draft-ietf-rtgwg-multihomed-prefix-lfa-09.txt   rfc8518.txt 
Routing Area Working Group P. Sarkar, Ed. Internet Engineering Task Force (IETF) P. Sarkar, Ed.
Internet-Draft Arrcus, Inc. Request for Comments: 8518 Arrcus, Inc.
Updates: 5286 (if approved) U. Chunduri, Ed. Updates: 5286 U. Chunduri, Ed.
Intended status: Standards Track Huawei USA Category: Standards Track Huawei USA
Expires: May 25, 2019 S. Hegde ISSN: 2070-1721 S. Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
J. Tantsura J. Tantsura
Apstra, Inc. Apstra, Inc.
H. Gredler H. Gredler
RtBrick, Inc. RtBrick, Inc.
November 21, 2018 March 2019
Loop-Free Alternates selection for Multi-Homed Prefixes Selection of Loop-Free Alternates for Multi-Homed Prefixes
draft-ietf-rtgwg-multihomed-prefix-lfa-09
Abstract Abstract
Deployment experience gained from implementing algorithms to Deployment experience gained from implementing algorithms to
determine Loop-Free Alternates (LFAs) for multi-homed prefixes has determine Loop-Free Alternates (LFAs) for multi-homed prefixes (MHPs)
revealed some avenues for potential improvement. This document has revealed some avenues for potential improvement. This document
provides explicit inequalities that can be used to evaluate neighbors provides explicit inequalities that can be used to evaluate neighbors
as a potential alternates for multi-homed prefixes. It also provides as potential alternates for MHPs. It also provides detailed criteria
detailed criteria for evaluating potential alternates for external for evaluating potential alternates for external prefixes advertised
prefixes advertised by OSPF ASBRs. This documents updates and by OSPF ASBRs. This document updates Section 6 of RFC 5286 by
expands some of the "Routing Aspects" as specified in Section 6 of expanding some of the routing aspects.
RFC 5286.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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 is an Internet Standards Track document.
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
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on May 25, 2019. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8518.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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 ...................................................4
2. LFA inequalities for MHPs . . . . . . . . . . . . . . . . . . 4 1.2. Requirements Language ......................................4
3. LFA selection for the multi-homed prefixes . . . . . . . . . 5 2. LFA Inequalities for MHPs .......................................4
3.1. Improved coverage with simplified approach to MHPs . . . 7 3. LFA Selection for MHPs ..........................................6
3.2. IS-IS ATT Bit considerations . . . . . . . . . . . . . . 8 3.1. Improved Coverage with Simplified Approach to MHPs .........7
4. LFA selection for the multi-homed external prefixes . . . . . 9 3.2. IS-IS ATT Bit Considerations ...............................9
4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. LFA Selection for Multi-Homed External Prefixes ................10
4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. IS-IS .....................................................10
4.2.1. Rules to select alternate ASBR . . . . . . . . . . . 9 4.2. OSPF ......................................................10
4.2.1.1. Multiple ASBRs belonging different area . . . . . 11 4.2.1. Rules to Select Alternate ASBRs ....................10
4.2.1.2. Type 1 and Type 2 costs . . . . . . . . . . . . . 11 4.2.1.1. Multiple ASBRs Belonging to Different Areas ..12
4.2.1.3. RFC1583compatibility is set to enabled . . . . . 11 4.2.1.2. Type 1 and Type 2 Costs ......................12
4.2.1.4. Type 7 routes . . . . . . . . . . . . . . . . . . 11 4.2.1.3. RFC1583Compatibility is Set to "Enabled" .....12
4.2.2. Inequalities to be applied for alternate ASBR 4.2.1.4. Type 7 Routes ................................13
selection . . . . . . . . . . . . . . . . . . . . . . 12 4.2.2. Inequalities to Be Applied for Alternate ASBR
4.2.2.1. Forwarding address set to non-zero value . . . . 12 Selection ..........................................13
4.2.2.2. ASBRs advertising type1 and type2 cost . . . . . 13 4.2.2.1. Forwarding Address Set to Non-zero Value .....13
5. LFA Extended Procedures . . . . . . . . . . . . . . . . . . . 13 4.2.2.2. ASBRs Advertising Type 1 and Type 2 Costs ....14
5.1. Links with IGP MAX_METRIC . . . . . . . . . . . . . . . . 13 5. LFA Extended Procedures ........................................15
5.2. Multi Topology Considerations . . . . . . . . . . . . . . 14 5.1. Links with IGP MAX_METRIC .................................15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 5.2. MT Considerations .........................................16
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations ............................................16
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 7. Security Considerations ........................................17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8. References .....................................................17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References ......................................17
10.1. Normative References . . . . . . . . . . . . . . . . . . 16 8.2. Informative References ....................................17
10.2. Informative References . . . . . . . . . . . . . . . . . 16 Acknowledgements ..................................................19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Contributors ......................................................19
Authors' Addresses ................................................20
1. Introduction 1. Introduction
A framework for the development of IP fast-reroute mechanisms is A framework for the development of IP Fast Reroute (FRR) mechanisms
detailed in [RFC5714]. The use of LFAs for IP Fast Reroute is is detailed in [RFC5714]. The use of LFAs for IP FRR is specified in
specified in [RFC5286]. If a prefix is advertised by more than one [RFC5286]. If a prefix is advertised by more than one router, that
router that prefix is called as multi-homed prefix (MHP). MHPs prefix is called a "multi-homed prefix (MHP)". MHPs generally occur
generally occur for prefixes obtained from outside the routing domain for prefixes obtained from outside the routing domain by multiple
by multiple routers, for subnets on links where the subnet is routers, for subnets on links where the subnet is announced from
announced from multiple ends of the link, and for prefixes advertised multiple ends of the link, and for prefixes advertised by multiple
by multiple routers to provide resiliency. routers to provide resiliency.
Section 6.1 of [RFC5286] describes a method to determine LFAs for Section 6.1 of [RFC5286] describes a method to determine LFAs for
MHPs. This document describes a procedure using explicit MHPs. This document describes a procedure using explicit
inequalities that can be used by a computing router to evaluate a inequalities that can be used by a computing router to evaluate a
neighbor as a potential alternate for a MHP. The results obtained neighbor as a potential alternate for an MHP. The results obtained
are equivalent to those obtained using the method described in are equivalent to those obtained using the method described in
Section 6.1 of [RFC5286]. Section 6.1 of [RFC5286].
Section 6.3 of [RFC5286] discusses complications associated with Section 6.3 of [RFC5286] discusses complications associated with
computing LFAs for MHPs in OSPF. This document provides detailed computing LFAs for MHPs in OSPF. This document provides detailed
criteria for evaluating potential alternates for external prefixes criteria for evaluating potential alternates for external prefixes
advertised by OSPF ASBRs, as well as explicit inequalities. advertised by OSPF ASBRs, as well as explicit inequalities.
This document also provides clarifications, additional considerations This document also provides clarifications and additional
to [RFC5286], to address a few coverage and operational observations. considerations to [RFC5286] to address a few coverage and operational
These observations are in the area of handling IS-IS attach (ATT) bit observations. These observations are concerned with 1) the IS-IS ATT
in Level-1 (L1) area, links provisioned with MAX_METRIC (see (attach) bit in the Level 1 (L1) area, 2) links provisioned with
Section 5.1) for traffic engineering (TE) purposes and in the area of MAX_METRIC (see Section 5.1) for traffic engineering (TE) purposes,
Multi Topology (MT) IGP deployments. These are elaborated in detail and 3) multi-topology (MT) IGP deployments. These are elaborated in
in Section 3.2 and Section 5. detail in Sections 3.2 and 5.
This specification uses the same terminology introduced in [RFC5714] This specification uses the same terminology introduced in [RFC5714]
to represent LFA and builds on the inequalities notation used in to represent LFA and builds on the notation for inequalities used in
[RFC5286] to compute LFAs for MHPs. [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 Multipath
FRR - Fast Reroute
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 LFA - Loop-Free Alternate
LSP - IS-IS Link State PDU LSP - Link State PDU (IS-IS)
OSPF - Open Shortest Path First MHP - Multi-Homed Prefix
MHP - Multi-homed Prefix MT - Multi-Topology
MT - Multi Topology OSPF - Open Shortest Path First
SPF - Shortest Path First SPF - Shortest Path First
2. LFA inequalities for MHPs 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 MHPs. D_opt(X,Y) terminology selecting the most appropriate LFAs for MHPs. Distance_opt(X,Y)
is defined in [RFC5714], which is nothing but the metric sum of the (called "D_opt(X,Y)" in this document) is defined in [RFC5714] and is
shortest path from X to Y and Cost(X,Y) introduced in this document nothing but the metric sum of the shortest path from X to Y.
is defined as the metric value of prefix Y from the prefix Cost(X,Y), introduced in this document, is defined as the metric
advertising node X. These LFAs can be derived from the inequalities value of prefix Y from the prefix advertising node X. These LFAs can
in [RFC5286] combined with the observation that D_opt(N,P) = Min be derived from the inequalities in [RFC5286] combined with the
(D_opt(N,PO_i) + Cost(PO_i,P)) over all PO_i observation that D_opt(N,P) = Min (D_opt(N,PO_i) + Cost(PO_i,P)) over
all PO_i.
Link-Protection: Link-Protecting LFAs:
A neighbor N can provide a loop-free alternate (LFA) if and only if A neighbor N can provide an LFA if and only if
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-Protecting + Downstream-paths-only LFAs:
A subset of loop-free alternates are downstream paths that must meet A subset of loop-free alternates are downstream paths that must
a more restrictive condition that is applicable to more complex meet a more restrictive condition that is applicable to more
failure scenarios complex failure scenarios.
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-Protecting LFAs:
For an alternate next-hop N to protect against node failure of a For an alternate next hop N to protect against node failure of a
primary neighbor E for MHP P, N must be loop-free with primary neighbor E for MHP P, N must be loop-free with respect to
respect to both E and mhp P. In other words, N's path to MHP P must not go both E and MHP P. In other words, N's path to MHP P must not go
through E (where N is the neighbor providing a loop-free alternate) through E (where N is the neighbor providing a loop-free
alternate).
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
computing alternates
S - The computing router
N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to
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,P) - Cost of reaching the prefix P from prefix
originating node X.
D_opt(X,Y) - Distance on the shortest path from node X to node
Y.
Figure 1: LFA inequalities for MHPs P - The MHP being evaluated for computing alternates
3. LFA selection for the multi-homed prefixes S - The computing router
To compute a valid LFA for a given MHP P, a computing router S MUST N - The alternate router being evaluated
follow one of the appropriate procedures below, for each alternate
neighbor N and once for each remote node that originated the prefix E - The primary next hop on the shortest path from S to
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,P) - The cost of reaching the prefix P from prefix
originating node X
D_opt(X,Y) - The distance on the shortest path from node X to
node Y
3. LFA Selection for MHPs
To compute a valid LFA for a given MHP P, a computing router S MUST,
for each alternate neighbor N, follow one of the appropriate
procedures below once for each remote node that originated the prefix
P. P.
Link-Protection : Link-Protecting LFAs:
=================
1. if, in addition to being an alternate neighbor, N is also a prefix-originator of P,
1.a. Select N as a LFA for prefix P (irrespective of
the metric advertised by N for the prefix P).
2. Else, evaluate the link-protecting LFA inequality for P with
the N as the alternate neighbor.
2.a. If LFA inequality condition is met,
select N as a LFA for prefix P.
2.b. Else, N is not a LFA for prefix P.
Link-Protection + Downstream-paths-only : 1. If, in addition to being an alternate neighbor, N is also a
========================================= prefix originator of P,
1. Evaluate the link-protecting + downstream-only LFA inequality
for P with the N as the alternate neighbor.
1.a. If LFA inequality condition is met,
select N as a LFA for prefix P.
1.b. Else, N is not a LFA for prefix P.
Node-Protection : A. Select N as an LFA for prefix P (irrespective of the metric
================= advertised by N for the prefix P).
1. if, in addition to being an alternate neighbor, N is also a prefix-originator of P,
1.a. Select N as a LFA for prefix P (irrespective of
the metric advertised by N for the prefix P).
2. Else, evaluate the appropriate node-protecting LFA inequality
for P with the N as the alternate neighbor.
2.a. If LFA inequality condition is met,
select N as a LFA for prefix P.
2.b. Else, N is not a LFA for prefix P.
Figure 2: Rules for selecting LFA for MHPs 2. Else, evaluate the link-protecting LFA inequality for P with N as
the alternate neighbor.
In case an alternate neighbor N is also one of the prefix-originators A. If the LFA inequality condition is met, select N as an LFA
of prefix P, N being a prefix-originator it is guaranteed that N will for prefix P.
not loop back packets destined for prefix P to computing router S.
So N MUST be chosen as a valid LFA for prefix P, without evaluating
any of the inequalities in Figure 1 as long as downstream-paths-only
LFA is not desired. To ensure such a neighbor N also provides a
downstream-paths-only LFA, router S MUST also evaluate the
downstream-only LFA inequality specified in Figure 1 for neighbor N
and ensure router N satisfies the inequality.
However, if N is not a prefix-originator of P, the computing router B. Else, N is not an LFA for prefix P.
MUST evaluate one of the corresponding LFA inequalities, as mentioned
in Figure 1, once for each remote node that originated the prefix.
In case the inequality is satisfied by the neighbor N router S MUST
choose neighbor N, as one of the valid LFAs for the prefix P.
For more specific rules please refer to the later sections of this Link-Protecting + Downstream-paths-only LFAs:
document.
3.1. Improved coverage with simplified approach to MHPs 1. Evaluate the link-protecting + downstream-paths-only LFA
inequality for P with N as the alternate neighbor.
LFA base specification [RFC5286] Section 6.1 recommends that a router A. If the LFA inequality condition is met, select N as an LFA
computes the alternate next-hop for an IGP MHP by considering for prefix P.
alternate paths via all routers that have announced that prefix and
the same has been elaborated with appropriate inequalities in the B. Else, N is not an LFA for prefix P.
above section. However, [RFC5286] Section 6.1 also allows for the
router to simplify the MHP calculation by assuming that the MHP is Node-Protecting LFAs:
solely attached to the router that was its pre-failure optimal point
of attachment, at the expense of potentially lower coverage. If an 1. If, in addition to being an alternate neighbor, N is also a
implementation chooses to simplify the MHP calculation by assuming prefix originator of P,
that the MHP is solely attached to the router that was its pre-
failure optimal point of attachment, the procedure described in this A. Select N as an LFA for prefix P (irrespective of the metric
memo can potentially improve coverage for equal cost multi path advertised by N for the prefix P).
(ECMP) MHPs without incurring extra computational cost.
2. Else, evaluate the appropriate node-protecting LFA inequality for
P with N as the alternate neighbor.
A. If the LFA inequality condition is met, select N as an LFA
for prefix P.
B. Else, N is not an LFA for prefix P.
If an alternate neighbor N is also one of the prefix originators of
prefix P, it is guaranteed that N will not loop back packets destined
for prefix P to computing router S. Therefore, N MUST be chosen as a
valid LFA for prefix P without evaluating any of the inequalities in
Section 2 as long as a downstream-paths-only LFA is not desired. To
ensure such a neighbor N also provides a downstream-paths-only LFA,
router S MUST also evaluate the downstream-paths-only LFA inequality
specified in Section 2 for neighbor N and ensure router N satisfies
the inequality.
However, if N is not a prefix originator of P, the computing router
MUST evaluate one of the corresponding LFA inequalities defined in
Section 2 once for each remote node that originated the prefix. If
the inequality is satisfied by the neighbor N, router S MUST choose
neighbor N as one of the valid LFAs for the prefix P.
For more specific rules, please refer to Section 4.
3.1. Improved Coverage with Simplified Approach to MHPs
Section 6.1 of the LFA base specification [RFC5286] recommends that a
router computes the alternate next hop for an IGP MHP by considering
alternate paths via all routers that have announced that prefix. The
same has been elaborated with appropriate inequalities in the
previous section. However, Section 6.1 of [RFC5286] also allows for
the router to simplify the MHP calculation by assuming that the MHP
is solely attached to the router that was its pre-failure optimal
point of attachment, at the expense of potentially lower coverage.
If an implementation chooses to simplify the MHP calculation by
assuming that the MHP is solely attached to the router that was its
pre-failure optimal point of attachment, the procedure described in
this memo can potentially improve coverage for ECMP MHPs without
incurring extra 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 presented in Figure 3. The in the example network presented in Figure 1. The approach specified
approach specified here may also be applicable for handling default here may also be applicable for handling default routes as explained
routes as explained in Section 3.2. 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 1: MHP with Same ECMP Next Hop
In the above network a prefix P, is advertised from both Node E and In Figure 1, a prefix P is advertised from both node E and node F.
Node F. With simplified approach taken as specified in [RFC5286] With a simplified approach taken as specified in Section 6.1 of
Section 6.1, prefix P will get only link protection LFA through the [RFC5286], prefix P will get only a link-protecting 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. In this case, the better alternative is A.
However, in the below example network presented in Figure 4, prefix P However, in the example network presented in Figure 2, prefix P has
has an ECMP through both node E and node F with cost 20. Though it an ECMP through both node E and node F with cost 20. Though it has
has 2 pre-failure optimal points of attachment, the primary next-hop two pre-failure optimal points of attachment, the primary next hop to
to each pre-failure optimal point of attachment is different. In each pre-failure optimal point of attachment is different. In this
this case, prefix P MUST inherit corresponding LFAs of each primary case, prefix P MUST inherit the corresponding LFAs of each primary
next-hop calculated for the router advertising the same respectively. next hop calculated for the router advertising the same. In
In the below diagram that would be node E's and node F's LFA i.e., Figure 2, that would be the LFA for node E and node F, i.e., node N1
node N1 and node N2 respectively. and node N2, respectively.
4 +----+ 4 +----+
+------------------| N2 | +------------------| N2 |
| +----+ | +----+
| | 4 | | 4
10 +---+ 3 +---+ 10 +---+ 3 +---+
+------| S |----------------| B | +------| S |----------------| B |
| +---+ +---+ | +---+ +---+
| | | | | |
| 10 | 1 | | 10 | 1 |
| | | | | |
+----+ 5 +---+ 16 +---+ +----+ 5 +---+ 16 +---+
| N1 |----| E |-----------------| F | | N1 |----| E |-----------------| F |
+----+ +---+ +---+ +----+ +---+ +---+
| 10 16 | | 10 16 |
+-----------P---------+ +-----------P---------+
Figure 4: MHP with different ECMP Next-hops Figure 2: MHP with Different ECMP Next Hops
In summary, if there are multiple pre-failure points of attachment In summary, if there are multiple pre-failure points of attachment
for a MHP and primary next-hop of a MHP is same as that of the for an MHP, and the primary next hop of an MHP is the same as that of
primary next-hop of the router that was pre-failure optimal point of the primary next hop of the router that was the pre-failure optimal
attachment, an implementation MAY provide a better protection to MHP point of attachment, an implementation MAY provide a better
without incurring any additional computation cost. protection to the MHP without incurring any additional computation
cost.
3.2. IS-IS ATT Bit considerations 3.2. IS-IS ATT Bit Considerations
Per [RFC1195] a default route needs to be added in Level1 (L1) router Per [RFC1195], a default route needs to be added in the Level 1 (L1)
to the closest reachable Level1/Level2 (L1/L2) router in the network router to the closest reachable Level 1 / Level 2 (L1/L2) router in
advertising ATT (attach) bit in its LSP-0 fragment. All L1 routers the network advertising the ATT (attach) bit in its LSP-0 fragment.
in the area would do this during the decision process with the next- All L1 routers in the area would do this during the decision process
hop of the default route set to the adjacent router through which the with the next hop of the default route set to the adjacent router
closest L1/L2 router is reachable. The base LFA specification through which the closest L1/L2 router is reachable. The LFA base
[RFC5286] does not specify any procedure for computing LFA for a specification [RFC5286] does not specify any procedure for computing
default route in IS-IS L1 area. This document specifies, a node can LFA for a default route in the IS-IS L1 area. This document
consider a default route is being advertised from the border L1/L2 specifies that a node can consider a default route is being
router where ATT bit is set, and can do LFA computation for that advertised from the border L1/L2 router where the ATT bit is set and
default route. But, when multiple ECMP L1/L2 routers are reachable can do LFA computation for that default route. But, when multiple
in an L1 area corresponding best LFAs SHOULD be computed for each ECMP L1/L2 routers are reachable in an L1 area, corresponding best
primary next-hop associated with default route as this would be LFAs SHOULD be computed for each primary next hop associated with the
similar to ECMP MHP example as described in Section 3.1. default route as this would be similar to the ECMP MHP example
Considerations as specified in Section 3 and Section 3.1 are described in Section 3.1. Considerations specified in Sections 3 and
applicable for default routes, if the default route is considered as 3.1 are applicable for default routes if the default route is
ECMP MHP. Note that, this document doesn't alter any ECMP handling considered an ECMP MHP. Note that this document doesn't alter any
rules or computation of LFAs for ECMP in general as laid out in ECMP handling rules or computation of LFAs for ECMP in general as
[RFC5286]. laid out in [RFC5286].
4. LFA selection for the multi-homed external prefixes 4. LFA Selection for Multi-Homed External Prefixes
Redistribution of external routes into IGP is required in case of two Redistribution of external routes into IGP is required 1) when two
different networks getting merged into one or during protocol different networks get merged into one or 2) during protocol
migrations. External routes could be distributed into an IGP domain migrations.
via multiple nodes to avoid a single point of failure.
During LFA calculation, alternate LFA next-hops to reach the best During LFA calculation, alternate LFA next hops to reach the best
ASBR could be used as LFA for the routes redistributed via that ASBR. ASBR could be used as LFA for the routes redistributed via that ASBR.
When there is no LFA available to the best ASBR, it may be desirable When there is no LFA available to the best ASBR, it may be desirable
to consider the other ASBRs (referred to as alternate ASBR hereafter) to consider the other ASBRs (referred to as "alternate ASBRs"
redistributing the external routes for LFA selection as defined in hereafter) redistributing the external routes for LFA selection as
[RFC5286] and leverage the advantage of having multiple re- defined in [RFC5286] and leverage the advantage of having multiple
distributing nodes in the network. redistributing nodes in the network.
4.1. IS-IS 4.1. IS-IS
LFA evaluation for multi-homed external prefixes in IS-IS is same to LFA evaluation for multi-homed external prefixes in IS-IS is the same
the multi-homed internal prefixes. Inequalities described in as the multi-homed internal prefixes. Inequalities described in
Section 2 would also apply to multi-homed external prefixes. Section 2 would also apply to multi-homed external prefixes.
4.2. OSPF 4.2. OSPF
Loop Free Alternates [RFC5286] describes mechanisms to apply The LFA base specification [RFC5286] describes mechanisms to apply
inequalities to find the loop free alternate neighbor. For the inequalities to find the loop-free alternate neighbor. Additional
selection of alternate ASBR for LFA consideration, additional rules rules have to be applied in selecting the alternate ASBR for LFA
have to be applied in selecting the alternate ASBR due to the consideration due to the external route calculation rules imposed by
external route calculation rules imposed by [RFC2328]. [RFC2328].
This document defines inequalities specifically for the alternate This document defines inequalities specifically for alternate loop-
loop-free ASBR evaluation, based on those in [RFC5286]. free ASBR evaluation. These inequalities are based on those in
[RFC5286].
4.2.1. Rules to select alternate ASBR 4.2.1. Rules to Select Alternate ASBRs
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 process below is applied when a primary ASBR for
concerned prefix is chosen and there is an alternate ASBR originating the concerned prefix is chosen and there is an alternate ASBR
same prefix. originating the same prefix.
1. If RFC1583Compatibility is disabled 1. If RFC1583Compatibility is disabled:
1a. if primary ASBR and alternate ASBR belong to intra-area A. 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
intra-area backbone and/or inter-area path go
to step 2.
1c. for other paths, skip this alternate ASBR and
consider next ASBR.
2. Compare cost types (type 1/type 2) advertised by alternate ASBR and B. If primary ASBR and alternate ASBR belong to intra-area
by the primary ASBR backbone and/or inter-area path, go to step 2.
2a. If not the same type skip alternate ASBR and
consider next ASBR.
2b. If same proceed to step 3.
3.If cost types are type 1, compare costs advertised by alternate ASBR C. For other paths, skip this alternate ASBR and consider next
and by the primary ASBR ASBR.
3a. If costs are the same then program ECMP Fast ReRoute (FRR) and return.
3b. else go to step 5..
4 If cost types are type 2, compare costs advertised by alternate ASBR 2. Compare cost types (type 1 / type 2) advertised by alternate ASBR
and by the primary ASBR and primary ASBR:
4a. If costs are different, skip alternate ASBR and
consider next ASBR.
4b. If cost are the same, proceed to step 4c to compare
cost to reach ASBR/forwarding address.
4c. If cost to reach ASBR/forwarding address are also same
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) A. If not the same type, skip alternate ASBR and consider next
5a. If route type is same, check if the route p-bit and the ASBR.
forwarding address field for routes from both
ASBRs match. If p-bit and forwarding address matches
proceed to step 6.
If not, skip this alternate ASBR and consider
next ASBR.
5b. If route type is not same, skip this alternate ASBR
and consider next alternate ASBR.
6. Apply inequality on the alternate ASBR. B. If the same, proceed to step 3.
Figure 5: Rules for selecting alternate ASBR in OSPF 3. If cost types are type 1, compare costs advertised by alternate
ASBR and primary ASBR:
4.2.1.1. Multiple ASBRs belonging different area A. If costs are the same, then program ECMP FRR and return.
When "RFC1583compatibility" is set to disabled, OSPF [RFC2328] B. Else, go to step 5.
4. If cost types are type 2, compare costs advertised by alternate
ASBR and primary ASBR:
A. If costs are different, skip alternate ASBR and consider next
ASBR.
B. If costs are the same, proceed to step 4C to compare costs to
reach ASBR/forwarding address.
C. If costs to reach ASBR/forwarding address are also the same,
program ECMP FRR and return.
D. If costs to reach ASBR/forwarding address are different, go
to step 5.
5. Compare route types (type 5 and type 7) for alternate ASBR and
primary ASBR:
A. If route types are the same, check if route p-bit and
forwarding address field for routes from both ASBRs match.
If p-bit and forwarding address match, proceed to step 6. If
not, skip this alternate ASBR and consider next ASBR.
B. If route types are not the same, skip this alternate ASBR and
consider next alternate ASBR.
6. Apply inequality on alternate ASBR.
4.2.1.1. Multiple ASBRs Belonging to Different Areas
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 an 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 looping. cause looping.
When there are multiple ASBRs belonging to different area advertising When there are multiple ASBRs belonging to different areas
the same prefix, pruning rules as defined in [RFC2328] section 16.4 advertising the same prefix, pruning rules as defined in Section 16.4
are applied. The alternate ASBRs pruned using above rules are not of [RFC2328] are applied. The alternate ASBRs pruned using these
considered for LFA evaluation. rules are not 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 described in If there are multiple ASBRs not pruned via the rules described 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.
ASBRs advertising type 1 costs are preferred and the type 2 costs are ASBRs advertising type 1 costs are preferred, and the type 2 costs
pruned. If two ASBRs advertise same type 2 cost, the alternate ASBRs are pruned. If two ASBRs advertise the same type 2 cost, the
are considered along with their cost to reach ASBR/forwarding address alternate ASBRs are considered along with their cost to reach the
for evaluation. If the two ASBRs have same type 2 cost as well as ASBR/forwarding address for evaluation. If the two ASBRs have the
same cost to reach ASBR, ECMP FRR is programmed. When there are same type 2 cost as well as the same cost to reach the ASBR, ECMP FRR
multiple ASBRs advertising same type 2 cost for the prefix, primary is programmed. When there are multiple ASBRs advertising the same
Autonomous System (AS) external route calculation as described in type 2 cost for the prefix, primary Autonomous System (AS) external
[RFC2328] section 16.4.1 selects the route with lowest type 2 cost. route calculation, as described in Section 16.4.1 of [RFC2328],
ASBRs advertising different type 2 cost (higher cost) are not selects the route with the lowest type 2 cost. ASBRs advertising a
considered for LFA evaluation. Alternate ASBRs advertising type 2 different type 2 cost (higher cost) are not considered for LFA
cost for the prefix but are not chosen as primary due to higher cost evaluation. Alternate ASBRs advertising a type 2 cost for the prefix
to reach ASBR are considered for LFA evaluation. The inequalities but not chosen as primary due to a higher cost to reach ASBR are
for evaluating alternate ASBR for type 1 and type 2 costs are same, considered for LFA evaluation. The inequalities for evaluating
as the alternate ASBRs with different type 2 costs are pruned and the alternate ASBR for type 1 and type 2 costs are same, as the alternate
evaluation is based on equal type 2 cost ASBRS. ASBRs with different type 2 costs are pruned and the evaluation is
based on ASBRS with equal type 2 costs.
4.2.1.3. RFC1583compatibility is set to enabled 4.2.1.3. RFC1583Compatibility is Set to "Enabled"
When RFC1583Compatibility is set to enabled, multiple ASBRs belonging When RFC1583Compatibility is set to "enabled", multiple ASBRs
to different area advertising same prefix are chosen based on cost belonging to different areas advertising the same prefix are chosen
and hence are valid alternate ASBRs for the LFA evaluation. The based on cost and hence are valid alternate ASBRs for the LFA
inequalities described in Section 4.2.2 are applicable based on evaluation. The inequalities described in Section 4.2.2 are
forwarding address and cost type advertised in External Link State applicable based on forwarding address and cost type advertised in
Advertisement (LSA). the external Link State Advertisement (LSA).
4.2.1.4. Type 7 routes 4.2.1.4. 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 the same type.
Type 7 routes, routes with p-bit and forwarding address set have Among type 7 routes, routes with the p-bit and forwarding address set
higher preference than routes without these attributes. Alternate have a higher preference than routes without these attributes.
ASBRs selected for LFA comparison should have same p-bit and Alternate ASBRs selected for LFA comparison should have the same
forwarding address attributes. p-bit and forwarding address attributes.
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 the 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 the
inequalities. inequalities below.
4.2.2.1. Forwarding address set to non-zero value 4.2.2.1. Forwarding Address Set to Non-zero Value
Similar to inequalities as defined in Figure 1, the following Similar to the inequalities defined in Section 2, the following
inequalities are defined when forwarding address is a non-zero value. inequalities are defined when the forwarding address is a non-zero
value.
Link-Protection: Link-Protecting LFAs:
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) < D_opt(N,S) +
F_opt(N,PO_i)+ Cost(PO_i,P) < F_opt(S,PO_best) + Cost(PO_best,P) F_opt(S,PO_best) + Cost(PO_best,P)
Node-Protection: Link-Protecting + Downstream-paths-only LFAs:
F_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
F_opt(E,PO_best) + Cost(PO_best,P)
Where, F_opt(N,PO_i)+ Cost(PO_i,P) < F_opt(S,PO_best) + Cost(PO_best,P)
P - The multi-homed prefix being evaluated for
computing alternates
S - The computing router
N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to
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 is non- Node-Protecting LFAs:
zero
4.2.2.2. ASBRs advertising type1 and type2 cost F_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
F_opt(E,PO_best) + Cost(PO_best,P)
Similar to inequalities as defined in Figure 1, the following Where:
inequlities are defined for type1 and type2 cost.
Link-Protection: P - The MHP being evaluated for computing alternates
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: S - The computing router
D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(S,PO_best) + Cost(PO_best,P)
Node-Protection: N - The alternate router being evaluated
D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
D_opt(E,PO_best) + Cost(PO_best,P)
Where, E - The primary next hop on the shortest path from S to
P - The multi-homed prefix being evaluated for prefix P
computing alternates
S - The computing router
N - The alternate router being evaluated
E - The primary next-hop on shortest path from S to
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.
D_opt(X,Y) - Distance on the shortest path from node X to node Y.
Figure 7: LFA inequality definition for type1 and type2 cost 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) - The external cost for Y as advertised by X
F_opt(X,Y) - The distance on the shortest path from node X to
the forwarding address specified by ASBR Y
D_opt(X,Y) - The distance on the shortest path from node X to
node Y
4.2.2.2. ASBRs Advertising Type 1 and Type 2 Costs
Similar to the inequalities defined in Section 2, the following
inequalities are defined for type 1 and type 2 costs.
Link-Protecting LFAs:
D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,S) +
D_opt(S,PO_best) + Cost(PO_best,P)
Link-Protecting + Downstream-paths-only LFAs:
D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(S,PO_best) + Cost(PO_best,P)
Node-Protecting LFAs:
D_opt(N,PO_i)+ Cost(PO_i,P) < D_opt(N,E) +
D_opt(E,PO_best) + Cost(PO_best,P)
Where:
P - The MHP being evaluated for computing alternates
S - The computing router
N - The alternate router being evaluated
E - The primary next hop on the shortest path from S to
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) - The external cost for Y as advertised by X
D_opt(X,Y) - The distance on the shortest path from node X to
node Y
5. LFA Extended Procedures 5. LFA Extended Procedures
This section explains the additional considerations in various This section explains additional considerations to the LFA base
aspects as listed below to the base LFA specification [RFC5286]. specification [RFC5286].
5.1. Links with IGP MAX_METRIC 5.1. Links with IGP MAX_METRIC
Section 3.5 and 3.6 of [RFC5286] describe procedures for excluding Sections 3.5 and 3.6 of [RFC5286] describe 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. If these procedures are strictly followed, there are metric. If these procedures are strictly followed, there are
situations, as described below, where the only potential alternate situations, described below, where the only potential alternate
available which satisfies the basic loop-free condition will not be available that satisfies the basic loop-free condition will not be
considered as alternative. This document refers the maximum link considered as alternative. This document refers to the maximum link
metric in IGPs as the MAX_METRIC. MAX_METRIC is defined for IS-IS in metric in IGPs as the MAX_METRIC. MAX_METRIC is called "maximum link
metric" when defined for IS-IS in [RFC5305] and "MaxLinkMetric" when
[RFC5305], where it is called as "maximum link metric" and defined defined for OSPF in [RFC6987].
for OSPF in [RFC6987], where it is called as "MaxLinkMetric".
+---+ 10 +---+ 10 +---+ +---+ 10 +---+ 10 +---+
| S |------|N1 |-----|D1 | | S |------|N1 |-----|D1 |
+---+ +---+ +---+ +---+ +---+ +---+
| | | |
10 | 10 | 10 | 10 |
|MAX_METRIC(N2 to S) | |MAX_METRIC(N2 to S) |
| | | |
| +---+ | | +---+ |
+-------|N2 |--------+ +-------|N2 |--------+
+---+ +---+
10 | 10 |
+---+ +---+
|D2 | |D2 |
+---+ +---+
Figure 8: Link with IGP MAX_METRIC Figure 3: Link with IGP MAX_METRIC
In the simple example network, all the link costs have a cost of 10 In the simple example network in Figure 3, all the links have a cost
in both directions, except for the link between S and N2. The S-N2 of 10 in both directions, except for the link between S and N2. The
link has a cost of 10 in the forward direction i.e., from S to N2, S-N2 link has a cost of 10 in the forward direction, i.e., from S to
and a cost of MAX_METRIC (0xffffff /2^24 - 1 for IS-IS and 0xffff for N2, and a cost of MAX_METRIC (0xffffff /2^24 - 1 for IS-IS and 0xffff
OSPF) in the reverse direction i.e., from N2 to S for a specific end- for OSPF) in the reverse direction, i.e., from N2 to S for a specific
to-end Traffic Engineering (TE) requirement of the operator. At node end-to-end TE requirement of the operator. At node S, D1 is
S, D1 is reachable through N1 with cost 20, and D2 is reachable reachable through N1 with a cost of 20, and D2 is reachable through
through N2 with cost 20. Even though neighbor N2 satisfies basic N2 with a cost of 20. Even though neighbor N2 satisfies the basic
loop-free condition (inequality 1 of [RFC5286]) for D1, S's neighbor loop-free condition (inequality 1 of [RFC5286]) for D1, S's neighbor
N2 could be excluded as a potential alternative because of the N2 could be excluded as a potential alternative because of the
current exclusions as specified in section 3.5 and 3.6 procedure of current exclusions specified in Sections 3.5 and 3.6 of [RFC5286].
[RFC5286]. But, as the primary traffic destined to D2 continues to But, the primary traffic destined to D2 continues to use the link;
use the link and hence irrespective of the reverse metric in this hence, irrespective of the reverse metric in this case, the same link
case, same link MAY be used as a potential LFA for D1. MAY be used as a potential LFA for D1.
Alternatively, reverse metric of the link MAY be configured with Alternatively, the reverse metric of the link MAY be configured with
MAX_METRIC-1, so that the link can be used as an alternative while MAX_METRIC-1 so that the link can be used as an alternative while
meeting the operator's TE requirements and without having to update meeting the operator's TE requirements and without having to update
the router to fix this particular issue. the router to fix this particular issue.
5.2. Multi Topology Considerations 5.2. MT Considerations
Section 6.2 and 6.3.2 of [RFC5286] state that multi-topology OSPF and Sections 6.2 and 6.3.2 of [RFC5286] state that multi-topology OSPF
IS-IS are out of scope for that specification. This memo clarifies and IS-IS are out of scope for that specification. This memo
and describes the applicability. clarifies and describes the applicability.
In Multi Topology (MT) IGP deployments, for each MT ID, a separate In multi-topology IGP deployments, for each MT-ID, a separate
shortest path tree (SPT) is built with topology specific adjacencies, shortest path tree (SPT) is built with topology-specific adjacencies
so the LFA principles laid out in [RFC5286] are actually applicable so the LFA principles laid out in [RFC5286] are actually applicable
for MT IS-IS [RFC5120] LFA SPF. The primary difference in this case for MT IS-IS [RFC5120] LFA SPF. The primary difference in this case
is, identifying the eligible-set of neighbors for each LFA is identifying the eligible set of neighbors for each LFA
computation which is done per MT ID. The eligible-set for each MT ID computation; this is done per MT-ID. The eligible set for each MT-ID
is determined by the presence of IGP adjacency from Source to the is determined by the presence of IGP adjacency from the source to the
neighboring node on that MT-ID apart from the administrative neighboring node on that MT-ID apart from the administrative
restrictions and other checks laid out in [RFC5286]. The same is restrictions and other checks laid out in [RFC5286]. The same is
also applicable for MT-OSPF [RFC4915] or different AFs in multi also applicable for MT-OSPF [RFC4915] or different AFs in multi-
instance OSPFv3 [RFC5838]. instance OSPFv3 [RFC5838].
However for MT IS-IS, if a "standard topology" is used with MT-ID #0 However, for MT IS-IS, if a "standard unicast topology" is used with
[RFC5286] and both IPv4 [RFC5305] and IPv6 routes/AFs [RFC5308] are MT-ID #0 [RFC5120] and both IPv4 [RFC5305] and IPv6 routes/AFs
present, then the condition of network congruency is applicable for [RFC5308] are present, then the condition of network congruency is
LFA computation as well. Network congruency here refers to, having applicable for LFA computation as well. Network congruency here
same address families provisioned on all the links and all the nodes refers to having the same address families provisioned on all the
of the network with MT-ID #0. Here with single decision process both links and all the nodes of the network with MT-ID #0. Here, with a
IPv4 and IPv6 next-hops are computed for all the prefixes in the single-decision process, both IPv4 and IPv6 next hops are computed
network and similarly with one LFA computation from all eligible for all the prefixes in the network. Similarly, with one LFA
neighbors per [RFC5286], all potential alternatives can be computed. computation from all eligible neighbors per [RFC5286], all potential
alternatives can be computed.
6. IANA Considerations 6. IANA Considerations
This document has no actions for IANA. This document has no IANA actions.
7. Acknowledgements
Authors acknowledge 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. Thanks to Elwyn
Davies for reviewing and providing feedback as part of Gen-art
review. Thanks to Alvaro Retena, Adam Roach, Ben Campbell, Benjamin
Kaduk and sponsoring Routing Area Director Martin Vigoureux for
providing detailed feedback and suggestions.
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.net
Bruno Decraene
Orange,
France
Email: bruno.decraene@orange.com
9. Security Considerations 7. Security Considerations
The existing OSPF security considerations continue to apply, as do The existing OSPF security considerations continue to apply, as do
the recommended manual key management mechanisms specified in the recommended manual key management mechanisms specified in
[RFC7474]. The existing security considerations for IS-IS also [RFC7474]. The existing security considerations for IS-IS also
continue to apply, as specified in [RFC5304] and [RFC5310] and continue to apply, as specified in [RFC5304] and [RFC5310] and
extended by [RFC7645] for KARP. This document does not change any of extended by [RFC7645] for Keying and Authentication for Routing
the discussed protocol specifications [RFC1195] [RFC5120] [RFC2328] Protocols (KARP). This document does not change any of the discussed
[RFC5838], and the security considerations of the LFA base protocol specifications (i.e., [RFC1195], [RFC5120], [RFC2328], and
specification [RFC5286] therefore continue to apply. [RFC5838]); therefore, the security considerations of the LFA base
specification [RFC5286] continue to apply.
10. References 8. References
10.1. Normative References 8.1. 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>.
[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 8.2. 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>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", P. 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>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
skipping to change at page 17, line 46 skipping to change at page 18, line 37
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", [RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010, RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>. <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
McPherson, "OSPF Stub Router Advertisement", RFC 6987, D. 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>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key "Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>. <https://www.rfc-editor.org/info/rfc7474>.
[RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and [RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and
Authentication for Routing Protocol (KARP) IS-IS Security Authentication for Routing Protocol (KARP) IS-IS Security
Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015, Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015,
<https://www.rfc-editor.org/info/rfc7645>. <https://www.rfc-editor.org/info/rfc7645>.
Acknowledgements
The authors acknowledge Alia Atlas and Salih K.A. for their useful
feedback and input. Thanks to Stewart Bryant for being Document
Shepherd and providing detailed review comments. Thanks to Elwyn
Davies for reviewing and providing feedback as part of the Gen-ART
review. Thanks to Alvaro Retana, Adam Roach, Ben Campbell, Benjamin
Kaduk, and sponsoring Routing Area Director Martin Vigoureux for
providing detailed feedback and suggestions.
Contributors
The following people contributed substantially to the content of this
document and should be considered coauthors:
Chris Bowers
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
United States of America
Email: cbowers@juniper.net
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
Authors' Addresses Authors' Addresses
Pushpasis Sarkar (editor) Pushpasis Sarkar (editor)
Arrcus, Inc. Arrcus, Inc.
Email: pushpasis.ietf@gmail.com Email: pushpasis.ietf@gmail.com
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 United States of America
Email: uma.chunduri@huawei.com Email: uma.chunduri@huawei.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
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