draft-ietf-rtgwg-multihomed-prefix-lfa-07.txt   draft-ietf-rtgwg-multihomed-prefix-lfa-08.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) U. Chunduri, Ed. Updates: 5286 (if approved) U. Chunduri, Ed.
Intended status: Standards Track Huawei USA Intended status: Standards Track Huawei USA
Expires: March 23, 2019 S. Hegde Expires: April 19, 2019 S. Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
J. Tantsura J. Tantsura
Nuage Networks Apstra, Inc.
H. Gredler H. Gredler
RtBrick, Inc. RtBrick, Inc.
September 19, 2018 October 16, 2018
LFA selection for Multi-Homed Prefixes LFA selection for Multi-Homed Prefixes
draft-ietf-rtgwg-multihomed-prefix-lfa-07 draft-ietf-rtgwg-multihomed-prefix-lfa-08
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 (LFAs) for multi-homed prefixes.
particular, this document provides explicit inequalities that can be In particular, this document provides explicit inequalities that can
used to evaluate neighbors as a potential alternates for multi-homed be used to evaluate neighbors as a potential alternates for multi-
prefixes. It also provides detailed criteria for evaluating homed 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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC8174 [RFC8174]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC8174 [RFC2119] RFC8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
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
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 March 23, 2019.
This Internet-Draft will expire on April 19, 2019.
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
skipping to change at page 2, line 26 skipping to change at page 2, line 29
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
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. LFA inequalities for MHPs . . . . . . . . . . . . . . . . . . 4 2. LFA inequalities for MHPs . . . . . . . . . . . . . . . . . . 4
3. LFA selection for the multi-homed prefixes . . . . . . . . . 4 3. LFA selection for the multi-homed prefixes . . . . . . . . . 5
3.1. Improved coverage with simplified approach to MHPs . . . 6 3.1. Improved coverage with simplified approach to MHPs . . . 6
3.2. IS-IS ATT Bit considerations . . . . . . . . . . . . . . 7 3.2. IS-IS ATT Bit considerations . . . . . . . . . . . . . . 8
4. LFA selection for the multi-homed external prefixes . . . . . 8 4. LFA selection for the multi-homed external prefixes . . . . . 8
4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Rules to select alternate ASBR . . . . . . . . . . . 8 4.2.1. Rules to select alternate ASBR . . . . . . . . . . . 9
4.2.1.1. Multiple ASBRs belonging different area . . . . . 9 4.2.1.1. Multiple ASBRs belonging different area . . . . . 11
4.2.1.2. Type 1 and Type 2 costs . . . . . . . . . . . . . 10 4.2.1.2. Type 1 and Type 2 costs . . . . . . . . . . . . . 11
4.2.1.3. RFC1583compatibility is set to enabled . . . . . 10 4.2.1.3. RFC1583compatibility is set to enabled . . . . . 11
4.2.1.4. Type 7 routes . . . . . . . . . . . . . . . . . . 10 4.2.1.4. Type 7 routes . . . . . . . . . . . . . . . . . . 11
4.2.2. Inequalities to be applied for alternate ASBR 4.2.2. Inequalities to be applied for alternate ASBR
selection . . . . . . . . . . . . . . . . . . . . . . 11 selection . . . . . . . . . . . . . . . . . . . . . . 12
4.2.2.1. Forwarding address set to non-zero value . . . . 11 4.2.2.1. Forwarding address set to non-zero value . . . . 12
4.2.2.2. ASBRs advertising type1 and type2 cost . . . . . 11 4.2.2.2. ASBRs advertising type1 and type2 cost . . . . . 12
5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 12 5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13
5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 12 5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13
5.2. Multi Topology Considerations . . . . . . . . . . . . . . 13 5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 14 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
A framework for the development of IP fast- reroute mechanisms is A framework for the development of IP fast-reroute mechanisms is
detailed in [RFC5714]. The use of Loop-Free Alternates (LFA) for IP detailed in [RFC5714]. The use of LFAs for IP Fast Reroute is
Fast Reroute is specified in [RFC5286]. Section 6.1 of [RFC5286] specified in [RFC5286]. Section 6.1 of [RFC5286] describes a method
describes a method to determine loop-free alternates for multi-homed to determine LFAs for multi-homed prefixes (MHPs). This document
prefixes (MHPs). This document describes a procedure using explicit describes a procedure using explicit inequalities that can be used by
inequalities that can be used by a computing router to evaluate a a computing router to evaluate a neighbor as a potential alternate
neighbor as a potential alternate for a multi-homed prefix. The for a multi-homed prefix. The results obtained are equivalent to
results obtained are equivalent to those obtained using the method those obtained using the method described in Section 6.1 of
described in Section 6.1 of [RFC5286]. However, some may find this [RFC5286]. However, some may find this formulation useful.
formulation useful.
Section 6.3 of [RFC5286] discusses complications associated with Section 6.3 of [RFC5286] discusses complications associated with
computing LFAs for multi-homed prefixes in OSPF. This document computing LFAs for multi-homed prefixes in OSPF. This document
provides detailed criteria for evaluating potential alternates for provides detailed criteria for evaluating potential alternates for
external prefixes advertised by OSPF ASBRs, as well as explicit external prefixes advertised by OSPF ASBRs, as well as explicit
inequalities. inequalities.
This document also provides clarifications, additional considerations This document also provides clarifications, additional considerations
to [RFC5286], to address a few coverage and operational observations. to [RFC5286], to address a few coverage and operational observations.
These observations are in the area of handling IS-IS attach (ATT) bit These observations are in the area of handling IS-IS attach (ATT) bit
in Level-1 (L1) area, links provisioned with MAX_METRIC for traffic in Level-1 (L1) area, links provisioned with MAX_METRIC for traffic
engineering (TE) purposes and in the area of Multi Topology (MT) IGP engineering (TE) purposes and in the area of Multi Topology (MT) IGP
deployments. These are elaborated in detail in Section 3.2 and deployments. These are elaborated in detail in Section 3.2 and
Section 5. Section 5.
This specification uses the same terminology introduced in [RFC5714]
to represent LFA and builds on the inequalities notation used in
[RFC5286] to compute LFAs for MHPs.
1.1. Acronyms 1.1. Acronyms
AF - Address Family AF - Address Family
ATT - IS-IS Attach Bit ATT - IS-IS Attach Bit
ECMP - Equal Cost Multi Path ECMP - Equal Cost Multi Path
IGP - Interior Gateway Protocol IGP - Interior Gateway Protocol
IS-IS - Intermediate System to Intermediate System IS-IS - Intermediate System to Intermediate System
LFA - Loop-Free Alternate
LSP - IS-IS Link State PDU LSP - IS-IS Link State PDU
OSPF - Open Shortest Path First OSPF - Open Shortest Path First
MHP - Multi-homed Prefix MHP - Multi-homed Prefix
MT - Multi Topology MT - Multi Topology
SPF - Shortest Path First PDU SPF - Shortest Path First PDU
2. LFA inequalities for MHPs 2. LFA inequalities for MHPs
This document proposes the following set of LFA inequalities for This document proposes the following set of LFA inequalities for
selecting the most appropriate LFAs for multi-homed prefixes (MHPs). selecting the most appropriate LFAs for multi-homed prefixes (MHPs).
They can be derived from the inequalities in [RFC5286] combined with They can be derived from the inequalities in [RFC5286] combined with
the observation that D_opt(N,P) = Min (D_opt(N,PO_i) + cost(PO_i,P)) the observation that D_opt(N,P) = Min (D_opt(N,PO_i) + Cost(PO_i,P))
over all PO_i over all PO_i
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)
Node-Protection: Node-Protection:
D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) + D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
D_opt(E,PO_best) + cost(PO_best,P) D_opt(E,PO_best) + Cost(PO_best,P)
Where, Where,
P - The multi-homed prefix being evaluated for P - The multi-homed prefix being evaluated for
computing alternates computing alternates
S - The computing router S - The computing router
N - The alternate router being evaluated N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to E - The primary next-hop on shortest path from S to
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,P) - Cost of reaching the prefix P from prefix Cost(X,P) - Cost of reaching the prefix P from prefix
originating node X. originating node X.
D_opt(X,Y) - Distance on the shortest path from node X to node D_opt(X,Y) - Distance on the shortest path from node X to node
Y. Y.
Figure 1: LFA inequalities for MHPs Figure 1: LFA inequalities for MHPs
3. LFA selection for the multi-homed prefixes 3. LFA selection for the multi-homed prefixes
To compute a valid LFA for a given multi-homed prefix P, a computing To compute a valid LFA for a given multi-homed prefix P, a computing
router S MUST follow one of the appropriate procedures below, for router S MUST follow one of the appropriate procedures below, for
skipping to change at page 6, line 27 skipping to change at page 6, line 33
failure optimal point of attachment, at the expense of potentially failure optimal point of attachment, at the expense of potentially
lower coverage. If an implementation chooses to simplify the multi- lower coverage. If an implementation chooses to simplify the multi-
homed prefix calculation by assuming that the MHP is solely attached homed prefix calculation by assuming that the MHP is solely attached
to the router that was its pre-failure optimal point of attachment, to the router that was its pre-failure optimal point of attachment,
the procedure described in this memo can potentially improve coverage the procedure described in this memo can potentially improve coverage
for equal cost multi path (ECMP) MHPs without incurring extra for equal cost multi path (ECMP) MHPs without incurring extra
computational cost. computational cost.
This document improves the above approach to provide loop-free This document improves the above approach to provide loop-free
alternatives without any additional cost for ECMP MHPs as described alternatives without any additional cost for ECMP MHPs as described
through the below example network. The approach specified here MAY through the below example network presented in Figure 3. The
also be applicable for handling default routes as explained in approach specified here MAY also be applicable for handling default
Section 3.2. routes as explained in Section 3.2.
5 +---+ 8 +---+ 5 +---+ 5 +---+ 8 +---+ 5 +---+
+-----| S |------| A |-----| B | +-----| S |------| A |-----| B |
| +---+ +---+ +---+ | +---+ +---+ +---+
| | | | | |
| 5 | 5 | | 5 | 5 |
| | | | | |
+---+ 5 +---+ 4 +---+ 1 +---+ +---+ 5 +---+ 4 +---+ 1 +---+
| C |---| E |-----| M |-------| F | | C |---| E |-----| M |-------| F |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| 10 5 | | 10 5 |
+-----------P---------+ +-----------P---------+
Figure 3: MHP with same ECMP Next-hop Figure 3: MHP with same ECMP Next-hop
In the above network a prefix p, is advertised from both Node E and In the above network a prefix P, is advertised from both Node E and
Node F. With simplified approach taken as specified in [RFC5286] Node F. With simplified approach taken as specified in [RFC5286]
Section 6.1, prefix P will get only link protection LFA through the Section 6.1, prefix P will get only link protection LFA through the
neighbor C while a node protection path is available through neighbor neighbor C while a node protection path is available through neighbor
A. In this scenario, E and F both are pre-failure optimal points of A. In this scenario, E and F both are pre-failure optimal points of
attachment and share the same primary next-hop. Hence, an attachment and share the same primary next-hop. Hence, an
implementation MAY compare the kind of protection A provides to F implementation MAY compare the kind of protection A provides to F
(link-and-node protection) with the kind of protection C provides to (link-and-node protection) with the kind of protection C provides to
E (link protection) and inherit the better alternative to prefix P E (link protection) and inherit the better alternative to prefix P
and here it is A. and here it is A.
However, in the below network prefix P has an ECMP through both node However, in the below example network presented in Figure 4, prefix P
E and node F with cost 20. Though it has 2 pre-failure optimal has an ECMP through both node E and node F with cost 20. Though it
points of attachment, the primary next-hop to each pre-failure has 2 pre-failure optimal points of attachment, the primary next-hop
optimal point of attachment is different. In this case, prefix P to each pre-failure optimal point of attachment is different. In
MUST inherit corresponding LFAs of each primary next-hop calculated this case, prefix P MUST inherit corresponding LFAs of each primary
for the router advertising the same respectively. In the below next-hop calculated for the router advertising the same respectively.
diagram that would be node E's and node F's LFA i.e., node N1 and In the below diagram that would be node E's and node F's LFA i.e.,
node N2 respectively. node N1 and node N2 respectively.
4 +----+ 4 +----+
+------------------| N2 | +------------------| N2 |
| +----+ | +----+
| | 4 | | 4
10 +---+ 3 +---+ 10 +---+ 3 +---+
+------| S |----------------| B | +------| S |----------------| B |
| +---+ +---+ | +---+ +---+
| | | | | |
| 10 | 1 | | 10 | 1 |
skipping to change at page 9, line 7 skipping to change at page 10, line 7
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 belong to intra area 1a. if primary ASBR and alternate ASBR belong to intra-area
non-backbone go to step 2. non-backbone 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. Compare cost types (type 1/type 2) advertised by alternate ASBR and 2. Compare cost types (type 1/type 2) advertised by alternate ASBR and
by the primary ASBR by the primary ASBR
2a. If not the same type skip alternate ASBR and consider next ASBR. 2a. If not the same type skip alternate ASBR and
consider next ASBR.
2b. If same proceed to step 3. 2b. If same proceed to step 3.
3.If cost types are type 1, compare costs advertised by alternate ASBR 3.If cost types are type 1, compare costs advertised by alternate ASBR
and by the primary ASBR and by the primary ASBR
3a. If costs are the same then program ECMP FRR and return. 3a. If costs are the same then program ECMP FRR and return.
3b. else go to step 5.. 3b. else go to step 5..
4 If cost types are type 2, compare costs advertised by alternate ASBR 4 If cost types are type 2, compare costs advertised by alternate ASBR
and by the primary ASBR and by the primary ASBR
4a. If costs are different, skip alternate ASBR and 4a. If costs are different, skip alternate ASBR and
consider next ASBR. consider next ASBR.
4b. If cost are the same, proceed to step 4c to compare 4b. If cost are the same, proceed to step 4c to compare
cost to reach ASBR/forwarding address. cost to reach ASBR/forwarding address.
4c. If cost to reach ASBR/forwarding address are also same program ECMP FRR and return. 4c. If cost to reach ASBR/forwarding address are also same
4d. If cost to reach ASBR/forwarding address are different go to step 5. program ECMP FRR and return.
4d. If cost to reach ASBR/forwarding address are 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 and forwarding address matches proceed to step 6. ASBRs match. If p-bit and forwarding address 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
4.2.1.1. Multiple ASBRs belonging different area 4.2.1.1. 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 to ensure that the alternate neighbor does not should be applied to ensure that the alternate neighbor does not
cause loop. cause looping.
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.
4.2.1.2. Type 1 and Type 2 costs 4.2.1.2. Type 1 and Type 2 costs
If there are multiple ASBRs not pruned via rules defined in If there are multiple ASBRs not pruned via rules defined in
Section 4.2.1.1, the cost type advertised by the ASBRs is compared. Section 4.2.1.1, the cost type advertised by the ASBRs is compared.
skipping to change at page 11, line 14 skipping to change at page 12, line 16
4.2.2. Inequalities to be applied for alternate ASBR selection 4.2.2. 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
Section 4.2.1, are evaluated for Loop free criteria using below Section 4.2.1, are evaluated for Loop free criteria using below
inequalities. inequalities.
4.2.2.1. Forwarding address set to non-zero value 4.2.2.1. 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:
F_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) + F_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
F_opt(E,PO_best) + cost(PO_best,P) F_opt(E,PO_best) + Cost(PO_best,P)
Where, Where,
P - The multi-homed prefix being evaluated for P - The multi-homed prefix being evaluated for
computing alternates computing alternates
S - The computing router S - The computing router
N - The alternate router being evaluated N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to E - The primary next-hop on shortest path from S to
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 is non- Figure 6: LFA inequality definition when forwarding address is non-
zero zero
4.2.2.2. ASBRs advertising type1 and type2 cost 4.2.2.2. 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)
Node-Protection: Node-Protection:
D_opt(N,PO_i)+ cost(PO_i,P) < D_opt(N,E) + D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
D_opt(E,PO_best) + cost(PO_best,P) D_opt(E,PO_best) + Cost(PO_best,P)
Where, Where,
P - The multi-homed prefix being evaluated for P - The multi-homed prefix being evaluated for
computing alternates computing alternates
S - The computing router S - The computing router
N - The alternate router being evaluated N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to E - The primary next-hop on shortest path from S to
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.
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 7: LFA inequality definition for type1 and type 2 cost Figure 7: LFA inequality definition for type1 and type 2 cost
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
skipping to change at page 14, line 42 skipping to change at page 15, line 42
8. 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.net
Bruno Decraene Bruno Decraene
Orange, Orange,
France France
Email: bruno.decraene@orange.com Email: bruno.decraene@orange.com
9. Security Considerations 9. Security Considerations
Existing OSPF security considerations and stronger authentication and Existing OSPF security considerations and stronger authentication and
manual key management mechanisms are specified in [RFC7474] SHOULD be manual key management mechanisms are specified in [RFC7474] SHOULD be
considered for OSPF deployments. Security concerns for IS-IS are considered for OSPF deployments. Security concerns for IS-IS are
addressed in [RFC5304] and [RFC5310]. Further security analysis for addressed in [RFC5304] and [RFC5310]. Further security analysis for
IS-IS protocol is done in [RFC7645] SHOULD be considered for IS-IS IS-IS protocol is done in [RFC7645] SHOULD be considered for IS-IS
deployments. This document does not introduce any change in any of deployments. This document does not change any of the discussed
the protocol [RFC1195] [RFC5120] [RFC2328] [RFC5838] specifications protocol specifications [RFC1195] [RFC5120] [RFC2328] [RFC5838], and
discussed here and also this does not introduce any new security the security considerations of the LFA base specification [RFC5286]
issues other than as noted in the LFA base specification [RFC5286]. therefore continue to apply.
10. References 10. References
10.1. 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,
<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>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. 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>.
skipping to change at page 16, line 28 skipping to change at page 17, line 28
[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>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>. 2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>.
[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. [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987, McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013, DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>. <https://www.rfc-editor.org/info/rfc6987>.
skipping to change at page 17, line 26 skipping to change at page 18, line 29
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
Jeff Tantsura Jeff Tantsura
Nuage Networks Apstra, Inc.
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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