--- 1/draft-ietf-rtgwg-multihomed-prefix-lfa-04.txt 2018-02-06 21:13:08.370284163 -0800 +++ 2/draft-ietf-rtgwg-multihomed-prefix-lfa-05.txt 2018-02-06 21:13:08.406285028 -0800 @@ -1,25 +1,25 @@ Routing Area Working Group P. Sarkar, Ed. Internet-Draft Arrcus, Inc. Updates: 5286 (if approved) S. Hegde Intended status: Standards Track Juniper Networks, Inc. -Expires: June 4, 2018 U. Chunduri, Ed. - Huawei Technologies +Expires: August 10, 2018 U. Chunduri, Ed. + Huawei USA J. Tantsura Individual H. Gredler RtBrick, Inc. - December 1, 2017 + February 6, 2018 LFA selection for Multi-Homed Prefixes - draft-ietf-rtgwg-multihomed-prefix-lfa-04 + draft-ietf-rtgwg-multihomed-prefix-lfa-05 Abstract This document shares experience gained from implementing algorithms to determine Loop-Free Alternates for multi-homed prefixes. In particular, this document provides explicit inequalities that can be used to evaluate neighbors as a potential alternates for multi-homed prefixes. It also provides detailed criteria for evaluating potential alternates for external prefixes advertised by OSPF ASBRs. This documents updates and expands some of the "Routing Aspects" as @@ -38,25 +38,25 @@ 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 June 4, 2018. + This Internet-Draft will expire on August 10, 2018. Copyright Notice - Copyright (c) 2017 IETF Trust and the persons identified as the + 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 (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 @@ -78,26 +78,27 @@ 4.2.3. Type 1 and Type 2 costs . . . . . . . . . . . . . . . 11 4.2.4. RFC1583compatibility is set to enabled . . . . . . . 11 4.2.5. Type 7 routes . . . . . . . . . . . . . . . . . . . . 11 4.2.6. Inequalities to be applied for alternate ASBR selection . . . . . . . . . . . . . . . . . . . . . . 11 4.2.6.1. Forwarding address set to non-zero value . . . . 11 4.2.6.2. ASBRs advertising type1 and type2 cost . . . . . 12 5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13 5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13 5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14 - 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 - 7. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 - 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 - 9.1. Normative References . . . . . . . . . . . . . . . . . . 16 - 9.2. Informative References . . . . . . . . . . . . . . . . . 16 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 + 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 16 + 10.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction The use of Loop-Free Alternates (LFA) for IP Fast Reroute is specified in [RFC5286]. Section 6.1 of [RFC5286] describes a method to determine loop-free alternates for a multi-homed prefixes (MHPs). This document describes a procedure using explicit inequalities that can be used by a computing router to evaluate a neighbor as a potential alternate for a multi-homed prefix. The results obtained @@ -429,51 +430,52 @@ should be applied and ensured that the alternate neighbor does not loop the traffic back. When there are multiple ASBRs belonging to different area advertising the same prefix, pruning rules as defined in [RFC2328] section 16.4.1 are applied. The alternate ASBRs pruned using above rules are not considered for LFA evaluation. 4.2.3. Type 1 and Type 2 costs - If there are multiple ASBRs not pruned via rules defined in 3.2.2, - the cost type advertised by the ASBRs is compared. ASBRs advertising - Type1 costs are preferred and the type2 costs are pruned. If two - ASBRs advertise same type2 cost, the alternate ASBRs are considered - along with their type1 cost for evaluation. If the two ASBRs with - same type2 as well as type1 cost, ECMP FRR is programmed. If there - are two ASBRs with different type2 cost, the higher cost ASBR is - pruned. The inequalities for evaluating alternate ASBR for type 1 - and type 2 costs are same, as the alternate ASBRs with different - type2 costs are pruned and the evaluation is based on equal type 2 - cost ASBRS. + If there are multiple ASBRs not pruned via rules defined in + Section 4.2.2, the cost type advertised by the ASBRs is compared. + ASBRs advertising Type1 costs are preferred and the type2 costs are + pruned. If two ASBRs advertise same type2 cost, the alternate ASBRs + are considered along with their type1 cost for evaluation. If the + two ASBRs with same type2 as well as type1 cost, ECMP FRR is + programmed. If there are two ASBRs with different type2 cost, the + higher cost ASBR is pruned. The inequalities for evaluating + alternate ASBR for type 1 and type 2 costs are same, as the alternate + ASBRs with different type2 costs are pruned and the evaluation is + based on equal type 2 cost ASBRS. 4.2.4. RFC1583compatibility is set to enabled When RFC1583Compatibility is set to enabled, multiple ASBRs belonging to different area advertising same prefix are chosen based on cost and hence are valid alternate ASBRs for the LFA evaluation. 4.2.5. Type 7 routes Type 5 routes always get preference over Type 7 and the alternate ASBRs chosen for LFA calculation should belong to same type. Among Type 7 routes, routes with p-bit and forwarding address set have higher preference than routes without these attributes. Alternate ASBRs selected for LFA comparison should have same p-bit and forwarding address attributes. 4.2.6. Inequalities to be applied for alternate ASBR selection The alternate ASBRs selected using above mechanism described in - 3.2.1, are evaluated for Loop free criteria using below inequalities. + Section 4.2.1, are evaluated for Loop free criteria using below + inequalities. 4.2.6.1. Forwarding address set to non-zero value Link-Protection: F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) + F_opt(S,PO_best) + cost(PO_best,P) Link-Protection + Downstream-paths-only: F_opt(N,PO_i)+ cost(PO_i,P) < F_opt(S,PO_best) + cost(PO_best,P) Node-Protection: @@ -487,21 +489,21 @@ prefix P. PO_i - The specific prefix-originating router being evaluated. PO_best - The prefix-originating router on the shortest path from the computing router S to prefix P. cost(X,Y) - External cost for Y as advertised by X F_opt(X,Y) - Distance on the shortest path from node X to Forwarding address specified by ASBR Y. D_opt(X,Y) - Distance on the shortest path from node X to node Y. - Figure 6: LFA inequality definition when forwarding address in non- + Figure 6: LFA inequality definition when forwarding address is non- zero 4.2.6.2. ASBRs advertising type1 and type2 cost Link-Protection: D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) + D_opt(S,PO_best) + cost(PO_best,P) Link-Protection + Downstream-paths-only: D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P) @@ -526,21 +528,21 @@ 5. LFA Extended Procedures This section explains the additional considerations in various aspects as listed below to the base LFA specification [RFC5286]. 5.1. Links with IGP MAX_METRIC Section 3.5 and 3.6 of [RFC5286] describes procedures for excluding nodes and links from use in alternate paths based on the maximum link metric (as defined in for IS-IS in [RFC5305] or as defined in - [RFC3137] for OSPF). If these procedures are strictly followed, + [RFC6987] for OSPF). If these procedures are strictly followed, there are situations, as described below, where the only potential alternate available which satisfies the basic loop-free condition will not be considered as alternative. +---+ 10 +---+ 10 +---+ | S |------|N1 |-----|D1 | +---+ +---+ +---+ | | 10 | 10 | |MAX_MET(N2 to S) | @@ -596,80 +598,79 @@ However for MT IS-IS, if a "standard topology" is used with MT-ID #0 [RFC5286] and both IPv4 [RFC5305] and IPv6 routes/AFs [RFC5308] are present, then the condition of network congruency is applicable for LFA computation as well. Network congruency here refers to, having same address families provisioned on all the links and all the nodes of the network with MT-ID #0. Here with single decision process both IPv4 and IPv6 next-hops are computed for all the prefixes in the network and similarly with one LFA computation from all eligible neighbors per [RFC5286], all potential alternatives can be computed. -6. Acknowledgements +6. IANA Considerations + + This document has no actions for IANA. + +7. Acknowledgements Thanks to Alia Atlas and Salih K A for their useful feedback and inputs. Thanks to Stewart Bryant for being document shepherd and providing detailed review comments. -7. Contributing Authors +8. Contributing Authors The following people contributed substantially to the content of this document and should be considered co-authors. Chris Bowers Juniper Networks, Inc. 1194 N. Mathilda Ave, Sunnyvale, CA 94089, USA Email: cbowers@juniper.ne Bruno Decraene Orange, France Email: bruno.decraene@orange.com -8. Security Considerations +9. Security Considerations This document does not introduce any change in any of the protocol [RFC1195] [RFC5120] [RFC2328] [RFC5838] specifications discussed here and also this does not introduce any new security issues other than as noted in the LFA base specification [RFC5286]. -9. References +10. References -9.1. Normative References +10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, DOI 10.17487/RFC5286, September 2008, . -9.2. Informative References +10.2. Informative References [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . - [RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D. - McPherson, "OSPF Stub Router Advertisement", RFC 3137, - DOI 10.17487/RFC3137, June 2001, - . - [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, . @@ -680,37 +681,42 @@ [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, DOI 10.17487/RFC5308, October 2008, . [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and R. Aggarwal, "Support of Address Families in OSPFv3", RFC 5838, DOI 10.17487/RFC5838, April 2010, . + [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. + McPherson, "OSPF Stub Router Advertisement", RFC 6987, + DOI 10.17487/RFC6987, September 2013, + . + Authors' Addresses Pushpasis Sarkar (editor) Arrcus, Inc. Email: pushpasis.ietf@gmail.com Shraddha Hegde Juniper Networks, Inc. Electra, Exora Business Park Bangalore, KA 560103 India Email: shraddha@juniper.net Uma Chunduri (editor) - Huawei Technologies + Huawei USA 2330 Central Expressway Santa Clara, CA 95050 USA Email: uma.chunduri@huawei.com Jeff Tantsura Individual Email: jefftant.ietf@gmail.com