are outside of the scope of this
specification.
The ASLA sub-TLV is an optional sub-TLV of OSPFv2 Extended Link TLV
and OSPFv3 Router-Link TLV. Multiple ASLA sub-TLVs can be present in
its parent TLV when different applications want to control different
link attributes or when different value of the same attribute needs
to be advertised by multiple applications. The ASLA sub-TLV MUST be
used for advertisement of the link attributes listed at the end on
this section if these are advertised inside OSPFv2 Extended Link TLV
and OSPFv3 Router-Link TLV. It has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SABM Length | UDABM Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Standard Application Identifier Bit Mask |
+- -+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User Defined Application Identifier Bit Mask |
+- -+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute sub-sub-TLVs |
+- -+
| ... |
where:
Type: 10 (OSPFv2), 11 (OSPFv3)
Length: variable
SABM Length: Standard Application Identifier Bit Mask Length in
octets. The value MUST be 0, 4 or 8. If the Standard Application
Bit Mask is not present, the Standard Application Bit Mask Length
MUST be set to 0.
UDABM Length: User Defined Application Identifier Bit Mask Length
in octets. The value MUST be 0, 4 or 8. If the User Defined
Application Bit Mask is not present, the User Defined Application
Bit Mask Length MUST be set to 0.
Standard Application Identifier Bit Mask: Optional set of bits,
where each bit represents a single standard application. Bits are
defined in the Link Attribute Application Identifier Registry,
which has been defined in [I-D.ietf-isis-te-app]. Current
assignments are repeated here for informational purpose:
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+...
|R|S|F| ...
+-+-+-+-+-+-+-+-+...
Bit-0 (R-bit): RSVP-TE
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Bit-1 (S-bit): Segment Routing Policy
Bit-2 (F-bit): Loop Free Alternate (LFA). Includes all LFA
types
User Defined Application Identifier Bit Mask: Optional set of
bits, where each bit represents a single user defined application.
If the SABM or UDABM length is other than 0, 4, or 8, the ASLA sub-
TLV MUST be ignored by the receiver.
Standard Application Identifier Bits are defined/sent starting with
Bit 0. Undefined bits that are transmitted MUST be transmitted as 0
and MUST be ignored on receipt. Bits that are not transmitted MUST
be treated as if they are set to 0 on receipt. Bits that are not
supported by an implementation MUST be ignored on receipt.
User Defined Application Identifier Bits have no relationship to
Standard Application Identifier Bits and are not managed by IANA or
any other standards body. It is recommended that bits are used
starting with Bit 0 so as to minimize the number of octets required
to advertise all UDAs. Undefined bits which are transmitted MUST be
transmitted as 0 and MUST be ignored on receipt. Bits that are not
transmitted MUST be treated as if they are set to 0 on receipt. Bits
that are not supported by an implementation MUST be ignored on
receipt.
If the link attribute advertisement is intended to be only used by a
specific set of applications, corresponding Bit Masks MUST be present
and application-specific bit(s) MUST be set for all applications that
use the link attributes advertised in the ASLA sub-TLV.
Application Bit Masks apply to all link attributes that support
application-specific values and are advertised in the ASLA sub-TLV.
The advantage of not making the Application Bit Masks part of the
attribute advertisement itself is that the format of any previously
defined link attributes can be kept and reused when advertising them
in the ASLA sub-TLV.
If the same attribute is advertised in more than one ASLA sub-TLVs
with the application listed in the Application Bit Masks, the
application SHOULD use the first instance of advertisement and ignore
any subsequent advertisements of that attribute.
If link attributes are advertised with zero length Application
Identifier Bit Masks for both standard applications and user defined
applications, then any Standard Application and/or any User Defined
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Application is permitted to use that set of link attributes. If
support for a new application is introduced on any node in a network
in the presence of such advertisements, these advertisements are
permitted to be used by the new application. If this is not what is
intended, then existing advertisements MUST be readvertised with an
explicit set of applications specified before a new application is
introduced.
An application-specific advertisement (Application Identifier Bit
Mask with a matching Application Identifier Bit set) for an attribute
MUST always be preferred over the advertisement of the same attribute
with the zero length Application Identifier Bit Masks for both
standard applications and user defined applications on the same link.
This document defines the initial set of link attributes that MUST
use the ASLA sub-TLV if advertised in the OSPFv2 Extended Link TLV or
in the OSPFv3 Router-Link TLV. Documents which define new link
attributes MUST state whether the new attributes support application-
specific values and as such are advertised in an ASLA sub-TLV. The
standard link attributes that are advertised in ASLA sub-TLVs are:
- Shared Risk Link Group [RFC4203]
- Unidirectional Link Delay [RFC7471]
- Min/Max Unidirectional Link Delay [RFC7471]
- Unidirectional Delay Variation [RFC7471]
- Unidirectional Link Loss [RFC7471]
- Unidirectional Residual Bandwidth [RFC7471]
- Unidirectional Available Bandwidth [RFC7471]
- Unidirectional Utilized Bandwidth [RFC7471]
- Administrative Group [RFC3630]
- Extended Administrative Group [RFC7308]
- TE Metric [RFC3630]
7. Reused TE link attributes
This section defines the use case and indicates the code points
(Section 15) from the OSPFv2 Extended Link TLV Sub-TLV Registry and
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OSPFv3 Extended-LSA Sub-TLV Registry for some of the link attributes
that have been originally defined for RSVP-TE or GMPLS.
7.1. Shared Risk Link Group (SRLG)
The SRLG of a link can be used in OSPF calculated IPFRR (IP Fast
Reroute) [RFC5714] 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 for the sub-TLV defined in section 1.3 of [RFC4203]
is used and TLV type 11 is used. Similarly, for OSPFv3 to advertise
the SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used.
7.2. Extended Metrics
[RFC3630] defines several link bandwidth types. [RFC7471] defines
extended link metrics that are based on link bandwidth, delay and
loss characteristics. All of these can be used to compute primary
and backup 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 for the sub-TLVs defined in [RFC7471] is used with
the following TLV types:
12 - Unidirectional Link Delay
13 - Min/Max Unidirectional Link Delay
14 - Unidirectional Delay Variation
15 - Unidirectional Link Loss
16 - Unidirectional Residual Bandwidth
17 - Unidirectional Available Bandwidth
18 - Unidirectional Utilized Bandwidth
To advertise extended link metrics in the OSPFv3 Extended-LSA Router-
Link TLV, the same format for the sub-TLVs defined in [RFC7471] is
used with the following TLV types:
13 - Unidirectional Link Delay
14 - Min/Max Unidirectional Link Delay
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15 - Unidirectional Delay Variation
16 - Unidirectional Link Loss
17 - Unidirectional Residual Bandwidth
18 - Unidirectional Available Bandwidth
19 - Unidirectional Utilized Bandwidth
7.3. Administrative Group
[RFC3630] and [RFC7308] define the Administrative Group and Extended
Administrative Group sub-TLVs respectively.
To advertise the Administrative Group and Extended Administrative
Group in the OSPFv2 Extended Link TLV, the same format for the sub-
TLVs defined in [RFC3630] and [RFC7308] is used with the following
TLV types:
19 - Administrative Group
20 - Extended Administrative Group
To advertise Administrative Group and Extended Administrative Group
in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs
defined in [RFC3630] and [RFC7308] is used with the following TLV
types:
20 - Administrative Group
21 - Extended Administrative Group
7.4. Traffic Engineering Metric
[RFC3630] defines Traffic Engineering Metric.
To advertise the Traffic Engineering Metric in the OSPFv2 Extended
Link TLV, the same format for the sub-TLV defined in section 2.5.5 of
[RFC3630] is used and TLV type 22 is used. Similarly, for OSPFv3 to
advertise the Traffic Engineering Metric in the OSPFv3 Router-Link
TLV, TLV type 22 is used.
8. Maximum Link Bandwidth
Maximum link bandwidth is an application independent attribute of the
link that is defined in [RFC3630]. Because it is an application
independent attribute, it MUST NOT be advertised in ASLA sub-TLV.
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Instead, it MAY be advertised as a sub-TLV of the Extended Link
Opaque LSA Extended Link TLV in OSPFv2 [RFC7684] or sub-TLV of OSPFv3
E-Router-LSA Router-Link TLV in OSPFv3 [RFC8362].
To advertise the Maximum link bandwidth in the OSPFv2 Extended Link
TLV, the same format for sub-TLV defined in [RFC3630] is used with
TLV type 23.
To advertise the Maximum link bandwidth in the OSPFv3 Router-Link
TLV, the same format for sub-TLV defined in [RFC3630] is used with
TLV type 23.
9. Considerations for Extended TE Metrics
[RFC7471] defines a number of dynamic performance metrics associated
with a link. It is conceivable that such metrics could be measured
specific to traffic associated with a specific application.
Therefore this document includes support for advertising these link
attributes specific to a given application. However, in practice it
may well be more practical to have these metrics reflect the
performance of all traffic on the link regardless of application. In
such cases, advertisements for these attributes can be associated
with all of the applications utilizing that link. This can be done
either by explicitly specifying the applications in the Application
Identifier Bit Mask or by using a zero length Application Identifier
Bit Mask.
10. Local Interface IPv6 Address Sub-TLV
The Local Interface IPv6 Address Sub-TLV is an application
independent attribute of the link that is defined in [RFC5329].
Because it is an application independent attribute, it MUST NOT be
advertised in the ASLA sub-TLV. Instead, it MAY be advertised as a
sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].
To advertise the Local Interface IPv6 Address Sub-TLV in the OSPFv3
Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
used with TLV type 24.
11. Remote Interface IPv6 Address Sub-TLV
The Remote Interface IPv6 Address Sub-TLV is an application
independent attribute of the link that is defined in [RFC5329].
Because it is an application independent attribute, it MUST NOT be
advertised in the ASLA sub-TLV. Instead, it MAY be advertised as a
sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].
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To advertise the Remote Interface IPv6 Address Sub-TLV in the OSPFv3
Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
used with TLV type 25.
12. Attribute Advertisements and Enablement
This document defines extensions to support the advertisement of
application-specific link attributes.
There are applications where the application enablement on the link
is relevant - e.g., RSVP-TE - one needs to make sure that RSVP is
enabled on the link before sending a RSVP-TE signaling message over
it.
There are applications where the enablement of the application on the
link is irrelevant and has nothing to do with the fact that some link
attributes are advertised for the purpose of such application. An
example of this is LFA.
Whether the presence of link attribute advertisements for a given
application indicates that the application is enabled on that link
depends upon the application. Similarly, whether the absence of link
attribute advertisements indicates that the application is not
enabled depends upon the application.
In the case of RSVP-TE, the advertisement of application-specific
link attributes has no implication of RSVP-TE being enabled on that
link. The RSVP-TE enablement is solely derived from the information
carried in the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-
TE-LSA [RFC5329].
In the case of SR Policy, advertisement of application-specific link
attributes does not indicate enablement of SR Policy. The
advertisements are only used to support constraints that may be
applied when specifying an explicit path. SR Policy is implicitly
enabled on all links that are part of the Segment Routing enabled
topology independent of the existence of link attribute
advertisements
In the case of LFA, advertisement of application-specific link
attributes does not indicate enablement of LFA on that link.
Enablement is controlled by local configuration.
If, in the future, additional standard applications are defined to
use this mechanism, the specification defining this use MUST define
the relationship between application-specific link attribute
advertisements and enablement for that application.
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This document allows the advertisement of application-specific link
attributes with no application identifiers i.e., both the Standard
Application Identifier Bit Mask and the User Defined Application
Identifier Bit Mask are not present (See Section 6). This supports
the use of the link attribute by any application. In the presence of
an application where the advertisement of link attribute
advertisements is used to infer the enablement of an application on
that link (e.g., RSVP-TE), the absence of the application identifier
leaves ambiguous whether that application is enabled on such a link.
This needs to be considered when making use of the "any application"
encoding.
13. Deployment Considerations
13.1. Use of Legacy RSVP-TE LSA Advertisements
Bit Identifiers for Standard Applications are defined in Section 6.
All of the identifiers defined in this document are associated with
applications that were already deployed in some networks prior to the
writing of this document. Therefore, such applications have been
deployed using the RSVP-TE LSA advertisements. The Standard
Applications defined in this document may continue to use RSVP-TE LSA
advertisements for a given link so long as at least one of the
following conditions is true:
The application is RSVP-TE
The application is SR Policy or LFA and RSVP-TE is not deployed
anywhere in the network
The application is SR Policy or LFA, RSVP-TE is deployed in the
network, and both the set of links on which SR Policy and/or LFA
advertisements are required and the attribute values used by SR
Policy and/or LFA on all such links is fully congruent with the
links and attribute values used by RSVP-TE
Under the conditions defined above, implementations that support the
extensions defined in this document have the choice of using RSVP-TE
LSA advertisements or application-specific advertisements in support
of SR Policy and/or LFA. This will require implementations to
provide controls specifying which type of advertisements are to be
sent/ processed on receive for these applications. Further
discussion of the associated issues can be found in Section 13.2.
New applications that future documents define to make use of the
advertisements defined in this document MUST NOT make use of RSVP-TE
LSA advertisements. This simplifies deployment of new applications
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by eliminating the need to support multiple ways to advertise
attributes for the new applications.
13.2. Interoperability, Backwards Compatibility and Migration Concerns
Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the
legacy advertisements listed in Section 4. Routers which do not
support the extensions defined in this document will only process
legacy advertisements and are likely to infer that RSVP-TE is enabled
on the links for which legacy advertisements exist. It is expected
that deployments using the legacy advertisements will persist for a
significant period of time. Therefore deployments using the
extensions defined in this document in the presence of routers that
do not support these extensions need to be able to interoperate with
the use of legacy advertisements by the legacy routers. The
following sub-sections discuss interoperability and backwards
compatibility concerns for a number of deployment scenarios.
13.2.1. Multiple Applications: Common Attributes with RSVP-TE
In cases where multiple applications are utilizing a given link, one
of the applications is RSVP-TE, and all link attributes for a given
link are common to the set of applications utilizing that link,
interoperability is achieved by using legacy advertisements for RSVP-
TE. Attributes for applications other than RSVP-TE MUST be
advertised using application-specific advertisements. This results
in duplicate advertisements for those attributes.
13.2.2. Multiple Applications: Some Attributes Not Shared with RSVP-TE
In cases where one or more applications other than RSVP-TE are
utilizing a given link and one or more link attribute values are not
shared with RSVP-TE, interoperability is achieved by using legacy
advertisements for RSVP-TE. Attributes for applications other than
RSVP-TE MUST be advertised using application-specific advertisements.
In cases where some link attributes are shared with RSVP-TE, this
requires duplicate advertisements for those attributes
13.2.3. Interoperability with Legacy Routers
For the applications defined in this document, routers that do not
support the extensions defined in this document will send and receive
only legacy link attribute advertisements. So long as there is any
legacy router in the network that has any of the applications
enabled, all routers MUST continue to advertise link attributes using
legacy advertisements. In addition, the link attribute values
associated with the set of applications supported by legacy routers
(RSVP-TE, SR Policy, and/or LFA) are always shared since legacy
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routers have no way of advertising or processing application-specific
values. Once all legacy routers have been upgraded, migration from
legacy advertisements to application specific advertisements can be
achieved via the following steps:
1)Send new application-specific advertisements while continuing to
advertise using the legacy advertisement (all advertisements are then
duplicated). Receiving routers continue to use legacy
advertisements.
2)Enable the use of the application-specific advertisements on all
routers
3)Keep legacy advertisements if needed for RSVP-TE purposes.
When the migration is complete, it then becomes possible to advertise
incongruent values per application on a given link.
Documents defining new applications that make use of the application-
specific advertisements defined in this document MUST discuss
interoperability and backwards compatibility issues that could occur
in the presence of routers that do not support the new application.
13.2.4. Use of Application-Specific Advertisements for RSVP-TE
The extensions defined in this document support RSVP-TE as one of the
supported applications. It is however RECOMMENDED to advertise all
link-attributes for RSVP-TE in the existing OSPFv2 TE Opaque LSA
[RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329] to maintain backward
compatibility. RSVP-TE can eventually utilize the application-
specific advertisements for newly defined link attributes, that are
defined as application-specific.
Link attributes that are not allowed to be advertised in the ASLA
Sub-TLV, such as Maximum Reservable Link Bandwidth and Unreserved
Bandwidth MUST use the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3
Intra-Area-TE-LSA [RFC5329] and MUST NOT be advertised in ASLA Sub-
TLV.
14. Security Considerations
Existing security extensions as described in [RFC2328], [RFC5340] and
[RFC8362] apply to extensions defined in this document. While OSPF
is under a single administrative domain, there can be deployments
where potential attackers have access to one or more networks in the
OSPF routing domain. In these deployments, stronger authentication
mechanisms such as those specified in [RFC5709], [RFC7474], [RFC4552]
or [RFC7166] SHOULD be used.
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Implementations must assure that malformed TLV and Sub-TLV defined in
this document are detected and do not provide a vulnerability for
attackers to crash the OSPF router or routing process. Reception of
a malformed TLV or Sub-TLV SHOULD be counted and/or logged for
further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be
rate-limited to prevent a Denial of Service (DoS) attack (distributed
or otherwise) from overloading the OSPF control plane.
This document defines a new way to advertise link attributes.
Tampering with the information defined in this document may have an
effect on applications using it, including impacting Traffic
Engineering that uses various link attributes for its path
computation. This is similar in nature to the impacts associated
with (for example) [RFC3630]. As the advertisements defined in this
document limit the scope to specific applications, the impact of
tampering is similarly limited in scope.
15. IANA Considerations
This specifications updates two existing registries:
- OSPFv2 Extended Link TLV Sub-TLVs Registry
- OSPFv3 Extended-LSA Sub-TLV Registry
New values are allocated using the IETF Review procedure as described
in [RFC5226].
15.1. OSPFv2
The OSPFv2 Extended Link TLV Sub-TLVs Registry [RFC7684] defines sub-
TLVs at any level of nesting for OSPFv2 Extended Link TLVs. IANA has
assigned the following Sub-TLV types from the OSPFv2 Extended Link
TLV Sub-TLVs Registry:
10 - Application-Specific Link Attributes
11 - Shared Risk Link Group
12 - Unidirectional Link Delay
13 - Min/Max Unidirectional Link Delay
14 - Unidirectional Delay Variation
15 - Unidirectional Link Loss
16 - Unidirectional Residual Bandwidth
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17 - Unidirectional Available Bandwidth
18 - Unidirectional Utilized Bandwidth
19 - Administrative Group
20 - Extended Administrative Group
22 - TE Metric
23 - Maximum Link Bandwidth
15.2. OSPFv3
The OSPFv3 Extended-LSA Sub-TLV Registry [RFC8362] defines sub-TLVs
at any level of nesting for OSPFv3 Extended LSAs. IANA has assigned
the following Sub-TLV types from the OSPFv3 Extended-LSA Sub-TLV
Registry:
11 - Application-Specific Link Attributes
12 - Shared Risk Link Group
13 - Unidirectional Link Delay
14 - Min/Max Unidirectional Link Delay
15 - Unidirectional Delay Variation
16 - Unidirectional Link Loss
17 - Unidirectional Residual Bandwidth
18 - Unidirectional Available Bandwidth
19 - Unidirectional Utilized Bandwidth
20 - Administrative Group
21 - Extended Administrative Group
22 - TE Metric
23 - Maximum Link Bandwidth
24 - Local Interface IPv6 Address Sub-TLV
25 - Remote Interface IPv6 Address Sub-TLV
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16. Contributors
The following people contributed to the content of this document and
should be considered as co-authors:
Acee Lindem
Cisco Systems
301 Midenhall Way
Cary, NC 27513
USA
Email: acee@cisco.com
Ketan Talaulikar
Cisco Systems, Inc.
India
Email: ketant@cisco.com
Hannes Gredler
RtBrick Inc.
Austria
Email: hannes@rtbrick.com
17. Acknowledgments
Thanks to Chris Bowers for his review and comments.
Thanks to Alvaro Retana for his detailed review and comments.
18. References
18.1. Normative References
[I-D.ietf-isis-te-app]
Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes",
draft-ietf-isis-te-app-19 (work in progress), June 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://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,
<https://www.rfc-editor.org/info/rfc3630>.
[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,
<https://www.rfc-editor.org/info/rfc4203>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[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,
<https://www.rfc-editor.org/info/rfc7471>.
[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, <https://www.rfc-editor.org/info/rfc7684>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
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18.2. Informative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-07 (work in progress),
May 2020.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[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,
<https://www.rfc-editor.org/info/rfc5286>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
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Authors' Addresses
Peter Psenak (editor)
Cisco Systems
Eurovea Centre, Central 3
Pribinova Street 10
Bratislava 81109
Slovakia
Email: ppsenak@cisco.com
Les Ginsberg
Cisco Systems
821 Alder Drive
MILPITAS, CA 95035
USA
Email: ginsberg@cisco.com
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp, 2018 94089
Belgium
Email: wim.henderickx@nokia.com
Jeff Tantsura
Apstra
US
Email: jefftant.ietf@gmail.com
John Drake
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, California 94089
USA
Email: jdrake@juniper.net
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