Internet DRAFT - draft-jholland-mboned-cbacc
draft-jholland-mboned-cbacc
Mboned J. Holland
Internet-Draft Akamai Technologies, Inc.
Intended status: Standards Track March 09, 2020
Expires: September 10, 2020
Circuit Breaker Assisted Congestion Control
draft-jholland-mboned-cbacc-01
Abstract
This document specifies Circuit Breaker Assisted Congestion Control
(CBACC). CBACC enables fast-trip Circuit Breakers by publishing rate
metadata about multicast channels from senders to intermediate
network nodes or receivers. The circuit breaker behavior is defined
as a supplement to receiver driven congestion control systems, to
preserve network health if receivers subscribe to a volume of traffic
that exceeds capacity policies or capability for a network or
receiver.
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
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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 September 10, 2020.
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
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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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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. Background and Terminology . . . . . . . . . . . . . . . 3
2. Circuit Breaker Behavior . . . . . . . . . . . . . . . . . . 4
2.1. Functional Components . . . . . . . . . . . . . . . . . . 4
2.1.1. Ingress Meter . . . . . . . . . . . . . . . . . . . . 4
2.1.2. Egress Meter . . . . . . . . . . . . . . . . . . . . 4
2.1.3. Communication Method . . . . . . . . . . . . . . . . 5
2.1.4. Measurement Function . . . . . . . . . . . . . . . . 5
2.1.5. Trigger Function . . . . . . . . . . . . . . . . . . 6
2.1.6. Reaction . . . . . . . . . . . . . . . . . . . . . . 7
2.1.7. Feedback Control Mechanism . . . . . . . . . . . . . 7
2.2. States . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Interface State . . . . . . . . . . . . . . . . . . . 7
2.2.2. Flow State . . . . . . . . . . . . . . . . . . . . . 8
2.3. Implementation Design Considerations . . . . . . . . . . 8
2.3.1. Oversubscription Thresholds . . . . . . . . . . . . . 8
2.3.2. Fairness Functions . . . . . . . . . . . . . . . . . 9
3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Module . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
4.1. YANG Module Names Registry . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5.1. Metadata Security . . . . . . . . . . . . . . . . . . . . 11
5.2. Denial of Service . . . . . . . . . . . . . . . . . . . . 11
5.2.1. State Overload . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Overjoining . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
This document defines Circuit Breaker Assisted Congestion Control
(CBACC). CBACC defines a Network Transport Circuit Breaker (CB), as
described by [RFC8084].
The CB behavior defined in this document uses bit-rate metadata about
multicast data streams, coupled with policy, capacity, and load
information at a network node, to prune multicast channels so that
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the node's aggregate capacity is not exceeded by the subscribed
channels.
To communicate the required metadata, this document defines a YANG
[RFC7950] module that augments the DORMS
[I-D.draft-jholland-mboned-dorms-01] YANG module. DORMS provides a
mechanism for senders to publish metadata about the multicast streams
they're sending through a RESTCONF service, so that receivers or
forwarding nodes can discover and consume the metadata with a set of
standard methods. The metadata MAY be communicated to receivers or
forwarding nodes by some other method, but the definition of any
alternative methods is out of scope for this document.
The CB behavior defined in this document matches the description
provided in Section 3.2.3 of [RFC8084] of a unidirectional CB over a
controlled path. The control messages from that description are
composed of the messages containing the metadata required for
operation of the CB.
CBACC is designed to supplement protocols that use multicast IP and
rely on well-behaved receivers to achieve congestion control.
Examples of congestion control systems fitting this description
include [PLM], [RLM], [RLC], [FLID-DL], [SMCC], and WEBRC [RFC3738].
CBACC addresses a problem with "overjoining" by untrusted receivers.
In an overjoining condition, receivers (either malicious,
misconfigured, or with implementation errors) subscribe to multicast
channels but do not respond appropriately to congestion. When
sufficient multicast traffic is available for subscription by such
receivers, this can overload any network.
The overjoining problem is relevant to misbehaving receivers for both
receiver-driven and feedback-driven congestion control strategies, as
described in Section 4.1 of [RFC8085].
Overjoining attacks and the challenges they present are discussed in
more detail in Appendix A.
CBACC offers a solution for the recommendation in Section 4 of
[RFC8085] that circuit breaker solutions be used even where
congestion control is optional.
1.1. Background and Terminology
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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Circuit Breaker Behavior
2.1. Functional Components
This section maps the functional components described in Section 3.1
of [RFC8084] to the operational components of the CBACC CB defined by
this document.
2.1.1. Ingress Meter
The metadata provides an ingress meter in the form of an advertised
maximum data bit-rate, namely the "max-bits-per-second" field in the
YANG model in Section 3. This is a self-report by the sender about
the maximum amount of traffic a sender will send within the interval
given by the "data-rate-window" field, which is the measurement
interval.
The sender MUST NOT send more data for a data stream than the amount
of data implied by its advertised data rate within any measurement
window, and it's RECOMMENDED for the sender to provide some margin to
account for forwarding bursts. If an egress node observes a higher
data rate within any measurement window, it MAY circuit-break that
flow immediately.
2.1.2. Egress Meter
The node implementing the CB behavior has access to several pieces of
information that can be used as relevant egress metrics:
1. Physical capacity limits on each interface.
2. Configured capacity limits for multicast traffic for each
interface, if any.
3. The observed received data rates of subscribed multicast channels
with CBACC metadata.
4. The observed received data rates of subscribed multicast channels
without CBACC metadata.
5. The observed received data rates of competing non-multicast
traffic.
6. The loss rate for subscribed multicast channels, when available.
The loss rate is only sometimes observable at an egress node; for
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example, when using AMBI [I-D.draft-jholland-mboned-ambi-04], or
when the data stream carries a protocol that is known to the
egress node by some out of band means, and whose traffic can be
monitored for loss. When available, the loss rates may be used.
Note that any on-path router can be considered an egress node for
purposes of this CB, even though it may be forwarding traffic
downstream, and even though other egress points may also be operating
a downstream CB that covers the same data stream. Components in the
receiving devices, such as an operating system or browser can also
act as an egress node, as can a receiving application.
2.1.3. Communication Method
CBACC operates at an egress node, so the egress metrics in
Section 2.1.2 are available through system calls, or by communication
with various locally deployable system monitoring applications. Any
suitable application that provides the necessary egress meter is
appropriate.
The communication path defined in this document for the information
from the ingress meter is the use of DORMS
[I-D.draft-jholland-mboned-dorms-01]. Other methods MAY be used as
well, but are out of scope for this document.
2.1.4. Measurement Function
The measurement function maintains a few values for each interface,
computed from the egress and ingress meter values:
1. The aggregate advertised maximum bit-rate capacity consumed by
CBACC data streams. This is the sum of the max-bit-rate values
in the CBACC metadata for all data streams subscribed through an
interface
2. An oversubscription threshold for each interface. The
oversubscription threshold will be determined differently for CBs
in different contexts. In some network devices, it might be as
simple as an administratively configured absolute value or
proportion of an interface's capacity. For other situations,
like a CB operating in a context with loss visibility, it could
be a dynamically changing value that grows when data streams are
successfully subscribed and receiving data without loss, and
shrinks as loss is observed across subscribed data streams. The
oversubscription threshold calculation could also incorporate
other information like out-of-band path capacity measurements
with [PathChirp], if available.
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This document covers some non-normative examples of valid
oversubscription threshold functions in Section 2.3.1, but in
general, the oversubscription threshold is the primary parameter
that different CBs in different contexts can tune to provide the
safety guarantees necessary for their context.
2.1.5. Trigger Function
The trigger function fires when the aggregate advertised maximum bit-
rate exceeds the oversubscription threshold for any interface.
When oversubscribed, the trigger function changes the states of
subscribed channels to "blocked" until the aggregate subscribed bit-
rate is below the oversubscription threshold again.
2.1.5.1. Fairness and Inter-flow Ordering
The trigger function orders the monitored flows according to a
fairness function, and blocks flows in order as needed to ensure that
only a safe level of bandwidth can be consumed by subscribed flows.
The fairness function can be different for CBs in different contexts.
Flows from a single sender MUST be ordered according to their
priority field from the CBACC metadata when compared with each other.
Between-sender flows and flows from the same sender with the same
priority are ordered according to the fairness function. Where flows
from the same sender have a priority order that conflicts with the
ordering the fairness function would use, it's appropriate to treat
those out of order flows from the sender as an aggregate flow for
between-sender flow comparisons. (TBD: the aggregation algorithm
probably needs more explaining and good examples.)
A CB implementation SHOULD provide mechanisms for administrative
controls to configure explicit biases, as this may be necessary to
support Service Level Agreements for specific events or providers, or
to blacklist or de-prioritize channels with historically known
misbehavior.
Subject to the above constraints, where possible the default fairness
behavior SHOULD favor streams with many receivers over streams with
few receivers, and streams with a low bit-rate over streams with a
high bit-rate. For example, when receiver count is known, a good
fairness metric is max-bandwidth divided by receiver-count.
(Receiver count in some networks can be known through technologies
such as the experimental PIM extension for population count described
in [RFC6807], or other custom signaling methods.)
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An overview of some other approaches to appropriate fairness metrics
is given in Section 2.3 of [RFC5166].
2.1.6. Reaction
When the trigger function fires and a subscribed channel becomes
blocked, the reaction depends on whether it's an upstream interface
or a downstream interface.
If a channel is blocked on one downstream interface, it may still be
unblocked on other downstream interfaces. When this is the case,
traffic is simply not forwarded along blocked interfaces, even though
clients might still be joined.
When a channel is blocked on all downstream interfaces, or when the
upstream interface is oversubscribed, the channel is pruned so that
data no longer arrives from the network on the upstream interface, by
a PIM prune (Section 3.5 of [RFC7761]), or a "leave" operation with
IGMP, MLD, or another multicast signaling mechanism.
Once initially circuit-broken, a flow SHOULD remain circuit-broken
for no less than 3 minutes, even if space clears up, to ensure
downstream subscriptions will notice and respond. (3 minutes is
chosen to exceed the default maximum lifetime of 2 minutes that can
occur if an IGMP responder suddenly stops operation, and ceases
responding to IGMP queries with membership reports.)
When enough capacity is available for a circuit-broken stream to be
unblocked and the circuit-breaker hold-down time is expired, the
flows SHOULD be unblocked according to the priority order.
2.1.7. Feedback Control Mechanism
The metadata should be refreshed as needed to maintain up to date
values. When using DORMS and RESTCONF, the HTTP Cache Control
headers provide valid refresh time properties from the server, and
SHOULD be used if present. If No-Cache is used, the default refresh
timing SHOULD be 30 seconds plus a random value between 0 and 10
seconds.
2.2. States
2.2.1. Interface State
A CB holds the following state for each interface, for both the
inbound and outbound directions on that interface:
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o aggregate bandwidth: The sum of the bandwidths of all non-
circuit-broken CBACC flows which transit this interface in this
direction.
o bandwidth limit: The maximum aggregate CBACC advertised bandwidth
allowed, not including circuit-broken flows.
When reducing the bandwidth limit due to congestion, the circuit
breaker SHOULD NOT reduce the limit by more than half its value in
10 seconds, and SHOULD use a smoothing function to reduce the
limit gradually over time.
It is RECOMMENDED that no more than half the capacity for a link
be allocated to CBACC flows if the link might be shared with TCP
or other traffic that is responsive to congestion.
2.2.2. Flow State
Data streams with CBACC metadata have a state for the upstream
interface through which the stream is joined:
o 'subscribed' Indicates that the circuit breaker is subscribed
upstream to the flow and forwarding packets through zero or more
egress interfaces.
o 'pruned' Indicates that the flow has been circuit-broken. A
request to unsubscribe from the flow has been sent upstream, e.g.
a PIM prune (Section 3.5 of [RFC7761]) or a "leave" operation via
IGMP, MLD, or another group membership management mechanism.
Data streams also have a per-interface state for downstream
interfaces with subscribers, where the data is being forwarded. It's
one of:
o 'forwarding' Indicates that the flow is a non-circuit-broken flow
in steady state, forwarding packets downstream.
o 'blocked' Indicates that data packets for this flow are NOT
forwarded downstream via this interface.
2.3. Implementation Design Considerations
2.3.1. Oversubscription Thresholds
TBD.
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2.3.2. Fairness Functions
TBD.
3. YANG Module
3.1. Tree Diagram
module: ietf-cbacc
augment /dorms:metadata/dorms:sender/dorms:group/dorms:udp-stream:
+--rw cbacc!
+--rw max-bits-per-second uint32
+--rw max-mss? uint16
+--rw data-rate-window? uint32
+--rw priority? uint16
3.2. Module
<CODE BEGINS> file ietf-cbacc@2020-03-09.yang
module ietf-cbacc {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-cbacc";
prefix "ambi";
import ietf-dorms {
prefix "dorms";
reference "I-D.jholland-mboned-dorms";
}
organization "IETF";
contact
"Author: Jake Holland
<mailto:jholland@akamai.com>
";
description
"Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
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This version of this YANG module is part of
draft-jholland-mboned-cbacc. See the internet draft for full
legal notices.
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) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
This module contains the definition for bandwidth consumption
metadata for SSM channels, as an extension to DORMS
(draft-jholland-mboned-dorms).";
revision 2019-09-26 {
description "Initial revision as an extension.";
reference
"";
}
augment
"/dorms:metadata/dorms:sender/dorms:group/dorms:udp-stream" {
description "Definition of the manifest stream providing
integrity info for the data stream";
container cbacc {
presence "cbacc-enabled flow";
description "Information to enable fast-trip circuit breakers";
leaf max-bits-per-second {
type uint32;
mandatory true;
description "Maximum bitrate for this stream, in Kilobits
of IP packet data (including headers) of native
multicast traffic per second";
}
leaf max-mss {
type uint16;
default 1400;
description "Maximum payload size, in bytes";
}
leaf data-rate-window {
type uint32;
default 2000;
description "Time window over which data rate is guaranteed,
in milliseconds.";
/* TBD: range limits? */
}
leaf priority {
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type uint16;
default 256;
description "The relative preference level for keeping this
flow compared to other flows from this sender (higher
value is more preferred to keep)";
}
}
}
}
<CODE ENDS>
4. IANA Considerations
4.1. YANG Module Names Registry
This document adds one YANG module to the "YANG Module Names"
registry maintained at <https://www.iana.org/assignments/yang-
parameters>. The following registrations are made, per the format in
Section 14 of [RFC6020]:
name: ietf-cbacc
namespace: urn:ietf:params:xml:ns:yang:ietf-cbacc
prefix: cbacc
reference: I-D.draft-jholland-mboned-cbacc
5. Security Considerations
5.1. Metadata Security
Be sure to authenticate the metadata. See DORMS security
considerations, and don't accept unauthenticated metadata if using an
alternative means.
5.2. Denial of Service
5.2.1. State Overload
Since CBACC flows require state, it may be possible for a set of
receivers and/or senders, possibly acting in concert, to generate
many flows in an attempt to overflow the circuit breakers' state
tables.
It is permissible for a network node to behave as a CBACC circuit
breaker for some CBACC flows while treating other CBACC flows as non-
CBACC, as part of a load balancing strategy for the network as a
whole, or simply as defense against this concern when the number of
monitored flows exceeds some threshold.
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The same techniques described in Section 3.1 of [RFC4609] can be used
to help mitigate this attack, for much the same reasons. It is
RECOMMENDED that network operators implement measures to mitigate
such attacks.
6. Acknowledgements
Many thanks to Devin Anderson, Ben Kaduk, Cheng Jin, Scott Brown,
Miroslav Ponec, Bob Briscoe, Lenny Giuliani, and Christian Worm
Mortensen for their thoughtful comments and contributions.
7. References
7.1. Normative References
[I-D.draft-jholland-mboned-ambi-04]
Holland, J. and K. Rose, "Asymmetric Manifest Based
Integrity", draft-jholland-mboned-ambi-04 (work in
progress), September 2019.
[I-D.draft-jholland-mboned-dorms-01]
Holland, J., "Discovery Of Restconf Metadata for Source-
specific multicast", draft-jholland-mboned-dorms-01 (work
in progress), September 2019.
[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>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[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>.
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7.2. Informative References
[FLID-DL] Byers, J., Horn, G., Luby, M., Mitzenmacher, M., Shaver,
W., and IEEE, "FLID-DL: congestion control for layered
multicast", DOI 10.1109/JSAC.2002.803998, n.d.,
<https://ieeexplore.ieee.org/document/1038584>.
[PathChirp]
Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J.,
Cottrell, L., Department of Electrical and Computer
Engineering Rice University, and SLAC/SCS-Network
Monitoring, Stanford University, "pathChirp: Efficient
Available Bandwidth Estimation for Network Paths", 2003.
[PLM] Biersack, Institut EURECOM, A., "PLM: Fast Convergence for
Cumulative Layered Multicast Transmission Schemes", 1999.
[RFC3738] Luby, M. and V. Goyal, "Wave and Equation Based Rate
Control (WEBRC) Building Block", RFC 3738,
DOI 10.17487/RFC3738, April 2004,
<https://www.rfc-editor.org/info/rfc3738>.
[RFC4609] Savola, P., Lehtonen, R., and D. Meyer, "Protocol
Independent Multicast - Sparse Mode (PIM-SM) Multicast
Routing Security Issues and Enhancements", RFC 4609,
DOI 10.17487/RFC4609, October 2006,
<https://www.rfc-editor.org/info/rfc4609>.
[RFC5166] Floyd, S., Ed., "Metrics for the Evaluation of Congestion
Control Mechanisms", RFC 5166, DOI 10.17487/RFC5166, March
2008, <https://www.rfc-editor.org/info/rfc5166>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6807] Farinacci, D., Shepherd, G., Venaas, S., and Y. Cai,
"Population Count Extensions to Protocol Independent
Multicast (PIM)", RFC 6807, DOI 10.17487/RFC6807, December
2012, <https://www.rfc-editor.org/info/rfc6807>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
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[RLC] Rizzo, L., Vicisano, L., and J. Crowcroft, "The RLC
multicast congestion control algorithm", 1999.
[RLM] McCanne, S., Jacobson, V., Vetterli, M., University of
California, Berkeley, and Lawrence Berkeley National
Laboratory, "Receiver-driven Layered Multicast", 1995.
[SMCC] Kwon, G., Byers, J., and Computer Science Department,
Boston University, "Smooth Multirate Multicast Congestion
Control", 2002.
Appendix A. Overjoining
[RFC8085] describes several remedies for unicast congestion control
under UDP, even though UDP does not itself provide congestion
control. In general, any network node under congestion could in
theory collect evidence that a unicast flow's sending rate is not
responding to congestion, and would then be justified in circuit-
breaking it.
With multicast IP, the situation is different, especially in the
presence of malicious receivers. A well-behaved sender using a
receiver-controlled congestion scheme such as WEBRC does not reduce
its send rate in response to congestion, instead relying on receivers
to leave the appropriate multicast groups.
This leads to a situation where, when a network accepts inter-domain
multicast traffic, as long as there are senders somewhere in the
world with aggregate bandwidth that exceeds a network's capacity,
receivers in that network can join the flows and overflow the network
capacity. A receiver controlled by an attacker could do this at the
IGMP/MLD level without running the application layer protocol that
participates in the receiver-controlled congestion control.
A network might be able to detect and defend against the most naive
version of such an attack by blocking end users that try to join too
many flows at once. However, an attacker can achieve the same effect
by joining a few high-bandwidth flows, if those exist anywhere, and
an attacker that controls a few machines in a network can coordinate
the receivers so they join disjoint sets of non-responsive sending
flows.
This scenario will produce congestion in a middle node in the network
that can't be easily detected at the edge where the IGMP/MLD join is
accepted. Thus, an attacker with a small set of machines in a target
network can always trip a circuit breaker if present, or can induce
excessive congestion among the bandwidth allocated to multicast.
This problem gets worse as more multicast flows become available.
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Internet-Draft CBACC March 2020
Although the same can apply to non-responsive unicast traffic,
network operators can assume that non-responsive sending flows are in
violation of congestion control best practices, and can therefore cut
off flows associated with the misbehaving senders. By contrast, non-
responsive multicast senders are likely to be well-behaved
participants in receiver-controlled congestion control schemes.
However, receiver controlled congestion control schemes also show the
most promise for efficient massive scale content distribution via
multicast, provided network health can be ensured. Therefore,
mechanisms to mitigate overjoining attacks while still permitting
receiver-controlled congestion control are necessary.
Author's Address
Jake Holland
Akamai Technologies, Inc.
150 Broadway
Cambridge, MA 02144
United States of America
Email: jakeholland.net@gmail.com
Holland Expires September 10, 2020 [Page 15]
