< draft-amante-isis-reverse-metric-00.txt   draft-amante-isis-reverse-metric-01.txt >
IS-IS Working Group N. Shen IS-IS Working Group N. Shen
Internet-Draft T. Li Internet-Draft T. Li
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: April 16, 2011 S. Amante Expires: June 2, 2011 S. Amante
Level 3 Communications Level 3 Communications
M. Abrahamsson M. Abrahamsson
Tele2 Tele2
October 13, 2010 November 29, 2010
IS-IS Reverse Metric TLV for Network Maintenance Events IS-IS Reverse Metric TLV for Network Maintenance Events
draft-amante-isis-reverse-metric-00 draft-amante-isis-reverse-metric-01
Abstract Abstract
This document describes an improved IS-IS neighbor management scheme This document describes an improved IS-IS neighbor management scheme
which can be used to enhance network performance by allowing which can be used to enhance network performance by allowing
operators to quickly and accurately shift traffic away from a point- operators to quickly and accurately shift traffic away from a point-
to-point or multi-access LAN interface by allowing one IS-IS router to-point or multi-access LAN interface by allowing one IS-IS router
to signal to a second, adjacent IS-IS neighbor to adjust its IS-IS to signal to a second, adjacent IS-IS neighbor to adjust its IS-IS
metric that should be used to temporarily reach the first IS-IS metric that should be used to temporarily reach the first IS-IS
router during network maintenance events. router during network maintenance events.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 16, 2011. This Internet-Draft will expire on June 2, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 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 (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Link Isolation Challenges . . . . . . . . . . . . . . . . 3 1.1. Link Isolation Challenges . . . . . . . . . . . . . . . . 3
1.2. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . . 4 1.2. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . . 4
1.3. Specification of Requirements . . . . . . . . . . . . . . 4 1.3. Specification of Requirements . . . . . . . . . . . . . . 4
2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . . 4 2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . . 4
3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6 3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6
3.1. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 7 3.1. Processing Changes to Default Metric . . . . . . . . . . . 6
3.2. Processing Changes to Default Metric for
Multi-Topology IS-IS . . . . . . . . . . . . . . . . . . . 7
3.3. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 8
3.4. Order of Operations . . . . . . . . . . . . . . . . . . . 9
3.5. Operational Guidelines . . . . . . . . . . . . . . . . . . 9
4. Reverse Metric TLV Example Use Case . . . . . . . . . . . . . 8 4. Reverse Metric TLV Example Use Case . . . . . . . . . . . . . 10
5. Operational Considerations . . . . . . . . . . . . . . . . . . 9 5. Operational Considerations . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
The IS-IS [ISO 10589] routing protocol has been widely used in The IS-IS [ISO 10589] 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 one issue and a new mechanism for improving it. document describes one issue and a new mechanism for improving it.
1.1. Link Isolation Challenges 1.1. Link Isolation Challenges
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that specifies the number of bytes in the Value field and a variable- that specifies the number of bytes in the Value field and a variable-
length Value field. The Value field starts with a 1 octet field of length Value field. The Value field starts with a 1 octet field of
Flags followed by a 3 octet field containing an IS-IS Metric and, Flags followed by a 3 octet field containing an IS-IS Metric and,
lastly, a 1 octet Traffic Engineering (TE) sub-TLV length field lastly, a 1 octet Traffic Engineering (TE) sub-TLV length field
representing the length of a variable number of Extended Intermediate representing the length of a variable number of Extended Intermediate
System (IS) Reachability sub-TLV's. If the 'S' bit in the Flags System (IS) Reachability sub-TLV's. If the 'S' bit in the Flags
field is set to 1, then the Value field MUST also contain data of 1 field is set to 1, then the Value field MUST also contain data of 1
or more Extended IS Reachability sub-TLV's. or more Extended IS Reachability sub-TLV's.
The Reverse Metric TLV is optional. The Reverse Metric TLV may be The Reverse Metric TLV is optional. The Reverse Metric TLV may be
present in any IS-IS Hello PDU. present in any IS-IS Hello PDU. A sender MUST only transmit a single
Reverse Metric TLV in a IS-IS Hello PDU.
TYPE: TBD TYPE: TBD
LENGTH: variable (5 - 255 octets) LENGTH: variable (5 - 255 octets)
VALUE: VALUE:
Flags (1 octet) Flags (1 octet)
Metric (3 octets) Metric (3 octets)
TE sub-TLV length (1 octet) TE sub-TLV length (1 octet)
TE sub-TLV data (0 - 250 octets) TE sub-TLV data (0 - 250 octets)
Flags Flags
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Reserved |S|W| | Reserved |S|W|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 1: Flags Figure 1: Flags
The Reverse Metric TLV Type is TBD. Please refer to IANA The Reverse Metric TLV Type is TBD. Please refer to IANA
Considerations, in Section 7, for more details. Considerations, in Section 7, for more details.
The Metric field contains a 24-bit unsigned integer equal to the The Metric field contains a 24-bit unsigned integer of an IS-IS
IS-IS metric a neighbor SHOULD set in its own IS Neighbors TLV or metric a neighbor SHOULD add to the existing, configured "default
Extended IS Reachability TLV for point-to-point links, or Pseudonode metric" contained within its IS Neighbors TLV or Extended IS
LSP by the Designated Intermediate System (DIS) for multi-access Reachability TLV's for point-to-point links, or Pseudonode LSP by the
LAN's, back toward the router that originated this Reverse Metric Designated Intermediate System (DIS) for multi-access LAN's, back
TLV. An IS-IS neighbor MUST overwrite the existing IS-IS metric, in toward the router that originated this Reverse Metric TLV. Refer to
its corresponding IS Neighbors, Extended IS Reachability TLV or "Elements of Procedure", below in Section 3, for details of how an
Pseudonode LSP, with the value it received in the Metric field of the IS-IS router should process the Metric field in a Reverse Metric TLV.
Reverse Metric TLV.
The Metric field may be a "default metric", in the range of 0-63, or
a "Traffic Engineering Default Metric" [RFC5305], in the range of
0-2^(24-1) depending on the configuration of router's interface that
is originating the Reverse Metric TLV. It is RECOMMENDED that
implementations, by default, place the appropriate maximum default
metric value, 63 or 2^(24-1), in the Metric field of the Reverse
Metric TLV, since the most common use is to remove the link from the
topology, except for use as a last-resort path.
There is currently only two Flag bits defined. There is 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 LAN's. When a Reverse Metric TLV is transmitted from a multi-access LAN's. When a Reverse Metric TLV is transmitted from a
(non-DIS) node to the DIS, if the "Whole LAN" bit is set (1), then a (non-DIS) node to the DIS, if the "Whole LAN" bit is set (1), then a
DIS MUST replace the IS-IS metric for all nodes in the Pseudonode LSP DIS SHOULD add the received Metric value in the Reverse Metric TLV to
with the Metric value received in the Reverse Metric TLV. If the each node's existing "default metric" in the Pseudonode LSP. If the
"Whole LAN" bit is not set (0), then a DIS MUST replace the IS-IS "Whole LAN" bit is not set (0), then a DIS SHOULD add the received
metric in the Pseudonode LSP for just the node from whom the Reverse Metric value in the Reverse Metric TLV to the existing "default
Metric TLV was received. Please refer to the Elements of Procedure, metric" in the Pseudonode LSP for the single node from whom the
in Section 3, for additional details. In addition, the W bit MUST be Reverse Metric TLV was received. Please refer to "Multi-Access LAN
unset (0) when a Reverse Metric TLV is transmitted in a IIH PDU onto Procedures", in Section 3.3, for additional details. The W bit MUST
a point-to-point link to an IS-IS neighbor. be unset (0) when a Reverse Metric TLV is transmitted in a IIH PDU
onto a point-to-point link to an IS-IS neighbor.
S bit (0x02): The "TE sub-TLV" bit MUST be set (1) when an IS-IS S bit (0x02): The "TE sub-TLV" bit MUST be set (1) when an IS-IS
router wishes to signal that its neighbor alter parameters contained router wishes to signal that its neighbor alter parameters contained
in the neighbor's IPv4 and/or IPv6 Traffic Engineering "Extended IS in the neighbor's Traffic Engineering "Extended IS Reachability TLV",
Reachability TLV", as defined in [RFC5305] for IPv4 and as defined in [RFC5305]. This document defines that only the
[I-D.ietf-isis-ipv6-te] for IPv6. An IS-IS router MUST overwrite "Traffic Engineering Default Metric" sub-TLV, sub-TLV Type 18, may be
only the subset of its own TE sub-TLV's with those sub-TLV's received sent toward neighbors in the Reverse Metric TLV, because that is used
from a neighbor in the Reverse Metric TLV. in Constrained Shortest Path First (CSPF) computations. Upon receipt
of this TE sub-TLV in a Reverse Metric TLV, a node SHOULD add the
received TE default metric to its existing, configured TE default
metric within its Extended IS Reachability TLV. Use of other sub-
TLV's is outside the scope of this document.
The S bit MUST NOT be set (0) when an IS-IS router does not have TE The S bit MUST NOT be set (0) when an IS-IS router does not have TE
sub-TLV's that it wishes to send to its IS-IS neighbor. sub-TLV's that it wishes to send to its IS-IS neighbor.
The values used for the "IPv4 Interface Address" and "IPv6 Interface
Address" TE sub-TLV's MUST be set to all zero when sent inside a
Reverse Metric TLV. In addition, the "IPv4 Neighbor Address" and
"IPv6 Neighbor Address" TE sub-TLV's MUST be set to local node's
interface address(es) that is originating a Reverse Metric TLV.
3. Elements of Procedure 3. Elements of Procedure
A router SHOULD first update its own IS-IS metric and/or Traffic 3.1. Processing Changes to Default Metric
Engineering parameters in its IS Neighbors TLV, Extended IS
Reachability TLV or Pseudonode LSP, then recompute its SPF tree plus
corresponding route metrics and, lastly, flood its updated LSP's,
using normal IS-IS mechanisms, as well as start advertising a Reverse
Metric TLV in IIH's toward a neighbor. A router MUST advertise a
Reverse Metric TLV toward a neighbor only for the period during which
it wants a neighbor to temporarily update its IS-IS metric or TE
parameters.
When a router receives a Reverse Metric TLV it MUST immediately The Metric field, in the Reverse Metric TLV, is a "default metric"
update its own IS Neighbors TLV, Extended IS Reachability TLV or that will either be in the range of 0 - 63 when a "narrow" IS-IS
Pseudonode LSP with the received value(s) in the Metric field or TE metric is used (IS Neighbors TLV, Pseudonode LSP) [RFC1195] or in the
sub-TLV's, then recalculate its SPF tree and associated route metrics range of 0 - (2^24 - 2) when a "wide" Traffic Engineering metric
and, finally, flood its updated LSP's to other IS-IS routers. Note value is used, (Extended IS Reachability TLV) [RFC5305]. It is
that on a Multi-Access LAN, only the DIS SHOULD act upon information RECOMMENDED that implementations, by default, place the appropriate
contained in a received Reverse Metric TLV. All non-DIS nodes MUST maximum default metric value, 63 or (2^24 - 2), in the Metric field
silently ignore a received Reverse Metric TLV. Please refer to and TE Default Metric sub-TLV of the Reverse Metric TLV, since the
Section 3.1 for additional details with respect to Multi-Access LAN's most common use is to remove the link from the topology, except for
and the Reverse Metric TLV. use as a last-resort path.
Routers that receive a Reverse Metric TLV MAY send a syslog message In order to ensure that an individual TE link is used as a link of
or SNMP trap, in order to assist in rapidly identifying the node in last resort during SPF computation, its metric MUST NOT be greater
the network that is asserting an IS-IS metric or Traffic Engineering than or equal to (2^24 - 1) [RFC5305]. Therefore, a receiver of a
parameters different from that which is configured locally on the Reverse Metric TLV MUST use the numerically smallest value of either
device. Routers MUST scan the Metric value and TE sub-TLV's in all the sum of its existing default metric and the Metric value in the
subsequently received Reverse Metric TLV's. If changes are observed Reverse Metric TLV or (2^24 - 2), as the default metric when updating
by a receiver of the Reverse Metric TLV in the Metric value, number its Extended IS Reachability TLV and TE default-metric sub-TLV's that
of TE sub-TLV's or data in the TE sub-TLV's, the receiving router it will then flood throughout the IS-IS domain, using normal IS-IS
MUST update its advertised IS-IS metric or Traffic Engineering procedures. Likewise, originators of a Pseudonode LSP or IS
parameters in the appropriate TLV's, recompute its SPF tree and Neighbors TLV MUST use the numerically smallest value of either the
corresponding metrics to IP prefixes and, finally, flood new LSP's to sum of its existing default metric and the Metric value it receives
other IS-IS routers. in a Reverse Metric TLV or 63 when updating the corresponding
Pseudonode LSP or IS Neighbor TLV before they are flooded. This also
applies when an IS-IS router is only configured or capable of sending
a "narrow" IS-IS default metric, in the range of 0 - 63, but receives
a "wide" Metric value in a Reverse Metric TLV, in the range of 64 -
(2^24 - 2). In this case, the receiving router MUST use the maximum
"narrow" IS-IS default metric, 63, as its IS-IS default metric value
in its updated IS Neighbor TLV or Pseudonode LSP that it floods.
When a router stops receiving a Reverse Metric TLV it MUST If an IS-IS router is configured to originate a TE Default Metric
immediately update its own IS Neighbors TLV, Extended IS Reachability sub-TLV for a link, but receives a Reverse Metric TLV from its
TLV or Pseudonode LSP with the previously configured IS-IS metric neighbor that does not contain a TE Default Metric sub-TLV, then the
value and/or Traffic Engineering parameters, recalculate its SPF and IS-IS router MUST add the value in the Metric field of the Reverse
associated route metrics and flood updated LSP's within the IS-IS Metric TLV to its own TE Default Metric sub-TLV for that link. The
domain. IS-IS router should then flood the updated Extended IS Reachability
TLV, including its updated TE Default Metric sub-TLV, using normal
IS-IS procedures.
It is RECOMMENDED that implementations provide a capability to Routers MUST scan the Metric value and TE sub-TLV's in all
disable any changes to a node's default metric or Traffic Engineering subsequently received Reverse Metric TLV's. If changes are observed
parameters based upon receipt of properly formatted Reverse Metric by a receiver of the Reverse Metric TLV in the Metric value or TE
TLV's. Default Metric sub-TLV value, the receiving router MUST update its
advertised IS-IS default metric or Traffic Engineering parameters in
the appropriate TLV's, recompute its SPF tree and flood new LSP's to
other IS-IS routers, according to the recommendations outlined in
Section 3.4, Order of Operations, below.
If the router does not understand the Reverse Metric TLV or is If the router does not understand the Reverse Metric TLV or is
explicitly configured to ignore received Reverse Metric TLV's, then explicitly configured to ignore received Reverse Metric TLV's, then
it will not update nor flood a new IS Neighbors TLV, Extended IS it MUST NOT update the default metric in its IS Neighbors TLV,
Reachability TLV or Pseudonode LSP and should not recompute its SPF Extended IS Reachability TLV, TE Default Metric sub-TLV, Multi-
tree or update metrics associated with corresponding routes. Topology Intermediate Systems TLV or Pseudonode LSP nor execute other
procedures that would result from acting on a Reverse Metric TLV,
such as recomputing its SPF tree.
3.1. Multi-Access LAN Procedures 3.2. Processing Changes to Default Metric for Multi-Topology IS-IS
The Reverse Metric TLV is applicable to Multi-Topology IS-IS (M-ISIS)
[RFC5120] capable 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 PDU's toward its neighbor(s) on the designated link that is
about to undergo maintenance. When an M-ISIS router receives a
Reverse Metric TLV it MUST add the received Metric value to its
default metric in all Extended IS Reachability TLV's for all
topologies. If an M-ISIS router receives a Reverse Metric TLV with a
TE Default Metric sub-TLV, then the M-ISIS router MUST add the
received TE Default Metric value to each of its TE Default Metric
sub-TLV's in all of its MT Intermediate Systems TLV's. If an M-ISIS
router is configured to advertise TE Default Metric sub-TLV's for one
or more topologies, but does not receive a TE Default Metric sub-TLV
in a Reverse Metric TLV, then the M-ISIS router MUST add the value in
Metric field of the Reverse Metric TLV to each of the TE Default
Metric sub-TLV's for all topologies. The M-ISIS should flood its
newly updated MT IS TLV's and recompute its SPF/CSPF accordingly.
Multi-Topology IS-IS [RFC5120] specifies there is no change to
construction of the Pseudonode LSP, regardless of the Multi-Topology
capabilities of a multi-access LAN. If any MT capable node on the
LAN advertises the Reverse Metric TLV to the DIS, the DIS should act
according to the "Multi-Access LAN Procedures" in Section 3.3 to
update, as appropriate, the default metric contained in the
Pseudonode LSP. If the DIS updates the default metric in and floods
a new Pseudonode LSP, those default metric values will be applied to
all topologies during Multi-Topology SPF calculations.
3.3. Multi-Access LAN Procedures
On a Multi-Access LAN, only the DIS SHOULD act upon information
contained in a received Reverse Metric TLV. All non-DIS nodes MUST
silently ignore a received Reverse Metric TLV.
In the case of multi-access LAN's, the "W" Flags bit is used to In the case of multi-access LAN's, the "W" Flags bit is used to
signal from a non-DIS to the DIS whether to change the metric and/or signal from a non-DIS to the DIS whether to change the metric and
Traffic Engineering parameters for all nodes in the Pseudonode LSP or optionally Traffic Engineering parameters for all nodes in the
a single node on the LAN, (the originator of the Reverse Metric TLV). Pseudonode LSP or a single node on the LAN, (the originator of the
Reverse Metric TLV).
A non-DIS node, i.e.: 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 a Reverse Metric TLV with the W bit set to 0 to the DIS, when send a Reverse Metric TLV with the W bit set to 0 to the DIS, when
Router B wishes the DIS to replace the metric and/or TE parameters Router B wishes the DIS to add the Metric value to the default metric
contained in the Pseudonode LSP specific to just Router B. Other non- contained in the Pseudonode LSP specific to just Router B. Other non-
DIS nodes, i.e.: Routers C and D, may simultaneously send a Reverse DIS nodes, i.e.: Routers C and D, may simultaneously send a Reverse
Metric TLV with the W bit set to 0 to request the DIS replace their Metric TLV with the W bit set to 0 to request the DIS add their own
respective metric and/or TE parameters contained in the Pseudonode Metric value to their default metric contained in the Pseudonode LSP.
LSP. When the DIS receives a properly formatted Reverse Metric TLV When the DIS receives a properly formatted Reverse Metric TLV with
with the W bit set to 0, the DIS MUST only change the metric and/or the W bit set to 0, the DIS MUST only add the default metric
TE parameters contained in its Pseudonode LSP for the specific contained in its Pseudonode LSP for the specific neighbor that sent
neighbor that sent the Reverse Metric TLV. the Reverse Metric TLV.
It is possible for one node, Router A, to signal to the DIS with the It is possible for one node, Router A, to signal to the DIS with the
W bit set to 1, in which case the DIS would replace the metric and/or W bit set to 1, in which case the DIS would add the Metric value in
TE parameters for all neighbor adjacencies in the Pseudonode LSP with the Reverse Metric TLV to all neighbor adjacencies in the Pseudonode
the Metric value in the Reverse Metric TLV and transmit a new LSP and transmit a new Pseudonode LSP to all nodes in the IS-IS
Pseudonode LSP to all nodes in the IS-IS domain. Later, a second domain. Later, a second node on the LAN, Router B, could signal to
node on the LAN, Router B, could signal to the DIS with the W bit the DIS with the W bit also set to 1. In this case, the DIS MUST use
also set to 1. In this case, the DIS MUST use the Reverse Metric TLV the highest source MAC address from IIH PDU's containing Reverse
Value field(s) advertised by the router with highest MAC address of Metric TLV's it receives as the tie-breaker to determine the sole
the two routers from which it received a Reverse Metric TLV, Router A Reverse Metric TLV used as the source for the Metric value that will
or B. If Router B's MAC address was highest, then the DIS MUST update be added to the default metric for all nodes in the Pseudonode LSP.
the metric and/or Traffic Engineering parameters for all neighbors in If the source MAC address was highest in IIH PDU's containing a
its Pseudonode LSP and flood the LSP to all nodes in the IS-IS Reverse Metric TLV received from Router B, then the DIS MUST add the
domain. On the other hand, if Router A's MAC address was highest the Metric value to the default metric of all neighbors in its Pseudonode
DIS will ignore Router B's Reverse Metric TLV and continue to use LSP and flood the LSP to all nodes in the IS-IS domain. On the other
Router A's Reverse Metric TLV Value field(s) for all neighbors in the hand, if the DIS determines that Router A's IIH PDU's, containing
Pseudonode LSP. When this occurs, the DIS MAY send a single syslog Reverse Metric TLV's, have the highest source MAC address, then the
message or SNMP trap indicating that it has received a Reverse Metric DIS will ignore Router B's Reverse Metric TLV and continue to use the
TLV from a neighbor, but is ignoring it due to it being received from Metric value found in Router A's Reverse Metric TLV to add to the
a neighbor with a lower MAC address. default metric of all neighbors in the Pseudonode LSP. When this
occurs, the DIS MAY send a single syslog message or SNMP trap
indicating that it has received a Reverse Metric TLV from a neighbor,
but is ignoring it due to it being received from a neighbor with a
lower MAC address.
Another scenario is that one node, Router A, may signal the DIS with Another scenario is that one node, Router A, may signal the DIS with
the W bit set to 1. The DIS would update the metric for all the W bit set to 1. The DIS would add the Metric value to the
neighbors in the Pseudonode LSP and flood the LSP. Later, a second default metric for all neighbors in the Pseudonode LSP and flood the
node on the LAN, Router B, could signal the DIS with the W bit set to LSP. Later, a second node on the LAN, Router B, could signal the DIS
0, which indicates to the DIS that Router B is requesting the DIS with the W bit set to 0, which indicates to the DIS that Router B is
only update the metric and/or TE parameters for Router B in the requesting the DIS only add the Metric value in the Reverse Metric
TLV from Router B to the default metric for Router B in the
Pseudonode LSP. The DIS MUST honor a neighbor's Reverse Metric TLV Pseudonode LSP. The DIS MUST honor a neighbor's Reverse Metric TLV
to update its individual IS-IS metric and/or TE parameters in the to update its individual default metric in the Pseudonode LSP even if
Pseudonode LSP even if the DIS receives prior or later requests to the DIS receives prior or later requests to assert a Whole LAN metric
assert a Whole LAN metric or TE parameter(s) change from other nodes from other nodes on the same LAN.
on the same LAN.
In all cases above, the DIS is MUST use 0 as the base default-metric
value for each neighbor contained in the Pseudonode LSP to which the
DIS will add the Metric value in the Reverse Metric TLV(s) it
receives from neighbors on the LAN.
Local configuration on the DIS to adjust the default metric(s) Local configuration on the DIS to adjust the default metric(s)
contained in the Pseudonode LSP, as documented in contained in the Pseudonode LSP, as documented in
[I-D.shen-isis-oper-enhance] MUST take precedence over received [I-D.shen-isis-oper-enhance] MUST take precedence over received
Reverse Metric TLV's. Reverse Metric TLV's.
3.4. Order of Operations
When an IS-IS router starts or stops generating a Reverse Metric TLV,
it will go through a process of updating its own IS-IS metric and
optionally Traffic Engineering parameters in its IS Neighbors TLV,
Extended IS Reachbaility TLV or Pseudonode LSP, flooding updated
LSP's (using normal IS-IS mechanisms), recompute its SPF/CSPF tree
plus corresponding metrics to IP prefixes, update its FIB and begin
advertising the Reverse Metric TLV in IIH PDU's toward its
corresponding neighbor(s) on the appropriate link or LAN. Likewise,
when IS-IS neighbor(s) start or stop receiving a Reverse Metric TLV,
they will go through a similar process. It is critical that devices
which implement the Reverse Metric TLV conduct this process in a
deterministic order that minimizes the possibilities to generate
temporary micro forwarding loops during a metric increase and
decrease.
3.5. Operational Guidelines
A router MUST advertise a Reverse Metric TLV toward a neighbor only
for the period during which it wants a neighbor to temporarily update
its IS-IS metric or TE parameters.
During the period when a Reverse Metric TLV is used, IS-IS routers
that are generating and receiving a Reverse Metric TLV MUST NOT
change their existing IS-IS metric or Traffic Engineering parameters
in their stored (e.g.: hard disk, etc.) configurations, since those
parameters are carefully derived from off-line capacity planning
tools and are difficult to restore to their original values.
Routers that receive a Reverse Metric TLV MAY send a syslog message
or SNMP trap, in order to assist in rapidly identifying the node in
the network that is asserting an IS-IS metric or Traffic Engineering
parameters different from that which is configured locally on the
device.
It is RECOMMENDED that implementations provide a capability to
disable any changes to a node's, or individual interfaces of the
node, default metric or Traffic Engineering parameters based upon
receipt of properly formatted Reverse Metric TLV's.
4. Reverse Metric TLV Example Use Case 4. Reverse Metric TLV Example Use Case
The following is a brief example illustrating one use case of the The following is a brief example illustrating one use case of the
Reverse Metric TLV. In order to isolate a point-to-point link from Reverse Metric TLV. In order to isolate a point-to-point link from
the IS-IS network, an operator would configure one router, Router A, the IS-IS network, an operator would configure one router, Router A,
attached to a point-to-point link with a "Reverse Metric". This attached to a point-to-point link with a "Reverse Metric". This
should not affect the configuration of the existing IS-IS default should not affect the configuration of the existing IS-IS default
metric previously configured on the router's interface. Assuming metric previously configured on the router's interface. Assuming
Router A is using IS-IS Extensions for Traffic Engineering [RFC5305], Router A is using IS-IS Extensions for Traffic Engineering [RFC5305],
this should trigger Router A to update its Traffic Engineering this should trigger Router A to update its Traffic Engineering
Default Metric sub-TLV in its own Extended IS Reachability TLV, Default Metric sub-TLV in its own Extended IS Reachability TLV,
recompute its SPF tree and corresponding metrics to IP prefixes in recompute its SPF tree and corresponding metrics to IP prefixes in
the IS-IS domain and begin the process of flooding a new LSP the IS-IS domain and begin the process of flooding a new LSP
throughout the network. Router A would also begin transmitting a throughout the network. Router A would also begin transmitting a
Reverse Metric TLV, with an appropriate Metric value, in an IIH PDU, Reverse Metric TLV, with an appropriate Metric value, in an IIH PDU,
to its adjacent neighbor, Router B. Upon receipt of the Reverse to its adjacent neighbor, Router B. Upon receipt of the Reverse
Metric TLV, Router B would also update its Traffic Engineering Metric TLV, Router B would add the received Metric or TE default
Default Metric sub-TLV with the received Metric value in the Reverse metric sub-TLV value to its own Traffic Engineering Default Metric
Metric TLV, recalculate its SPF tree and associated route topology as sub-TLV, recalculate its SPF tree and associated route topology as
well as start flooding a new LSP containing the updated Extended IS well as start flooding a new LSP containing the updated Extended IS
Reachability TLV throughout the network. As nodes in the network Reachability TLV throughout the network. As nodes in the network
receive the associated LSP's from Router A and B and recalculate a receive the associated LSP's from Router A and B and recalculate a
new SPF tree, and route topology, traffic should gracefully shift new SPF tree, and route topology, traffic should gracefully shift
onto alternate paths away from the A-B link; ultimately, after all onto alternate paths away from the A-B link; ultimately, after all
nodes in the network recompute their SPF tree link A-B should only be nodes in the network recompute their SPF tree link A-B should only be
used as a link of last-resort. The operator can inspect traffic used as a link of last-resort. The operator can inspect traffic
counters on the A-B interface to determine if the link was counters on the A-B interface to determine if the link was
successfully isolated from the topology and proceed with necessary successfully isolated from the topology and proceed with necessary
fault diagnosis or maintenance of the associated link. fault diagnosis or maintenance of the associated link.
skipping to change at page 9, line 35 skipping to change at page 11, line 21
5. Operational Considerations 5. Operational Considerations
Since the Reverse Metric TLV may not be recognized by adjacent IS-IS Since the Reverse Metric TLV may not be recognized by adjacent IS-IS
neighbors, operators should inspect input and output traffic neighbors, operators should inspect input and output traffic
throughput counters on the local router to ensure that traffic has throughput counters on the local router to ensure that traffic has
bidirectionally shifted away from a link before starting any bidirectionally shifted away from a link before starting any
maintenance activities. maintenance activities.
6. Security Considerations 6. Security Considerations
This document raises no new security issues for IS-IS. The enhancement in this document makes it possible for one IS-IS
router to manipulate the IS-IS default metric or optionally Traffic
Engineering parameters of adjacent IS-IS neighbors. Although IS-IS
routers within a single Autonomous System nearly always reside under
the control of a single administrative authority, it is highly
RECOMMENDED that operators configure authentication of IS-IS PDU's to
mitigate use of the Reverse Metric TLV as a potential attack vector,
particularly on multi-access LAN's.
7. IANA Considerations 7. IANA Considerations
This document requests that IANA allocate from the IS-IS TLV This document requests that IANA allocate from the IS-IS TLV
Codepoints Registry a new TLV, referred to as the "Reverse Metric" Codepoints Registry a new TLV, referred to as the "Reverse Metric"
TLV, with the following attributes: IIH = y, LSP = n, SNP = n, Purge TLV, with the following attributes: IIH = y, LSP = n, SNP = n, Purge
= n. = n.
8. Acknowledgements 8. Acknowledgements
The authors would like to thank Mike Shand, Dave Katz, Guan Deng, The authors would like to thank Mike Shand, Dave Katz, Guan Deng,
Ilya Varlashkin, Jay Chen, Les Ginsberg and Peter Ashwood-Smith for Ilya Varlashkin, Jay Chen, Les Ginsberg and Peter Ashwood-Smith,
their contributions. Jonathan Harrison, Dave Ward and Himanshu Shah for their
contributions.
9. References 9. References
9.1. Normative References 9.1. Normative References
[I-D.ietf-isis-ipv6-te]
Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", draft-ietf-isis-ipv6-te-08 (work in
progress), September 2010.
[ISO 10589] [ISO 10589]
ISO, "Intermediate system to Intermediate system routeing ISO, "Intermediate system to Intermediate system 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.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[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, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[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, October 2008. Engineering", RFC 5305, October 2008.
9.2. Informative References 9.2. Informative References
[I-D.shen-isis-oper-enhance] [I-D.shen-isis-oper-enhance]
Shen, N., Li, T., Amante, S., and M. Abrahamsson, "IS-IS Shen, N., Li, T., Amante, S., and M. Abrahamsson, "IS-IS
Operational Enhancements for Network Maintenance Events", Operational Enhancements for Network Maintenance Events",
draft-shen-isis-oper-enhance-00 (work in progress), draft-shen-isis-oper-enhance-00 (work in progress),
October 2010. October 2010.
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