draft-ietf-rtgwg-multihomed-prefix-lfa-05.txt   draft-ietf-rtgwg-multihomed-prefix-lfa-06.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: August 10, 2018 U. Chunduri, Ed. Expires: August 12, 2018 U. Chunduri, Ed.
Huawei USA Huawei USA
J. Tantsura J. Tantsura
Individual Nuage Networks
H. Gredler H. Gredler
RtBrick, Inc. RtBrick, Inc.
February 6, 2018 February 8, 2018
LFA selection for Multi-Homed Prefixes LFA selection for Multi-Homed Prefixes
draft-ietf-rtgwg-multihomed-prefix-lfa-05 draft-ietf-rtgwg-multihomed-prefix-lfa-06
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 [RFC 5286]. 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
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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 August 10, 2018. This Internet-Draft will expire on August 12, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 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
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This document also defines the inequalities defined in [RFC5286] This document also defines the inequalities defined in [RFC5286]
specifically for the alternate loop-free ASBR evaluation. specifically for the alternate loop-free ASBR evaluation.
4.2.1. Rules to select alternate ASBR 4.2.1. Rules to select alternate ASBR
The process to select an alternate ASBR is best explained using the The process to select an alternate ASBR is best explained using the
rules below. The below process is applied when primary ASBR for the rules below. The below process is applied when primary ASBR for the
concerned prefix is chosen and there is an alternate ASBR originating concerned prefix is chosen and there is an alternate ASBR originating
same prefix. same prefix.
1. If RFC1583Compatibility is disabled 1. If RFC1583Compatibility is disabled
1a. if primary ASBR and alternate ASBR are intra area 1a. if primary ASBR and alternate ASBR are intra area
non-backbone path go to step 2. non-backbone path go to step 2.
1b. If primary ASBR and alternate ASBR belong to 1b. If primary ASBR and alternate ASBR belong to
intra-area backbone and/or inter-area path go intra-area backbone and/or inter-area path go
to step 2. to step 2.
1c. for other paths, skip this alternate ASBR and 1c. for other paths, skip this alternate ASBR and
consider next ASBR. consider next ASBR.
2. If cost type (type1/type2) advertised by alternate 2. If cost type (type1/type2) advertised by alternate
ASBR same as primary ASBR same as primary
2a. If not, same skip alternate ASBR and consider 2a. If not, same skip alternate ASBR and consider next ASBR.
next ASBR. 2b. If same proceed to step 3.
2b. If same proceed to step 3.
3. If cost type is type1 3. If cost type is type1
3a. If cost is same, program ECMP and return. 3a. If cost is same, program ECMP and return.
3b. else go to step 5. 3b. else go to step 5.
4 If cost type is type 2 4 If cost type is type 2
4a. If cost is different, skip alternate ASBR and 4a. If cost is different, skip alternate ASBR and
consider next ASBR. consider next ASBR.
4b. If type2 cost is same, proceed to step 4c to compare 4b. If type2 cost is same, proceed to step 4c to compare
compare type 1 cost. compare type 1 cost.
4c. If type1 cost is also same program ECMP and return. 4c. If type1 cost is also same program ECMP and return.
4d. If type 1 cost is different go to step 5. 4d. If type 1 cost is different go to step 5.
5. If route type (type 5/type 7) 5. If route type (type 5/type 7)
5a. If route type is same, check route p-bit, 5a. If route type is same, check route p-bit,
forwarding address field for routes from both forwarding address field for routes from both
ASBRs match. If p-bit matches proceed to step 6. ASBRs match. If p-bit matches proceed to step 6.
If not, skip this alternate ASBR and consider If not, skip this alternate ASBR and consider
next ASBR. next ASBR.
5b. If route type is not same, skip this alternate ASBR 5b. If route type is not same, skip this alternate ASBR
and consider next alternate ASBR. and consider next alternate ASBR.
6. Apply inequality on the alternate ASBR. 6. Apply inequality on the alternate ASBR.
Figure 5: Rules for selecting alternate ASBR in OSPF Figure 5: Rules for selecting alternate ASBR in OSPF
4.2.2. Multiple ASBRs belonging different area 4.2.2. Multiple ASBRs belonging different area
When "RFC1583compatibility" is set to disabled, OSPF [RFC2328] When "RFC1583compatibility" is set to disabled, OSPF [RFC2328]
defines certain rules of preference to choose the ASBRs. While defines certain rules of preference to choose the ASBRs. While
selecting alternate ASBR for loop evaluation for LFA, these rules selecting alternate ASBR for loop evaluation for LFA, these rules
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.
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Uma Chunduri (editor) Uma Chunduri (editor)
Huawei USA 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 Nuage Networks
755 Ravendale Drive
Mountain View, CA 94043
USA
Email: jefftant.ietf@gmail.com Email: jefftant.ietf@gmail.com
Hannes Gredler Hannes Gredler
RtBrick, Inc. RtBrick, Inc.
Email: hannes@rtbrick.com Email: hannes@rtbrick.com
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