Networking Working Group N. Shen
Internet-Draft Cisco Systems
Intended status: Standards Track S. Amante
Expires: January 3, 2019 Apple, Inc.
M. Abrahamsson
T-Systems Nordic
July 2, 2018
IS-IS Routing with Reverse Metric
draft-ietf-isis-reverse-metric-11
Abstract
This document describes a mechanism to allow IS-IS routing to quickly
and accurately shift traffic away from either a point-to-point or
multi-access LAN interface during network maintenance or other
operational events. This is accomplished by signaling adjacent IS-IS
neighbors with a higher reverse metric, i.e., the metric towards the
signaling IS-IS router.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on January 3, 2019.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Node and Link Isolation . . . . . . . . . . . . . . . . . 2
1.2. Distributed Forwarding Planes . . . . . . . . . . . . . . 3
1.3. Spine-Leaf Applications . . . . . . . . . . . . . . . . . 3
1.4. LDP IGP Synchronization . . . . . . . . . . . . . . . . . 3
1.5. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . 3
1.6. Specification of Requirements . . . . . . . . . . . . . . 4
2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . 4
3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6
3.1. Processing Changes to Default Metric . . . . . . . . . . 6
3.2. Multi-Topology IS-IS Support on Point-to-point links . . 7
3.3. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 7
3.4. Point-To-Point Link Procedures . . . . . . . . . . . . . 8
3.5. LDP/IGP Synchronization on LANs . . . . . . . . . . . . . 8
3.6. Operational Guidelines . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Node Isolation Challenges . . . . . . . . . . . . . 11
Appendix B. Link Isolation Challenges . . . . . . . . . . . . . 12
Appendix C. Contributors' Addresses . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The IS-IS [ISO10589] routing protocol has been widely used in
Internet Service Provider IP/MPLS networks. Operational experience
with the protocol, combined with ever increasing requirements for
lossless operations have demonstrated some operational issues. This
document describes the issues and a mechanism for mitigating them.
1.1. Node and Link Isolation
IS-IS routing mechanism has the overload-bit, which can be used by
operators to perform disruptive maintenance on the router. But in
many operational maintenance cases, it is not necessary to divert all
the traffic away from this node. It is necessary to avoid only a
single link during the maintenance. More detailed descriptions of
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the challenges can be found in Appendix A and Appendix B of this
document.
1.2. Distributed Forwarding Planes
In a distributed forwarding platform, different forwarding line-cards
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
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
VPN. An IS-IS adjacency may be established with a neighbor router
long before the entire BGP VPN prefixes are downloaded to the
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
adjacency inbound to this router if possible. Temporarily signaling
the 'Reverse Metric' over this link to discourage the traffic via the
corresponding line-card will help to reduce the traffic loss in the
network. In the meantime, the remote PE routers will select a
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
resetting.
1.3. Spine-Leaf Applications
In the IS-IS Spine-Leaf extension [I-D.shen-isis-spine-leaf-ext], the
leaf nodes will perform equal-cost or unequal-cost load sharing
towards all the spine nodes. In certain operational cases, for
instance, when one of the backbone links on a spine node is
congested, a spine node can push a higher metric towards the
connected leaf nodes to reduce the transit traffic through the
corresponding spine node or link.
1.4. LDP IGP Synchronization
In the [RFC5443], a mechanism is described to achieve LDP IGP
synchronization by using the maximum link metric value on the
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
to the maximum link metric value, as described in [RFC6138]. In this
case, the Reverse Metric can be used to discourage both outbound and
inbound traffic without affecting the traffic of other IS-IS nodes on
the LAN.
1.5. IS-IS Reverse Metric
This document uses the routing protocol itself as the transport
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
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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
and have traffic bidirectionally shift away from that link gracefully
to alternate, viable paths.
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
protocol currently does not have a way to influence the traffic
towards a particular node on LAN links. This mechanism provides IS-
IS routing the capability of altering traffic in both 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 TE metric in the
sub-TLV being advertised is an offset or relative metric to be added
to the existing local link and TE metric values of the receiver.
1.6. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. IS-IS Reverse Metric TLV
The Reverse Metric TLV is composed of a 1 octet field of Flags, a 3
octet field containing an IS-IS Metric Value, and a 1 octet Traffic
Engineering (TE) sub-TLV length field representing the length of a
variable number of Extended Intermediate System (IS) Reachability
sub-TLVs. If the "sub-TLV len" is non-zero, then the Value field
MUST also contain one or more Extended IS Reachability sub-TLVs.
The Reverse Metric TLV is optional. 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 Hello PDU. If a received IS-IS Hello
PDU contains more than one Reverse Metric TLV, an implementation
SHOULD ignore all the Reverse Metric TLVs and treat it as an error
condition.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Metric
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Metric (Continue) | sub-TLV Len |Optional sub-TLV
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reverse Metric TLV
TYPE: TBD (be replaced by the value that IANA allocates)
LENGTH: variable (5 - 255 octets)
VALUE:
Flags (1 octet)
Metric (3 octets)
sub-TLV length (1 octet)
sub-TLV data (0 - 250 octets)
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |U|W|
+-+-+-+-+-+-+-+-+
Figure 1: Flags
The Metric field contains a 24-bit unsigned integer. This value is a
metric offset that a neighbor SHOULD add to the existing, configured
"default metric" for the IS-IS link. Refer to "Elements of
Procedure", in Section 3 for details on how an IS-IS router should
process the Metric field in a Reverse Metric TLV.
There are currently only two Flag bits defined.
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
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
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 SHOULD add the received Metric value in the Reverse Metric TLV to
the existing "default metric" in the Pseudonode LSP for the single
node from whom the Reverse Metric TLV was received. Please refer to
"Multi-Access LAN Procedures", in Section 3.3, for additional
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
ignored when received on a point-to-point link.
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U bit (0x02): The "Unreachable" bit specifies that the metric
calculated by addition of the reverse metric value to the "default
metric" is limited to (2^24-1). This "U" bit applies to both the
default metric in the Extended IS Reachability TLV and the TE
default-metric sub-TLV of the link. This is only relevant to the IS-
IS "wide" metric mode.
The Reverse Metric TLV can include sub-TLVs when an IS-IS router
wishes to signal to its neighbor to raise its Traffic Engineering
(TE) Metric over the link. In this document, only the "Traffic
Engineering Default Metric" sub-TLV [RFC5305], sub-TLV Type 18, is
defined and MAY be included in the Reverse Metric TLV, because that
is a similar 'reverse metric' operation to be used in TE
computations. Upon receiving this TE METRIC sub-TLV in a Reverse
Metric TLV, a node SHOULD add the received TE metric offset value to
its existing, configured TE default metric within its Extended IS
Reachability TLV. Use of other 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 TE sub-TLVs that it wishes to send to its IS-IS
neighbor.
3. Elements of Procedure
3.1. Processing Changes to Default Metric
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"
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
metric value is used, (Extended IS Reachability TLV) [RFC5305]
[RFC5817]. It is important to use the same IS-IS metric mode on both
ends of the link. On the receiving side of the 'reverse-metric' TLV,
the accumulated value of configured metric and the reverse-metric
needs to be limited to 63 in "narrow" metric mode and to (2^24 - 2)
in "wide" metric mode. This applies to both the default metric of
Extended IS Reachability TLV and the TE default-metric sub-TLV in LSP
or Pseudonode LSP for the "wide" metric mode case. If the "U" bit is
present in the flags, the accumulated metric value is to be limited
to (2^24 - 1) for both the normal link metric and TE metric in IS-IS
"wide" metric mode.
If an IS-IS router is configured to originate a TE Default Metric
sub-TLV for a link, but receives a Reverse Metric TLV from its
neighbor that does not contain a TE Default Metric sub-TLV, then the
IS-IS router MUST NOT change the value of its TE Default Metric sub-
TLV for that link.
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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)
[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
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
to its default metric in all Extended IS Reachability TLVs 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-TLVs in all of its MT Intermediate Systems TLVs. If an M-ISIS
router is configured to advertise TE Default Metric sub-TLVs 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 NOT change the
value in each of the TE Default Metric sub-TLVs for all topologies.
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. The decision process
of the routers on the LAN MUST follow the procedure in section
7.2.8.2 of [ISO10589], and use the "Two-way connectivity check"
during the topology and route calculation.
The Reverse Metric TE sub-TLV also applies to the DIS. If a DIS is
configured to apply TE over a link and it receives TE metric sub-TLV
in a Reverse Metric TLV, it should update the TE Default Metric sub-
TLV value of the corresponding Extended IS Reachability TLV or insert
a new one if not present.
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,
optionally Traffic Engineering parameters for all nodes in the
Pseudonode LSP or solely the node on the LAN originating the Reverse
Metric TLV.
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
wishes the DIS to add the Metric value to the default metric
contained in the Pseudonode LSP specific to just Router B. Other
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
their own Metric value to their default metric contained in the
Pseudonode LSP. When the DIS receives a properly formatted Reverse
Metric TLV with the W bit clear, the DIS MUST only add the default
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metric contained in its Pseudonode LSP for the specific neighbor that
sent the corresponding Reverse Metric TLV.
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
Reverse Metric TLV to all neighbor adjacencies in the Pseudonode LSP,
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 of the highest source MAC address Non-DIS advertising the
Reverse Metric TLV with the W bit set. The DIS MUST use the metric
value towards the nodes which explicitly advertise the Reverse Metric
TLV.
Local provisioning on the DIS to adjust the default metric(s)
contained in the Pseudonode LSP MUST take precedence over received
Reverse Metric TLVs. For instance, local policy on the DIS may be
provisioned to ignore the W bit signaling on a LAN.
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
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.
3.4. Point-To-Point Link Procedures
On a point-to-point link, there is already a "configured" IS-IS
interface metric to be applied over the link towards the IS-IS
neighbor.
When IS-IS receives the IIH PDU with the "Reverse Metric" on a point-
to-point link and if the local policy allows the supporting of
"Reverse Metric", it MUST add the metric value in "reverse metric"
TLV according to the rules described in Section 3.1 and Section 3.2.
3.5. LDP/IGP Synchronization on LANs
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
nodes on the LAN to advertise maximum link metric. [RFC6138]
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.
With the introduction of Reverse Metric in this document, a simpler
alternative solution to the above mentioned problem can be used. The
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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
new node in the last resort position without impacting the other IS-
IS nodes on the same LAN.
Specifically, when IS-IS adjacencies are being established by the new
node on the LAN, besides setting the maximum link metric value (2^24
- 2) on the interface of the LAN for LDP IGP synchronization as
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
SHOULD continue this advertisement until it completes all the LDP
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
exceeding the provisioned timeout value for the node LDP/IGP
synchronization.
3.6. 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 towards it.
The use of Reverse Metric does not alter IS-IS metric parameters
stored in a router's persistent provisioning database.
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 advertising an IS-IS metric or Traffic
Engineering parameters different from that which is configured
locally on the device.
When the link TE metric is raised to (2^24 - 1) [RFC5817], either due
to the reverse-metric mechanism or by explicit user configuration,
this SHOULD immediately trigger the CSPF re-calculation to move the
TE traffic away from that link. It is RECOMMENDED also that the CSPF
does the immediate CSPF re-calculation when the TE metric is raised
to (2^24 - 2) to be the last resort link.
It is RECOMMENDED that implementations provide a capability to
disable any changes to a node's individual interface default metric
or Traffic Engineering parameters based upon receiving a properly
formatted Reverse Metric TLVs.
4. Security Considerations
The enhancement in this document makes it possible for one IS-IS
router to manipulate the IS-IS default metric and, optionally,
Traffic Engineering parameters of adjacent IS-IS neighbors. Although
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IS-IS routers within a single Autonomous System nearly always are
under the control of a single administrative authority, it is highly
RECOMMENDED that operators configure authentication of IS-IS PDUs to
mitigate use of the Reverse Metric TLV as a potential attack vector,
particularly on multi-access LANs.
5. IANA Considerations
This document requests that IANA allocate from the IS-IS TLV
Codepoints Registry a new TLV, referred to as the "Reverse Metric"
TLV, possibly from the "Unassigned" range of 244-250, with the
following attributes: IIH = y, LSP = n, SNP = n, Purge = n.
6. 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
Razsuk, Tom Petch and Acee Lindem for their comments and
contributions.
This document was produced using Marshall Rose's xml2rfc tool.
7. References
7.1. Normative References
[ISO10589]
ISO, "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network
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, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008, <https://www.rfc-
editor.org/info/rfc5120>.
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[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[I-D.shen-isis-spine-leaf-ext]
Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS
Routing for Spine-Leaf Topology", draft-shen-isis-spine-
leaf-ext-03 (work in progress), March 2017.
[RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP
Synchronization", RFC 5443, DOI 10.17487/RFC5443, March
2009, <https://www.rfc-editor.org/info/rfc5443>.
[RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
"Graceful Shutdown in MPLS and Generalized MPLS Traffic
Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
April 2010, <https://www.rfc-editor.org/info/rfc5817>.
[RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
"Signaling LDP Label Advertisement Completion", RFC 5919,
DOI 10.17487/RFC5919, August 2010, <https://www.rfc-
editor.org/info/rfc5919>.
[RFC6138] Kini, S., Ed. and W. Lu, Ed., "LDP IGP Synchronization for
Broadcast Networks", RFC 6138, DOI 10.17487/RFC6138,
February 2011, <https://www.rfc-editor.org/info/rfc6138>.
Appendix A. Node Isolation Challenges
On rare occasions, it is necessary for an operator to perform
disruptive network maintenance on an entire IS-IS router node, i.e.,
major software upgrades, power/cooling augments, etc. In these
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
to undergo maintenance. The IS-IS router immediately floods its
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
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
maintenance from the topology, thus preventing it from receiving any
transit traffic during the maintenance period.
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After the maintenance activity has completed, the operator resets the
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.
All IS-IS routers recalculate their SPF tree and now include the
original IS-IS router in their topology calculations, allowing it to
be used for transit traffic again.
Isolating an entire IS-IS router from the topology can be especially
disruptive due to the displacement of a large volume of traffic
through an entire IS-IS router to other, sub-optimal paths, (e.g.,
those with significantly larger delay). Thus, in the majority of
network maintenance scenarios, where only a single link or LAN needs
to be augmented to increase its physical capacity or is experiencing
an intermittent failure, it is much more common and desirable to
gracefully remove just the targeted link or LAN from service,
temporarily, so that the least amount of user-data traffic is
affected during the link-specific network maintenance.
Appendix B. Link Isolation Challenges
Before network maintenance events are performed on individual
physical links or LANs, operators substantially increase the IS-IS
metric simultaneously on both devices attached to the same link or
LAN. In doing so, the devices generate new Link State Protocol Data
Units (LSPs) that are flooded throughout the network and cause all
routers to gradually shift traffic onto alternate paths with very
little or no disruption to in-flight communications by applications
or end-users. When performed successfully, this allows the operator
to confidently perform disruptive augmentation, fault diagnosis or
repairs on a link without disturbing ongoing communications in the
network.
There are a number of challenges with the above solution. First, it
is quite common to have routers with several hundred interfaces and
individual interfaces that are from several hundred Gigabits/second
to Terabits/second of traffic. Thus, it is imperative that operators
accurately identify the same point-to-point link on two, separate
devices in order to increase (and, afterward, decrease) the IS-IS
metric appropriately. Second, the aforementioned solution is very
time consuming and even more error-prone to perform when it's
necessary to temporarily remove a multi-access LAN from the network
topology. Specifically, the operator needs to configure ALL devices
that have interfaces attached to the multi-access LAN with an
appropriately high IS-IS metric, (and then decrease the IS-IS metric
to its original value afterward). Finally, with respect to multi-
access LANs, there is currently no method to bidirectionally isolate
only a single node's interface on the LAN when performing more fine-
grained diagnosis and repairs to the multi-access LAN.
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In theory, use of a Network Management System (NMS) could improve the
accuracy of identifying the appropriate subset of routers attached to
either a point-to-point link or a multi-access LAN as well as
signaling from the NMS to those devices, using a network management
protocol to adjust the IS-IS metrics on the pertinent set of
interfaces. The reality is that NMSs are, to a very large extent,
not used within Service Provider's networks for a variety of reasons.
In particular, NMSs do not interoperate very well across different
vendors or even separate platform families within the same vendor.
The risks of misidentifying one side of a point-to-point link or one
or more interfaces attached to a multi-access LAN and subsequently
increasing its IS-IS metric and potentially increased latency, jitter
or packet loss. This is unacceptable given the necessary performance
requirements for a variety of reasons including the customer
perception for near lossless operations and the associated demanding
Service Level Agreement's (SLAs) for all network services.
Appendix C. Contributors' Addresses
Tony Li
Email: tony.li@tony.li
Authors' Addresses
Naiming Shen
Cisco Systems
560 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: naiming@cisco.com
Shane Amante
Apple, Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email: samante@apple.com
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Mikael Abrahamsson
T-Systems Nordic
Kistagangen 26
Stockholm
SE
Email: Mikael.Abrahamsson@t-systems.se
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