IS-IS Flooding Parameters advertisement
draft-decraene-lsr-isis-flooding-speed-06

Document Type Active Internet-Draft (individual)
Authors Bruno Decraene  , Chris Bowers  , Jayesh  , Tony Li  , Gunter Van de Velde 
Last updated 2021-06-16
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Network Working Group                                        B. Decraene
Internet-Draft                                                    Orange
Intended status: Standards Track                               C. Bowers
Expires: December 18, 2021                                     Jayesh. J
                                                  Juniper Networks, Inc.
                                                                   T. Li
                                                         Arista Networks
                                                         G. Van de Velde
                                                                   Nokia
                                                           June 16, 2021

                IS-IS Flooding Parameters advertisement
               draft-decraene-lsr-isis-flooding-speed-06

Abstract

   This document proposes a mechanism to adjust IS-IS flooding speed
   between two adjacent routers by adjusting the sender flooding speed
   to the capability of the receiver.  This helps improving the flooding
   throughput, reducing LSPs losses and retransmissions due to receiver
   overload, and avoiding manual tuning of flooding parameters by the
   network operator.  This document defines a new TLV for SNP and/or
   Hello messages.  This TLV may carry a set of parameters indicating
   the performance capacity to receive LSPs.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 18, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Parameters TLV . . . . . . . . . . . . . . . . . . .   4
     3.1.  InterfaceLSPReceiveWindow sub-TLV . . . . . . . . . . . .   5
     3.2.  minimumInterfaceLSPTransmissionInterval sub-TLV . . . . .   5
     3.3.  minimumLSPTransmissionInterval sub-TLV  . . . . . . . . .   5
   4.  Flow control  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Operation on a point to point interface . . . . . . . . .   6
     4.2.  Faster acknowledgments of LSPs  . . . . . . . . . . . . .   6
     4.3.  Operation on a LAN interface  . . . . . . . . . . . . . .   7
   5.  Congestion control  . . . . . . . . . . . . . . . . . . . . .   8
   6.  Faster loss detection and recovery  . . . . . . . . . . . . .   9
   7.  Interaction with other LSP rate limiting mechanisms . . . . .  10
   8.  Determining values to be advertised in the Flooding
       Parameters TLV  . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Changes / Author Notes . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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
   packet loss.  The latter translates to routing inconsistencies and
   possibly micro-loops leading to packet loss, link overload, and
   jitter for all classes of service.  Note that across the network,

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   multiple links may be affected by these forwarding issues, even in
   the case of a single link failure.

   In addition, one single event in the network can require the flooding
   of multiple LSPs.  The typical case is a node failure which requires
   the flooding of at least one LSP 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 LSPs.  The
   network won't be able to converge to the new topology until all N
   LSPs are received by all nodes.  Hence there is a need to be able to
   quickly exchange N LSPs.  This document addresses this requirement by
   allowing the fast flooding of a number of consecutive LSPs.

   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 receiver is sufficient.

   Improving the communication speed and efficiency between IS-IS
   neighbors improves IS-IS scaling.  These extensions do not compete
   with proposed extensions to reduce LSP flooding traffic by reducing
   the flooding topology such as [I-D.ietf-lsr-dynamic-flooding].  On
   the contrary, this extension complements those proposals.  Indeed
   reducing the flooding topology does not reduce the size of the LSDB
   or the total number of LSPs to exchange between two nodes.  So
   increasing the overall flooding speed can be beneficial for nodes
   implementing dynamic flooding.  The reverse is also true: as dynamic
   flooding reduces the number of neighbors with flooding enabled, this
   allows nodes implementing the flooding parameter extensions to focus
   their flooding resources on those neighbors by sending better
   parameters to the selected flooding nodes and worse parameters to
   non-selected flooding nodes.

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.  Overview

   Ensuring the goodput between two entities is a layer 4 responsibility
   as per the OSI model and a typical example is the TCP protocol
   defined in RFC 793 [RFC0793].  It typically relies on the following
   sub-functions: flow control, congestion control and reliability.

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   Flow control is about creating a control loop between a single
   transmitter and single receiver.  TCP provides a mean for the
   receiver to govern the amount of data sent by the sender.  This is
   achieved by advertising a "receive window", in units of octets, with
   every ACK.  This document proposes to use the same mechanism by
   advertising a receive window, in units of LSP packets, in either IS-
   IS xSNP (ack) or IS-IS Hello.  The window indicates an allowed number
   of LSPs that the sender may transmit before receiving acknowledgment
   of those LSPs.  There is an assumption that this is related to the
   currently available data buffer space available for this adjacency.
   Indicating a large window encourages transmissions.

   Congestion control is about creating multiple interacting control
   loops between multiple transmitters and multiple receivers.  Whereas
   flow control prevents the sender from overwhelming the receiver,
   congestion control prevents senders from overwhelming the network.
   For an IS-IS adjacency, the network between two IS-IS neighbors is
   relatively limited in scope and consist in a link which is typically
   over-sized compared to the capability of the IS-IS speakers, but also
   includes components inside both routers such as a fabric switch, line
   card CPU and forwarding plane buffers which may experience
   congestion.  For congestion avoidance in steady state TCP uses the
   AIMD (Additive Increase Multiplicative Decrease) algorithm to react
   to packet loss.  This document proposes to use the same principle.

   Reliability relies on loss detection and recovery.  IS-IS already has
   mechanisms to ensure the reliable transmission of LSPs.  However the
   reaction time is hard coded in the specification and may be too long
   in some situation.  This document proposes that the delay before
   assuming a lost packet be advertised by the receiver.  This permits a
   faster receiver to allow for a faster loss detection on the sender
   side.

3.  Flooding Parameters TLV

   This document defines a new TLV called "Flooding Parameters TLV" that
   may be included in SNP and/or IIH PDUs.  It allows the LSP receiver
   to advertise receiver related parameters and capabilities which
   allows the LSP sender to better adapt to the receiver.

   Type: TBD1.

   Length: variable, the size in octet of the Value field.

   Value: a list of sub-TLVs.

   Three sub-TLVs are defined in this document.

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3.1.  InterfaceLSPReceiveWindow sub-TLV

   The sub-TLV InterfaceLSPReceiveWindow advertises the maximum number
   of un-acknowledged LSPs that the node can receive/process with no
   separation interval between LSPs.

   Type: 1.

   Length: 4 octets.

   Value: number of un-acknowledged LSPs which can be sent back to back.

3.2.  minimumInterfaceLSPTransmissionInterval sub-TLV

   The sub-TLV minimumInterfaceLSPTransmissionInterval advertises the
   minimum interval, in micro-seconds, between LSPs arrivals which can
   be processed/received on this interface, after the maximum number of
   un-acknowledged LSPs has been sent.

   Type: 2.

   Length: 4 octets.

   Value: minimum interval, in micro-seconds, between two consecutive
   LSPs sent after the receive window has been used.

3.3.  minimumLSPTransmissionInterval sub-TLV

   The sub-TLV minimumLSPTransmissionInterval advertises the ISO
   minimumLSPTransmissionInterval, in micro-seconds, that the LSP
   transmitter may use.

   Type: 3.

   Length: 4 octets.

   Value: minimum interval, in micro-seconds, before further propagating
   another Link State PDU from the same source system.

4.  Flow control

   Flow control is about creating a control loop between a single
   transmitter and single receiver.  This document proposes to use a
   mechanism similar to the TCP receive window to allow the receiver to
   govern the amount of data sent by the sender.  This receive window
   indicates an allowed number of LSPs that the sender may transmit
   before receiving acknowledgment of those LSPs.  This receive window,

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   in units of LSPs, is advertised in the sub-TLV
   InterfaceLSPReceiveWindow in either IS-IS SNP (ack) or IS-IS Hello.

4.1.  Operation on a point to point interface

   By sending the InterfaceLSPReceiveWindow sub-TLV with a value N1, the
   node advertises to its IS-IS neighbor, its ability to receive, over
   that interface, a maximum of N1 un-acknowledged LSPs with no
   separation interval.  This is akin to a reception window or sliding
   window in flow control.

   By sending the minimumInterfaceLSPTransmissionInterval sub-TLV with a
   value N2, the node advertises to its IS-IS neighbor, its ability to
   receive, over that interface, after the receive window is full, LSPs
   separated by at least N2 micro-seconds.

   The IS transmitter MUST NOT exceed these parameters.  After having
   send N1 un-acknowledged LSPs, it MUST send the following LSPs with an
   interval of at least N2 micro-seconds between each LSP.

   Note however that if either the LSP transmitter or receiver does not
   adhere to these parameters, for example because of transient
   conditions, this causes no fatal condition to the operation of IS-IS.
   The worst case, the loss of LSP on the IS receiver, 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 LSPs.  This worst case,
   overrunning the receiver, should however be avoided as those
   additional seconds are impacting the network and the traffic as the
   LSDB in not fully synchronized.  Hence it is better to err on the
   conservative side and to underun the receiver rather then overrun it.

   For a given IS-IS adjacency, the Flooding Parameters TLV does not
   need to be advertised in each SNP and IIS.  The IS transmitter uses
   the latest value received of each parameter (sub-TLV) until a new
   value is advertised by the IS receiver.  Note however that CSNP and
   IIH are not reliability exchanged, hence some PDU may never be
   received.  For a parameter which has never been advertised, the IS
   transmitter use its local default value.  That value SHOULD be
   configurable on a per node basis and MAY be configurable on a per
   interface basis.

4.2.  Faster acknowledgments of LSPs

   As per [ISO10589], on point to point interfaces, the LSP receiver
   dynamically acknowledges the received LSPs by sending PSNP messages.

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   By acknowledging the LSPs before the InterfaceLSPReceiveWindow is
   exhausted, the receiver can achieve dynamic flow control and increase
   the flooding throughput without risking to overload any IS-IS router.
   If the InterfaceLSPReceiveWindow is large enough, the downstream
   flooding node can acknowledge a set of multiple LSPs up to the
   maximum size of a PSNP (90 LSPs) which allows dynamic flow control
   with limited or even no increase in the number of sent PSNPs.

   In order to avoid reducing the throughput, the receiver should avoid
   letting the receive window exhaust.  Therefore, the receiver SHOULD
   acknowledge the LSP more quickly than the default specified in
   [ISO10589].  This is beneficial both to the LSP sender which receives
   faster feedback and to the LSP receiver which have more time to
   acknowledge many LSPs before the sender times out and resend the LSP.
   The way LSPs are acknowledged faster is a local decision on the
   receiving IS.

   Receiver MAY reduce partialSNPInterval.  Possibly reduce it even
   further when the IS-IS adjacency initially transitions to the UP
   state, or when a large number of LSPs need to be received quickly, or
   until the LSDB has been synchronized.  The choice of this lower value
   is a local choice.  It may depends on the (available) processing
   power of the node, the number of adjacencies been brought up at the
   same time, the requirement to synchronize the LSDB more quickly.

   In addition to the timer based partialSNPInterval, the receiver
   SHOULD keep track of the number of unacknowledged LSPs per circuit
   and level.  When this number exceeds a preset threshold, the receiver
   SHOULD immediately send a PSNP without waiting for the PSNP timer to
   expire.  In case of a burst of LSPs, this allows for more frequent
   PSNPs, hence a faster feedback loop to the sender.  While in the
   absence of a burst of LSP, the usual time-based PSNP approach comes
   into effect.  By deploying both the time-based and the threshold-
   based PSNP approaches, the receiver can be adaptive to both LSP
   bursts and infrequent LSP updates.  This number SHOULD be lower or
   equal to 90 as this is the maximum number of LSPs that can be
   acknowledged in a PSNP, hence waiting longer would not reduce the
   number of PSNPs sent but would delay the acknoledgements.  This
   number SHOULD also be lower or equal to the advertised receive window
   InterfaceLSPReceiveWindow, e.g., InterfaceLSPReceiveWindow/2.  Based
   on experimental evidence, 15 unacknowledged LSPs is a right value.

4.3.  Operation on a LAN interface

   On a LAN interface an IS receiver will generally receive LSPs from
   many IS transmitters.  And the LSPs sent by a given IS transmitter
   will be received by all of the IS receivers on that LAN.  In this

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   section, we clarify how the flooding parameters should be interpreted
   in the context of a LAN.

   An IS receiver on a LAN will communicate its desired flooding
   parameters using a single Flooding Parameters TLV, copies of which
   will be received by all N transmitters.  The flooding parameters sent
   by the IS receiver MUST be understood as instructions from the
   receiver to each transmitter about the desired maximum transmit
   characteristics of each transmitter.  The receiver is aware that
   there are N transmitters that can send LSPs to the receiver LAN
   interface.  The receiver might want to take that into account by
   advertising a higher value of InterfaceLSPTransmissionInterval on
   this LAN interface than what it would advertise on a point to point
   interface.  When the transmitters receive the
   InterfaceLSPTransmissionInterval value advertised by the DIS
   receiver, the transmitters should rate limit LSPs according to the
   advertised flooding parameters.  They should not apply any further
   interpretation to the flooding parameters advertised by the receiver.

   A given IS transmitter will receive flooding parameter advertisements
   from N different Flooding Parameters TLVs, which may carry different
   flooding parameter values.  A given transmitter SHOULD adjust the
   flooding behavior on this LAN interface such that none of the
   receivers receives more un-acknowledged LSPs or LSPs at a higher rate
   than indicated by their individual flooding parameter advertisements.

   In order for the InterfaceLSPReceiveWindow to be a useful parameter,
   an IS transmitter needs to be able to keep track of the number of un-
   acknowledged LSPs it has sent to a given IS receiver.  On a LAN there
   is no explicit acknowledgment of the receipt of LSPs between a given
   IS transmitter and a given IS receiver.  However, an IS transmitter
   on a LAN can infer whether or not any IS receivers on the LAN have
   requested retransmission of LSPs from the DIS by monitoring PSNPs
   generated on the LAN.  If no PSNPs have been generated on the LAN for
   a suitable period of time, then an IS transmitter can safely set the
   number of un-acknowledged LSPs to zero.

5.  Congestion control

   Whereas flow control prevents the sender from overwhelming the
   receiver, congestion control prevents senders from overwhelming the
   network.  For an IS-IS adjacency, the network between two IS-IS
   neighbors is relatively limited in scope and include in a single link
   which is typically over-sized compared to the capability of the IS-IS
   speakers.  But also includes components inside both routers such as a
   fabric switch, line card CPU and forwarding plane buffers which may
   experience congestion.  For congestion avoidance in steady state, TCP
   uses the AIMD (Additive Increase Multiplicative Decrease) algorithm

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   to react to packet loss.  This document proposes to use the same
   principle.  This document proposes one congestion control algorithm
   but implementations may choose a different one.

   The congestion control algorithm uses

   o  a moderate starting rate based on the receive window advertised by
      the receiver;

   o  an Additive Increase proportional to the number of LSPs correctly
      received (acknowledged);

   o  an exponential reduction in case of LSP loss.

   When a new set of LSPs need to be sent, the sender start with a
   congestion window set to half of the receive window.

   When the reception of N LSPs is acknowledged, the congestion window
   is increased by N, without exceeding the received windows.

   When the loss of LSP is detected, the congestion window is divided by
   two.

   Note that this congestion control algorithm benefits from the
   extensions proposed in this document, namely the advertisement of a
   receive window from the receiver (Section 4) which avoid the use of
   an arbitrary value by the sender, the faster acknowledgment of LSP
   (Section 4.2) which allows for a faster control loop and hence a
   faster increase of the congestion window in the absence of
   congestion, and the faster detection of lost LSP (Section 6) which
   allows for a faster control loop and hence a decrease of the
   congestion window in case of congestion.

6.  Faster loss detection and recovery

   As per [ISO10589], an LSP transmitter resends a un-acknowledged LSP
   no sooner than minimumLSPTransmissionInterval, which is 5 seconds by
   default.  As the goal is to increase the speed of reliable
   transmission of LSP, the transmitter should be able to retransmit
   faster in case of LSP loss.  The delay need to be compatible (higher)
   than the partialSNPInterval or the delay needed by the IS receiver to
   acknowledge the received LSPs.  This document allows the receiver to
   advertise to the sender a more realistic value for
   minimumLSPTransmissionInterval, with a goal to advertise a smaller
   value than the ISO default value and hence allow for a faster
   recovery of lost LSPs.

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   The reception of the parameter minimumLSPTransmissionInterval means
   that the IS transmitter MAY set its minimumLSPTransmissionInterval to
   this value or higher.

   The interval advertised in minimumLSPTransmissionInterval MUST be
   higher than the effective partialSNPInterval of the receiver plus the
   Round Trip Time (RTT) of the interface.  The effective
   partialSNPInterval of the receiver is the maximum amount of time that
   the receiver is expected to take to acknowledge the LSP.  This would
   be the partialSNPInterval on a receiver following only [ISO10589], or
   an effective value if the receiver has implemented a faster method to
   acknowledge LSPs, as discussed in Section 4.2.  The receiver should
   not be telling the transmitter to resend un-acknowledged LSPs before
   the receiver had time to acknowledge LSPs it has actually received.

   An LSP receiver MAY update this value depending on certain
   conditions.  For example, it can advertise a higher
   minimumLSPTransmissionInterval value when a large number of LSPs are
   been received and hence it is experiencing high load.  Or it can
   advertise a lower value when an LSP storm has passed, especially if
   there is reason to believe that some LSPs may have been lost.

7.  Interaction with other LSP rate limiting mechanisms

   [ISO10589] describes a mechanism that limits the rate at which LSPs
   from the same source system are sent out on interfaces.  (See the
   description of the parameter
   minimumBroadcastLSPTranLSPTransmissionInterval in section 7.3.15.6 of
   [ISO10589] .) In practice, however, router vendors have implemented
   mechanisms that limit the rate of LSPs 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 LSPs sent on a given interface, by using parameters
   advertised by the LSP receiver.  When the mechanism described in the
   current document is used, the mechanism described in section 7.3.15.6
   of [ISO10589] is not used.

8.  Determining values to be advertised in the Flooding Parameters TLV

   The values that a receiving IS advertises do not need to be close to
   perfection.  It is OK to be too low and hence not to use the full
   bandwidth or CPU resources.  It is OK to be too high during some
   situation and hence have the receiver drop some LSPs as the IS-IS
   protocol has mechanisms to recover.  What is not OK is to flood
   multiple order of magnitudes slower than both nodes can achieve, or
   to consistently overload the receiver.

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   The values may not need to be dynamic as a form of dynamic is
   provided by the dynamic acknowledgment of LSPs in SNP messages.
   Acknowledgments provides a feedback loop on how fast/slower the LSPs
   are processed by the receiver.  They also signal that the LSPs have
   been processed by the receiver hence removed from receive window,
   explicitly signaling to the sender that more LSPs may be sent.  By
   advertising relatively static parameters, we expect to produce
   overall flooding behavior similar to what might be achieved by
   manually configuring per-interface LSP rate limiting on all
   interfaces in the network.  The advertised values may be based, for
   example, on an off line tests of the overall LSP 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 Parameters TLV would only change when additional IS-IS
   interfaces are configured.

   The values MAY be updated dynamically, to reflect the relative change
   of load of the receiver, by improving the values when the receiver
   load is getting lower and degrading the values when the receiver load
   is getting higher.  For example, if LSPs are regularly dropped, or
   the queue regularly comes close to being filled, then values may be
   too high.  On the other hand, if the queue is barely used (by IS-IS),
   then values may be too low.

   The values MAY may also be absolute value reflecting relevant
   (averaged) hardware resources that are been monitored, typically the
   amount of buffer space used by incoming LSPs.  In this case, care
   must be taken when choosing the parameters influencing the values, in
   order to avoid undesirable or instable feedback loops.  It would be
   undesirable to use a formula that depends, for example, on an active
   measurement of the instantaneous CPU load to modify the values
   advertised in the Flooding Parameters TLV.  This could introduce
   feedback into the IGP flooding process that could produce unexpected
   behavior.

9.  IANA Considerations

   IANA is requested to allocate one TLV from the IS-IS TLV codepoint
   registry.

        Type    Description                    IIH   LSP   SNP   Purge
        ----    ---------------------------    ---   ---   ---   ---
        TBD1    Flooding Parameters TLV         y     n     y     n

                                 Figure 1

   This document creates the following sub-TLV Registry:

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   Name: Sub-TLVs for TLV TBD1 (Flooding Parameters TLV).

   Registration Procedure: Expert Review [RFC8126].

            +-------+-----------------------------------------+
            |  Type | Description                             |
            +-------+-----------------------------------------+
            |   0   | Reserved                                |
            |   1   | InterfaceLSPReceiveWindow               |
            |   2   | minimumInterfaceLSPTransmissionInterval |
            |   3   | minimumLSPTransmissionInterval          |
            | 4-255 | Unassigned                              |
            +-------+-----------------------------------------+

                       Table 1: Initial allocations

10.  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 SNP or 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 SNP or IIH message, the relevant
   cryptographic authentication is for SNP and IIH message.

   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 SNP/IHH without having access to the link layer.

   If a false SNP/IIH is sent with a Flooding Parameters TLV set to
   conservative values, the attacker can reduce the flooding speed
   between the two adjacent neighbors which can result in LSDB
   inconsistencies and transient forwarding loops.  However, it 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 LSPs at a regular speed from its other neighbors and hence
   would maintain LSDB consistency.

   If a false SNP/IIH is sent with a Flooding Parameters TLV set to
   aggressive values, the attacker can increase the flooding speed which
   can either overload a node or more likely generate loss of LSPs.
   However, it is not significantly different than sending many LSPs

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   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 LSPs and recover.

   This TLV advertisement is not flooded across the network but only
   sent between adjacent IS-IS neighbors.  This would limit the
   consequences in case of forged messages, and also limits the
   dissemination of such information.

11.  Acknowledgments

   The authors would like to thank Henk Smit, Sarah Chen, and Xuesong
   Geng for their reviews, comments and suggestions.

   The authors would like to thank David Jacquet, Sarah Chen, and
   Qiangzhou Gao for the tests performed on commercial implementations
   and their identification of some limiting factors.

12.  References

12.1.  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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

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   [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>.

12.2.  Informative References

   [I-D.ietf-lsr-dynamic-flooding]
              Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
              T., Cooper, D., Jalil, L., Dontula, S., and G. S. Mishra,
              "Dynamic Flooding on Dense Graphs", draft-ietf-lsr-
              dynamic-flooding-08 (work in progress), December 2020.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

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.

   03:

   o  Flooding Parameters TLV: name changed, advertised in both Hello
      and SNP rather than just Hello, contains sub-TLVs, parameters
      encoded in 4 octets.

   o  Terminology: upstream/downstream terms removed, in favor of terms
      from ISO specification (transmitter, receiver); burst-size rename
      to receive-window.

   o  Significant editorials changes.

   o  New section on the faster acknowledgment of LSPs.

   o  New section on the faster retransmission of lost LSPs.

   04:

   o  Adding general introduction on flow control, congestion control,
      loss detection and recovery.

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   o  Reorganizing sections as per the high level functions: flow
      control, congestion control, loss detection and recovery.

   o  Adding a section on congestion control.

   05:

   o  Some editorials changes.

   o  Updating section "Faster acknowledgements of LSPs" following the
      IS-IS flooding performance tests presented during IETF 108.

   o  Updated IANA section (new registry).

Authors' Addresses

   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

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   Gunter Van de Velde
   Nokia
   Copernicuslaan 50
   Antwerp  2018
   Belgium

   Email: gunter.van_de_velde@nokia.com

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