--- 1/draft-ietf-isis-te-app-14.txt 2020-06-11 10:13:09.099797605 -0700 +++ 2/draft-ietf-isis-te-app-15.txt 2020-06-11 10:13:09.143798727 -0700 @@ -1,38 +1,38 @@ Networking Working Group L. Ginsberg Internet-Draft P. Psenak Intended status: Standards Track Cisco Systems -Expires: December 5, 2020 S. Previdi +Expires: December 13, 2020 S. Previdi Huawei W. Henderickx Nokia J. Drake Juniper Networks - June 3, 2020 + June 11, 2020 IS-IS TE Attributes per application - draft-ietf-isis-te-app-14 + draft-ietf-isis-te-app-15 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 Traffic Engineering, Loop Free Alternate) have been - defined which 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 - which address both of these shortcomings. + 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 @@ -43,163 +43,164 @@ 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 December 5, 2020. + This Internet-Draft will expire on December 13, 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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Discussion . . . . . . . . . . . . . . . . . . . 4 - 3. Legacy Advertisements . . . . . . . . . . . . . . . . . . . . 4 + 3. Legacy Advertisements . . . . . . . . . . . . . . . . . . . . 5 3.1. Legacy sub-TLVs . . . . . . . . . . . . . . . . . . . . . 5 - 3.2. Legacy SRLG Advertisements . . . . . . . . . . . . . . . 5 + 3.2. Legacy SRLG Advertisements . . . . . . . . . . . . . . . 6 4. Advertising Application Specific Link Attributes . . . . . . 6 4.1. Application Identifier Bit Mask . . . . . . . . . . . . . 6 - 4.2. Application Specific Link Attributes sub-TLV . . . . . . 8 + 4.2. Application Specific Link Attributes sub-TLV . . . . . . 9 4.2.1. Special Considerations for Maximum Link Bandwidth . . 10 4.2.2. Special Considerations for Reservable/Unreserved Bandwidth . . . . . . . . . . . . . . . . . . . . . . 10 4.2.3. Considerations for Extended TE Metrics . . . . . . . 10 4.3. Application Specific SRLG TLV . . . . . . . . . . . . . . 11 5. Attribute Advertisements and Enablement . . . . . . . . . . . 12 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 13 6.1. Use of Legacy Advertisements . . . . . . . . . . . . . . 13 - 6.2. Use of Zero Length Application Identifier Bit Masks . . . 13 + 6.2. Use of Zero Length Application Identifier Bit Masks . . . 14 6.3. Interoperability, Backwards Compatibility and Migration Concerns . . . . . . . . . . . . . . . . . . . . . . . . 14 6.3.1. Multiple Applications: Common Attributes with RSVP- TE . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.3.2. Multiple Applications: All Attributes Not Shared with RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . 14 6.3.3. Interoperability with Legacy Routers . . . . . . . . 15 6.3.4. Use of Application Specific Advertisements for RSVP- TE . . . . . . . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7.1. Application Specific Link Attributes sub-TLV . . . . . . 16 7.2. Application Specific SRLG TLV . . . . . . . . . . . . . . 16 7.3. Application Specific Link Attributes sub-sub-TLV Registry 16 7.4. Link Attribute Application Identifier Registry . . . . . 17 7.5. SRLG sub-TLVs . . . . . . . . . . . . . . . . . . . . . . 18 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.1. Normative References . . . . . . . . . . . . . . . . . . 19 10.2. Informative References . . . . . . . . . . . . . . . . . 20 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 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 - which makes use of link attribute advertisements - examples of which - are listed in Section 3. + 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 have been introduced which have use - cases for many of the link attributes historically used by RSVP-TE. - Such applications include Segment Routing Traffic Engineering (SRTE) + 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 SRTE support (for - example) it is not possible to unambiguously indicate which + 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 SRTE. If the topologies are fully congruent this may - not be an issue, but any incongruence leads to ambiguity. + 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 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 which 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 which + 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 - so any discussion of existing use cases is - limited to requirements which 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 - which justify the key points identified in the introduction - which - are: + 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 SRTE which is defined in - [I-D.ietf-spring-segment-routing-policy]. If both RSVP-TE and SRTE - 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 SRTE 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. + 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 which may wish to utilize link + 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. 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 https://www.iana.org/assignments/isis- - tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints- - 22-23-25-141-222-223 and https://www.iana.org/assignments/isis-tlv- - codepoints/isis-tlv-codepoints.xhtml . + 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 Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 +-------------------------------------------+ | Type | Description | +-------------------------------------------+ | 3 | Administrative group (color) | +-------------------------------------------+ @@ -244,21 +246,21 @@ Two new code points are defined in support of Application Specific Link Attribute Advertisements: 1) Application Specific Link Attributes 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 which identifies the application(s) associated with a + mask is defined that identifies the application(s) associated with a given advertisement (defined in Section 4.1). 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- @@ -281,42 +283,42 @@ SABM Length + Flag (1 octet) Standard Application Identifier Bit Mask Length + Flag 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| SABM Length | +-+-+-+-+-+-+-+-+ L-flag: Legacy Flag. - See the following section for a description of how + 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 which are set. + 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 which are set. + 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 ... +-+-+-+-+-+-+-+-+... @@ -314,26 +316,26 @@ 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 - Traffic Engineering (SRTE) + S-bit: Set to specify Segment Routing Policy F-bit: Set to specify Loop Free Alternate (LFA) (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 ... @@ -341,49 +343,59 @@ | ... +-+-+-+-+-+-+-+-+... 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. 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. + 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 which + 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. 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 Identifer Bit Mask is + 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. @@ -399,47 +411,51 @@ 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 which is associated with a non-zero + 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 which defines + 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 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 which are making use of the - value for that link. + 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 @@ -486,27 +503,28 @@ 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. TLVs which do not meet this requirement + 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 which are + 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 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 @@ -519,26 +537,27 @@ 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 SRTE, advertisement of application specific link - attributes does not indicate enablement of SRTE on that link. The - advertisements are only used to support constraints which may be - applied when specifying an explicit path. SRTE is implicitly enabled - on all links which are part of the Segment Routing enabled topology - independent of the existence of link attribute advertisements + 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. @@ -556,74 +575,74 @@ 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 which were already deployed in some networks prior to - the writing of this document. Therefore, such applications have been + 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 SRTE or LFA and RSVP-TE is not deployed + o The application is SR Policy or LFA and RSVP-TE is not deployed anywhere in the network - o The application is SRTE or LFA, RSVP-TE is deployed in the - network, and both the set of links on which SRTE and/or LFA - advertisements are required and the attribute values used by SRTE - and/or LFA on all such links is fully congruent with the links and - attribute values used by RSVP-TE + 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 which support the + 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 - SRTE and/or LFA. This will require implementations to provide + 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 which future documents define to make use of the + 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. 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, SRTE, and/or LFA utilize the legacy - advertisements listed in Section 3. 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 + 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 which + 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, @@ -632,100 +651,101 @@ 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 which have the L-flag clear. In cases where + 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. - The discussion in this section applies 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 + 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 which do not + 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 which has any of the applications + 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, SRTE, 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 application specific advertisements can be achieved - via the following steps: + (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 application specific advertisements can be + achieved via the following steps: 1)Send application specific 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 application specific 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 which make use of the application + 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 which do not support the new application. + 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 2)Advertise all legacy link attributes using application specific - advertisements with L-flag clear and R-bit set. + 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. + 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. + 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- @@ -751,24 +771,24 @@ 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 - which defines the encoding is different from the document which - assigns the codepoint, the encoding reference MUST be to the document - which defines the encoding. + 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 @@ -776,21 +796,21 @@ the assignment of Application Identifier Bits. The suggested name of the new registry is "Link Attribute Applications". The registration policy for this registry is "Standards Action" [RFC8126]. Bit definitions SHOULD be assigned in ascending bit order beginning with Bit 0 so as to minimize the number of octets that will need to be transmitted. The following assignments are made by this document: Bit # Name --------------------------------------------------------- 0 RSVP-TE (R-bit) - 1 Segment Routing Traffic Engineering (S-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 @@ -803,37 +823,40 @@ 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 - which defines the encoding is different from the document which - assigns the codepoint, the encoding reference MUST be to the document - which defines the encoding. + 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]. + 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. This is similar in nature to the impacts associated - with (for example) [RFC5305]. As the advertisements defined in this - document limit the scope to specific applications, the impact of - tampering is similarly limited in scope. + Engineering as discussed in [RFC8570]. As the advertisements defined + 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