Internet DRAFT - draft-ietf-isis-te-app
draft-ietf-isis-te-app
Networking Working Group L. Ginsberg
Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems
Expires: December 31, 2020 S. Previdi
Huawei
W. Henderickx
Nokia
J. Drake
Juniper Networks
June 29, 2020
IS-IS Application-Specific Link Attributes
draft-ietf-isis-te-app-19
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) that also make use of
the link attribute advertisements have been defined . 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 that address
both of these shortcomings.
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.
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/.
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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 December 31, 2020.
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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Discussion . . . . . . . . . . . . . . . . . . . 4
3. Legacy Advertisements . . . . . . . . . . . . . . . . . . . . 5
3.1. Legacy sub-TLVs . . . . . . . . . . . . . . . . . . . . . 5
3.2. Legacy SRLG Advertisements . . . . . . . . . . . . . . . 6
4. Advertising Application-Specific Link Attributes . . . . . . 7
4.1. Application Identifier Bit Mask . . . . . . . . . . . . . 7
4.2. Application-Specific Link Attributes sub-TLV . . . . . . 9
4.2.1. Special Considerations for Maximum Link Bandwidth . . 11
4.2.2. Special Considerations for Reservable/Unreserved
Bandwidth . . . . . . . . . . . . . . . . . . . . . . 11
4.2.3. Considerations for Extended TE Metrics . . . . . . . 11
4.3. Application-Specific SRLG TLV . . . . . . . . . . . . . . 12
5. Attribute Advertisements and Enablement . . . . . . . . . . . 13
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 14
6.1. Use of Legacy Advertisements . . . . . . . . . . . . . . 14
6.2. Use of Zero Length Application Identifier Bit Masks . . . 15
6.3. Interoperability, Backwards Compatibility and Migration
Concerns . . . . . . . . . . . . . . . . . . . . . . . . 15
6.3.1. Multiple Applications: Common Attributes with RSVP-
TE . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.3.2. Multiple Applications: All Attributes Not Shared with
RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 15
6.3.3. Interoperability with Legacy Routers . . . . . . . . 16
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6.3.4. Use of Application-Specific Advertisements for RSVP-
TE . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. Application-Specific Link Attributes sub-TLV . . . . . . 17
7.2. Application-Specific SRLG TLV . . . . . . . . . . . . . . 17
7.3. Application-Specific Link Attributes sub-sub-TLV Registry 17
7.4. Link Attribute Application Identifier Registry . . . . . 18
7.5. SRLG sub-TLVs . . . . . . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Advertisement of link attributes by the Intermediate-System-to-
Intermediate-System (IS-IS) protocol in support of traffic
engineering (TE) was introduced by [RFC5305] and extended by
[RFC5307], [RFC6119], [RFC7308], and [RFC8570]. 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 3.
In recent years new applications that have use cases for many of the
link attributes historically used by RSVP-TE have been introduced.
Such applications include Segment Routing Policy (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 where
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
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setup an RSVP-TE path via that link, it will result in a 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
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 to the introduction of new applications and new
use cases.
2. 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 IS-IS, 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
applications to link attributes without altering the format of the
advertisements or introducing new backwards compatibility issues.
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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.
3. Legacy Advertisements
There are existing advertisements used in support of RSVP-TE. These
advertisements include sub-TLVs for TLVs 22, 23, 25, 141, 222, and
223 and TLVs for Shared Risk Link Group (SRLG) advertisement.
Sub-TLV values are defined in the Sub-TLVs for TLVs 22, 23, 25, 141,
222, and 223 registry.
TLVs are defined in the TLV Codepoints Registry.
3.1. Legacy sub-TLVs
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Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223
+-------------------------------------------+
| Type | Description |
+-------------------------------------------+
| 3 | Administrative group (color) |
+-------------------------------------------+
| 9 | Maximum link bandwidth |
+-------------------------------------------+
| 10 | Maximum reservable link bandwidth |
+-------------------------------------------+
| 11 | Unreserved bandwidth |
+-------------------------------------------+
| 14 | Extended Administrative Group |
+-------------------------------------------+
| 18 | TE Default Metric |
+-------------------------------------------+
| 33 | Unidirectional Link Delay |
+-------------------------------------------+
| 34 | Min/Max Unidirectional Link Delay |
+-------------------------------------------+
| 35 | Unidirectional Delay Variation |
+-------------------------------------------+
| 36 | Unidirectional Link Loss |
+-------------------------------------------+
| 37 | Unidirectional Residual Bandwidth |
+-------------------------------------------+
| 38 | Unidirectional Available Bandwidth |
+-------------------------------------------+
| 39 | Unidirectional Utilized Bandwidth |
+-------------------------------------------+
3.2. Legacy SRLG Advertisements
TLV 138 GMPLS-SRLG
Supports links identified by IPv4 addresses and
unnumbered links
TLV 139 IPv6 SRLG
Supports links identified by IPv6 addresses
Note that [RFC6119] prohibits the use of TLV 139 when it is possible
to use TLV 138.
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4. Advertising Application-Specific Link Attributes
Two new code points are defined in support of Application-Specific
Link Attribute (ASLA) Advertisements:
1) ASLA sub-TLV for TLVs 22, 23, 25, 141, 222, and 223 (defined in
Section 4.2 ).
2)Application-Specific Shared Risk Link Group (SRLG) TLV (defined in
Section 4.3).
In support of these new advertisements, an application identifier bit
mask is defined that identifies the application(s) associated with a
given advertisement (defined in Section 4.1).
In addition to supporting the advertisement of link attributes used
by standardized applications, link attributes can also be advertised
for use by user defined applications. Such applications are not
subject to standardization and are outside the scope of this
document.
The following sections define the format of these new advertisements.
4.1. Application Identifier Bit Mask
Identification of the set of applications associated with link
attribute advertisements utilizes two bit masks. One bit mask is for
standard applications where the definition of each bit is defined in
a new IANA controlled registry. A second bit mask is for non-
standard User Defined Applications (UDAs).
The encoding defined below is used by both the Application-Specific
Link Attributes sub-TLV and the Application-Specific SRLG TLV.
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| SABM Length + Flag | 1 octet
+--+--+--+--+--+--+--+--+
| UDABM Length + Flag | 1 octet
+--+--+--+--+--+--+--+--+
| SABM ... 0 - 8 octets
+--+--+--+--+--+--+--+--+
| UDABM ... 0 - 8 octets
+--+--+--+--+--+--+--+--+
SABM Length + Flag (1 octet)
Standard Application Identifier Bit Mask
Length + Flag
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| SABM Length |
+-+-+-+-+-+-+-+-+
L-flag: Legacy Flag.
See Section 4.2 for a description of how
this flag is used.
SABM Length: Indicates the length in octets (0-8) of the
Standard Application Identifier Bit Mask. The length SHOULD
be the minimum required to send all bits that are set.
UDABM Length + Flag (1 octet)
User Defined Application Identifier Bit Mask
Length + Flag
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R| UDABM Length|
+-+-+-+-+-+-+-+-+
R: Reserved. SHOULD be transmitted as 0 and
MUST be ignored on receipt
UDABM Length: Indicates the length in octets (0-8) of the
User Defined Application Identifier Bit Mask. The length SHOULD
be the minimum required to send all bits that are set.
SABM (variable length)
Standard Application Identifier Bit Mask
(SABM Length * 8) bits
This field is omitted if SABM Length is 0.
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+...
|R|S|F| ...
+-+-+-+-+-+-+-+-+...
R-bit: Set to specify RSVP-TE
S-bit: Set to specify Segment Routing Policy
F-bit: Set to specify Loop Free Alternate (LFA)
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(includes all LFA types)
UDABM (variable length)
User Defined Application Identifier Bit Mask
(UDABM Length * 8) bits
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+...
| ...
+-+-+-+-+-+-+-+-+...
This field is omitted if UDABM Length is 0.
NOTE: SABM/UDABM Length is arbitrarily limited to 8 octets in order
to insure that sufficient space is left to advertise link attributes
without overrunning the maximum length of a sub-TLV.
Standard Application Identifier Bits are defined/sent starting with
Bit 0.
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.
In the case of both SABM and UDABM, the following rules apply:
o Undefined bits that are transmitted MUST be transmitted as 0 and
MUST be ignored on receipt
o Bits that are not transmitted MUST be treated as if they are set
to 0 on receipt.
o Bits that are not supported by an implementation MUST be ignored
on receipt.
.
4.2. Application-Specific Link Attributes sub-TLV
A new sub-TLV for TLVs 22, 23, 25, 141, 222, and 223 is defined that
supports specification of the applications and application-specific
attribute values.
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Type: 16 (temporarily assigned by IANA)
Length: Variable (1 octet)
Value:
Application Identifier Bit Mask
(as defined in Section 4.1)
Link Attribute sub-sub-TLVs - format matches the
existing formats defined in [RFC5305], [RFC7308],
and [RFC8570]
If the SABM or UDABM length in the Application Identifier Bit Mask is
greater than 8, the entire sub-TLV MUST be ignored.
When the L-flag is set in the Application Identifier Bit Mask, all of
the applications specified in the bit mask MUST use the legacy
advertisements for the corresponding link found in TLVs 22, 23, 25,
141, 222, and 223 or TLV 138 or TLV 139 as appropriate. Link
attribute sub-sub-TLVs for the corresponding link attributes MUST NOT
be advertised for the set of applications specified in the Standard/
User Application Identifier Bit Masks and all such advertisements
MUST be ignored on receipt.
Multiple Application-Specific Link Attribute sub-TLVs for the same
link MAY be advertised. When multiple sub-TLVs for the same link are
advertised, they SHOULD advertise non-conflicting application/
attribute pairs. A conflict exists when the same application is
associated with two different values for the same link attribute for
a given link. In cases where conflicting values for the same
application/attribute/link are advertised the first advertisement
received in the lowest numbered LSP SHOULD be used and subsequent
advertisements of the same attribute SHOULD be ignored.
For a given application, the setting of the L-flag MUST be the same
in all sub-TLVs for a given link. In cases where this constraint is
violated, the L-flag MUST be considered set for this application.
If link attributes are advertised associated with zero length
Application Identifier Bit Masks for both standard applications and
user defined applications, then any Standard Application and/or any
User Defined Application is permitted to use that set of link
attributes so long as there is not another set of attributes
advertised on that same link that is associated with a non-zero
length Application Identifier Bit Mask with a matching Application
Identifier Bit set.
A new registry of sub-sub-TLVs is to be created by IANA that defines
the link attribute sub-sub-TLV code points. This document defines a
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sub-sub-TLV for each of the existing sub-TLVs listed in Section 3.1
except as noted below. The format of the sub-sub-TLVs matches the
format of the corresponding legacy sub-TLV and IANA is requested to
assign the legacy sub-TLV identifier to the corresponding sub-sub-
TLV.
4.2.1. Special Considerations for Maximum Link Bandwidth
Maximum link bandwidth is an application independent attribute of the
link. When advertised using the Application-Specific Link Attributes
sub-TLV, multiple values for the same link MUST NOT be advertised.
This can be accomplished most efficiently by having a single
advertisement for a given link where the Application Identifier Bit
Mask identifies all the applications that are making use of the value
for that link.
It is also possible to advertise the same value for a given link
multiple times with disjoint sets of applications specified in the
Application Identifier Bit Mask. This is less efficient but still
valid.
It is also possible to advertise a single advertisement with zero
length SABM and UDABM so long as the constraints discussed in
Section 4.2 and Section 6.2 are acceptable.
If different values for Maximum Link Bandwidth for a given link are
advertised, all values MUST be ignored.
4.2.2. Special Considerations for Reservable/Unreserved Bandwidth
Maximum Reservable Link Bandwidth and Unreserved Bandwidth are
attributes specific to RSVP-TE. When advertised using the
Application-Specific Link Attributes sub-TLV, bits other than the
RSVP-TE (R-bit) MUST NOT be set in the Application Identifier Bit
Mask. If an advertisement of Maximum Reservable Link Bandwidth or
Unreserved Bandwidth is received with bits other than the RSVP-TE bit
set, the advertisement MUST be ignored.
4.2.3. Considerations for Extended TE Metrics
[RFC8570] 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 will be associated
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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.
4.3. Application-Specific SRLG TLV
A new TLV is defined to advertise application-specific SRLGs for a
given link. Although similar in functionality to TLV 138 [RFC5307]
and TLV 139 [RFC6119], a single TLV provides support for IPv4, IPv6,
and unnumbered identifiers for a link. Unlike TLVs 138/139, it
utilizes sub-TLVs to encode the link identifiers in order to provide
the flexible formatting required to support multiple link identifier
types.
Type: 238 (Temporarily assigned by IANA)
Length: Number of octets in the value field (1 octet)
Value:
Neighbor System-ID + pseudo-node ID (7 octets)
Application Identifier Bit Mask
(as defined in Section 4.1)
Length of sub-TLVs (1 octet)
Link Identifier sub-TLVs (variable)
0 or more SRLG Values (Each value is 4 octets)
The following Link Identifier sub-TLVs are defined.
The values chosen are intentionally matching the equivalent
sub-TLVs from [RFC5305], [RFC5307], and [RFC6119].
Type Description
4 Link Local/Remote Identifiers [RFC5307]
6 IPv4 interface address [RFC5305]
8 IPv4 neighbor address [RFC5305]
12 IPv6 Interface Address [RFC6119]
13 IPv6 Neighbor Address [RFC6119]
At least one set of link identifiers (IPv4, IPv6, or Link Local/
Remote) MUST be present. Multiple occurrences of the same identifier
type MUST NOT be present. TLVs that do not meet this requirement
MUST be ignored.
Multiple TLVs for the same link MAY be advertised.
When the L-flag is set in the Application Identifier Bit Mask, SRLG
values MUST NOT be included in the TLV. Any SRLG values that are
advertised MUST be ignored. Based on the link identifiers advertised
the corresponding legacy TLV (see Section 3.2) can be identified and
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the SRLG values advertised in the legacy TLV MUST be used by the set
of applications specified in the Application Identifier Bit Mask.
For a given application, the setting of the L-flag MUST be the same
in all TLVs for a given link. In cases where this constraint is
violated, the L-flag MUST be considered set for this application.
5. Attribute Advertisements and Enablement
This document defines extensions to support the advertisement of
application-specific link attributes.
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 implies that RSVP is enabled on that link. The
absence of RSVP-TE application-specific link attributes in
combination with the absence of legacy advertisements implies that
RSVP is not enabled on that link.
In the case of SR Policy, advertisement of application-specific link
attributes does not indicate enablement of SR Policy on that link.
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.
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 4.1). 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
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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.
6. Deployment Considerations
This section discuss deployment considerations associated with the
use of application-specific link attribute advertisements.
6.1. Use of Legacy Advertisements
Bit Identifiers for Standard Applications are defined in Section 4.1.
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 legacy advertisements. The Standard Applications
defined in this document may continue to use legacy advertisements
for a given link so long as at least one of the following conditions
is true:
o The application is RSVP-TE
o The application is SR Policy or LFA and RSVP-TE is not deployed
anywhere in the network
o 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 legacy
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 6.3.
New applications that future documents define to make use of the
advertisements defined in this document MUST NOT make use of legacy
advertisements. This simplifies deployment of new applications by
eliminating the need to support multiple ways to advertise attributes
for the new applications.
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6.2. Use of Zero Length Application Identifier Bit Masks
Link attribute advertisements associated with zero length Application
Identifier Bit Masks for both standard applications and user defined
applications are usable by any application, subject to the
restrictions specified in Section 4.2. 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.
6.3. Interoperability, Backwards Compatibility and Migration Concerns
Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the
legacy advertisements listed in Section 3. Routers that 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.
6.3.1. 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 and
sending application-specific advertisements with L-flag set and no
link attribute values. This avoids duplication of link attribute
advertisements.
6.3.2. Multiple Applications: All 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, it is necessary to use application-specific
advertisements as defined in this document. Attributes for
applications other than RSVP-TE MUST be advertised using application-
specific advertisements that have the L-flag clear. In cases where
some link attributes are shared with RSVP-TE, this requires duplicate
advertisements for those attributes.
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These guidelines apply to cases where RSVP-TE is not using any
advertised attributes on a link and to cases where RSVP-TE is using
some link attribute advertisements on the link but some link
attributes cannot be shared with RSVP-TE.
6.3.3. 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
routers have no way of advertising or processing application-specific
values. Once all legacy routers have been upgraded, migration from
legacy advertisements to ASLA advertisements can be achieved via the
following steps:
1)Send ASLA advertisements while continuing to advertise using legacy
(all advertisements are then duplicated). Receiving routers continue
to use legacy advertisements.
2)Enable the use of the ASLA advertisements on all routers
3)Remove legacy advertisements
When the migration is complete, it then becomes possible to advertise
incongruent values per application on a given link.
Note that the use of the L-flag is of no value in the migration.
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.
6.3.4. Use of Application-Specific Advertisements for RSVP-TE
The extensions defined in this document support RSVP-TE as one of the
supported applications. This allows that RSVP-TE could eventually
utilize the application-specific advertisements. This can be done in
the following step-wise manner:
1)Upgrade all routers to support the extensions in this document
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2)Advertise all legacy link attributes using ASLA advertisements with
L-flag clear and R-bit set. At this point both legacy and
application-specific advertisements are being sent.
3)Remove legacy advertisements
7. IANA Considerations
This section lists the protocol code point changes introduced by this
document and the related IANA changes required.
For new registries defined under IS-IS TLV Codepoints Registry with
registration procedure "Expert Review", guidance for designated
experts can be found in [RFC7370].
7.1. Application-Specific Link Attributes sub-TLV
This document defines a new sub-TLV in the Sub-TLVs for TLVs 22, 23,
25, 141, 222, and 223 registry. See Section 4.2
Type Description 22 23 25 141 222 223
---- --------------------- ---- ---- ---- ---- ---- ----
16 Application-Specific y y y(s) y y y
Link Attributes
7.2. Application-Specific SRLG TLV
This document defines one new TLV in the IS-IS TLV Codepoints
Registry. See Section 4.3
Type Description IIH LSP SNP Purge
---- --------------------- --- --- --- -----
238 Application-Specific n y n n
SRLG
7.3. Application-Specific Link Attributes sub-sub-TLV Registry
This document requests a new IANA registry under the IS-IS TLV
Codepoints Registry be created to control the assignment of sub-sub-
TLV codepoints for the Application-Specific Link Attributes sub-TLV
defined in Section 7.1. The suggested name of the new registry is
"sub-sub-TLV code points for application-specific link attributes".
The registration procedure is "Expert Review" as defined in
[RFC8126]. The following assignments are made by this document:
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Type Description Encoding
Reference
---------------------------------------------------------
0-2 Unassigned
3 Administrative group (color) RFC5305
4-8 Unassigned
9 Maximum link bandwidth RFC5305
10 Maximum reservable link bandwidth RFC5305
11 Unreserved bandwidth RFC5305
12-13 Unassigned
14 Extended Administrative Group RFC7308
15-17 Unassigned
18 TE Default Metric RFC5305
19-32 Unassigned
33 Unidirectional Link Delay RFC8570
34 Min/Max Unidirectional Link Delay RFC8570
35 Unidirectional Delay Variation RFC8570
36 Unidirectional Link Loss RFC8570
37 Unidirectional Residual Bandwidth RFC8570
38 Unidirectional Available Bandwidth RFC8570
39 Unidirectional Utilized Bandwidth RFC8570
40-255 Unassigned
Note to IANA: For future codepoints, in cases where the document that
defines the encoding is different from the document that assigns the
codepoint, the encoding reference MUST be to the document that
defines the encoding.
Note to designated experts: If a link attribute can be advertised
both as a sub-TLV of TLVs 22, 23, 25, 141, 222, and 223 and as a sub-
sub-TLV of the Application-Specific Link Attributes sub-TLV defined
in this document, then the same numerical code should be assigned to
the link attribute whenever possible.
7.4. Link Attribute Application Identifier Registry
This document requests a new IANA registry be created, under the
category of "Interior Gateway Protocol (IGP) Parameters", to control
the assignment of Application Identifier Bits. The suggested name of
the new registry is "Link Attribute Applications". The registration
policy for this registry is "Expert Review" [RFC8126]. Bit
definitions SHOULD be assigned such that all bits in the lowest
available octet are allocated before assigning bits in the next
octet. This minimizes the number of octets that will need to be
transmitted. The following assignments are made by this document:
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Bit # Name
---------------------------------------------------------
0 RSVP-TE (R-bit)
1 Segment Routing Policy (S-bit)
2 Loop Free Alternate (F-bit)
3-63 Unassigned
7.5. SRLG sub-TLVs
This document requests a new IANA registry be created under the IS-IS
TLV Codepoints Registry to control the assignment of sub-TLV types
for the application-specific SRLG TLV. The suggested name of the new
registry is "Sub-TLVs for TLV 238". The registration procedure is
"Expert Review" as defined in [RFC8126]. The following assignments
are made by this document:
Value Description Encoding
Reference
---------------------------------------------------------
0-3 Unassigned
4 Link Local/Remote Identifiers [RFC5307]
5 Unassigned
6 IPv4 interface address [RFC5305]
7 Unassigned
8 IPv4 neighbor address [RFC5305]
9-11 Unassigned
12 IPv6 Interface Address [RFC6119]
13 IPv6 Neighbor Address [RFC6119]
14-255 Unassigned
Note to IANA: For future codepoints, in cases where the document that
defines the encoding is different from the document that assigns the
codepoint, the encoding reference MUST be to the document that
defines the encoding.
8. Security Considerations
Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
and [RFC5310]. While IS-IS is deployed under a single administrative
domain, there can be deployments where potential attackers have
access to one or more networks in the IS-IS routing domain. In these
deployments, the stronger authentication mechanisms defined in the
aforementioned documents SHOULD be used.
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 as discussed in [RFC8570]. As the advertisements defined
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in this document limit the scope to specific applications, the impact
of tampering is similarly limited in scope.
9. Acknowledgements
The authors would like to thank Eric Rosen and Acee Lindem for their
careful review and content suggestions.
10. References
10.1. Normative References
[ISO10589]
International Organization for Standardization,
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", ISO/
IEC 10589:2002, Second Edition, Nov 2002.
[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>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
<https://www.rfc-editor.org/info/rfc5307>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
February 2011, <https://www.rfc-editor.org/info/rfc6119>.
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[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>.
[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints
Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,
<https://www.rfc-editor.org/info/rfc7370>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
10.2. 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>.
[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>.
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>.
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Authors' Addresses
Les Ginsberg
Cisco Systems
821 Alder Drive
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
Peter Psenak
Cisco Systems
Apollo Business Center Mlynske nivy 43
Bratislava 821 09
Slovakia
Email: ppsenak@cisco.com
Stefano Previdi
Huawei
Email: stefano@previdi.net
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018 94089
Belgium
Email: wim.henderickx@nokia.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
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