IS-IS Working Group N. Shen
Internet-Draft T. Li
Intended status: Standards Track Cisco Systems, Inc.
Expires: April 16, 2011 S. Amante
Level 3 Communications
M. Abrahamsson
Tele2
October 13, 2010
IS-IS Reverse Metric TLV for Network Maintenance Events
draft-amante-isis-reverse-metric-00
Abstract
This document describes an improved IS-IS neighbor management scheme
which can be used to enhance network performance by allowing
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 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
router during network maintenance events.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 16, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Shen, et al. Expires April 16, 2011 [Page 1]
Internet-Draft IS-IS Reverse Metric October 2010
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Link Isolation Challenges . . . . . . . . . . . . . . . . 3
1.2. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . . 4
1.3. Specification of Requirements . . . . . . . . . . . . . . 4
2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . . 4
3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6
3.1. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 7
4. Reverse Metric TLV Example Use Case . . . . . . . . . . . . . 8
5. Operational Considerations . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Shen, et al. Expires April 16, 2011 [Page 2]
Internet-Draft IS-IS Reverse Metric October 2010
1. Introduction
The IS-IS [ISO 10589] 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 one issue and a new mechanism for improving it.
1.1. Link Isolation Challenges
During network maintenance events, operators substantially increase
the IS-IS metric simultaneously on both devices attached to the same
link. In doing so, the devices generate new Link State Protocol Data
Units (LSP's) that are flooded throughout the network and cause all
routers to gradually shift traffic onto alternate paths with very
little, to no, disruption to in-flight communications by applications
or end-users. When performed successfully, this allows the operator
to confidently perform disruptive fault diagnosis and restoration on
a link without disturbing ongoing communications in the network.
The challenge with the above solution are as follows. First, it is
quite common to have routers with several hundred interfaces onboard
and individual interfaces that are transferring 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 its necessary to temporarily remove a multi-access LAN from the
network topology. Specifically, the operator needs to configure ALL
devices's 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 LAN's, there is currently no method to bidirectionally
isolate only a single node's interface on the LAN when performed more
fine-grained diagnosis and repairs to the multi-access LAN.
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 NMS are, to a very large extent, not
used within Service Provider's networks for a variety of reasons. In
particular, NMS 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
Shen, et al. Expires April 16, 2011 [Page 3]
Internet-Draft IS-IS Reverse Metric October 2010
or more interfaces attached to a multi-access LAN and subsequently
increasing its IS-IS metric are potentially increased latency, jitter
or packet loss. This is unacceptable given the necessary performance
requirements for a variety of applications, the customer perception
for near lossless operations and the associated, demanding Service
Level Agreement's (SLA's) for all network services.
1.2. IS-IS Reverse Metric
This document proposes that the routing protocol itself be the
transport mechanism to allow one IS-IS router to advertise to an
adjacent node on a point-to-point or multi-access LAN link a "reverse
metric" in a IS-IS Hello (IIH) PDU. This would allow an operator to
only configure a single router, set a "reverse metric" on a link and
have traffic bidirectionally shift away from that link gracefully to
alternate, viable paths.
1.3. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. IS-IS Reverse Metric TLV
The Reverse Metric TLV is composed of 1 octet for the Type, 1 octet
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
Flags followed by a 3 octet field containing an IS-IS Metric and,
lastly, a 1 octet Traffic Engineering (TE) sub-TLV length field
representing the length of a variable number of Extended Intermediate
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
or more Extended IS Reachability sub-TLV's.
The Reverse Metric TLV is optional. The Reverse Metric TLV may be
present in any IS-IS Hello PDU.
TYPE: TBD
LENGTH: variable (5 - 255 octets)
VALUE:
Flags (1 octet)
Metric (3 octets)
TE sub-TLV length (1 octet)
TE sub-TLV data (0 - 250 octets)
Shen, et al. Expires April 16, 2011 [Page 4]
Internet-Draft IS-IS Reverse Metric October 2010
Flags
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |S|W|
+-+-+-+-+-+-+-+-+
Figure 1: Flags
The Reverse Metric TLV Type is TBD. Please refer to IANA
Considerations, in Section 7, for more details.
The Metric field contains a 24-bit unsigned integer equal to the
IS-IS metric a neighbor SHOULD set in its own IS Neighbors TLV or
Extended IS Reachability TLV for point-to-point links, or Pseudonode
LSP by the Designated Intermediate System (DIS) for multi-access
LAN's, back toward the router that originated this Reverse Metric
TLV. An IS-IS neighbor MUST overwrite the existing IS-IS metric, in
its corresponding IS Neighbors, Extended IS Reachability TLV or
Pseudonode LSP, with the value it received in the Metric field of the
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.
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
(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
with the Metric value received in the Reverse Metric TLV. If the
"Whole LAN" bit is not set (0), then a DIS MUST replace the IS-IS
metric in the Pseudonode LSP for just the node from whom the Reverse
Metric TLV was received. Please refer to the Elements of Procedure,
in Section 3, for additional details. In addition, the W bit MUST 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
router wishes to signal that its neighbor alter parameters contained
in the neighbor's IPv4 and/or IPv6 Traffic Engineering "Extended IS
Shen, et al. Expires April 16, 2011 [Page 5]
Internet-Draft IS-IS Reverse Metric October 2010
Reachability TLV", as defined in [RFC5305] for IPv4 and
[I-D.ietf-isis-ipv6-te] for IPv6. An IS-IS router MUST overwrite
only the subset of its own TE sub-TLV's with those sub-TLV's received
from a neighbor in the Reverse Metric TLV.
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.
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
A router SHOULD first update its own IS-IS metric and/or Traffic
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
update its own IS Neighbors TLV, Extended IS Reachability TLV or
Pseudonode LSP with the received value(s) in the Metric field or TE
sub-TLV's, then recalculate its SPF tree and associated route metrics
and, finally, flood its updated LSP's to other IS-IS routers. Note
that 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. Please refer to
Section 3.1 for additional details with respect to Multi-Access LAN's
and the Reverse Metric TLV.
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. Routers MUST scan the Metric value and TE sub-TLV's in all
subsequently received Reverse Metric TLV's. If changes are observed
by a receiver of the Reverse Metric TLV in the Metric value, number
of TE sub-TLV's or data in the TE sub-TLV's, the receiving router
MUST update its advertised IS-IS metric or Traffic Engineering
parameters in the appropriate TLV's, recompute its SPF tree and
Shen, et al. Expires April 16, 2011 [Page 6]
Internet-Draft IS-IS Reverse Metric October 2010
corresponding metrics to IP prefixes and, finally, flood new LSP's to
other IS-IS routers.
When a router stops receiving a Reverse Metric TLV it MUST
immediately update its own IS Neighbors TLV, Extended IS Reachability
TLV or Pseudonode LSP with the previously configured IS-IS metric
value and/or Traffic Engineering parameters, recalculate its SPF and
associated route metrics and flood updated LSP's within the IS-IS
domain.
It is RECOMMENDED that implementations provide a capability to
disable any changes to a node's default metric or Traffic Engineering
parameters based upon receipt of properly formatted Reverse Metric
TLV's.
If the router does not understand the Reverse Metric TLV or is
explicitly configured to ignore received Reverse Metric TLV's, then
it will not update nor flood a new IS Neighbors TLV, Extended IS
Reachability TLV or Pseudonode LSP and should not recompute its SPF
tree or update metrics associated with corresponding routes.
3.1. Multi-Access LAN Procedures
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
Traffic Engineering parameters for all nodes in the 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
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
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
Metric TLV with the W bit set to 0 to request the DIS replace their
respective metric and/or TE parameters contained in the Pseudonode
LSP. When the DIS receives a properly formatted Reverse Metric TLV
with the W bit set to 0, the DIS MUST only change the metric and/or
TE parameters contained in its Pseudonode LSP for the specific
neighbor that sent the Reverse Metric TLV.
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
TE parameters for all neighbor adjacencies in the Pseudonode LSP with
the Metric value in the Reverse Metric TLV and transmit a new
Pseudonode LSP to all nodes in the IS-IS domain. Later, a second
node on the LAN, Router B, could signal to the DIS with the W bit
also set to 1. In this case, the DIS MUST use the Reverse Metric TLV
Value field(s) advertised by the router with highest MAC address of
Shen, et al. Expires April 16, 2011 [Page 7]
Internet-Draft IS-IS Reverse Metric October 2010
the two routers from which it received a Reverse Metric TLV, Router A
or B. If Router B's MAC address was highest, then the DIS MUST update
the metric and/or Traffic Engineering parameters for all neighbors in
its Pseudonode LSP and flood the LSP to all nodes in the IS-IS
domain. On the other hand, if Router A's MAC address was highest the
DIS will ignore Router B's Reverse Metric TLV and continue to use
Router A's Reverse Metric TLV Value field(s) for 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
the W bit set to 1. The DIS would update the metric for all
neighbors in the Pseudonode LSP and flood the LSP. Later, a second
node on the LAN, Router B, could signal the DIS with the W bit set to
0, which indicates to the DIS that Router B is requesting the DIS
only update the metric and/or TE parameters for Router B in the
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
Pseudonode LSP even if the DIS receives prior or later requests to
assert a Whole LAN metric or TE parameter(s) change from other nodes
on the same LAN.
Local configuration on the DIS to adjust the default metric(s)
contained in the Pseudonode LSP, as documented in
[I-D.shen-isis-oper-enhance] MUST take precedence over received
Reverse Metric TLV's.
4. Reverse Metric TLV Example Use Case
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
the IS-IS network, an operator would configure one router, Router A,
attached to a point-to-point link with a "Reverse Metric". This
should not affect the configuration of the existing IS-IS default
metric previously configured on the router's interface. Assuming
Router A is using IS-IS Extensions for Traffic Engineering [RFC5305],
this should trigger Router A to update its Traffic Engineering
Default Metric sub-TLV in its own Extended IS Reachability TLV,
recompute its SPF tree and corresponding metrics to IP prefixes in
the IS-IS domain and begin the process of flooding a new LSP
throughout the network. Router A would also begin transmitting a
Reverse Metric TLV, with an appropriate Metric value, in an IIH PDU,
to its adjacent neighbor, Router B. Upon receipt of the Reverse
Metric TLV, Router B would also update its Traffic Engineering
Default Metric sub-TLV with the received Metric value in the Reverse
Shen, et al. Expires April 16, 2011 [Page 8]
Internet-Draft IS-IS Reverse Metric October 2010
Metric TLV, recalculate its SPF tree and associated route topology as
well as start flooding a new LSP containing the updated Extended IS
Reachability TLV throughout the network. As nodes in the network
receive the associated LSP's from Router A and B and recalculate a
new SPF tree, and route topology, traffic should gracefully shift
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
used as a link of last-resort. The operator can inspect traffic
counters on the A-B interface to determine if the link was
successfully isolated from the topology and proceed with necessary
fault diagnosis or maintenance of the associated link.
When the maintenance activity is complete, the operator would remove
the reverse metric configuration from Router A, which would cease
advertisement of the Reverse Metric TLV in IIH PDU's to Router B.
Both routers would revert to their originally configured IS-IS
metric, recompute new SPF trees and corresponding metrics to IP
prefixes and originate new LSP's. As the new LSP's are received and
SPF is recalculated by nodes in the IS-IS domain, traffic should
gradually shift back onto link A-B.
5. Operational Considerations
Since the Reverse Metric TLV may not be recognized by adjacent IS-IS
neighbors, operators should inspect input and output traffic
throughput counters on the local router to ensure that traffic has
bidirectionally shifted away from a link before starting any
maintenance activities.
6. Security Considerations
This document raises no new security issues for IS-IS.
7. 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, with the following attributes: IIH = y, LSP = n, SNP = n, Purge
= n.
8. Acknowledgements
The authors would like to thank Mike Shand, Dave Katz, Guan Deng,
Ilya Varlashkin, Jay Chen, Les Ginsberg and Peter Ashwood-Smith for
Shen, et al. Expires April 16, 2011 [Page 9]
Internet-Draft IS-IS Reverse Metric October 2010
their contributions.
9. 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, "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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
9.2. Informative References
[I-D.shen-isis-oper-enhance]
Shen, N., Li, T., Amante, S., and M. Abrahamsson, "IS-IS
Operational Enhancements for Network Maintenance Events",
draft-shen-isis-oper-enhance-00 (work in progress),
October 2010.
Authors' Addresses
Naiming Shen
Cisco Systems, Inc.
225 West Tasman Drive
San Jose, CA 95134
USA
Email: naiming@cisco.com
Shen, et al. Expires April 16, 2011 [Page 10]
Internet-Draft IS-IS Reverse Metric October 2010
Tony Li
Cisco Systems, Inc.
225 West Tasman Drive
San Jose, CA 95134
USA
Email: tli@cisco.com
Shane Amante
Level 3 Communications
1025 Eldorado Blvd
Broomfield, CO 80021
USA
Email: shane@level3.net
Mikael Abrahamsson
Tele2
Email: swmike@swm.pp.se
Shen, et al. Expires April 16, 2011 [Page 11]