IS-IS Flooding Speed advertisement
draft-decraene-lsr-isis-flooding-speed-02
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| Authors | Bruno Decraene , Chris Bowers , Jayesh , Tony Li , Gunter Van de Velde | ||
| Last updated | 2020-01-06 | ||
| Replaced by | draft-decraeneginsberg-lsr-isis-fast-flooding | ||
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draft-decraene-lsr-isis-flooding-speed-02
Network Working Group B. Decraene
Internet-Draft Orange
Intended status: Standards Track C. Bowers
Expires: July 9, 2020 Jayesh. J
Juniper Networks, Inc.
T. Li
Arista Networks
G. Van de Velde
Nokia
January 6, 2020
IS-IS Flooding Speed advertisement
draft-decraene-lsr-isis-flooding-speed-02
Abstract
This document proposes a mechanism that can be used to increase the
speed at which link state information is flooded across a network
when multiple LSPDUs need to be flooded, such as in case of a node
failure. It also reduces the likelihood of overloading the
downstream flooding neighbors. This document defines a new TLV to be
advertised in IS-IS Hello messages. This TLV carries two parameters
indicating the performance capacity to receive LSPDUs: the minimum
delay between two consecutive LSPDUs and the number of LSPDUs which
can the received back to back.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 9, 2020.
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Copyright Notice
Copyright (c) 2020 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Flooding Speed TLV . . . . . . . . . . . . . . . . . . . . . 4
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Interaction with other LSPDU rate limiting mechanisms . . . . 6
5. Determining values to be advertised in the Flooding Speed TLV 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
IGP flooding is paramount for Link State IGP as routing computations
assume that the Link State DataBases (LSDBs) are always in sync
across all nodes in the flooding domain.
Slow flooding directly translates to delayed network reaction to
failure and LSDB inconsistencies across nodes. The former increases
packets losses. The latter translates to routing inconsistencies and
micro-loops leading to packets losses, link(s) overload, and jitter
for all classes of services. Note that the link(s) affected by those
forwarding issues may be any link in the network and not necessarily
the links whose IGP status has changed.
IGP flooding is hard. One would want fast flooding when the network
is stable and slow enough flooding to not overload the neighbor(s)
when the network is less stable. Since flooding is performed hop by
hop, not overloading the adjacent neighbors is sufficient. This
document addresses these requirements by shaping LSPDUs with a
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minimal delay between two consecutive LSPDUs. This flooding behavior
is already largely implemented by most implementations and hence
doesn't require changes in the basic flooding behavior. However
existing implementations rely on a shaping delay configured on the
node sending the LSPDUs. But since the need is to not overload the
downstream flooding node, the need is for the upstream flooding node
to know the receiving speed of its downstream flooding neighbors.
Although in theory this parameter could be configured on each
upstream flooding node, given the knowledge of each of its neighbor
in the topology and the receiving speed of those neighbors, in
practice this configuration is difficult to maintain over time as the
network topology change. In addition, as things currently stand,
each network operator needs to evaluate the receiving capacity of
each type of platform, depending on its hardware, software version
and number of IS-IS adjacencies. Such platform performance is better
known by its designer (the vendor) and even if validation tests are
required, one single validation test by the vendor is more effective
than N validations from N network providers. Finally, the reasoning
behind the original choices of default value is not clear. Default
values have largely remained unchanged over many years, despite very
large increases in interface speeds and processing speed. This has
resulted in default values that are likely to be very sub-optimal.
For example, typical default values are one LSPDU per 33ms or 100ms,
resulting in the ability to only send 30 or 10 LSPDUs per second.
However, the same vendors recommend setting a BGP DDoS policer to
10,000 packets per second or more on the same control plane hardware,
indicating that the control plane is capable of processing BGP
packets at a rate of 10,000 packets per second.
This document proposes that the downstream flooding node advertises
its LSPDU receiving speed for a single interface to the upstream
flooding node in IS-IS hellos. This allows the sender to take into
account the actual speed of the receiver. It also creates an
incentive for vendors to improve this speed over time and to innovate
to advertise a value reflecting the speed in the deployed environment
(for example, by taking into account the number of IS-IS neighbors,
which may send LSPDUs at the same time).
In addition, one single event in the network can require the flooding
of multiple LSPDUs. The typical case is a node failure which
requires the flooding of at least one LSPDU per neighbor of the
failed node. Hence, if a node has N IGP neighbors, the failure of
this node requires the advertisement and flooding of at least N
LSPDUs. The network won't be able to converge to the new topology
until all N LSPDUs are received by all nodes. Hence there is a need
to be able to quickly flood N LSPDUs. This document addresses this
requirement by allowing the fast flooding of some number of
consecutive LSPDUs.
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This document defines a new TLV for IS-IS hello that allows a given
node to be able to advertise the rate at which the node can be
expected to safely receive and process IS-IS LSPDUs from a given
upstream flooding neighbor on a given interface. Each upstream
flooding neighbor listens to the value advertised by the downstream
flooding neighbor. This allows the fast flooding of LSPDUs while at
the same time protecting the downstream flooding neighbor from
receiving more LSPDUs than it can safely process in the event of
network instability.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
2. Flooding Speed TLV
This document defines a new TLV called "Flooding Speed TLV" to be
included in IIH PDUs. All IIHs transmitted by a router that support
this capability MUST include this TLV.
Type is TBD1.
Length is 4 octets.
Value field has two two-octets fields:
o minimumInterfaceLSPTransmissionInterval: the minimum interval, in
milliseconds, between two LSPDUs consecutively sent by the
upstream flooding node on a single interface;
o maximumInterfaceLSPTransmissionBurst: the maximum number of un-
acknowledged LSPDUs that can be transmitted by the upstream
flooding node on a single interface with a separation interval
shorter than minimumInterfaceLSPTransmissionInterval (or even
'back to back').
+-----------------------------------------------------+
| minimumInterfaceLSPTransmissionInterval (2 octets) |
+-----------------------------------------------------+
| maximumInterfaceLSPTransmissionBurst (2 octets) |
+-----------------------------------------------------+
Figure 1: Flooding Speed TLV
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3. Operation
By sending the Flooding Speed TLV the node advertises to its IS-IS
neighbor(s) its ability to receive, from the upstream flooding
neighbor receiving this Flooding Speed TLV:
o minimumInterfaceLSPTransmissionInterval: the minimum interval, in
milliseconds, between two LSPDUs consecutively sent by the
upstream flooding node on a single interface;
o maximumInterfaceLSPTransmissionBurst: the maximum number of un-
acknowledged LSPDUs that can be transmitted by the upstream
flooding node on a single interface with a separation interval
shorter than minimumInterfaceLSPTransmissionInterval (or even
'back to back').
The node sending the Flooding Speed TLV is the downstream flooding
neighbor. It MUST be prepared to sustain, for a long duration, the
reception of one LSPDU every minimumInterfaceLSPTransmissionInterval
milliseconds. In addition, it MUST be capable of receiving
maximumInterfaceLSPTransmissionBurst un-acknowledged LSPDUs with a
shorter separation interval, provided than no more than 1000/
minimumInterfaceLSPTransmissionInterval un-acknowledged LSPDUs are
transmitted in any one second period.
Note that if the above two "MUST" cannot be fulfilled because of
transient conditions, this cause no severe harm to the operation of
IS-IS as this condition is already accounted for in [ISO10589]. As
per [ISO10589], after a few seconds, respectively 2 and 10 by default
in [ISO10589], neighbors will exchange PSNP (for point to point
interface) or CSNP (for broadcast interface) and recover from the
lost LSPDUs.
Note that, as per [ISO10589], the downstream flooding node
dynamically acknowledges the received LSPDUs by sending CSNP or PSNP
. By acknowledging the LSPDUs before the
maximumInterfaceLSPTransmissionBurst is exhausted, the downstream
flooding neighbor can achieve dynamic flow control and increase the
flooding speed with its upstream flooding node without risking to
overload any IS-IS router. If the
maximumInterfaceLSPTransmissionBurst is large enough, on a point to
point interface the downstream flooding node can acknowledge a set of
multiple LSPDUs up to the maximum size of a PSNP (up to 90 LPDUs)
which allows dynamic flow control without even increasing the number
of PSNPs.
The node receiving the Flooding Speed TLV is the upstream flooding
neighbor. The upstream flooding neighbor MUST NOT transmit LSPDUs at
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a sustained rate greater than one LSPDU every
minimumInterfaceLSPTransmissionInterval milliseconds. The upstream
flooding neighbor MAY transmit maximumInterfaceLSPTransmissionBurst
un-acknowledged LSPDUs with a shorter separation interval, provided
than no more than 1000/minimumInterfaceLSPTransmissionInterval LSPDUs
are transmitted in any one second period.
4. Interaction with other LSPDU rate limiting mechanisms
[ISO10589] describes a mechanism that limits the rate at which LSPDUs
from the same source system are sent out all interfaces. (See the
description of the parameter minimumLSPTransmissionInterval in
sections 7.3.21 and 7.3.15.5 of [ISO10589] .) In practice, however,
router vendors have implemented mechanisms that limit the rate of
LSPDUs sent on a given interface. This is often configurable on a
per-interface basis using 'lsp-interval' or 'lsp-pacing-interval' CLI
configuration.) The mechanism described in the current document
extends the practice of limiting the rate of LSPDUs sent on a given
interface, by using parameters advertised by the downstream flooding
neighbor. When the mechanism described in the current document is
used, the mechanism described in section 7.3.15.5 of [ISO10589] is
not used.
5. Determining values to be advertised in the Flooding Speed TLV
The values that a downstream flooding neighbor advertises in the
Flooding Speed TLV should not change often. For example, in order to
compute the values in the Flooding Speed TLV, a reasonable choice
might be for a node to use a formula based on an off line tests of
the overall LSPDU processing speed for a particular set of hardware
and the number of interfaces configured for IS-IS. With such a
formula, the values advertised in the Flooding Speed TLV would only
change when additional IS-IS interfaces are configured. On the other
hand, it would be undesirable to use a formula that depends, for
example, on an active measurement of the CPU load to modify the
values advertised in the Flooding Speed TLV. This could introduce
feedback into the IGP flooding process that could produce unexpected
behavior. Since correct IGP flooding is so fundamental to network
operation, we do not want to introduce new dynamic behavior to it.
By requiring that the values advertised in the Flooding Speed TLV not
change very often, we expect to produce overall flooding behavior
similar to what might be achieved by manually configuring per-
interface LSPDU rate limiting on all interfaces in the network.
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6. IANA Considerations
IANA is requested to allocate one TLV from the IS-IS TLV codepoint
registry.
Type Description IIH LSP SNP Purge
---- --------------------------- --- --- --- ---
TBD Flooding Speed TLV y n n n
Figure 2
7. Security Considerations
Any new security issues raised by the procedures in this document
depend upon the ability of an attacker to inject a false but
apparently valid IIH, the ease/difficulty of which has not been
altered.
As with others TLV advertisements, the use of a cryptographic
authentication as defined in [RFC5304] or [RFC5310] allows the
authentication of the peer and the integrity of the message. As this
document defines a TLV for IS-IS Hello message (IIH), the relevant
cryptographic authentication is for IS-IS Hello message (IIH).
In the absence of cryptographic authentication, as IS-IS does not run
over IP but directly over the link layer, it's considered difficult
to inject false IIH without having access to the link layer.
If a false IIH is sent with a Flooding Speed TLV set to low values,
the attacker can reduce the flooding speed between the two adjacent
neighbors which can result in LSDB inconsistencies and transient
forwarding loops. However, is not significantly different than
filtering or altering LSPDUs which would also be possible with access
to the link layer. In addition, if the downstream flooding neighbor
has multiple IGP neighbors, which is typically the case for
reliability or topological reasons, it would receive LSPDUs at a
regular speed from its other neighbors and hence would maintain LSDB
consistency.
If a false IIH is sent with a Flooding Speed TLV set to high values,
the attacker can increase the flooding speed which can either
overload a node or more likely generate loss of LSPDUs. However, is
not significantly different than sending many LSPDUs which would also
be possible with access to the link layer, even with cryptographic
authentication enabled. In addition, IS-IS has procedures to detect
the loss of LSPDUs and recover.
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This TLV advertisement is not flooded across the network but only
sent between two adjacent IS-IS neighbors. This would limit the
consequences in case of forged messages, and also limits the
dissemination of such information.
8. Normative References
[ISO10589]
International Organization for Standardization,
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", ISO/
IEC 10589:2002, Second Edition, Nov 2002.
[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>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[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>.
Appendix A. Changes / Author Notes
[RFC Editor: Please remove this section before publication]
00: Initial version.
01: Two notes added in section 3 "Operation".
02: Refresh, no technical change.
Authors' Addresses
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Bruno Decraene
Orange
Email: bruno.decraene@orange.com
Chris Bowers
Juniper Networks, Inc.
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
USA
Email: cbowers@juniper.net
Jayesh J
Juniper Networks, Inc.
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
USA
Email: jayeshj@juniper.net
Tony Li
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
USA
Email: tony.li@tony.li
Gunter Van de Velde
Nokia
Copernicuslaan 50
Antwerp 2018
Belgium
Email: gunter.van_de_velde@nokia.com
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