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| author | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
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| committer | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
| commit | 4bfd864f10b68b71482b35c818559068ef8d5797 (patch) | |
| tree | e3989f47a7994642eb325063d46e8f08ffa681dc /doc/rfc/rfc7813.txt | |
| parent | ea76e11061bda059ae9f9ad130a9895cc85607db (diff) | |
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diff --git a/doc/rfc/rfc7813.txt b/doc/rfc/rfc7813.txt new file mode 100644 index 0000000..9b677d2 --- /dev/null +++ b/doc/rfc/rfc7813.txt @@ -0,0 +1,1851 @@ + + + + + + +Internet Engineering Task Force (IETF) J. Farkas, Ed. +Request for Comments: 7813 Ericsson +Category: Standards Track N. Bragg +ISSN: 2070-1721 Ciena + P. Unbehagen + Avaya + G. Parsons + Ericsson + P. Ashwood-Smith + Huawei Technologies + C. Bowers + Juniper Networks + June 2016 + + + IS-IS Path Control and Reservation + +Abstract + + IEEE 802.1Qca Path Control and Reservation (PCR) specifies explicit + path control via IS-IS in Layer 2 networks in order to move beyond + the shortest path capabilities provided by IEEE 802.1aq Shortest Path + Bridging (SPB). IS-IS PCR provides capabilities for the + establishment and control of explicit forwarding trees in a Layer 2 + network domain. This document specifies the sub-TLVs for IS-IS PCR. + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 7841. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc7813. + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 1] + +RFC 7813 IS-IS PCR June 2016 + + +Copyright Notice + + Copyright (c) 2016 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 + 3. Terminology and Definitions . . . . . . . . . . . . . . . . . 4 + 4. Explicit Trees . . . . . . . . . . . . . . . . . . . . . . . 6 + 5. Explicit ECT Algorithms . . . . . . . . . . . . . . . . . . . 9 + 6. IS-IS PCR Sub-TLVs . . . . . . . . . . . . . . . . . . . . . 11 + 6.1. Topology Sub-TLV . . . . . . . . . . . . . . . . . . . . 11 + 6.2. Hop Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . 15 + 6.3. Bandwidth Constraint Sub-TLV . . . . . . . . . . . . . . 19 + 6.4. Bandwidth Assignment Sub-TLV . . . . . . . . . . . . . . 21 + 6.5. Timestamp Sub-TLV . . . . . . . . . . . . . . . . . . . . 23 + 7. MRT-FRR Application . . . . . . . . . . . . . . . . . . . . . 24 + 8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 29 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 30 + 11.2. Informative References . . . . . . . . . . . . . . . . . 31 + Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 32 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 2] + +RFC 7813 IS-IS PCR June 2016 + + +1. Introduction + + IEEE 802.1Qca Path Control and Reservation (PCR) [IEEE8021Qca] + specifies extensions to IS-IS for the control of Explicit Trees + (ETs). The PCR extensions are compatible with the Shortest Path + Bridging (SPB) extensions to IS-IS specified by [RFC6329] and + [IEEE8021aq] (already rolled into [IEEE8021Q]). Furthermore, IS-IS + with PCR extensions relies on the SPB architecture and terminology, + and some of the IS-IS SPB sub-TLVs are also leveraged. IS-IS PCR + builds upon IS-IS and uses IS-IS in a similar way to SPB. IS-IS PCR + only addresses point-to-point physical links, although IS-IS also + supports shared media LANs. + + This document specifies five IS-IS sub-TLVs for the control of + explicit trees by IS-IS PCR in a Layer 2 network as specified by IEEE + Std 802.1Qca. In addition to the sub-TLVs specified here, IS-IS PCR + relies on the following IS-IS SPB sub-TLVs specified by [RFC6329]: + + o SPB Link Metric sub-TLV + + o SPB Base VLAN-Identifiers sub-TLV + + o SPB Instance sub-TLV + + o SPBV MAC address sub-TLV + + o SPBM Service Identifier and Unicast Address sub-TLV + + These sub-TLVs are used to provide the link metric and the + associations among bridges, Media Access Control (MAC) addresses, + VLAN IDs (VIDs), and I-SIDs within an IS-IS domain. The use of these + SPB sub-TLVs for PCR is specified by IEEE Std 802.1Qca. Note that + IS-IS PCR does not require the implementation of the full IS-IS SPB + protocol but only the support of these SPB sub-TLVs. A bridge can + support both IS-IS SPB and IS-IS PCR at the same time; however, when + it supports both, they are implemented by the same IS-IS entity on a + per-instance basis. + + The sub-TLVs specified in this document can also be applied for Fast + Reroute using Maximally Redundant Trees (MRT-FRR) [RFC7812] in a + Layer 2 network. Maximally Redundant Trees (MRTs) are computed as + specified in [RFC7811]. If MRT computation is split such that the + Generalized Almost Directed Acyclic Graph (GADAG) is computed + centrally, then these sub-TLVs can be used to distribute the GADAG, + which is identical for each network node throughout a network domain. + + PCR uses IS-IS, the SPB sub-TLVs listed above, and the new sub-TLVs + defined in this document. IS-IS PCR has no impact on IETF protocols. + + + +Farkas, et al. Standards Track [Page 3] + +RFC 7813 IS-IS PCR June 2016 + + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + +3. Terminology and Definitions + + This document uses the terminology defined in [RFC7812]. Only the + abbreviations are resolved here for the MRT terms; please refer to + [RFC7812] for the complete definition. + + ADAG: Almost Directed Acyclic Graph [RFC7812] + + B-VID: Backbone VID [IEEE8021Q] + + Base VID: The VID used to identify a VLAN in management operations. + [IEEE8021Q] + + BLCE: Bridge Local Computation Engine - A computation engine in a + bridge that performs path and routing computations. The BLCE + implements e.g., SPF, CSPF, or the Maximally Redundant Trees + algorithm. [IEEE8021Qca] + + Constrained tree: A tree meeting a certain constraint, e.g., + providing minimally available bandwidth. [IEEE8021Qca] + + CSPF: Constrained Shortest Path First + + DAG: Directed Acyclic Graph [RFC7812] + + DEI: Drop Eligible Indicator [IEEE8021Q] + + ECT Algorithm: Equal-Cost Tree algorithm - The algorithm and + mechanism that is used for the control of the active topology, + i.e., forwarding trees. It can be one of the shortest path + algorithms specified by [IEEE8021Q]. It can be also one of the + explicit path-control algorithms specified by [IEEE8021Qca]. Each + ECT Algorithm has a 32-bit unique ID. + + ET: Explicit Tree - An explicitly defined tree, which is specified + by its Edge Bridges and the paths among the Edge Bridges. If only + the Edge Bridges are specified but the paths are not, then it is a + loose explicit tree. If the paths are also specified, then it is + a strict explicit tree. [IEEE8021Qca] + + ETDB: Explicit Tree Database - A database storing explicit trees. + [IEEE8021Qca] + + + +Farkas, et al. Standards Track [Page 4] + +RFC 7813 IS-IS PCR June 2016 + + + FDB: Filtering Database [IEEE8021Q] + + GADAG: Generalized ADAG [RFC7812] + + Hop: A hop is specified by two nodes. A strict hop has no + intermediate nodes, whereas a loose hop can have one or more + intermediate nodes. IS-IS PCR specifies an explicit tree by an + ordered list of hops starting at the root, each successive hop + being defined by the next element of the list. [IEEE8021Qca] + + I-SID: Backbone Service Instance Identifier - A 24-bit ID. + [IEEE8021Q] + + LSDB: Link State Database + + MRT: Maximally Redundant Trees [RFC7812] + + MRT-Blue: MRT-Blue is used to describe one of the two MRTs. + [RFC7812] + + MRT-Red: MRT-Red is used to describe one of the two MRTs. [RFC7812] + + MRT Root: The common root of the two MRTs: MRT-Blue and MRT-Red. + + MSRP: Multiple Stream Registration Protocol, standardized as IEEE + Std 802.1Qat, already rolled into [IEEE8021Q]. + + PCA: Path Control Agent - The agent that is part of the IS-IS domain + and thus can perform IS-IS operations on behalf of a PCE, e.g., + maintain the LSDB and send LSPs. [IEEE8021Qca] + + PCE: Path Computation Element - An entity that is capable of + computing a path through a network based on a representation of + the topology of the network (obtained by undefined means external + to the PCE). [RFC4655] + + PCP: Priority Code Point, which identifies a traffic class. + [IEEE8021Q] + + PTP: Precision Time Protocol specified by [IEEE1588]. + + SPB: Shortest Path Bridging + + SPBM: SPB MAC - The SPB mode where a MAC or its shorthand + (SPSourceID: Shortest Path Source ID) is used to identify an SPT. + [IEEE8021Q] + + + + + +Farkas, et al. Standards Track [Page 5] + +RFC 7813 IS-IS PCR June 2016 + + + SPBV: SPB VID - The SPB mode where a unique VID is assigned to each + SPT Root bridge and is used to identify an SPT. [IEEE8021Q] + + SPF: Shortest Path First + + SPT: Shortest Path Tree [IEEE8021Q] + + SRLG: Shared Risk Link Group - A set of links that share a resource + whose failure affects each link. [RFC5307] + + TAI: Temps Atomique International - International Atomic Time + [IEEE1588] + + TED: Traffic Engineering Database - A database storing the traffic + engineering information propagated by IS-IS. [RFC5305] + + VID: VLAN ID [IEEE8021Q] + + VLAN: Virtual Local Area Network [IEEE8021Q] + +4. Explicit Trees + + Explicit trees may be determined in some fashion. For example, an + explicit tree may be determined by a Path Computation Element (PCE) + [RFC4655]. A PCE is an entity that is capable of computing a + topology for forwarding based on a network topology, its + corresponding attributes, and potential constraints. If a PCE is + used, it MUST explicitly specify an explicit tree as described in + Section 6.1. Either a single PCE or multiple PCEs determine explicit + trees for a domain. Even if there are multiple PCEs in a domain, + each explicit tree MUST only be determined by one PCE, which is + referred to as the owner PCE of the tree. PCEs and IS-IS PCR can be + used in combination with IS-IS SPB shortest path routing. The + remainder of this section, and subsequent sections, are written + assuming PCE use. + + The PCE interacts with the active topology control protocol, i.e., + with IS-IS. The collaboration with IS-IS can be provided by a Path + Control Agent (PCA) on behalf of a PCE. Either the PCE or the + corresponding PCA is part of the IS-IS domain. If the PCE is not + part of the IS-IS domain, then the PCE MUST be associated with a PCA + that is part of the IS-IS domain. The PCE or its PCA MUST establish + IS-IS adjacency in order to receive all the LSPs transmitted by the + bridges in the domain. The PCE, either on its own or via its PCA, + can control the establishment of explicit trees in that domain by + injecting an LSP conveying an explicit tree and thus instruct IS-IS + to set up the explicit tree determined by the PCE. If instructed to + do so by a PCE, IS-IS MAY also record and communicate bandwidth + + + +Farkas, et al. Standards Track [Page 6] + +RFC 7813 IS-IS PCR June 2016 + + + assignments, which MUST NOT be applied if reservation protocol (e.g., + Multiple Stream Registration Protocol (MSRP)) is used in the domain. + Both MSRP and IS-IS MUST NOT be used to make bandwidth assignments in + the same domain. + + The operation details of the PCE are not specified by this document + or by IEEE Std 802.1Qca. If the PCE is part of the IS-IS domain, + then the PCE uses IS-IS PDUs to communicate with the IS-IS domain and + the PCE has a live IS-IS LSDB (i.e., the PCE implements the PCA + functions too). A PCE can instead communicate with the IS-IS domain + via a PCA, e.g., to retrieve the LSDB or instruct the creation of an + explicit tree. However, the means of communication between the PCE + and the PCA is not specified by this document or by IEEE Std + 802.1Qca. + + An Explicit Tree (ET) is an undirected loop-free topology, whose use + is under the control of the owner PCE by means of associating VIDs + and MAC addresses with it. An ET MUST NOT contain cycles. As it is + undirected, an ET contains no assumptions about the direction of any + flows that use it; it can be used in either direction as specified by + the VIDs and MAC addresses associated with it. It is the + responsibility of the PCE to ensure reverse-path congruency and + multicast-unicast congruency if that is required. + + An explicit tree is either strict or loose. A strict explicit tree + specifies all bridges and paths it comprises. A loose tree only + specifies the bridges as a list of hops that have a special role in + the tree, e.g., an Edge Bridge, and no path or path segment is + specified between the bridges, which are therefore loose hops even if + Edge Bridges are adjacent neighbors. The special role of a hop can + be: Edge Bridge, root, leaf, a bridge to be avoided, or a transit hop + in case of a tree with a single leaf. The path for a loose hop is + determined by the Bridge Local Computation Engine (BLCE) of the + bridges. The shortest path is used for a loose hop unless specified + otherwise by the descriptor (Section 6.1) of the tree or by the + corresponding ECT Algorithm (Section 5). + + A loose explicit tree is constrained if the tree descriptor includes + one or more constraints, e.g., the administrative group that the + links of the tree have to belong to. The BLCE of the bridges then + applies the Constrained Shortest Path First (CSPF) algorithm, which + is Shortest Path First (SPF) on the topology that only contains the + links meeting the constraint(s). + + An explicit tree is specified by a Topology sub-TLV (Section 6.1). + The Topology sub-TLV associates one or more VIDs with an explicit + tree. The Topology sub-TLV includes two or more Hop sub-TLVs + (Section 6.2), and a hop is specified by an IS-IS System ID. A Hop + + + +Farkas, et al. Standards Track [Page 7] + +RFC 7813 IS-IS PCR June 2016 + + + sub-TLV MAY include a delay constraint for a loose hop. A Topology + sub-TLV MAY also include further sub-TLVs to constrain loose hops. + The bridges involved in an explicit tree store the corresponding + Topology sub-TLVs in their Explicit Tree Database (ETDB). + + Explicit trees are propagated and set up by IS-IS PCR in a domain. + The PCE or its PCA assembles the Topology sub-TLVs (Section 6.1), and + adds it into an LSP, which is flooded throughout the domain. The + Topology sub-TLV is flooded by the same techniques used for the SPB + LSPs. The bridges then MUST process the Topology sub-TLV upon + reception. If the Topology sub-TLV specifies one or more loose + trees, then the path for the loose hops is determined by the BLCE of + the bridges. The bridges then install the appropriate FDB entries + for frame forwarding along the tree described by the Topology sub-TLV + or the trees computed based on the Topology sub-TLV. Dynamic + Filtering Entries are maintained by IS-IS for the [VID, MAC address] + two-tuples associated with an ET. + + Due to the LSP aging of IS-IS, the Topology sub-TLVs (Section 6.1) + have to be refreshed similar to other IS-IS TLVs in order to keep the + integrity of the LSDB. The corresponding Dynamic Filtering Entries + are also refreshed in the FDB when a Topology sub-TLV is refreshed. + Refreshing Topology sub-TLVs is the task of the entity being part of + the IS-IS domain, i.e., either the PCE or the PCA. + + The owner PCE can withdraw an explicit tree by sending an updated LSP + that does not include the Topology sub-TLV (Section 6.1). If a + Topology sub-TLV is removed from an LSP (or has been changed) so that + (previous) Topology sub-TLV is no longer present (or has been + changed) in the LSDB, then that (previous) Topology sub-TLV is + implicitly withdrawn. IS-IS PCR then removes (or updates) the + explicit tree. + + There is no precedence order between explicit trees. Precedence + order among bandwidth assignments recorded by IS-IS PCR is specified + in Section 6.4. + + If it is not possible to install an explicit tree, e.g., + constraint(s) cannot be met or the Topology sub-TLV is ill-formed, + then no tree is installed, but a management report is generated. + + The bridges MAY support the following IS-IS features for the + computation of explicit trees. The Extended IS Reachability TLV + (type 22) specified in [RFC5305] provides the following link + attribute IS-IS sub-TLVs: + + o Administrative Group (color) (sub-TLV type 3), + + + + +Farkas, et al. Standards Track [Page 8] + +RFC 7813 IS-IS PCR June 2016 + + + o Maximum Link Bandwidth (sub-TLV type 9), + + o Maximum Reservable Link Bandwidth (sub-TLV type 10), + + o Unreserved Bandwidth (sub-TLV type 11), + + o TE Default Metric (sub-TLV type 18). + + When the Unreserved Bandwidth sub-TLV is used in a Layer 2 bridge + network, the priority value encoded in the sub-TLV provides the PCP, + i.e., identifies a traffic class (not a setup priority level). + + Further attributes are provided by the IS-IS TE Metric Extension link + attribute sub-TLVs specified in [RFC7810]: + + o Unidirectional Link Delay (sub-TLV type 33), + + o Min/Max Unidirectional Link Delay (sub-TLV type 34), + + o Unidirectional Delay Variation (sub-TLV type 35), + + o Unidirectional Link Loss (sub-TLV type 36), + + o Unidirectional Residual Bandwidth (sub-TLV type 37), + + o Unidirectional Available Bandwidth (sub-TLV type 38), + + o Unidirectional Utilized Bandwidth (sub-TLV type 39). + + The Shared Risk Link Group (SRLG) information provided by the SRLG + TLV (type 138) [RFC5307] MAY also be used. In order to indicate that + the interface is unnumbered in this case, the corresponding flag + takes value 0. The Link Local Identifier is an Extended Local + Circuit Identifier and the Link Remote Identifier is a Neighbor + Extended Local Circuit ID. + +5. Explicit ECT Algorithms + + The exact IS-IS control mode of operation MUST be selected for a VLAN + by associating its Base VID with the appropriate ECT Algorithm in the + SPB Base VLAN-Identifiers sub-TLV [RFC6329], in addition to + allocating the Base VID to IS-IS control. There are five distinct + ECT Algorithms for the five explicit path control modes. The + operation details of the explicit ECT Algorithms and their + configuration is specified by IEEE Std 802.1Qca; a high-level + overview is given here. An ECT Algorithm value consists of the IEEE + 802.1 OUI (Organizationally Unique Identifier) value 00-80-C2 + concatenated with an index [RFC6329]. + + + +Farkas, et al. Standards Track [Page 9] + +RFC 7813 IS-IS PCR June 2016 + + + The Strict Tree (ST) ECT Algorithm MUST be used for a strict explicit + tree. A strict ET is static, as no other entity can update it but + the owner PCE. In case of a topology change, it is the task of the + owner PCE to detect the topology change, e.g., based on the changes + in the LSDB and to update the strict trees if needed. That is, the + owner PCE computes the new tree, assembles its descriptor + (Section 6.1), and then instructs IS-IS PCR to install it. The value + for the ST ECT Algorithm is 00-80-C2-17. + + The Loose Tree (LT) ECT Algorithm MAY also be supported. It is used + for a single loose explicit tree. The path for loose hops is + determined by the BLCE of the bridges; therefore, the Topology sub- + TLV (Section 6.1) specifying the tree MUST indicate which hop is the + root of the tree. The loose hops are maintained by IS-IS, i.e., + restored upon a topology change if a loop-free path is available. If + the tree computed by the BLCE visits the same bridge twice (implying + that a loop or hairpin has been created), then that loop or hairpin + MUST be pruned from the tree even if it contains a hop specified by + the Topology sub-TLV. It is a constraint if a bridge is not to be + included, which can be specified by the Exclude flag of a Hop sub-TLV + (Section 6.2) conveyed by the Topology sub-TLV specifying the tree. + The range of values for the LT ECT Algorithms is + 00-80-C2-21...00-80-C2-30. + + The Loose Tree Set (LTS) ECT Algorithm MAY also be supported. It is + used if connectivity among the Edge Bridges specified by the Topology + sub-TLV (Section 6.1) is to be provided by a set of loose trees such + that one tree is rooted at each Edge Bridge. The BLCE of the bridges + compute the loose trees, which are maintained by IS-IS, i.e., + restored upon a topology change. One constraint can be to avoid some + bridges in these trees, which can be specified by the Exclude flag + (item c.6. in Section 6.2). Further constraints can be specified by + the Topology sub-TLV. The range of values for the LT ECT Algorithms + is 00-80-C2-31...00-80-C2-40. + + The LT and LTS ECT Algorithms use the shortest paths after pruning + the topology according to the constraint(s), if any. The shortest + path tie-breaking specified by Section 12 of [RFC6329] is applied + (see also subclauses 28.5 - 28.8 of [IEEE8021aq]), that's why range + of values are associated with the LT and LTS ECT Algorithms. In case + of the LT ECT Algorithm, the indexes are 0x21...0x30, and + ECT-MASK{index-0x20} is applied to retrieve the ECT-MASK of + Section 12 of [RFC6329]. In case of the LTS ECT Algorithm, the + indexes are 0x31...0x40, and ECT-MASK{index-0x30} is applied to + retrieve the ECT-MASK for shortest path tie-breaking. + + + + + + +Farkas, et al. Standards Track [Page 10] + +RFC 7813 IS-IS PCR June 2016 + + + The MRT ECT Algorithm MAY also be supported. It is used for the + establishment and maintenance of MRTs in a distributed fashion. The + MRT Lowpoint algorithm specified by [RFC7811] MUST be used for the + computation of MRTs. The MRT Lowpoint algorithm first computes the + GADAG and then produces two MRTs for each MRT Root: MRT-Blue and MRT- + Red. If the level of redundancy provided by each bridge being an MRT + Root is not required, then the MRT Roots can be specified by a + Topology sub-TLV (Section 6.1). Both the GADAG and the MRT + computation steps are performed distributed, i.e., by each bridge. + The value for the MRT ECT Algorithm is 00-80-C2-18. + + The MRT GADAG (MRTG) ECT Algorithm MAY also be supported. It splits + the computation into two. As the GADAG is identical for each MRT + within a domain, it is computed by a single entity, which is the + GADAG Computer. The GADAG is then described in a Topology sub-TLV + (Section 6.1), which is flooded in the domain. The bridges then + compute the MRTs for the MRT Roots based on the GADAG received. + Section 7 provides more details on the description of the GADAG. The + value for the MRTG ECT Algorithm is 00-80-C2-19. + + MRTs are loose trees as bridges are involved in their computation and + restoration. Thus, both the MRT and the MRTG ECT Algorithms provide + a set of loose trees: two MRTs for each MRT Root. + + The SPB Link Metric sub-TLV [RFC6329] specifies the metric of each + link for IS-IS PCR if the LT, the LTS, the MRT, or the MRTG ECT + Algorithm is used. If the SPB Link Metric values advertised by + different ends of an adjacency are different, then the maximum value + MUST be used. + +6. IS-IS PCR Sub-TLVs + + The following sub-TLVs are specified for IS-IS PCR. The Topology + sub-TLV MUST be carried in an MT-Capability TLV, the rest of the sub- + TLVs are conveyed by the Topology sub-TLV. + +6.1. Topology Sub-TLV + + An explicit tree MUST be described by the variable-length Topology + sub-TLV. A Generalized Almost Directed Acyclic Graph (GADAG) MAY be + described by a Topology sub-TLV as explained in Section 7 in detail. + The Topology sub-TLV MUST be carried in an MT-Capability TLV (type + 144) [RFC6329] in a Link State PDU. A Topology sub-TLV specifying an + explicit tree conveys one or more Base VIDs, two or more Hop sub-TLVs + (Section 6.2). A Topology sub-TLV describing a loose tree MAY also + convey further sub-TLVs to specify constraints. Figure 1 shows the + format of the Topology sub-TLV. + + + + +Farkas, et al. Standards Track [Page 11] + +RFC 7813 IS-IS PCR June 2016 + + + 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 | (1 byte) + +-+-+-+-+-+-+-+-+ + | Length | (1 byte) + +-+-+-+-+-+-+-+-+ + | Num Base VIDs | (1 byte) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Res | Base VID 1 (12 bits) | (2 bytes if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ................. + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Res | Base VID n (12 bits) | (2 bytes if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | sub-TLV 1 (variable) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ................. + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | sub-TLV m (variable) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 1: Topology Sub-TLV + + The parameters of explicit trees are encoded by the Topology sub-TLV + as follows: + + a. Type (8 bits): The type of the sub-TLV, its value is 21. + + b. Length (8 bits): The total number of bytes contained in the Value + field. + + c. Number of Base VIDs (8 bits): The number of Base VIDs carried in + the Topology sub-TLV. Its minimum value is 1 if the Topology + sub-TLV specifies one or more explicit trees. Its value can be 0 + if the Topology sub-TLV specifies a GADAG. + + d. Reserved (Res) (4 bits): The reserved bits MUST be set to 0 on + transmission and the value MUST be ignored on reception. + + e. Base VID (12 bits): The Base VID parameter provides the Base VID + of the VLAN that is associated with the explicit tree. Multiple + Base VIDs can be associated with the same explicit tree. In + addition to the Base VID, some of the explicit ECT Algorithms + (Section 5) require further VIDs that are associated with the + VLAN via the SPB Instance sub-TLV [RFC6329]. A Topology sub-TLV + specifying a GADAG can have zero Base VID parameters. In this + + + + +Farkas, et al. Standards Track [Page 12] + +RFC 7813 IS-IS PCR June 2016 + + + case, the given GADAG MUST be applied for each VLAN associated + with the MRTG ECT Algorithm (Section 5). + + f. sub-TLVs: The rest conveys further sub-TLVs that specify the hops + of the topology and can also specify constraints as described in + the following. + + A topology is specified by a list of Hop sub-TLVs (Section 6.2), and + a hop is specified by an IS-IS System ID. An ill-formed Topology + sub-TLV (e.g., specifying an invalid or inconsistent tree) is + ignored; no tree is installed, but a management report is generated. + + The Topology sub-TLV specifies a strict tree by decomposing the tree + to branches. Each branch is a point-to-point path specified by an + ordered list of hops where the end of each branch is a leaf. Each + element of a branch is the direct link between adjacent neighbor + bridges whose Hop sub-TLV is next to each other in the Topology sub- + TLV. The first hop of the Topology sub-TLV is the root; hence, the + first branch originates from the root. The rest of the branches fork + from another branch. The first hop of a branch is a bridge that is + already part of a former branch, and the last hop is a leaf bridge. + Therefore, the hop after a leaf hop is the beginning of a new branch, + if any. A hop of a branch is created if and only if the bridge + specified for that hop is directly connected to the preceding bridge + of the same branch. The first branch MUST begin with the root; after + that, the order of the branches does not matter within the Topology + sub-TLV. Figure 2 shows an example strict tree and its description. + + + + + + + + + + + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 13] + +RFC 7813 IS-IS PCR June 2016 + + + +-----------+ + | A | + +-----------+ + | I | + +-----------+ + | H | + [B]---[A]---[I] +-----------+ + | | | G | + | | +-----------+ + | | | E | + [C]---[F] [H] +-----------+ + | | | A | + | | +-----------+ + | | | B | + [D] [E]---[G] +-----------+ + | C | + +-----------+ + | D | + +-----------+ + | C | + +-----------+ + | F | + +-----------+ + + Figure 2: A Strict Tree and Its Description; Root = Node A + + The Topology sub-TLV of a loose tree does not provide any path or + path segment other than the hops that are to participate. The root + MUST be the first hop. The leaves of a single loose tree MUST also + be specified. Hop sub-TLVs can be included in a Topology sub-TLV to + specify bridges that have to be avoided. If the Topology sub-TLV + only specifies a single leaf, then one or more transit hops can be + specified by the Topology sub-TLV to direct the path along a sequence + of bridges, specified by the order of hops. If bridges whose + respective Hop sub-TLVs are adjacent to each other in the Topology + sub-TLV are not topology neighbors, then it is a loose hop. If a + Topology sub-TLV conveys one or more loose hops, then that sub-TLV + defines a loose explicit tree and each hop is considered to be a + loose hop. The path of a loose hop MUST be pruned from the tree if + the path would create a loop or hairpin. + + If the Base VIDs of the Topology sub-TLV are associated with the LTS + ECT Algorithm or the MRT ECT Algorithm, then the Hop sub-TLVs + conveyed by the Topology sub-TLV belong to Edge Bridges or bridges to + be excluded. The BLCEs compute the loose trees, e.g., MRTs, such + that they span the Edge Bridges and are rooted at an Edge Bridge. + + + + + +Farkas, et al. Standards Track [Page 14] + +RFC 7813 IS-IS PCR June 2016 + + + The Topology sub-TLV specifies a GADAG if the Base VIDs conveyed by + the Topology sub-TLV are associated with the MRTG ECT Algorithm. + Section 7 provides the details on the description of a GADAG by a + Topology sub-TLV. + + Each Edge Bridge of an explicit tree MUST always be specified in the + Topology sub-TLV by the inclusion of the Hop sub-TLVs corresponding + to the Edge Bridges. The Edge Bridges of a tree are identified by + setting the Edge Bridge flag (item c.3. in Section 6.2) in the + appropriate Hop sub-TLVs. + + If the explicit tree is loose, then the Topology sub-TLV MAY convey + further sub-TLVs to specify constraints, e.g., an Administrative + Group sub-TLV [RFC5305] or a Bandwidth Constraint (Section 6.3). If + it is not possible to meet the constraint(s) specified by the + Topology sub-TLV, then no tree is installed but a management report + is generated. + + IS-IS PCR MAY be used for recording bandwidth assignment. In that + case, the Topology sub-TLV conveys Bandwidth Assignment sub-TLV + (Section 6.4), and it MAY also convey Timestamp sub-TLV + (Section 6.5). If assignment of the bandwidth indicated by the + Bandwidth Assignment sub-TLV of the Topology sub-TLV would result in + overbooking any link of the explicit tree, then bandwidth assignment + MUST NOT be performed and a management report is generated. If the + Topology sub-TLV specifies a new valid explicit tree, then the tree + is installed without bandwidth assignment. + +6.2. Hop Sub-TLV + + The Hop sub-TLV MUST be used to specify a hop of a topology. Each + Hop sub-TLV conveys an IS-IS System ID, which specifies a hop. A Hop + sub-TLV is conveyed by a Topology sub-TLV (Section 6.1). A strict + explicit tree is decomposed to branches where each branch is a point- + to-point path specified by an ordered list of Hop sub-TLVs as + specified in Section 6.1. A hop of a branch is created if and only + if the bridge specified for that hop is directly connected to the + preceding bridge in the path. That is, a point-to-point LAN is + identified by the two bridges it interconnects; and the LAN is part + of the strict tree if and only if the Hop sub-TLVs of the two bridges + are next to each other in the Topology sub-TLV. A Hop sub-TLV can + convey a Circuit ID in order to distinguish multiple links between + adjacent neighbor bridges. A Hop sub-TLV also specifies the role of + a bridge, e.g., if it is the root or an Edge Bridge. The Topology + sub-TLV of a loose tree only comprises the Hop sub-TLV of the bridges + that have a special role in the tree. The Hop sub-TLV MAY also + specify a delay budget for a loose hop. + + + + +Farkas, et al. Standards Track [Page 15] + +RFC 7813 IS-IS PCR June 2016 + + + By default, the Edge Bridges both transmit and receive with respect + to each VID associated with an explicit tree, except for an LTS + (Section 5) associated with a learning VLAN, which uses a + unidirectional VID per bridge. The Hop sub-TLV allows different + configuration by means of the Transmit (T) and Receive (R) flags + conveyed in the sub-TLV. The VID and its T/R flags are only present + in the Hop sub-TLV if the behavior of the Edge Bridges differs from + the default. + + Figure 3 shows the format of the variable length Hop sub-TLV, which + MUST be conveyed by a Topology sub-TLV (Section 6.1). + + 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 | (1 byte) + +-+-+-+-+-+-+-+-+ + | Length | (1 byte) + +-+-+-+-+-+-+-+-+ + |C|V|B|R|L|E|Res| (1 byte) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | System ID | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | System ID | (6 bytes) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Extended Local Circuit ID (4 bytes if present) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Num of VIDs | (1 byte if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |T|R|Res| VID 1 (12 bits) | (2 bytes if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ................. + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |T|R|Res| VID n (12 bits) | (2 bytes if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Delay Constraint | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Delay Constraint | (6 bytes if present) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 3: Hop Sub-TLV + + The parameters of a hop are encoded as follows: + + a. Type (8 bits): The type of the sub-TLV, its value is 22. + + b. Length (8 bits): The total number of bytes contained in the Value + field. + + + +Farkas, et al. Standards Track [Page 16] + +RFC 7813 IS-IS PCR June 2016 + + + c. Hop Flags (8 bits): The Hop sub-TLV conveys six one-bit flags. + The Circuit and the VID flags influence the length of the Hop + sub-TLV. Two bits are reserved for future use, transmitted as 0 + and ignored on receipt. + + 1. Circuit (C) flag (1 bit): The Circuit flag is a one-bit flag + to indicate whether or not the Extended Local Circuit ID + parameter is present. If the flag is set, then an Extended + Local Circuit ID is also included in the Hop sub-TLV. + + 2. VID (V) flag (1 bit): The VID flag is a one-bit flag to + indicate whether or not one or more VIDs are conveyed by the + Hop sub-TLV. If the flag is set, then the Number of VIDs + parameter is present and indicates how many VIDs are conveyed + by the Hop sub-TLV. If the VID flag is reset, then neither + the Number of VIDs parameter nor VIDs are present in the Hop + sub-TLV. + + 3. Edge Bridge (B) flag (1 bit): The Edge Bridge flag is a one- + bit flag to indicate whether or not the given System is an + Edge Bridge, i.e., transmitter and/or receiver. If the + System is an Edge Bridge, then the Edge Bridge flag MUST be + set. The Edge Bridge flag indicates that FDB entries have to + be installed for the given hop as specified by the SPBV MAC + address sub-TLV or SPBM Service Identifier and Unicast + Address sub-TLV of the hop. + + 4. Root (R) flag (1 bit): The Root flag is a one-bit flag to + indicate whether or not the given System is a root of the + explicit tree specified by the Topology sub-TLV. If the + System is a root of a tree, then the Root flag MUST be set. + If the Topology sub-TLV specifies a single tree, i.e., the + Base VIDs conveyed by the Topology sub-TLV are associated + with either the ST ECT Algorithm or the LT ECT Algorithm + (Section 5), then the Root flag is only set for one of the + Systems conveyed by the Topology sub-TLV. Furthermore, the + first Hop sub-TLV of the Topology sub-TLV conveys the System + that is the root of the tree. + If the Topology sub-TLV specifies a Loose Tree Set, i.e., the + Base VIDs conveyed by the Topology sub-TLV are associated + with the LTS ECT Algorithm (Section 5), then the Root flag is + set for each Edge Bridge as each of them roots a tree. + If the Topology sub-TLV is used for MRT operations, i.e., the + Base VIDs conveyed by the Topology sub-TLV are associated + with either the MRT ECT Algorithm or the MRTG ECT algorithm + (Section 5), then the Root flag is set for each MRT Root. If + no MRT Root is specified by a Topology sub-TLV specifying a + GADAG, then each SPT Root is an MRT Root as well. + + + +Farkas, et al. Standards Track [Page 17] + +RFC 7813 IS-IS PCR June 2016 + + + If the Base VIDs conveyed by the Topology sub-TLV are + associated with the MRTG ECT algorithm (Section 5), then the + Topology sub-TLV specifies a GADAG and the very first Hop + sub-TLV specifies the GADAG Root. There is no flag for + indicating the GADAG Root. + + 5. Leaf (L) flag (1 bit): The Leaf flag is a one-bit flag to + indicate whether or not the given System is a leaf of the + explicit tree specified by the Topology sub-TLV. If the + System is a leaf, then the Leaf flag MUST be set. The Leaf + flag is only used to mark a leaf of a tree if the Topology + sub-TLV specifies a single tree. The Leaf flag MUST be used + to indicate the end of a topology block if the Topology sub- + TLV specifies a GADAG, see Section 7. + + 6. Exclude (E) flag (1 bit): The Exclude flag is a one-bit flag + to indicate if the given System MUST be excluded from the + topology. The Exclude flag and the Root flag cannot be set + for a given hop at the same time. + + 7. Reserved (Res) (2 bits): The reserved bits MUST be set to 0 + on transmission, and the value MUST be ignored on reception. + + d. System ID (48 bits): The six-byte IS-IS System Identifier of the + bridge to which the Hop sub-TLV refers. + + e. Extended Local Circuit ID (32 bits): The Extended Local Circuit + ID [RFC5303] parameter is not necessarily present in the Hop sub- + TLV. Its presence is indicated by the Circuit flag. Parallel + links corresponding to different IS-IS adjacencies between a pair + of neighbor bridges can be distinguished by means of the Extended + Local Circuit ID. The Extended Local Circuit ID is conveyed by + the Hop sub-TLV specifying the bridge nearer to the root of the + tree, and identifies a circuit that attaches the given bridge to + its neighbor cited by the next Hop sub-TLV of the Topology sub- + TLV. The Extended Local Circuit ID can only be used in strict + trees. + + f. Number of VIDs (8 bits): The Number of VIDs parameter is not + present if the Hop sub-TLV does not convey VIDs, which is + indicated by the VID flag. + + g. VID and its T/R flags (14 bits): The VID and its T/R flags are + only present in the Hop sub-TLV if the given bridge is an Edge + Bridge and it behaves differently from the default with respect + to that particular VID. + + + + + +Farkas, et al. Standards Track [Page 18] + +RFC 7813 IS-IS PCR June 2016 + + + 1. T flag (1 bit): This is the Transmit allowed flag for the VID + following the flag. + + 2. R flag (1 bit): This is the Receive allowed flag for the VID + following the flag. + + 3. Reserved (Res) (2 bits): The reserved bits MUST be set to 0 + on transmission, and the value MUST be ignored on reception. + + 4. VID (12 bits): A VID. + + h. Delay Constraint (48 bits): A Hop sub-TLV MAY specify a delay + constraint. The Length of the Hop sub-TLV indicates whether or + not a delay constraint is present because the Length of a Hop + sub-TLV conveying a delay constraint is six bytes greater than it + would be without the delay constraint. The last six bytes then + specify a delay constraint if they convey a Unidirectional Link + Delay sub-TLV [RFC7810]. The delay constraint MAY be used in a + Topology sub-TLV that specifies a single loose tree, i.e., the + Base VIDs are associated with the LT ECT Algorithm (Section 5). + If the delay constraint is applied, then the loose hop MUST fit + in the delay budget specified by the Delay parameter of the + Unidirectional Link Delay sub-TLV conveyed by the Hop sub-TLV. + If the Topology sub-TLV specifies a single leaf, then the path + between the preceding Hop sub-TLV and the current Hop sub-TLV + MUST meet the delay budget. If the Topology sub-TLV specifies + multiple leaves, then the path between the root and the current + Hop sub-TLV MUST to meet the delay budget. If the tree is used + as a reverse congruent tree, then the delay constraint applies in + both directions. If the tree is used as a directed tree, then + the delay constraint applies in the direction of the tree. If it + is not possible to meet the delay constraint specified by the + Topology sub-TLV, then no tree is installed but a management + report is generated. + +6.3. Bandwidth Constraint Sub-TLV + + The Bandwidth Constraint sub-TLV MAY be included in a Topology sub- + TLV (Section 6.1) in order to specify how much available bandwidth is + to be provided by the constrained tree. Each loose hop MUST meet the + bandwidth constraint. The bandwidth value of the constraint is a + total value or it only refers to a single PCP as specified by the + sub-TLV. Figure 4 shows the format of the Bandwidth Constraint sub- + TLV. + + + + + + + +Farkas, et al. Standards Track [Page 19] + +RFC 7813 IS-IS PCR June 2016 + + + 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 | (1 byte) + +-+-+-+-+-+-+-+-+ + | Length | (1 byte) + +-+-+-+-+-+-+-+-+ + | PCP |D|P| Res | (1 byte) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Available Bandwidth (4 bytes) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 4: Bandwidth Constraint Sub-TLV + + The parameters of the bandwidth constraint are encoded as follows: + + a. Type (8 bits): The type of the sub-TLV, its value is 23. + + b. Length (8 bits): The total number of bytes contained in the Value + field. The value of the Length field is 5 bytes. + + c. PCP (4 bits): The Priority Code Point (PCP) parameter identifies + the traffic class the Available Bandwidth parameter refers to, if + any. + + d. DEI (D) (1 bit): This is the Drop Eligible Indicator (DEI) + parameter. If the DEI parameter is clear, then the bandwidth + constraint refers to committed information rate. If the DEI + parameter is set, then the bandwidth constraint refers to the + peak information rate. + + e. PCP (P) flag (1 bit): If this flag is set, then the PCP parameter + is taken into account. + + f. Reserved (Res) (3 bits): The reserved bits MUST be set to 0 on + transmission, and the value MUST be ignored on reception. + + g. Available Bandwidth (32 bits): The Available Bandwidth is + specific to the traffic class identified by the PCP parameter if + the PCP flag is set; otherwise, it is total bandwidth. In line + with the bandwidth parameters specified in [RFC5305], the + Available Bandwidth is encoded as a 32-bit IEEE floating-point + number [IEEE754], and the units are bytes (not bits!) per second. + When the Unreserved Bandwidth sub-TLV (sub-TLV type 11 specified + by [RFC5305]) is used in a Layer 2 bridge network, the priority + value encoded in the Unreserved Bandwidth sub-TLV provides the + PCP, i.e., identifies a traffic class (not a setup priority + level). Thus, the Available Bandwidth of a traffic class is + + + +Farkas, et al. Standards Track [Page 20] + +RFC 7813 IS-IS PCR June 2016 + + + easily comparable with the Unreserved Bandwidth stored in the TED + for the given traffic class. The bandwidth constraint applies + for both directions in case of symmetric explicit trees. + Nevertheless, a VID associated with an explicit tree can be made + unidirectional by means of the T/R flags belonging to the VID in + the Hop sub-TLV (item g. in Section 6.2) of the Edge Bridges. If + all the VIDs of the Topology sub-TLV (Section 6.1) are + unidirectional and all belong to the traffic class identified by + the PCP parameter of the Bandwidth Constraint sub-TLV, then it is + enough to meet the bandwidth constraint in the direction applied + for those VIDs. + +6.4. Bandwidth Assignment Sub-TLV + + IS-IS PCR MAY be used for recording bandwidth assignment for + explicitly placed data traffic in a domain if MSRP is not used within + the domain. If MSRP is used in a domain, then only MSRP performs + reservations and IS-IS does not. Both MSRP and IS-IS MUST NOT be + used to make bandwidth assignments in the same domain. + + The Bandwidth Assignment sub-TLV can be used to define the amount of + bandwidth whose assignment is to be recorded by IS-IS PCR at each hop + of the explicit tree described by the corresponding Topology sub-TLV + (Section 6.1). The Bandwidth Assignment sub-TLV is used by IS-IS PCR + for the recording of bandwidth assignment for a traffic class + identified by the PCP parameter of a VLAN tag. If precedence order + has to be determined among bandwidth assignments in a domain with + multiple PCEs, then IS-IS PCR does it as described below. If the + bandwidth assignment specified by the Topology sub-TLV is not + possible, e.g., due to overbooking, then bandwidth recording MUST NOT + be performed and a management report is generated. If the Topology + sub-TLV specifies a new valid explicit tree, then the tree is + installed without bandwidth assignment. The Bandwidth Assignment + sub-TLV is conveyed by a Topology sub-TLV (Section 6.1). Figure 5 + shows the format of the Bandwidth Assignment sub-TLV. + + + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 21] + +RFC 7813 IS-IS PCR June 2016 + + + 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 | (1 byte) + +-+-+-+-+-+-+-+-+ + | Length | (1 byte) + +-+-+-+-+-+-+-+-+ + | PCP |D| Imp |R| (1 byte) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Bandwidth (4 bytes) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: Bandwidth Assignment Sub-TLV + + The parameters of the bandwidth assignment are encoded as follows: + + a. Type (8 bits): The type of the sub-TLV, its value is 24. + + b. Length (8 bits): The total number of bytes contained in the Value + field. The value of the Length field is 5 bytes. + + c. PCP (3 bits): The PCP parameter identifies the traffic class for + which the bandwidth is to be assigned. + + d. DEI (D) (1 bit): This is the Drop Eligible Indicator (DEI) + parameter. If the DEI parameter is clear, then the bandwidth + assignment is performed for providing the committed information + rate. If the DEI parameter is set, then the bandwidth assignment + is performed for providing the peak information rate. + + e. Importance (Imp) (3 bits): This is the Importance parameter for + determining precedence order among bandwidth assignments within a + PCP as described below. A lower numerical value indicates more + important bandwidth assignment within a PCP. The default value + of the Importance parameter is 7. + + f. Reserved (R) (1 bit): The reserved bit MUST be set to 0 on + transmission, and the value MUST be ignored on reception. + + g. Bandwidth (32 bits): This is the amount of bandwidth to be + assigned for the traffic class identified by the PCP parameter. + In line with the bandwidth values specified in [RFC5305], the + Bandwidth parameter is encoded as a 32-bit IEEE floating-point + number [IEEE754], and the units are bytes (not bits!) per second. + The bandwidth assignment applies for both directions in case of + symmetric explicit trees. + + + + + +Farkas, et al. Standards Track [Page 22] + +RFC 7813 IS-IS PCR June 2016 + + + The PCEs are collectively responsible for making a consistent set of + bandwidth assignments when IS-IS PCR is used for recording bandwidth + allocations. If, despite that, precedence ordering is required among + bandwidth assignments, then ordering based on the following + parameters MUST be applied: + + 1. PCP parameter of Bandwidth Assignment sub-TLV, + + 2. Importance parameter of Bandwidth Assignment sub-TLV, + + 3. Timestamp sub-TLV (if present in the Topology sub-TLV). + + A bandwidth assignment takes precedence if it has a higher PCP, or a + higher Importance within a PCP, or an earlier timestamp in case of + equal Importance within a PCP. A bandwidth assignment associated + with a timestamp takes precedence over a bandwidth assignment without + a timestamp when PCP and Importance of different bandwidth + assignments are both equal. If resolution is not possible based on + the above parameters or they are not available, e.g., each bandwidth + assignment lacks a timestamp or the precedence order has to be + determined for the use of a VID, then the item is granted to the PCE + whose LSP has the numerically lowest LSP ID. + +6.5. Timestamp Sub-TLV + + The Timestamp sub-TLV MAY be included in a Topology sub-TLV + (Section 6.1) in order to provide precedence order among equally + important bandwidth assignments within a PCP as described in + Section 6.4. Figure 6 shows the format of the Timestamp sub-TLV. + + 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 | (1 byte) + +-+-+-+-+-+-+-+-+ + | Length | (1 byte) + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Time (4 bytes) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: Timestamp Sub-TLV + + The timestamp represents a positive time with respect to the + Precision Time Protocol (PTP) epoch, and it is encoded as follows: + + a. Type (8 bits): The type of the sub-TLV; its value is 25. + + + + + +Farkas, et al. Standards Track [Page 23] + +RFC 7813 IS-IS PCR June 2016 + + + b. Length (8 bits): The total number of bytes contained in the Value + field. The value of the Length field is 4 bytes. + + c. Time (32 bits): This is the time in units of seconds with respect + to the PTP epoch. + + The Timestamp sub-TLV carries the seconds portion of PTP as specified + by [IEEE1588]. The epoch is 1970-01-01 00:00:00 TAI (i.e., the PTP + time does not include leap seconds). + +7. MRT-FRR Application + + The application of MRT by [IEEE8021Qca] is discussed in detail in + [MRT-IEEE8021qca]. This section describes some special + considerations for the use of the MRT Lowpoint algorithm [RFC7811], + which are applicable both to the MRT ECT Algorithm and the MRTG ECT + Algorithm. This section also explains details related to the MRTG + ECT Algorithm and the application of the Topology sub-TLV in + particular. + + IS-IS PCR does not use the MRT Profile specified in [RFC7812]. IS-IS + PCR only relies on the algorithm specification in [RFC7811]. Both + the MRT ECT Algorithm and the MRTG ECT Algorithm use the MRT Lowpoint + algorithm specified in [RFC7811]. + + The SPB Link Metric sub-TLV [RFC6329] specifies the metric of each + link for IS-IS PCR including the MRT algorithms. If the SPB Link + Metric values advertised by different ends of an adjacency are + different, then the maximum value MUST be used. If equal cost + (sub-)paths are found during the MRT computation, then the default + tie-breaking specified by Section 11 of [RFC6329] MUST be used, which + is based on the lower BridgeID. (The BridgeID is an 8-byte quantity + whose upper 2 bytes are the node's BridgePriority and lower 6 bytes + are the node's System ID.) Note that if MRTs are used for source- + specific multicast (see [IEEE8021Qca] for details), then the bridges + have to compute the MRTs of the other bridges in addition to their + own in order to be able to install the appropriated FDB entries. + (This is similar to the need for all pairs shortest path computation + instead of Dijkstra for source-specific shortest path multicast + trees.) + + The GADAG is identical for all the MRTs within a network domain, as a + consequence of the use of the MRT Lowpoint algorithm [RFC7811]. + Therefore, it is beneficial to compute the GADAG by a single entity, + which is referred to as the GADAG Computer and is either a PCE or the + GADAG Root. If the MRTG ECT Algorithm is applied, then the GADAG + MUST be computed only by the GADAG Computer, which then MUST flood + + + + +Farkas, et al. Standards Track [Page 24] + +RFC 7813 IS-IS PCR June 2016 + + + the descriptor Topology sub-TLV of the GADAG. The bridges then + compute the MRTs based on the received GADAG. + + The GADAG computation requires the selection of the GADAG Root. The + bridge with the best BridgeID MUST be selected as the GADAG Root, + where the numerically lower value indicates the better identifier. + The Bridge Priority component of the BridgeID allows the + configuration of the GADAG Root by management action. The Bridge + Priority is conveyed by the SPB Instance sub-TLV [RFC6329]. + + The GADAG Computer MUST perform the GADAG computation as specified by + the MRT Lowpoint algorithm [RFC7811]. The GADAG Computer then MUST + encode the GADAG in a Topology sub-TLV (Section 6.1), which is then + flooded throughout the domain. A GADAG is encoded in a Topology sub- + TLV by means of directed ear decomposition as follows. A directed + ear is a directed point-to-point path whose end points can coincide + but no other element of the path is repeated in the ear. Each ear is + specified by an ordered list of hops such that the order of hops is + according to the direction of the arcs in the GADAG. There are no + leaves in a GADAG; hence, the Leaf flag (item c.5. in Section 6.2) is + used to mark the end of a topology block. (A GADAG with multiple + blocks is illustrated in Figure 8.) The sequence of ears in the + Topology sub-TLV is such that the end points of an ear belong to + preceding ears. The GADAG Root is not marked by any flag, but the + GADAG Root is the first hop in the Topology sub-TLV; correspondingly, + the first ear starts and ends with the GADAG Root. MRT Roots MUST be + marked by the Root flag (item c.4. in Section 6.2) and all other Edge + Bridges are leaves of the given MRTs. If no MRT Root is specified, + then each SPT Root is also an MRT Root. + + Figure 7 shows an example GADAG. The figure also illustrates the + description of the GADAG; it shows the System ID parameter of the Hop + sub-TLV (Section 6.2) and the order of hops in the Topology sub-TLV + (Section 6.1). + + + + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 25] + +RFC 7813 IS-IS PCR June 2016 + + + Leaf + Hop flag + +-----------+---+ + | A | | + +-----------+---+ + | B | | + +-----------+---+ + | C | | + +-----------+---+ + | F | | + [B]<---[A]<---[I] +-----------+---+ + | ^ ^ | A | | + | | | +-----------+---+ + V | | | C | | + [C]--->[F]--->[H] +-----------+---+ + | ^ | D | | + | | +-----------+---+ + V | | E | | + [D]--->[E]--->[G] +-----------+---+ + | G | | + +-----------+---+ + | H | | + +-----------+---+ + | I | | + +-----------+---+ + | A | | + +-----------+---+ + | F | | + +-----------+---+ + | H | X | + +-----------+---+ + + Figure 7: A GADAG and Its Description; GADAG Root = Node A + + A topology can comprise multiple blocks, like the one illustrated in + Figure 8(a). This example topology comprises four blocks as each + cut-link is a block. A-B-C-D-E-F is a block, D-G is another block, + G-H, and H-J-K are further blocks. A GADAG for this topology is + shown in Figure 8(b). Note that two arcs with opposite directions + represent a cut-link in a GADAG; see, for example, the cut-link + between D and G. The encoding starts with the block (ADAG) involving + the GADAG Root as illustrated in Figure 8. The first hop in the + Topology sub-TLV is the GADAG Root (node A in this example). The + ADAG of the first block is then described using the ear + decomposition, as described above. In this example, the first block + has been completely traversed at the second occurrence of node A in + the GADAG descriptor. The end of a block is indicated by setting the + Leaf flag for the last hop of the block, e.g., for the second + + + +Farkas, et al. Standards Track [Page 26] + +RFC 7813 IS-IS PCR June 2016 + + + occurrence of node A in the example GADAG descriptor. The next node + that appears in the GADAG descriptor (D in this case) is the + localroot for the nodes in the next block. Continuing this process, + the Leaf flag is set for the third occurrence of D, the third + occurrence of G, and the third occurrence of H, each indicating the + end of a block. The first hop of the first block is the GADAG Root, + the fist hop in the rest of the blocks is the localroot. The + position of the set Leaf flags helps to determine the localroot, + which is the next hop. In the example GADAG descriptor, one can + determine that A is the localroot for B, C, D, E, F (and A is the + GADAG Root). D is the localroot for G. G is the localroot for H. + And H is the localroot for J and K. The GADAG Root is assigned a + localroot of None. + + Block IDs are reconstructed while parsing a Topology sub-TLV + specifying a GADAG. The current Block ID starts at 0 and is assigned + to the GADAG Root. A node appearing in the GADAG descriptor without + a previously assigned Block ID value is assigned the current Block + ID. And the current Block ID is incremented by 1 after processing + the localroot of a block. Note that the localroot of a block will + keep the Block ID of the first block in which it is assigned a Block + ID. In the example in Figure 8, A has Block ID=0. B, C, D, E, and F + have Block ID=1. G has Block ID=2. H has Block ID=3. J and K have + Block ID=4. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 27] + +RFC 7813 IS-IS PCR June 2016 + + + Leaf + Hop flag + [F]--[E] +--[K] +-----------+---+ + | | | | | A | | + | | | | +-----------+---+ + [A] [D]--[G]--[H] | | B | | + | | | | +-----------+---+ + | | | | | C | | + [B]--[C] +--[J] +-----------+---+ + | D | | + (a) Topology +-----------+---+ + | E | | + +-----------+---+ + | F | | + +-----------+---+ + | A | X | + +-----------+---+ + +-+ +-+ +-+ | D | | + |F|<-|E| +--|K| +-----------+---+ + +-+ +-+ | +-+ | G | | + | ^ | ^ +-----------+---+ + | | V | | D | X | + V +-+ +-+ +-+ | +-----------+---+ + +-+ | |->| |->| | | | G | | + |A| |D| |G| |H| | +-----------+---+ + +-+ | |<-| |<-| | | | H | | + | +-+ +-+ +-+ | +-----------+---+ + | ^ | | | G | X | + V | | | +-----------+---+ + +-+ +-+ | +-+ | H | | + |B|->|C| +->|J| +-----------+---+ + +-+ +-+ +-+ | J | | + +-----------+---+ + (b) GADAG | K | | + +-----------+---+ + | H | X | + +-----------+---+ + + (c) GADAG Descriptor + + Figure 8: A GADAG with Cut-Links and Its Description; GADAG Root = + Node A + + + + + + + + + +Farkas, et al. Standards Track [Page 28] + +RFC 7813 IS-IS PCR June 2016 + + +8. Summary + + This document specifies IS-IS sub-TLVs for the control of explicit + trees in Layer 2 networks. These sub-TLVs can be also used for the + distribution of a centrally computed GADAG or MRTs if MFT-FRR is + used. + +9. IANA Considerations + + This document defines the following IS-IS sub-TLVs within the + MT-Capability TLV (type 144). They are listed in the "IS-IS TLV + Codepoints" registry. + + Type Description Length + ---- ---------------------------- -------- + 21 Topology variable + 22 Hop variable + 23 Bandwidth Constraint 5 + 24 Bandwidth Assignment 5 + 25 Timestamp 4 + +10. Security Considerations + + This document adds no additional security risks to IS-IS, nor does it + provide any additional security for IS-IS when used in a configured + environment or a single-operator domain such as a data center. IS-IS + PCR is not for zero-configuration environments. + + Any mechanism that chooses forwarding paths, and allocates resources + to those paths, is potentially vulnerable to attack. The security + considerations section of [RFC4655] describes the risks associated + with the use of PCE for this purpose and should be referred to. Use + of any other means to determine paths should only be used after + considering similar concerns. + + Because the mechanism assumed for distributing tree information + relies on IS-IS routing, IS-IS routing security considerations + (Section 6, [RFC1195]) and mechanisms (e.g., [RFC5310]) used to + authenticate peer advertisements apply. + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 29] + +RFC 7813 IS-IS PCR June 2016 + + +11. References + +11.1. Normative References + + [IEEE8021Qca] + IEEE, "IEEE Standard for Local and metropolitan area + networks - Bridges and Bridged Networks - Amendment 24: + Path Control and Reservation", IEEE 802.1Qca-2015, + DOI 10.1109/IEEESTD.2016.7434544, 2016, + <https://standards.ieee.org/findstds/ + standard/802.1Qca-2015.html>. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + <http://www.rfc-editor.org/info/rfc2119>. + + [RFC5303] Katz, D., Saluja, R., and D. Eastlake 3rd, "Three-Way + Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303, + DOI 10.17487/RFC5303, October 2008, + <http://www.rfc-editor.org/info/rfc5303>. + + [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic + Engineering", RFC 5305, DOI 10.17487/RFC5305, October + 2008, <http://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, + <http://www.rfc-editor.org/info/rfc5307>. + + [RFC6329] Fedyk, D., Ed., Ashwood-Smith, P., Ed., Allan, D., Bragg, + A., and P. Unbehagen, "IS-IS Extensions Supporting IEEE + 802.1aq Shortest Path Bridging", RFC 6329, + DOI 10.17487/RFC6329, April 2012, + <http://www.rfc-editor.org/info/rfc6329>. + + [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and + Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", + RFC 7810, DOI 10.17487/RFC7810, May 2016, + <http://www.rfc-editor.org/info/rfc7810>. + + [RFC7811] Enyedi, G., Csaszar, A., Atlas, A., Bowers, C., and A. + Gopalan, "An Algorithm for Computing IP/LDP Fast Reroute + Using Maximally Redundant Trees (MRT-FRR)", RFC 7811, + DOI 10.17487/RFC7811, June 2016, + <http://www.rfc-editor.org/info/rfc7811>. + + + + +Farkas, et al. Standards Track [Page 30] + +RFC 7813 IS-IS PCR June 2016 + + +11.2. Informative References + + [IEEE1588] IEEE, "IEEE Standard for a Precision Clock Synchronization + Protocol for Networked Measurement and Control Systems", + IEEE 1588-2008, DOI 10.1109/IEEESTD.2008.4579760, 2008, + <http://standards.ieee.org/findstds/ + standard/1588-2008.html>. + + [IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", + IEEE 754-2008, DOI 10.1109/IEEESTD.2008.4610935, 2008, + <http://standards.ieee.org/findstds/ + standard/754-2008.html>. + + [IEEE8021aq] + IEEE, "IEEE Standard for Local and metropolitan area + networks -- Media Access Control (MAC) Bridges and Virtual + Bridged Local Area Networks -- Amendment 20: Shortest Path + Bridging", IEEE 802.1aq-2012, + DOI 10.1109/IEEESTD.2012.6231597, 2012, + <https://standards.ieee.org/findstds/ + standard/802.1aq-2012.html>. + + [IEEE8021Q] + IEEE, "IEEE Standard for Local and metropolitan area + networks--Bridges and Bridged Networks", IEEE 802.1Q-2014, + DOI 10.1109/IEEESTD.2014.6991462, 2014, + <https://standards.ieee.org/findstds/ + standard/802.1Q-2014.html>. + + [MRT-IEEE8021qca] + Bowers, C. and J. Farkas, "Applicability of Maximally + Redundant Trees to IEEE 802.1Qca Path Control and + Reservation", Work in Progress, draft-bowers-rtgwg-mrt- + applicability-to-8021qca-01, July 2015. + + [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and + dual environments", RFC 1195, DOI 10.17487/RFC1195, + December 1990, <http://www.rfc-editor.org/info/rfc1195>. + + [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation + Element (PCE)-Based Architecture", RFC 4655, + DOI 10.17487/RFC4655, August 2006, + <http://www.rfc-editor.org/info/rfc4655>. + + [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, <http://www.rfc-editor.org/info/rfc5310>. + + + +Farkas, et al. Standards Track [Page 31] + +RFC 7813 IS-IS PCR June 2016 + + + [RFC7812] Atlas, A., Bowers, C., and G. Enyedi, "An Architecture for + IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT- + FRR)", RFC 7812, DOI 10.17487/RFC7812, June 2016, + <http://www.rfc-editor.org/info/rfc7812>. + +Acknowledgements + + The authors would like to thank Don Fedyk and Eric Gray for their + comments and suggestions. + +Authors' Addresses + + Janos Farkas (editor) + Ericsson + Konyves Kalman krt. 11/B + Budapest 1097 + Hungary + + Email: janos.farkas@ericsson.com + + + Nigel Bragg + Ciena + 43-51 Worship Street + London EC2A 2DX + United Kingdom + + Email: nbragg@ciena.com + + + Paul Unbehagen Jr + Avaya + 1300 W. 120th Avenue + Westminster, CO 80234 + United States + + Email: unbehagen@avaya.com + + + Glenn Parsons + Ericsson + 349 Terry Fox Drive + Ottawa ON, K2K 2V6 + Canada + + Email: glenn.parsons@ericsson.com + + + + + +Farkas, et al. Standards Track [Page 32] + +RFC 7813 IS-IS PCR June 2016 + + + Peter Ashwood-Smith + Huawei Technologies + 303 Terry Fox Drive, Suite 400 + Ottawa ON, K2K 3J1 + Canada + + Email: Peter.AshwoodSmith@huawei.com + + + Chris Bowers + Juniper Networks + 1194 N. Mathilda Ave. + Sunnyvale, CA 94089 + United States + + Email: cbowers@juniper.net + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Farkas, et al. Standards Track [Page 33] + |