Preferred Path Route Graph Structure
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|Authors||Uma Chunduri , Toerless Eckert|
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LSR Working Group U. Chunduri Internet-Draft T. Eckert Intended status: Standards Track Huawei USA Expires: April 25, 2019 October 22, 2018 Preferred Path Route Graph Structure draft-ce-lsr-ppr-graph-00 Abstract This document defines a graph structure for the Preferred Path Route (PPR) for IS-IS, OSPFv2 and OSPFv3 protocols. This structure helps further scale of the PPR and reduce domain level global entries needed in some data planes. Requirements Language 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 [RFC2119], RFC8174 [RFC8174] when, and only when they appear in all capitals, as shown here. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 April 25, 2019. Copyright Notice Copyright (c) 2018 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 Chunduri & Eckert Expires April 25, 2019 [Page 1] Internet-Draft Preferred Path Route Graph Structure October 2018 (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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 2. PPR Graph TLVs . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. IS-IS TLVs . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1. Branch-ID Sub-TLV . . . . . . . . . . . . . . . . . . 5 2.1.2. PPR PDE Sub-TLV . . . . . . . . . . . . . . . . . . . 5 2.2. OSPF TLVs . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. OSPFv2 TLVs . . . . . . . . . . . . . . . . . . . . . 6 2.2.2. OSPFv3 TLVs . . . . . . . . . . . . . . . . . . . . . 6 3. Encoding and Processing details . . . . . . . . . . . . . . . 6 3.1. S And D bits in PDEs . . . . . . . . . . . . . . . . . . 7 3.2. Graph processing procedure example . . . . . . . . . . . 7 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5.1. IS-IS IANA . . . . . . . . . . . . . . . . . . . . . . . 9 5.2. OSPFv2 IANA . . . . . . . . . . . . . . . . . . . . . . . 9 5.3. OSPFv3 IANA . . . . . . . . . . . . . . . . . . . . . . . 9 5.4. IGP Parameter IANA . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction Preferred Path Routing (PPR) is concerned with the creation of a routing path as specified in the PPR-Path that can be used in IGPs along with a data plane identifier (PPR-ID). With this, any packet destined to the PPR-ID would use the PPR-Path instead of the IGP computed shortest path to the destination as indicated by the PPR-ID. PPR-Paths and relevant IGP extensions are defined in [I-D.chunduri-lsr-isis-preferred-path-routing] and [I-D.chunduri-lsr-ospf-preferred-path-routing]. In these IGP extensions, PPR-Paths are described as a path structure, which is an ordered linear list of path elements with all nodes, links or services on the nodes described in the path using Path Description Chunduri & Eckert Expires April 25, 2019 [Page 2] Internet-Draft Preferred Path Route Graph Structure October 2018 Elements (PDEs). A separate PPR-ID is required for every possible path, even if one path is just a subset of another path. To provide PPR-Paths from N possible source nodes to one destination node, N PPR-IDs are necessary. To create full-mesh connectivity via PPR- Paths between N nodes, N^2 PPR-Paths and N^2 PPR-IDs are necessary. Even though in a larger network, only a smaller percentage of nodes want to use PPR-Paths. However, to further scale in-terms of number of PPR-IDs needed on the destination nodes, number of forwarding entries needed on the nodes in the paths (for overlapping paths), or to optimize flooding needed in the IGP domain this document introduces a graph structure in (Section 2) . 1.1. Acronyms MPLS - Multi Protocol Label Switching MSD - Maximum SID Depth PDE - Path Description Element PPG - Preferred Path Graph PPR - Preferred Path Routing/Route PPR-ID - Preferred Path Route Identifier, a data plane identifier SID - Segment Identifier SPF - Shortest Path First SR-MPLS - Segment Routing with MPLS data plane SRH - Segment Routing Header - IPv6 routing Extension header SRv6 - Segment Routing with Ipv6 data plane with SRH TE - Traffic Engineering 2. PPR Graph TLVs 2.1. IS-IS TLVs This section describes the encoding of IS-IS PPR Tree TLV. This TLV can be seen as having 4 logical section viz., encoding of the PPR- Prefix (IS-IS Prefix), encoding of PPG-ID, encoding of path description with an ordered PDE (Path Description Element) Sub-TLVs, belonging to one or more Branch-IDs and a set of optional PPR Chunduri & Eckert Expires April 25, 2019 [Page 3] Internet-Draft Preferred Path Route Graph Structure October 2018 attribute Sub-TLVs, which can be used to describe PPR Graph common parameters. Multiple instances of this TLV MAY be advertised in IS- IS LSPs with different PPG-ID Type and with corresponding Branch-ID/ PDE Sub-TLVS. The PPR Graph TLV has Type TBD (suggested value xxx), and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Graph-Type | Graph-Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PPR-Prefix Sub-TLV (variable size) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L| Frag-ID | PPG-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Branch-ID Sub-TLV and PPR-PDE Sub-TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PPR-Attribute Sub-TLVs(variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: PPR Tree TLV Format o Type - TBD (IANA) from IS-IS top level TLV registry. o Length - Total length of the value field in bytes (variable). o Graph-Type - 1 Octet value (0-255, IANA Registry TBD). 0 - defines a tree structure (this document). o Graph-Flags - 1 Octet flags for this TLV are described below. o Frag-ID - 1 Octet TLV Fragment-ID, with 7-bit Identifier value (0-127). L bit MUST be set if a graph has only one fragment or if it is the last Fragment of the graph. PPG-ID value for all fragments MUST be the same. o PPG-ID - 3 byte Preferred Path Graph Identifier. Originator of the graph MUST ensure uniqueness across the domain. o Branch-ID Sub-TLV is defined in Section 2.1.1. This represents the branch-id of the structure followed by PDE Sub-TLVs in that branch. Different branches of the graph can be in different fragments of this TLV. However, a complete set of PDE Sub-TLVs MUST be specified in one TLV fragment. o PPR-PDE Sub-TLV defined in [I-D.chunduri-lsr-isis-preferred-path-routing]. Additional information in the PPR-PDE Sub-TLV is described in Section 2.1.2. Chunduri & Eckert Expires April 25, 2019 [Page 4] Internet-Draft Preferred Path Route Graph Structure October 2018 o PPR-Attribute Sub-TLVs defined in [I-D.chunduri-lsr-isis-preferred-path-routing] are applicable here. PPR-Flags field of PPR TLV has the following flag bits defined. These flags, at this point mostly related to applicability of this TLV in an L1 area or entire IS-IS domain or from where the PPR-Prefix is being originated: PPR Graph-Flags Format 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |S|D| Reserved | +-+-+-+-+-+-+-+-+ 1. S - If set, the PPR Graph TLV MUST be flooded across the entire routing domain. If the S flag is not set, the PPR Graph TLV MUST NOT be leaked between IS-IS levels. This bit MUST NOT be altered during the TLV leaking 2. D - when the PPR Graph TLV is leaked from IS-IS level-2 to level- 1, the D bit MUST be set. Otherwise, this bit MUST be clear. PPR TLVs with the D bit set MUST NOT be leaked from level-1 to level-2. This is to prevent TLV looping across levels. 3. Reserved - reserved bits for future use. Reserved bits MUST be reset on transmission and ignored on receive. 2.1.1. Branch-ID Sub-TLV Branch-ID Sub-TLVs represent the branch of the graph described. This is a new Sub-TLV type (IANA TBD) in PPR TLV [I-D.chunduri-lsr-isis-preferred-path-routing]. Type TBD (Suggested Value - IANA TBD), with a length of 1 byte, and Value is the branch identification number in the range of 0 to 255. 2.1.2. PPR PDE Sub-TLV PPR PDE Sub-TLV is defined in [I-D.chunduri-lsr-isis-preferred-path-routing]. This document extends the same with the following: 1. PPR-PDE Flags (Bit position 2), S: Source Bit. Indicates the PPR head-end and MUST be set if this PDE corresponds to the same. Chunduri & Eckert Expires April 25, 2019 [Page 5] Internet-Draft Preferred Path Route Graph Structure October 2018 2. PPR-ID Sub-Sub-TLV: Type 1 (Suggested Value, TBD IANA from the PDE Sub-TLV Registry), length and value fields would be same as PPR-ID Sub-TLV defined in [I-D.chunduri-lsr-isis-preferred-path-routing]. This Sub-Sub-TLV MUST be present only when 'D' flag is set in the PPR-PDE Flags field. PPR-PDE Flags field is defined in PPR-PDE Sub-TLV [I-D.chunduri-lsr-isis-preferred-path-routing]. 2.2. OSPF TLVs 2.2.1. OSPFv2 TLVs TBD. 2.2.2. OSPFv3 TLVs TBD. 3. Encoding and Processing details [I-D.chunduri-lsr-isis-preferred-path-routing] describes how a PPR path can be established. This document builds on the same base concept but expands the same with a graph structure as defined in Section 2. The key new encoding element here over prior PPR Paths is the existence of multiple Branches in the PPR Graph description. Each Branch-ID sub-TLV is followed by ordered sequence of PDEs. A PPR Graph can be constructed from one or more PPR Branches. Branches are stitched together by using the same PDE in two branches. To simplify parsing of branches, only the last PDE of a branch can be stitched to another branch. In result, any PDE can only be a non- last PDE in one Branch but last PDE in more than one branch. A PPG- ID field is defined in this document. This MUST be unique in the domain and represents the graph structure as whole. A complete Graph may not fit into maximum allowable size of the IS-IS TLV. To overcome this a 7 bit Frag-ID field is defined (Section 2). With this, a single PPR Graph is represented via one or more fragmented PPR Graph TLVs all having the same PPG-ID. Each Fragment carries the PPG-ID as well as a numeric Frag-ID from 0 to (N-1), when N fragments are needed to describe the PPR Graph (where N>1). In this case Fragment (N-1) MUST set the L bit to indicate it is the last fragment. The optional PPR Attribute Sub-TLVs which describe the Graph overall MUST be included in the last fragment only. Chunduri & Eckert Expires April 25, 2019 [Page 6] Internet-Draft Preferred Path Route Graph Structure October 2018 3.1. S And D bits in PDEs In PPR paths as defined currently [draft) only a simple linear path structure for a destination node is possible. However, with a bit on path element source and a bit for destination (refer section) - same path ID/PPR-ID can be used to represent multiple paths if some of the nodes are also sources and terminating on the same destination node. 1. A Linear path structure: PDE1 --> PDE2 --> PDE3 --> PDE4 --> PDE5 [First PDE always Source and last PDE is always Destination] 2. A PPR Graph with S and D bits: PDE1(with-S-bit-set)-->PDE2-->PDE3(with-S-bit-set).. ..-->PDE4(with-D-bit-set)-->PDE5(with-D-bit-Set) ==> PDE1 --> PDE2 --> PDE3 --> PDE4 ==> PDE1 --> PDE2 --> PDE3 --> PDE4 --> PDE5 ==> PDE3 --> PDE4 ==> PDE3 --> PDE4 --> PDE5 Figure 2: PPR Graph with S and D bits In the above Figure 2 example, in (1) a linear path list of 5 nodes are described where PDE1 is the source/ingress-point and PDE5 is the destination/egress point of the path. In (2), the path can be defined in this document, where some PDEs can have S(ource) and/or D(estination) bit or both can be set. Here, PDE1 and PDE3 have the Source bit set, PDE4 and PDE5 the Destination bit set. This Branch structure is equivalent to the set of 4 PPR-PDE lists as shown: PDE1->PDE5, PDE1->PDE45, PDE3->PDE4, PDE3->PDE5. This reduces the amount of information that needs to be sent across the IGP and that needs to be processed by each node. If the bits and branch structure were not used, the 4 PPR PDE lists would have required each a unique PPR-ID (and the resulting forwarding entries created), but the Branch requires only 2 PPR-IDs: one for both paths terminating in PDE4, and one for both paths terminating in PDE5. 3.2. Graph processing procedure example Chunduri & Eckert Expires April 25, 2019 [Page 7] Internet-Draft Preferred Path Route Graph Structure October 2018 Brach0 Branch1 Branch2 PDE1 PDE12(S-bit) PDE6 \ \ / PDE2 PDE11 PDE7 \ \ / PDE3 PDE10 PDE8 (S-bit) \ \ / PDE4 PDE9 \ / \ / PDE5 (D-bit) Figure 3: PPR Graph (Tree) Example With a PPR Tree structure both flooding optimization and reduction in the number of SIDs needed at the destination can be achieved. To do this encoding as specified in Section 2 (a) Every PDE-ID can be non- last-PDE in at most one Branch. It can be last-PDE in one or more Branches (ex: PDE9). (b) Branches form a tree by joining nodes with same PDE-ID (PDE9 and PDE5 in the above example). Leafs of the tree must be S(ources), e.g.: PDE1, PDE12, PDE6. Root of the tree must be the only D(estination) of the tree (e.g.: PDE5). How to build forwarding entry (referring to the Figure 3 above): 1. If PPR-ID in PDE of PPR Graph is indicating this node (example: PDE5): This node is D(estination) of this tree. Forwarding state is built for this PPR-Tree like for PPR-Path, no changes. 2. If PPR-ID is NOT indicating this node, then this node MAY be source (PDE12, PDE8) or midpoint (PDE9, neither source nor destination): a. Node sequentially examines all branches until it finds a PDE with its own PDE-ID. It then establishes a forwarding entry for the PPR-ID indicated in the PPR header with the next-hop being the next PDE in the current branch. b. This nodes PDE may be the last PDE in a Branch, for example PDE9 in Branch1. In this case, the node ignores this branch because it cannot build a complete forwarding entry from it. Instead, it will build the forwarding entry from another branch, e.g.: Node with PDE9 will build forwarding entry for destination PDE5 when it examines Branch2 because there it will have a next hop PDE5. After forwarding entry is built, node can stop examining rest of Branch or further Branches. Chunduri & Eckert Expires April 25, 2019 [Page 8] Internet-Draft Preferred Path Route Graph Structure October 2018 c. If node does not find its own PDE in any branch it is not on the graph and ignores this PPR-Graph. 4. Acknowledgements Thanks to Yingzhen Qu and Richard Li for multiple discussions on this topic. 5. IANA Considerations 5.1. IS-IS IANA This document requests the following new TLV in IANA IS-IS TLV code- point registry. TLV # Name ----- -------------- TBD PPR Graph TLV This document requests IANA to create a new Sub-TLV registry for PPR TLV Section 2 with the following initial entries (suggested values): Sub-TLV # Sub-TLV Name --------- --------------------------------------------------------- TBD Branch-ID (Section 2) 5.2. OSPFv2 IANA 5.3. OSPFv3 IANA 5.4. IGP Parameter IANA This document requests additional IANA registries in an IANA managed registry "Interior Gateway Protocol (IGP) Parameters" for various PPR TLV parameters. The registration procedure is based on the "Expert Review" as defined in [RFC8126]. The suggested registry names are: o "Graph-Type" - Types are an unsigned 8 bit numbers. Values are as defined in Section 2 of this document. o "Graph-Flags" - 1 Octet. Bits as described in Section 2 of this document. Chunduri & Eckert Expires April 25, 2019 [Page 9] Internet-Draft Preferred Path Route Graph Structure October 2018 6. Security Considerations Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310]. Further security analysis for IS-IS protocol is done in [RFC7645] with detailed analysis of various security threats and why [RFC5304] should not be used in the deployments. OSPF security extensions are described in [RFC2328] and [RFC7684] and these apply to the extensions specified in this document. While OSPF is under a single administrative domain, there can be deployments where potential attackers have access to one or more networks in the OSPF routing domain. In these deployments, stronger authentication mechanisms such as those specified in [RFC7474] SHOULD be used. Advertisement of the additional information defined in this document introduces no new security concerns in IS-IS or OSPF protocols. 7. References 7.1. Normative References [I-D.chunduri-lsr-isis-preferred-path-routing] Chunduri, U., Li, R., White, R., Tantsura, J., Contreras, L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS", draft-chunduri-lsr-isis-preferred-path-routing-01 (work in progress), July 2018. [I-D.chunduri-lsr-ospf-preferred-path-routing] Chunduri, U., Qu, Y., White, R., Tantsura, J., and L. Contreras, "Preferred Path Routing (PPR) in OSPF", draft- chunduri-lsr-ospf-preferred-path-routing-01 (work in progress), July 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. 7.2. Informative References [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, <https://www.rfc-editor.org/info/rfc2328>. [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008, <https://www.rfc-editor.org/info/rfc5304>. Chunduri & Eckert Expires April 25, 2019 [Page 10] Internet-Draft Preferred Path Route Graph Structure October 2018 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, <https://www.rfc-editor.org/info/rfc5305>. [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, <https://www.rfc-editor.org/info/rfc5310>. [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., "Security Extension for OSPFv2 When Using Manual Key Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, <https://www.rfc-editor.org/info/rfc7474>. [RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and Authentication for Routing Protocol (KARP) IS-IS Security Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015, <https://www.rfc-editor.org/info/rfc7645>. [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, <https://www.rfc-editor.org/info/rfc7684>. [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. Authors' Addresses Uma Chunduri Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: firstname.lastname@example.org Chunduri & Eckert Expires April 25, 2019 [Page 11] Internet-Draft Preferred Path Route Graph Structure October 2018 Toerless Eckert Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: email@example.com Chunduri & Eckert Expires April 25, 2019 [Page 12]