draft-ietf-rtgwg-multihomed-prefix-lfa-04.txt   draft-ietf-rtgwg-multihomed-prefix-lfa-05.txt 
Routing Area Working Group P. Sarkar, Ed. Routing Area Working Group P. Sarkar, Ed.
Internet-Draft Arrcus, Inc. Internet-Draft Arrcus, Inc.
Updates: 5286 (if approved) S. Hegde Updates: 5286 (if approved) S. Hegde
Intended status: Standards Track Juniper Networks, Inc. Intended status: Standards Track Juniper Networks, Inc.
Expires: June 4, 2018 U. Chunduri, Ed. Expires: August 10, 2018 U. Chunduri, Ed.
Huawei Technologies Huawei USA
J. Tantsura J. Tantsura
Individual Individual
H. Gredler H. Gredler
RtBrick, Inc. RtBrick, Inc.
December 1, 2017 February 6, 2018
LFA selection for Multi-Homed Prefixes LFA selection for Multi-Homed Prefixes
draft-ietf-rtgwg-multihomed-prefix-lfa-04 draft-ietf-rtgwg-multihomed-prefix-lfa-05
Abstract Abstract
This document shares experience gained from implementing algorithms This document shares experience gained from implementing algorithms
to determine Loop-Free Alternates for multi-homed prefixes. In to determine Loop-Free Alternates for multi-homed prefixes. In
particular, this document provides explicit inequalities that can be particular, this document provides explicit inequalities that can be
used to evaluate neighbors as a potential alternates for multi-homed used to evaluate neighbors as a potential alternates for multi-homed
prefixes. It also provides detailed criteria for evaluating prefixes. It also provides detailed criteria for evaluating
potential alternates for external prefixes advertised by OSPF ASBRs. potential alternates for external prefixes advertised by OSPF ASBRs.
This documents updates and expands some of the "Routing Aspects" as This documents updates and expands some of the "Routing Aspects" as
specified in Section 6 of [RFC5286]. specified in Section 6 of [RFC 5286].
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119]. document are to be interpreted as described in RFC2119 [RFC2119].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
skipping to change at page 2, line 4 skipping to change at page 2, line 4
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 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. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 44 skipping to change at page 2, line 44
4.2.3. Type 1 and Type 2 costs . . . . . . . . . . . . . . . 11 4.2.3. Type 1 and Type 2 costs . . . . . . . . . . . . . . . 11
4.2.4. RFC1583compatibility is set to enabled . . . . . . . 11 4.2.4. RFC1583compatibility is set to enabled . . . . . . . 11
4.2.5. Type 7 routes . . . . . . . . . . . . . . . . . . . . 11 4.2.5. Type 7 routes . . . . . . . . . . . . . . . . . . . . 11
4.2.6. Inequalities to be applied for alternate ASBR 4.2.6. Inequalities to be applied for alternate ASBR
selection . . . . . . . . . . . . . . . . . . . . . . 11 selection . . . . . . . . . . . . . . . . . . . . . . 11
4.2.6.1. Forwarding address set to non-zero value . . . . 11 4.2.6.1. Forwarding address set to non-zero value . . . . 11
4.2.6.2. ASBRs advertising type1 and type2 cost . . . . . 12 4.2.6.2. ASBRs advertising type1 and type2 cost . . . . . 12
5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13 5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13
5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13 5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13
5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14 5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
The use of Loop-Free Alternates (LFA) for IP Fast Reroute is The use of Loop-Free Alternates (LFA) for IP Fast Reroute is
specified in [RFC5286]. Section 6.1 of [RFC5286] describes a method specified in [RFC5286]. Section 6.1 of [RFC5286] describes a method
to determine loop-free alternates for a multi-homed prefixes (MHPs). to determine loop-free alternates for a multi-homed prefixes (MHPs).
This document describes a procedure using explicit inequalities that This document describes a procedure using explicit inequalities that
can be used by a computing router to evaluate a neighbor as a can be used by a computing router to evaluate a neighbor as a
potential alternate for a multi-homed prefix. The results obtained potential alternate for a multi-homed prefix. The results obtained
skipping to change at page 11, line 12 skipping to change at page 11, line 12
should be applied and ensured that the alternate neighbor does not should be applied and ensured that the alternate neighbor does not
loop the traffic back. loop the traffic back.
When there are multiple ASBRs belonging to different area advertising When there are multiple ASBRs belonging to different area advertising
the same prefix, pruning rules as defined in [RFC2328] section 16.4.1 the same prefix, pruning rules as defined in [RFC2328] section 16.4.1
are applied. The alternate ASBRs pruned using above rules are not are applied. The alternate ASBRs pruned using above rules are not
considered for LFA evaluation. considered for LFA evaluation.
4.2.3. Type 1 and Type 2 costs 4.2.3. Type 1 and Type 2 costs
If there are multiple ASBRs not pruned via rules defined in 3.2.2, If there are multiple ASBRs not pruned via rules defined in
the cost type advertised by the ASBRs is compared. ASBRs advertising Section 4.2.2, the cost type advertised by the ASBRs is compared.
Type1 costs are preferred and the type2 costs are pruned. If two ASBRs advertising Type1 costs are preferred and the type2 costs are
ASBRs advertise same type2 cost, the alternate ASBRs are considered pruned. If two ASBRs advertise same type2 cost, the alternate ASBRs
along with their type1 cost for evaluation. If the two ASBRs with are considered along with their type1 cost for evaluation. If the
same type2 as well as type1 cost, ECMP FRR is programmed. If there two ASBRs with same type2 as well as type1 cost, ECMP FRR is
are two ASBRs with different type2 cost, the higher cost ASBR is programmed. If there are two ASBRs with different type2 cost, the
pruned. The inequalities for evaluating alternate ASBR for type 1 higher cost ASBR is pruned. The inequalities for evaluating
and type 2 costs are same, as the alternate ASBRs with different alternate ASBR for type 1 and type 2 costs are same, as the alternate
type2 costs are pruned and the evaluation is based on equal type 2 ASBRs with different type2 costs are pruned and the evaluation is
cost ASBRS. based on equal type 2 cost ASBRS.
4.2.4. RFC1583compatibility is set to enabled 4.2.4. RFC1583compatibility is set to enabled
When RFC1583Compatibility is set to enabled, multiple ASBRs belonging When RFC1583Compatibility is set to enabled, multiple ASBRs belonging
to different area advertising same prefix are chosen based on cost to different area advertising same prefix are chosen based on cost
and hence are valid alternate ASBRs for the LFA evaluation. and hence are valid alternate ASBRs for the LFA evaluation.
4.2.5. Type 7 routes 4.2.5. Type 7 routes
Type 5 routes always get preference over Type 7 and the alternate Type 5 routes always get preference over Type 7 and the alternate
ASBRs chosen for LFA calculation should belong to same type. Among ASBRs chosen for LFA calculation should belong to same type. Among
Type 7 routes, routes with p-bit and forwarding address set have Type 7 routes, routes with p-bit and forwarding address set have
higher preference than routes without these attributes. Alternate higher preference than routes without these attributes. Alternate
ASBRs selected for LFA comparison should have same p-bit and ASBRs selected for LFA comparison should have same p-bit and
forwarding address attributes. forwarding address attributes.
4.2.6. Inequalities to be applied for alternate ASBR selection 4.2.6. Inequalities to be applied for alternate ASBR selection
The alternate ASBRs selected using above mechanism described in 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 4.2.6.1. Forwarding address set to non-zero value
Link-Protection: Link-Protection:
F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) + F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +
F_opt(S,PO_best) + cost(PO_best,P) F_opt(S,PO_best) + cost(PO_best,P)
Link-Protection + Downstream-paths-only: Link-Protection + Downstream-paths-only:
F_opt(N,PO_i)+ cost(PO_i,P) < F_opt(S,PO_best) + cost(PO_best,P) F_opt(N,PO_i)+ cost(PO_i,P) < F_opt(S,PO_best) + cost(PO_best,P)
Node-Protection: Node-Protection:
skipping to change at page 12, line 29 skipping to change at page 12, line 29
prefix P. prefix P.
PO_i - The specific prefix-originating router being PO_i - The specific prefix-originating router being
evaluated. evaluated.
PO_best - The prefix-originating router on the shortest path PO_best - The prefix-originating router on the shortest path
from the computing router S to prefix P. from the computing router S to prefix P.
cost(X,Y) - External cost for Y as advertised by X 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 F_opt(X,Y) - Distance on the shortest path from node X to Forwarding
address specified by ASBR Y. address specified by ASBR Y.
D_opt(X,Y) - Distance on the shortest path from node X to node 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 zero
4.2.6.2. ASBRs advertising type1 and type2 cost 4.2.6.2. ASBRs advertising type1 and type2 cost
Link-Protection: Link-Protection:
D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) + D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,S) +
D_opt(S,PO_best) + cost(PO_best,P) D_opt(S,PO_best) + cost(PO_best,P)
Link-Protection + Downstream-paths-only: Link-Protection + Downstream-paths-only:
D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P) D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(S,PO_best) + cost(PO_best,P)
skipping to change at page 13, line 39 skipping to change at page 13, line 39
5. LFA Extended Procedures 5. LFA Extended Procedures
This section explains the additional considerations in various This section explains the additional considerations in various
aspects as listed below to the base LFA specification [RFC5286]. aspects as listed below to the base LFA specification [RFC5286].
5.1. Links with IGP MAX_METRIC 5.1. Links with IGP MAX_METRIC
Section 3.5 and 3.6 of [RFC5286] describes procedures for excluding 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 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 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 there are situations, as described below, where the only potential
alternate available which satisfies the basic loop-free condition alternate available which satisfies the basic loop-free condition
will not be considered as alternative. will not be considered as alternative.
+---+ 10 +---+ 10 +---+ +---+ 10 +---+ 10 +---+
| S |------|N1 |-----|D1 | | S |------|N1 |-----|D1 |
+---+ +---+ +---+ +---+ +---+ +---+
| | | |
10 | 10 | 10 | 10 |
|MAX_MET(N2 to S) | |MAX_MET(N2 to S) |
skipping to change at page 15, line 22 skipping to change at page 15, line 22
However for MT IS-IS, if a "standard topology" is used with MT-ID #0 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 [RFC5286] and both IPv4 [RFC5305] and IPv6 routes/AFs [RFC5308] are
present, then the condition of network congruency is applicable for present, then the condition of network congruency is applicable for
LFA computation as well. Network congruency here refers to, having LFA computation as well. Network congruency here refers to, having
same address families provisioned on all the links and all the nodes 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 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 IPv4 and IPv6 next-hops are computed for all the prefixes in the
network and similarly with one LFA computation from all eligible network and similarly with one LFA computation from all eligible
neighbors per [RFC5286], all potential alternatives can be computed. 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 Thanks to Alia Atlas and Salih K A for their useful feedback and
inputs. Thanks to Stewart Bryant for being document shepherd and inputs. Thanks to Stewart Bryant for being document shepherd and
providing detailed review comments. providing detailed review comments.
7. Contributing Authors 8. Contributing Authors
The following people contributed substantially to the content of this The following people contributed substantially to the content of this
document and should be considered co-authors. document and should be considered co-authors.
Chris Bowers Chris Bowers
Juniper Networks, Inc. Juniper Networks, Inc.
1194 N. Mathilda Ave, 1194 N. Mathilda Ave,
Sunnyvale, CA 94089, USA Sunnyvale, CA 94089, USA
Email: cbowers@juniper.ne Email: cbowers@juniper.ne
Bruno Decraene Bruno Decraene
Orange, Orange,
France France
Email: bruno.decraene@orange.com Email: bruno.decraene@orange.com
8. Security Considerations 9. Security Considerations
This document does not introduce any change in any of the protocol This document does not introduce any change in any of the protocol
[RFC1195] [RFC5120] [RFC2328] [RFC5838] specifications discussed here [RFC1195] [RFC5120] [RFC2328] [RFC5838] specifications discussed here
and also this does not introduce any new security issues other than and also this does not introduce any new security issues other than
as noted in the LFA base specification [RFC5286]. 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 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286, IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008, DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>. <https://www.rfc-editor.org/info/rfc5286>.
9.2. Informative References 10.2. Informative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195, dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>. December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
[RFC3137] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
DOI 10.17487/RFC3137, June 2001,
<https://www.rfc-editor.org/info/rfc3137>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007, RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>. <https://www.rfc-editor.org/info/rfc4915>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008, DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>. <https://www.rfc-editor.org/info/rfc5120>.
skipping to change at page 17, line 10 skipping to change at page 17, line 14
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008, DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>. <https://www.rfc-editor.org/info/rfc5308>.
[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
R. Aggarwal, "Support of Address Families in OSPFv3", R. Aggarwal, "Support of Address Families in OSPFv3",
RFC 5838, DOI 10.17487/RFC5838, April 2010, RFC 5838, DOI 10.17487/RFC5838, April 2010,
<https://www.rfc-editor.org/info/rfc5838>. <https://www.rfc-editor.org/info/rfc5838>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
Authors' Addresses Authors' Addresses
Pushpasis Sarkar (editor) Pushpasis Sarkar (editor)
Arrcus, Inc. Arrcus, Inc.
Email: pushpasis.ietf@gmail.com Email: pushpasis.ietf@gmail.com
Shraddha Hegde Shraddha Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
Electra, Exora Business Park Electra, Exora Business Park
Bangalore, KA 560103 Bangalore, KA 560103
India India
Email: shraddha@juniper.net Email: shraddha@juniper.net
Uma Chunduri (editor) Uma Chunduri (editor)
Huawei Technologies Huawei USA
2330 Central Expressway 2330 Central Expressway
Santa Clara, CA 95050 Santa Clara, CA 95050
USA USA
Email: uma.chunduri@huawei.com Email: uma.chunduri@huawei.com
Jeff Tantsura Jeff Tantsura
Individual Individual
Email: jefftant.ietf@gmail.com Email: jefftant.ietf@gmail.com
 End of changes. 20 change blocks. 
39 lines changed or deleted 45 lines changed or added

This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/