draft-ietf-isis-reverse-metric-17.txt   rfc8500.txt 
Networking Working Group N. Shen Internet Engineering Task Force (IETF) N. Shen
Internet-Draft Cisco Systems Request for Comments: 8500 Cisco Systems
Intended status: Standards Track S. Amante Category: Standards Track S. Amante
Expires: June 6, 2019 Apple, Inc. ISSN: 2070-1721 Apple Inc.
M. Abrahamsson M. Abrahamsson
T-Systems Nordic T-Systems Nordic
December 3, 2018 February 2019
IS-IS Routing with Reverse Metric IS-IS Routing with Reverse Metric
draft-ietf-isis-reverse-metric-17
Abstract Abstract
This document describes a mechanism to allow IS-IS routing to quickly This document describes a mechanism to allow IS-IS routing to quickly
and accurately shift traffic away from either a point-to-point or and accurately shift traffic away from either a point-to-point or
multi-access LAN interface during network maintenance or other multi-access LAN interface during network maintenance or other
operational events. This is accomplished by signaling adjacent IS-IS operational events. This is accomplished by signaling adjacent IS-IS
neighbors with a higher reverse metric, i.e., the metric towards the neighbors with a higher reverse metric, i.e., the metric towards the
signaling IS-IS router. signaling IS-IS router.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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 June 6, 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/rfc8500.
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.
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
(http://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Node and Link Isolation . . . . . . . . . . . . . . . . . 3 1.1. Node and Link Isolation . . . . . . . . . . . . . . . . . 2
1.2. Distributed Forwarding Planes . . . . . . . . . . . . . . 3 1.2. Distributed Forwarding Planes . . . . . . . . . . . . . . 3
1.3. Spine-Leaf Applications . . . . . . . . . . . . . . . . . 3 1.3. Spine-Leaf Applications . . . . . . . . . . . . . . . . . 3
1.4. LDP IGP Synchronization . . . . . . . . . . . . . . . . . 3 1.4. LDP IGP Synchronization . . . . . . . . . . . . . . . . . 3
1.5. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . 4 1.5. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . 3
1.6. Specification of Requirements . . . . . . . . . . . . . . 4 1.6. Specification of Requirements . . . . . . . . . . . . . . 4
2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . 4 2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . 4
3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 7 3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6
3.1. Processing Changes to Default Metric . . . . . . . . . . 7 3.1. Processing Changes to Default Metric . . . . . . . . . . 6
3.2. Multi-Topology IS-IS Support on Point-to-point links . . 7 3.2. Multi-Topology IS-IS Support on Point-to-Point Links . . 7
3.3. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 7 3.3. Multi-access LAN Procedures . . . . . . . . . . . . . . . 7
3.4. LDP/IGP Synchronization on LANs . . . . . . . . . . . . . 9 3.4. LDP/IGP Synchronization on LANs . . . . . . . . . . . . . 8
3.5. Operational Guidelines . . . . . . . . . . . . . . . . . 9 3.5. Operational Guidelines . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 11 6.2. Informative References . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Node Isolation Challenges . . . . . . . . . . . . . 13
Appendix A. Node Isolation Challenges . . . . . . . . . . . . . 12
Appendix B. Link Isolation Challenges . . . . . . . . . . . . . 13 Appendix B. Link Isolation Challenges . . . . . . . . . . . . . 13
Appendix C. Contributors' Addresses . . . . . . . . . . . . . . 14 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
The IS-IS [ISO10589] routing protocol has been widely used in The IS-IS [ISO10589] routing protocol has been widely used in
Internet Service Provider IP/MPLS networks. Operational experience Internet Service Provider IP/MPLS networks. Operational experience
with the protocol, combined with ever increasing requirements for with the protocol combined with ever increasing requirements for
lossless operations have demonstrated some operational issues. This lossless operations have demonstrated some operational issues. This
document describes the issues and a mechanism for mitigating them. document describes the issues and a mechanism for mitigating them.
This document defines the IS-IS "Reverse Metric" mechanism that This document defines the IS-IS "Reverse Metric" mechanism that
allows an IS-IS node to send a "Reverse Metric" TLV through the IS-IS allows an IS-IS node to send a Reverse Metric TLV through the IS-IS
Hello (IIH) PDU to the neighbor or pseudo-node to adjust the routing Hello (IIH) PDU to the neighbor or pseudonode to adjust the routing
metric on the inbound direction. metric on the inbound direction.
1.1. Node and Link Isolation 1.1. Node and Link Isolation
IS-IS routing mechanism has the overload-bit, which can be used by The IS-IS routing mechanism has the overload bit, which can be used
operators to perform disruptive maintenance on the router. But in by operators to perform disruptive maintenance on the router. But in
many operational maintenance cases, it is not necessary to divert all many operational maintenance cases, it is not necessary to divert all
the traffic away from this node. It is necessary to avoid only a the traffic away from this node. It is necessary to avoid only a
single link during the maintenance. More detailed descriptions of single link during the maintenance. More detailed descriptions of
the challenges can be found in Appendix A and Appendix B of this the challenges can be found in Appendices A and B of this document.
document.
1.2. Distributed Forwarding Planes 1.2. Distributed Forwarding Planes
In a distributed forwarding platform, different forwarding line-cards In a distributed forwarding platform, different forwarding line cards
may have interfaces and IS-IS connections to neighbor routers. If may have interfaces and IS-IS connections to neighbor routers. If
one of the line-card's software resets, it may take some time for the one of the line card's software resets, it may take some time for the
forwarding entries to be fully populated on the line-card, in forwarding entries to be fully populated on the line card, in
particular if the router is a PE (Provider Edge) router in ISP's MPLS particular if the router is a PE (Provider Edge) router in an ISP's
VPN. An IS-IS adjacency may be established with a neighbor router MPLS VPN. An IS-IS adjacency may be established with a neighbor
long before the entire BGP VPN prefixes are downloaded to the router long before the entire BGP VPN prefixes are downloaded to the
forwarding table. It is important to signal to the adjacent IS-IS forwarding table. It is important to signal to the adjacent IS-IS
routers to raise metric values and not to use the corresponding IS-IS routers to raise metric values and not to use the corresponding IS-IS
adjacency inbound to this router if possible. Temporarily signaling adjacency inbound to this router if possible. Temporarily signaling
the 'Reverse Metric' over this link to discourage the traffic via the the 'Reverse Metric' over this link to discourage the traffic via the
corresponding line-card will help to reduce the traffic loss in the corresponding line card will help to reduce the traffic loss in the
network. In the meantime, the remote PE routers will select a network. In the meantime, the remote PE routers will select a
different set of PE routers for the BGP best path calculation or use different set of PE routers for the BGP best path calculation or use
a different link towards the same PE router on which a line-card is a different link towards the same PE router on which a line card is
resetting. resetting.
1.3. Spine-Leaf Applications 1.3. Spine-Leaf Applications
In the IS-IS Spine-Leaf extension [I-D.shen-isis-spine-leaf-ext], the In the IS-IS Spine-Leaf extension [IS-IS-SL-EXT], the leaf nodes will
leaf nodes will perform equal-cost or unequal-cost load sharing perform equal-cost or unequal-cost load sharing towards all the spine
towards all the spine nodes. In certain operational cases, for nodes. In certain operational cases, for instance, when one of the
instance, when one of the backbone links on a spine node is backbone links on a spine node is congested, a spine node can push a
congested, a spine node can push a higher metric towards the higher metric towards the connected leaf nodes to reduce the transit
connected leaf nodes to reduce the transit traffic through the traffic through the corresponding spine node or link.
corresponding spine node or link.
1.4. LDP IGP Synchronization 1.4. LDP IGP Synchronization
In the [RFC5443], a mechanism is described to achieve LDP IGP In [RFC5443], a mechanism is described to achieve LDP IGP
synchronization by using the maximum link metric value on the synchronization by using the maximum link metric value on the
interface. But in the case of a new IS-IS node joining the broadcast interface. But in the case of a new IS-IS node joining the broadcast
network (LAN), it is not optimal to change all the nodes on the LAN network (LAN), it is not optimal to change all the nodes on the LAN
to the maximum link metric value, as described in [RFC6138]. In this to the maximum link metric value, as described in [RFC6138]. In this
case, the Reverse Metric can be used to discourage both outbound and case, the Reverse Metric can be used to discourage both outbound and
inbound traffic without affecting the traffic of other IS-IS nodes on inbound traffic without affecting the traffic of other IS-IS nodes on
the LAN. the LAN.
1.5. IS-IS Reverse Metric 1.5. IS-IS Reverse Metric
This document uses the routing protocol itself as the transport This document uses the routing protocol itself as the transport
mechanism to allow one IS-IS router to advertise a "reverse metric" mechanism to allow one IS-IS router to advertise a "reverse metric"
in an IS-IS Hello (IIH) PDU to an adjacent node on a point-to-point in an IS-IS Hello (IIH) PDU to an adjacent node on a point-to-point
or multi-access LAN link. This would allow the provisioning to be or multi-access LAN link. This would allow the provisioning to be
performed only on a single node, setting a "reverse metric" on a link performed only on a single node, setting a "reverse metric" on a link
and have traffic bidirectionally shift away from that link gracefully and having traffic bidirectionally shift away from that link
to alternate, viable paths. gracefully to alternate viable paths.
This Reverse Metric mechanism is used for both point-to-point and This Reverse Metric mechanism is used for both point-to-point and
multi-access LAN links. Unlike the point-to-point links, the IS-IS multi-access LAN links. Unlike the point-to-point links, the IS-IS
protocol currently does not have a way to influence the traffic protocol currently does not have a way to influence the traffic
towards a particular node on LAN links. This mechanism provides IS- towards a particular node on LAN links. This mechanism provides
IS routing the capability of altering traffic in both directions on IS-IS routing with the capability of altering traffic in both
either a point-to-point link or a multi-access link of an IS-IS node. directions on either a point-to-point link or a multi-access link of
an IS-IS node.
The metric value in the "reverse metric" TLV and the Traffic The metric value in the Reverse Metric TLV and the Traffic
Engineering metric in the sub-TLV being advertised is an offset or Engineering metric in the sub-TLV being advertised are offsets or
relative metric to be added to the existing local link and Traffic relative metrics to be added to the existing local link and Traffic
Engineering metric values of the receiver, the accumulated metric Engineering metric values of the receiver; the accumulated metric
value is bounded as described in Section 2. value is bounded as described in Section 2.
1.6. Specification of Requirements 1.6. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. IS-IS Reverse Metric TLV 2. IS-IS Reverse Metric TLV
The Reverse Metric TLV is a new TLV to be used inside an IS-IS Hello The Reverse Metric TLV is a new TLV to be used inside an IS-IS Hello
PDU. This TLV is used to support the IS-IS Reverse Metric mechanism PDU. This TLV is used to support the IS-IS Reverse Metric mechanism
that allows a "reverse metric" to be sent to the IS-IS neighbor. that allows a "reverse metric" to be sent to the IS-IS neighbor.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Metric | Type | Length | Flags | Metric
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Metric (Continue) | sub-TLV Len |Optional sub-TLV Metric (Continued) | sub-TLV Len |Optional sub-TLV
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Reverse Metric TLV Figure 1: Reverse Metric TLV
The Value part of the Reverse Metric TLV is composed of a 3 octet The Value part of the Reverse Metric TLV is composed of a 3 octet
field containing an IS-IS Metric Value, a 1 octet field of Flags, and field containing an IS-IS Metric value, a 1 octet field of Flags, and
a 1 octet Reverse Metric sub-TLV length field representing the length a 1 octet Reverse Metric sub-TLV length field representing the length
of a variable number of sub-TLVs. If the "sub-TLV len" is non-zero, of a variable number of sub-TLVs. If the "sub-TLV Len" is non-zero,
then the Value field MUST also contain one or more sub-TLVs. then the Value field MUST also contain one or more sub-TLVs.
The Reverse Metric TLV MAY be present in any IS-IS Hello PDU. A The Reverse Metric TLV MAY be present in any IS-IS Hello PDU. A
sender MUST only transmit a single Reverse Metric TLV in a IS-IS sender MUST only transmit a single Reverse Metric TLV in an IS-IS
Hello PDU. If a received IS-IS Hello PDU contains more than one Hello PDU. If a received IS-IS Hello PDU contains more than one
Reverse Metric TLV, an implementation MUST ignore all the Reverse Reverse Metric TLV, an implementation MUST ignore all the Reverse
Metric TLVs. Metric TLVs.
TYPE: 16 TYPE: 16
LENGTH: variable (5 - 255 octets) LENGTH: variable (5 - 255 octets)
VALUE: VALUE:
Flags (1 octet) Flags (1 octet)
Metric (3 octets) Metric (3 octets)
skipping to change at page 5, line 44 skipping to change at page 5, line 24
sub-TLV data (0 - 250 octets) sub-TLV data (0 - 250 octets)
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Reserved |U|W| | Reserved |U|W|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 2: Flags Figure 2: Flags
The Metric field contains a 24-bit unsigned integer. This value is a The Metric field contains a 24-bit unsigned integer. This value is a
metric offset that a neighbor SHOULD add to the existing, configured metric offset that a neighbor SHOULD add to the existing configured
Default Metric for the IS-IS link [ISO10589]. Refer to "Elements of Default Metric for the IS-IS link [ISO10589]. Refer to "Elements of
Procedure", in Section 3 for details on how an IS-IS router should Procedure" in Section 3 of this document for details on how an IS-IS
process the Metric field in a Reverse Metric TLV. router should process the Metric field in a Reverse Metric TLV.
The Metric field, in the Reverse Metric TLV, is a "reverse offset The Metric field, in the Reverse Metric TLV, is a "reverse offset
metric" that will either be in the range of 0 - 63 when a "narrow" metric" that will either be in the range of 0 - 63 when a "narrow"
IS-IS metric is used (IS Neighbors TLV, Pseudonode LSP) [RFC1195] or IS-IS metric is used (IS Neighbors TLV / Pseudonode LSP) [RFC1195] or
in the range of 0 - (2^24 - 2) when a "wide" Traffic Engineering in the range of 0 - (2^24 - 2) when a "wide" Traffic Engineering
metric value is used, (Extended IS Reachability TLV) [RFC5305] metric value is used (Extended IS Reachability TLV) [RFC5305]
[RFC5817]. As described below, when the U bit is set, the [RFC5817]. As described below, when the U bit is set, the
accumulated value of the wide metric is in the range of 0 - (2^24 - accumulated value of the wide metric is in the range of
1), with (2^24 - 1) metric as non-reachable in IS-IS routing. The 0 - (2^24 - 1), with the (2^24 - 1) metric value as non-reachable in
IS-IS metric value of (2^24 - 2) serves as the link of last resort. IS-IS routing. The IS-IS metric value of (2^24 - 2) serves as the
link of last resort.
There are currently only two Flag bits defined. There are currently only two Flag bits defined.
W bit (0x01): The "Whole LAN" bit is only used in the context of W bit (0x01): The "Whole LAN" bit is only used in the context of
multi-access LANs. When a Reverse Metric TLV is transmitted from a multi-access LANs. When a Reverse Metric TLV is transmitted from a
node to the Designated Intermediate System (DIS), if the "Whole LAN" node to the Designated Intermediate System (DIS), if the "Whole LAN"
bit is set (1), then a DIS SHOULD add the received Metric value in bit is set (1), then a DIS SHOULD add the received Metric value in
the Reverse Metric TLV to each node's existing Default Metric in the the Reverse Metric TLV to each node's existing Default Metric in the
Pseudonode LSP. If the "Whole LAN" bit is not set (0), then a DIS Pseudonode LSP. If the "Whole LAN" bit is not set (0), then a DIS
SHOULD add the received Metric value in the Reverse Metric TLV to the SHOULD add the received Metric value in the Reverse Metric TLV to the
existing "default metric" in the Pseudonode LSP for the single node existing "default metric" in the Pseudonode LSP for the single node
from whom the Reverse Metric TLV was received. Please refer to from whom the Reverse Metric TLV was received. Please refer to
"Multi-Access LAN Procedures", in Section 3.3, for additional "Multi-access LAN Procedures", in Section 3.3, for additional
details. The W bit MUST be clear when a Reverse Metric TLV is details. The W bit MUST be clear when a Reverse Metric TLV is
transmitted in an IIH PDU on a point-to-point link, and MUST be transmitted in an IIH PDU on a point-to-point link and MUST be
ignored when received on a point-to-point link. ignored when received on a point-to-point link.
U bit (0x02): The "Unreachable" bit specifies that the metric U bit (0x02): The "Unreachable" bit specifies that the metric
calculated by addition of the reverse metric to the "default metric" calculated by the addition of the reverse metric to the "default
is limited to the maximum value of (2^24-1). This "U" bit applies to metric" is limited to the maximum value of (2^24-1). This "U" bit
both the default metric in the Extended IS Reachability TLV and the applies to both the default metric in the Extended IS Reachability
Traffic Engineering Default Metric sub-TLV of the link. This is only TLV and the Traffic Engineering Default Metric sub-TLV of the link.
relevant to the IS-IS "wide" metric mode. This is only relevant to the IS-IS "wide" metric mode.
The Reserved bits of Flags field MUST be set to zero and MUST be The Reserved bits of Flags field MUST be set to zero and MUST be
ignored when received. ignored when received.
The Reverse Metric TLV MAY include sub-TLVs when an IS-IS router The Reverse Metric TLV MAY include sub-TLVs when an IS-IS router
wishes to signal additional information to its neighbor. In this wishes to signal additional information to its neighbor. In this
document, the Reverse Metric Traffic Engineering Metric sub-TLV, with document, the Reverse Metric Traffic Engineering Metric sub-TLV, with
Type 18, is defined. This Traffic Engineering Metric contains a Type 18, is defined. This Traffic Engineering Metric contains a
24-bit unsigned integer. This sub-TLV is optional, if it appears 24-bit unsigned integer. This sub-TLV is optional; if it appears
more than once, then the entire Reverse Metric TLV MUST be ignored. more than once, then the entire Reverse Metric TLV MUST be ignored.
Upon receiving this Traffic Engineering METRIC sub-TLV in a Reverse Upon receiving this Traffic Engineering METRIC sub-TLV in a Reverse
Metric TLV, a node SHOULD add the received Traffic Engineering Metric Metric TLV, a node SHOULD add the received Traffic Engineering Metric
offset value to its existing, configured Traffic Engineering Default offset value to its existing configured Traffic Engineering Default
Metric within its Extended IS Reachability TLV. The use of other Metric within its Extended IS Reachability TLV. The use of other
sub-TLVs is outside the scope of this document. The "sub-TLV Len" sub-TLVs is outside the scope of this document. The "sub-TLV Len"
value MUST be set to zero when an IS-IS router does not have Traffic value MUST be set to zero when an IS-IS router does not have Traffic
Engineering sub-TLVs that it wishes to send to its IS-IS neighbor. Engineering sub-TLVs that it wishes to send to its IS-IS neighbor.
3. Elements of Procedure 3. Elements of Procedure
3.1. Processing Changes to Default Metric 3.1. Processing Changes to Default Metric
It is important to use the same IS-IS metric type on both ends of the It is important to use the same IS-IS metric type on both ends of the
link and in the entire IS-IS area or level. On the receiving side of link and in the entire IS-IS area or level. On the receiving side of
the 'reverse-metric' TLV, the accumulated value of configured metric the 'reverse-metric' TLV, the accumulated value of the configured
and the reverse-metric needs to be limited to 63 in "narrow" metric metric and the reverse-metric needs to be limited to 63 in "narrow"
mode and to (2^24 - 2) in "wide" metric mode. This applies to both metric mode and to (2^24 - 2) in "wide" metric mode. This applies to
the Default Metric of Extended IS Reachability TLV and the Traffic both the Default Metric of Extended IS Reachability TLV and the
Engineering Default Metric sub-TLV in LSP or Pseudonode LSP for the Traffic Engineering Default Metric sub-TLV in LSP or Pseudonode LSP
"wide" metric mode case. If the "U" bit is present in the flags, the for the "wide" metric mode case. If the "U" bit is present in the
accumulated metric value is to be limited to (2^24 - 1) for both the flags, the accumulated metric value is to be limited to (2^24 - 1)
normal link metric and Traffic Engineering metric in IS-IS "wide" for both the normal link metric and Traffic Engineering metric in
metric mode. IS-IS "wide" metric mode.
If an IS-IS router is configured to originate a Traffic Engineering If an IS-IS router is configured to originate a Traffic Engineering
Default Metric sub-TLV for a link, but receives a Reverse Metric TLV Default Metric sub-TLV for a link but receives a Reverse Metric TLV
from its neighbor that does not contain a Traffic Engineering Default from its neighbor that does not contain a Traffic Engineering Default
Metric sub-TLV, then the IS-IS router MUST NOT change the value of Metric sub-TLV, then the IS-IS router MUST NOT change the value of
its Traffic Engineering Default Metric sub-TLV for that link. its Traffic Engineering Default Metric sub-TLV for that link.
3.2. Multi-Topology IS-IS Support on Point-to-point links 3.2. Multi-Topology IS-IS Support on Point-to-Point Links
The Reverse Metric TLV is applicable to Multi-Topology IS-IS (M-ISIS) The Reverse Metric TLV is applicable to Multi-topology IS-IS (M-ISIS)
[RFC5120]. On point-to-point links, if an IS-IS router is configured [RFC5120]. On point-to-point links, if an IS-IS router is configured
for M-ISIS, it MUST send only a single Reverse Metric TLV in IIH PDUs for M-ISIS, it MUST send only a single Reverse Metric TLV in IIH PDUs
toward its neighbor(s) on the designated link. When an M-ISIS router toward its neighbor(s) on the designated link. When an M-ISIS router
receives a Reverse Metric TLV, it MUST add the received Metric value receives a Reverse Metric TLV, it MUST add the received Metric value
to its Default Metric of the link in all Extended IS Reachability to its Default Metric of the link in all Extended IS Reachability
TLVs for all topologies. If an M-ISIS router receives a Reverse TLVs for all topologies. If an M-ISIS router receives a Reverse
Metric TLV with a Traffic Engineering Default Metric sub-TLV, then Metric TLV with a Traffic Engineering Default Metric sub-TLV, then
the M-ISIS router MUST add the received Traffic Engineering Default the M-ISIS router MUST add the received Traffic Engineering Default
Metric value to each of its Default Metric sub-TLVs in all of its MT Metric value to each of its Default Metric sub-TLVs in all of its MT
Intermediate Systems TLVs. If an M-ISIS router is configured to Intermediate Systems TLVs. If an M-ISIS router is configured to
advertise Traffic Engineering Default Metric sub-TLVs for one or more advertise Traffic Engineering Default Metric sub-TLVs for one or more
topologies, but does not receive a Traffic Engineering Default Metric topologies but does not receive a Traffic Engineering Default Metric
sub-TLV in a Reverse Metric TLV, then the M-ISIS router MUST NOT sub-TLV in a Reverse Metric TLV, then the M-ISIS router MUST NOT
change the value in each of the Traffic Engineering Default Metric change the value in each of the Traffic Engineering Default Metric
sub-TLVs for all topologies. sub-TLVs for all topologies.
3.3. Multi-Access LAN Procedures 3.3. Multi-access LAN Procedures
On a Multi-Access LAN, only the DIS SHOULD act upon information On a Multi-access LAN, only the DIS SHOULD act upon information
contained in a received Reverse Metric TLV. All non-DIS nodes MUST contained in a received Reverse Metric TLV. All non-DIS nodes MUST
silently ignore a received Reverse Metric TLV. The decision process silently ignore a received Reverse Metric TLV. The decision process
of the routers on the LAN MUST follow the procedure in section of the routers on the LAN MUST follow the procedure in
7.2.8.2 of [ISO10589], and use the "Two-way connectivity check" Section 7.2.8.2 of [ISO10589], and use the "Two-way connectivity
during the topology and route calculation. check" during the topology and route calculation.
The Reverse Metric Traffic Engineering sub-TLV also applies to the The Reverse Metric Traffic Engineering sub-TLV also applies to the
DIS. If a DIS is configured to apply Traffic Engineering over a link DIS. If a DIS is configured to apply Traffic Engineering over a link
and it receives Traffic Engineering Metric sub-TLV in a Reverse and it receives Traffic Engineering Metric sub-TLV in a Reverse
Metric TLV, it should update the Traffic Engineering Default Metric Metric TLV, it should update the Traffic Engineering Default Metric
sub-TLV value of the corresponding Extended IS Reachability TLV or sub-TLV value of the corresponding Extended IS Reachability TLV or
insert a new one if not present. insert a new one if not present.
In the case of multi-access LANs, the "W" Flags bit is used to signal In the case of multi-access LANs, the "W" Flags bit is used to signal
from a non-DIS to the DIS whether to change the metric and, from a non-DIS to the DIS whether or not to change the metric and,
optionally, Traffic Engineering parameters for all nodes in the optionally, Traffic Engineering parameters for all nodes in the
Pseudonode LSP or solely the node on the LAN originating the Reverse Pseudonode LSP or solely the node on the LAN originating the Reverse
Metric TLV. Metric TLV.
A non-DIS node, e.g., Router B, attached to a multi-access LAN will A non-DIS node, e.g., Router B, attached to a multi-access LAN will
send the DIS a Reverse Metric TLV with the W bit clear when Router B send the DIS a Reverse Metric TLV with the W bit clear when Router B
wishes the DIS to add the Metric value to the Default Metric wishes the DIS to add the Metric value to the Default Metric
contained in the Pseudonode LSP specific to just Router B. Other contained in the Pseudonode LSP specific to just Router B. Other
non-DIS nodes, e.g., Routers C and D, may simultaneously send a non-DIS nodes, e.g., Routers C and D, may simultaneously send a
Reverse Metric TLV with the W bit clear to request the DIS to add Reverse Metric TLV with the W bit clear to request the DIS to add
skipping to change at page 8, line 39 skipping to change at page 8, line 19
As long as at least one IS-IS node on the LAN sending the signal to As long as at least one IS-IS node on the LAN sending the signal to
DIS with the W bit set, the DIS would add the metric value in the DIS with the W bit set, the DIS would add the metric value in the
Reverse Metric TLV to all neighbor adjacencies in the Pseudonode LSP, Reverse Metric TLV to all neighbor adjacencies in the Pseudonode LSP,
regardless if some of the nodes on the LAN advertise the Reverse regardless if some of the nodes on the LAN advertise the Reverse
Metric TLV without the W bit set. The DIS MUST use the reverse Metric TLV without the W bit set. The DIS MUST use the reverse
metric of the highest source MAC address Non-DIS advertising the metric of the highest source MAC address Non-DIS advertising the
Reverse Metric TLV with the W bit set. Reverse Metric TLV with the W bit set.
Local provisioning on the DIS to adjust the Default Metric(s) is Local provisioning on the DIS to adjust the Default Metric(s) is
another way to insert Reverse Metric in the Pseudonode LSP towards an another way to insert Reverse Metric in the Pseudonode LSP towards an
IS-IS node on a LAN. In the case where Reverse Metric TLV is also IS-IS node on a LAN. In the case where a Reverse Metric TLV is also
used in the IS-IS Hello PDU of the node, the local provisioning MUST used in the IS-IS Hello PDU of the node, the local provisioning MUST
take precedence over received Reverse Metric TLVs. For instance, take precedence over received Reverse Metric TLVs. For instance,
local policy on the DIS may be provisioned to ignore the W bit local policy on the DIS may be provisioned to ignore the W bit
signaling on a LAN. signaling on a LAN.
Multi-Topology IS-IS [RFC5120] specifies there is no change to Multi-topology IS-IS [RFC5120] specifies there is no change to
construction of the Pseudonode LSP, regardless of the Multi-Topology construction of the Pseudonode LSP regardless of the Multi-topology
capabilities of a multi-access LAN. If any MT capable node on the (MT) capabilities of a multi-access LAN. If any MT capable node on
LAN advertises the Reverse Metric TLV to the DIS, the DIS should the LAN advertises the Reverse Metric TLV to the DIS, the DIS should
update, as appropriate, the Default Metric contained in the update, as appropriate, the Default Metric contained in the
Pseudonode LSP. If the DIS updates the Default Metric in and floods Pseudonode LSP. If the DIS updates the Default Metric and floods a
a new Pseudonode LSP, those default metric values will be applied to new Pseudonode LSP, those default metric values will be applied to
all topologies during Multi-Topology SPF calculations. all topologies during Multi-topology Shortest Path First
calculations.
3.4. LDP/IGP Synchronization on LANs 3.4. LDP/IGP Synchronization on LANs
As described in [RFC6138] when a new IS-IS node joins a broadcast As described in [RFC6138], when a new IS-IS node joins a broadcast
network, it is unnecessary and sometimes even harmful for all IS-IS network, it is unnecessary and sometimes even harmful for all IS-IS
nodes on the LAN to advertise maximum link metric. [RFC6138] nodes on the LAN to advertise the maximum link metric. [RFC6138]
proposes a solution to have the new node not advertise its adjacency proposes a solution to have the new node not advertise its adjacency
towards the pseudo-node when it is not in a "cut-edge" position. towards the pseudonode when it is not in a "cut-edge" position.
With the introduction of Reverse Metric in this document, a simpler With the introduction of Reverse Metric in this document, a simpler
alternative solution to the above mentioned problem can be used. The alternative solution to the above mentioned problem can be used. The
Reverse Metric allows the new node on the LAN to advertise its Reverse Metric allows the new node on the LAN to advertise its
inbound metric value to be the maximum and this puts the link of this inbound metric value to be the maximum, and this puts the link of
new node in the last resort position without impacting the other IS- this new node in the last resort position without impacting the other
IS nodes on the same LAN. IS-IS nodes on the same LAN.
Specifically, when IS-IS adjacencies are being established by the new Specifically, when IS-IS adjacencies are being established by the new
node on the LAN, besides setting the maximum link metric value (2^24 node on the LAN, besides setting the maximum link metric value
- 2) on the interface of the LAN for LDP IGP synchronization as (2^24 - 2) on the interface of the LAN for LDP IGP synchronization as
described in [RFC5443], it SHOULD advertise the maximum metric offset described in [RFC5443], it SHOULD advertise the maximum metric offset
value in the Reverse Metric TLV in its IIH PDU sent on the LAN. It value in the Reverse Metric TLV in its IIH PDU sent on the LAN. It
SHOULD continue this advertisement until it completes all the LDP SHOULD continue this advertisement until it completes all the LDP
label binding exchanges with all the neighbors over this LAN, either label binding exchanges with all the neighbors over this LAN, either
by receiving the LDP End-of-LIB [RFC5919] for all the sessions or by by receiving the LDP End-of-LIB [RFC5919] for all the sessions or by
exceeding the provisioned timeout value for the node LDP/IGP exceeding the provisioned timeout value for the node LDP/IGP
synchronization. synchronization.
3.5. Operational Guidelines 3.5. Operational Guidelines
For the use case in Section 1.1, a router SHOULD limit the period of For the use case in Section 1.1, a router SHOULD limit the period of
advertising a Reverse Metric TLV towards a neighbor only for the advertising a Reverse Metric TLV towards a neighbor only for the
duration of network maintenance window. duration of a network maintenance window.
The use of Reverse Metric does not alter IS-IS metric parameters The use of a Reverse Metric does not alter IS-IS metric parameters
stored in a router's persistent provisioning database. stored in a router's persistent provisioning database.
If routers that receive a Reverse Metric TLV sends a syslog message If routers that receive a Reverse Metric TLV send a syslog message or
or SNMP trap, this will assist in rapidly identifying the node in the SNMP trap, this will assist in rapidly identifying the node in the
network that is advertising an IS-IS metric or Traffic Engineering network that is advertising an IS-IS metric or Traffic Engineering
parameters different from that which is configured locally on the parameters different from that which is configured locally on the
device. device.
When the link Traffic Engineering metric is raised to (2^24 - 1) When the link Traffic Engineering metric is raised to (2^24 - 1)
[RFC5817], either due to the reverse-metric mechanism or by explicit [RFC5817], either due to the Reverse Metric mechanism or by explicit
user configuration, this SHOULD immediately trigger the CSPF user configuration, this SHOULD immediately trigger the CSPF
(Constrained Shortest Path First) re-calculation to move the Traffic (Constrained Shortest Path First) recalculation to move the Traffic
Engineering traffic away from that link. It is RECOMMENDED also that Engineering traffic away from that link. It is RECOMMENDED also that
the CSPF does the immediate CSPF re-calculation when the Traffic the CSPF does the immediate CSPF recalculation when the Traffic
Engineering metric is raised to (2^24 - 2) to be the last resort Engineering metric is raised to (2^24 - 2) to be the last resort
link. link.
It is advisable that implementations provide a configuration It is advisable that implementations provide a configuration
capability to disable any IS-IS metric changes by Reverse Metric capability to disable any IS-IS metric changes by a Reverse Metric
mechanism through neighbor's Hello PDUs. mechanism through neighbors' Hello PDUs.
If an implementation enables this mechanism by default, it is If an implementation enables this mechanism by default, it is
RECOMMENDED that it be disabled by the operators when not explicitly RECOMMENDED that it be disabled by the operators when not explicitly
using it. using it.
4. Security Considerations 4. Security Considerations
Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
[RFC5310], and with various deployment and operational security [RFC5310], and with various deployment and operational security
considerations in [RFC7645]. The enhancement in this document makes considerations in [RFC7645]. The enhancement in this document makes
it possible for one IS-IS router to manipulate the IS-IS Default it possible for one IS-IS router to manipulate the IS-IS Default
Metric and, optionally, Traffic Engineering parameters of adjacent Metric and, optionally, Traffic Engineering parameters of adjacent
IS-IS neighbors on point-to-point or LAN interfaces. Although IS-IS IS-IS neighbors on point-to-point or LAN interfaces. Although IS-IS
routers within a single Autonomous System nearly always are under the routers within a single Autonomous System nearly always are under the
control of a single administrative authority, it is highly control of a single administrative authority, it is highly
recommended that operators configure authentication of IS-IS PDUs to recommended that operators configure authentication of IS-IS PDUs to
mitigate use of the Reverse Metric TLV as a potential attack vector. mitigate use of the Reverse Metric TLV as a potential attack vector.
5. IANA Considerations 5. IANA Considerations
IANA has allocated IS-IS TLV Codepoints of 16 for the Reverse Metric IANA has allocated IS-IS TLV Codepoint 16 for the Reverse Metric TLV.
TLV. This new TLV has the following attributes: IIH = y, LSP = n, This new TLV has the following attributes: IIH = y, LSP = n, SNP = n,
SNP = n, Purge = n. Purge = n.
This document also introduces a new registry for sub-TLVs of the This document also introduces a new registry for sub-TLVs of the
Reverse Metric TLV. The registration policy is Expert Review as Reverse Metric TLV. The registration policy is Expert Review as
defined in [RFC8126]. This registry is part of the "IS-IS TLV defined in [RFC8126]. This registry is part of the "IS-IS TLV
Codepoints" registry. The name of the registry is "Sub-TLVs for Codepoints" registry. The name of the registry is "Sub-TLVs for TLV
Reverse Metric TLV". The defined values are: 16 (Reverse Metric TLV)". The defined values are:
0: Reserved 0: Reserved
1-17: Unassigned 1-17: Unassigned
18: Traffic Engineering Metric sub-TLV, as specified in this 18: Traffic Engineering Metric as specified in this document
document (Section 2) (Section 2)
19-255: Unassigned 19-255: Unassigned
6. Acknowledgments 6. References
The authors would like to thank Mike Shand, Dave Katz, Guan Deng,
Ilya Varlashkin, Jay Chen, Les Ginsberg, Peter Ashwood-Smith, Uma
Chunduri, Alexander Okonnikov, Jonathan Harrison, Dave Ward, Himanshu
Shah, Wes George, Danny McPherson, Ed Crabbe, Russ White, Robert
Raszuk, Tom Petch, Stewart Bryant and Acee Lindem for their comments
and contributions.
This document was produced using Marshall Rose's xml2rfc tool.
7. References
7.1. Normative References 6.1. Normative References
[ISO10589] [ISO10589] ISO, "Information technology -- Telecommunications and
ISO, "Intermediate system to Intermediate system routeing information exchange between systems -- Intermediate
System to Intermediate System intra-domain routeing
information exchange protocol for use in conjunction with information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network the protocol for providing the connectionless-mode network
Service (ISO 8473)", ISO/IEC 10589:2002. service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
November 2002.
[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>.
[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, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[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, <https://www.rfc- DOI 10.17487/RFC5120, February 2008,
editor.org/info/rfc5120>. <https://www.rfc-editor.org/info/rfc5120>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>. 2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP [RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP
Synchronization", RFC 5443, DOI 10.17487/RFC5443, March Synchronization", RFC 5443, DOI 10.17487/RFC5443, March
2009, <https://www.rfc-editor.org/info/rfc5443>. 2009, <https://www.rfc-editor.org/info/rfc5443>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[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>.
7.2. Informative References 6.2. Informative References
[I-D.shen-isis-spine-leaf-ext] [IS-IS-SL-EXT]
Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS
Routing for Spine-Leaf Topology", draft-shen-isis-spine- Routing for Spine-Leaf Topology", Work in Progress,
leaf-ext-07 (work in progress), October 2018. draft-ietf-lsr-isis-spine-leaf-ext-00, December 2018.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>. 2008, <https://www.rfc-editor.org/info/rfc5304>.
[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>.
[RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton, [RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
"Graceful Shutdown in MPLS and Generalized MPLS Traffic "Graceful Shutdown in MPLS and Generalized MPLS Traffic
Engineering Networks", RFC 5817, DOI 10.17487/RFC5817, Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
April 2010, <https://www.rfc-editor.org/info/rfc5817>. April 2010, <https://www.rfc-editor.org/info/rfc5817>.
[RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas, [RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
"Signaling LDP Label Advertisement Completion", RFC 5919, "Signaling LDP Label Advertisement Completion", RFC 5919,
DOI 10.17487/RFC5919, August 2010, <https://www.rfc- DOI 10.17487/RFC5919, August 2010,
editor.org/info/rfc5919>. <https://www.rfc-editor.org/info/rfc5919>.
[RFC6138] Kini, S., Ed. and W. Lu, Ed., "LDP IGP Synchronization for [RFC6138] Kini, S., Ed. and W. Lu, Ed., "LDP IGP Synchronization for
Broadcast Networks", RFC 6138, DOI 10.17487/RFC6138, Broadcast Networks", RFC 6138, DOI 10.17487/RFC6138,
February 2011, <https://www.rfc-editor.org/info/rfc6138>. February 2011, <https://www.rfc-editor.org/info/rfc6138>.
[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>.
Appendix A. Node Isolation Challenges Appendix A. Node Isolation Challenges
On rare occasions, it is necessary for an operator to perform On rare occasions, it is necessary for an operator to perform
disruptive network maintenance on an entire IS-IS router node, i.e., disruptive network maintenance on an entire IS-IS router node, i.e.,
major software upgrades, power/cooling augments, etc. In these major software upgrades, power/cooling augments, etc. In these
cases, an operator will set the IS-IS Overload Bit (OL-bit) within cases, an operator will set the IS-IS Overload Bit (OL bit) within
the Link State Protocol Data Units (LSPs) of the IS-IS router about the Link State Protocol Data Units (LSPs) of the IS-IS router about
to undergo maintenance. The IS-IS router immediately floods its to undergo maintenance. The IS-IS router immediately floods its
updated LSPs to all IS-IS routers in the IS-IS domain. Upon receipt updated LSPs to all IS-IS routers in the IS-IS domain. Upon receipt
of the updated LSPs, all IS-IS routers recalculate their Shortest of the updated LSPs, all IS-IS routers recalculate their Shortest
Path First (SPF) tree excluding IS-IS routers whose LSPs have the OL- Path First (SPF) tree excluding IS-IS routers whose LSPs have the OL
bit set. This effectively removes the IS-IS router about to undergo bit set. This effectively removes the IS-IS router about to undergo
maintenance from the topology, thus preventing it from receiving any maintenance from the topology, thus preventing it from receiving any
transit traffic during the maintenance period. transit traffic during the maintenance period.
After the maintenance activity has completed, the operator resets the After the maintenance activity has completed, the operator resets the
IS-IS Overload Bit within the LSPs of the original IS-IS router IS-IS Overload Bit within the LSPs of the original IS-IS router
causing it to flood updated IS-IS LSPs throughout the IS-IS domain. causing it to flood updated IS-IS LSPs throughout the IS-IS domain.
All IS-IS routers recalculate their SPF tree and now include the All IS-IS routers recalculate their SPF tree and now include the
original IS-IS router in their topology calculations, allowing it to original IS-IS router in their topology calculations, allowing it to
be used for transit traffic again. be used for transit traffic again.
Isolating an entire IS-IS router from the topology can be especially Isolating an entire IS-IS router from the topology can be especially
disruptive due to the displacement of a large volume of traffic disruptive due to the displacement of a large volume of traffic
through an entire IS-IS router to other, sub-optimal paths, (e.g., through an entire IS-IS router to other suboptimal paths (e.g., those
those with significantly larger delay). Thus, in the majority of with significantly larger delay). Thus, in the majority of network
network maintenance scenarios, where only a single link or LAN needs maintenance scenarios, where only a single link or LAN needs to be
to be augmented to increase its physical capacity or is experiencing augmented to increase its physical capacity, or is experiencing an
an intermittent failure, it is much more common and desirable to intermittent failure, it is much more common and desirable to
gracefully remove just the targeted link or LAN from service, gracefully remove just the targeted link or LAN from service
temporarily, so that the least amount of user-data traffic is temporarily, so that the least amount of user-data traffic is
affected during the link-specific network maintenance. affected during the link-specific network maintenance.
Appendix B. Link Isolation Challenges Appendix B. Link Isolation Challenges
Before network maintenance events are performed on individual Before network maintenance events are performed on individual
physical links or LANs, operators substantially increase the IS-IS physical links or LANs, operators substantially increase the IS-IS
metric simultaneously on both devices attached to the same link or metric simultaneously on both devices attached to the same link or
LAN. In doing so, the devices generate new Link State Protocol Data LAN. In doing so, the devices generate new Link State Protocol Data
Units (LSPs) that are flooded throughout the network and cause all Units (LSPs) that are flooded throughout the network and cause all
routers to gradually shift traffic onto alternate paths with very routers to gradually shift traffic onto alternate paths with very
little or no disruption to in-flight communications by applications little or no disruption to in-flight communications by applications
or end-users. When performed successfully, this allows the operator or end users. When performed successfully, this allows the operator
to confidently perform disruptive augmentation, fault diagnosis or to confidently perform disruptive augmentation, fault diagnosis, or
repairs on a link without disturbing ongoing communications in the repairs on a link without disturbing ongoing communications in the
network. network.
There are a number of challenges with the above solution. First, it There are a number of challenges with the above solution. First, it
is quite common to have routers with several hundred interfaces and is quite common to have routers with several hundred interfaces and
individual interfaces that are from several hundred Gigabits/second individual interfaces that move anywhere from several hundred
to Terabits/second of traffic. Thus, it is imperative that operators gigabits/second to terabits/second of traffic. Thus, it is
accurately identify the same point-to-point link on two, separate imperative that operators accurately identify the same point-to-point
devices in order to increase (and, afterward, decrease) the IS-IS link on two separate devices in order to increase (and afterward
metric appropriately. Second, the aforementioned solution is very decrease) the IS-IS metric appropriately. Second, the aforementioned
time consuming and even more error-prone to perform when it's solution is very time-consuming and even more error-prone to perform
necessary to temporarily remove a multi-access LAN from the network when it's necessary to temporarily remove a multi-access LAN from the
topology. Specifically, the operator needs to configure ALL devices network topology. Specifically, the operator needs to configure ALL
that have interfaces attached to the multi-access LAN with an devices that have interfaces attached to the multi-access LAN with an
appropriately high IS-IS metric, (and then decrease the IS-IS metric appropriately high IS-IS metric (and then decrease the IS-IS metric
to its original value afterward). Finally, with respect to multi- to its original value afterward). Finally, with respect to multi-
access LANs, there is currently no method to bidirectionally isolate access LANs, there is currently no method to bidirectionally isolate
only a single node's interface on the LAN when performing more fine- only a single node's interface on the LAN when performing more fine-
grained diagnosis and repairs to the multi-access LAN. grained diagnoses and repairs to the multi-access LAN.
In theory, use of a Network Management System (NMS) could improve the In theory, use of a Network Management System (NMS) could improve the
accuracy of identifying the appropriate subset of routers attached to accuracy of identifying the appropriate subset of routers attached to
either a point-to-point link or a multi-access LAN as well as either a point-to-point link or a multi-access LAN. It could also
signaling from the NMS to those devices, using a network management signal to those devices, using a network management protocol, to
protocol to adjust the IS-IS metrics on the pertinent set of adjust the IS-IS metrics on the pertinent set of interfaces. The
interfaces. The reality is that NMSs are, to a very large extent, reality is that NMSs are, to a very large extent, not used within
not used within Service Provider's networks for a variety of reasons. Service Provider's networks for a variety of reasons. In particular,
In particular, NMSs do not interoperate very well across different NMSs do not interoperate very well across different vendors or even
vendors or even separate platform families within the same vendor. separate platform families within the same vendor.
Appendix C. Contributors' Addresses Acknowledgments
The authors would like to thank Mike Shand, Dave Katz, Guan Deng,
Ilya Varlashkin, Jay Chen, Les Ginsberg, Peter Ashwood-Smith, Uma
Chunduri, Alexander Okonnikov, Jonathan Harrison, Dave Ward, Himanshu
Shah, Wes George, Danny McPherson, Ed Crabbe, Russ White, Robert
Raszuk, Tom Petch, Stewart Bryant, and Acee Lindem for their comments
and contributions.
Contributors
Tony Li Tony Li
Email: tony.li@tony.li Email: tony.li@tony.li
Authors' Addresses Authors' Addresses
Naiming Shen Naiming Shen
Cisco Systems Cisco Systems
560 McCarthy Blvd. 560 McCarthy Blvd.
Milpitas, CA 95035 Milpitas, CA 95035
USA United States of America
Email: naiming@cisco.com Email: naiming@cisco.com
Shane Amante Shane Amante
Apple, Inc. Apple Inc.
1 Infinite Loop One Apple Park Way
Cupertino, CA 95014 Cupertino, CA 95014
USA United States of America
Email: amante@apple.com
Email: samante@apple.com
Mikael Abrahamsson Mikael Abrahamsson
T-Systems Nordic T-Systems Nordic
Kistagangen 26 Kistagangen 26
Stockholm Stockholm
SE Sweden
Email: Mikael.Abrahamsson@t-systems.se Email: Mikael.Abrahamsson@t-systems.se
 End of changes. 91 change blocks. 
202 lines changed or deleted 200 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/