draft-ietf-tsvwg-le-phb-03.txt   draft-ietf-tsvwg-le-phb-04.txt 
Internet Engineering Task Force R. Bless Internet Engineering Task Force R. Bless
Internet-Draft Karlsruhe Institute of Technology (KIT) Internet-Draft Karlsruhe Institute of Technology (KIT)
Obsoletes: 3662 (if approved) February 5, 2018 Obsoletes: 3662 (if approved) March 5, 2018
Updates: 4594 (if approved) Updates: 4594,8325 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: August 9, 2018 Expires: September 6, 2018
A Lower Effort Per-Hop Behavior (LE PHB) A Lower Effort Per-Hop Behavior (LE PHB)
draft-ietf-tsvwg-le-phb-03 draft-ietf-tsvwg-le-phb-04
Abstract Abstract
This document specifies properties and characteristics of a Lower This document specifies properties and characteristics of a Lower
Effort (LE) per-hop behavior (PHB). The primary objective of this LE Effort (LE) per-hop behavior (PHB). The primary objective of this LE
PHB is to protect best-effort (BE) traffic (packets forwarded with PHB is to protect best-effort (BE) traffic (packets forwarded with
the default PHB) from LE traffic in congestion situations, i.e., when the default PHB) from LE traffic in congestion situations, i.e., when
resources become scarce, best-effort traffic has precedence over LE resources become scarce, best-effort traffic has precedence over LE
traffic and may preempt it. There are numerous uses for this PHB, traffic and may preempt it. There are numerous uses for this PHB,
e.g., for background traffic of low precedence, such as bulk data e.g., for background traffic of low precedence, such as bulk data
transfers with low priority in time, non time-critical backups, transfers with low priority in time, non time-critical backups,
larger software updates, web search engines while gathering larger software updates, web search engines while gathering
information from web servers and so on. This document recommends a information from web servers and so on. This document recommends a
standard DSCP value for the LE PHB. standard DSCP value for the LE PHB. This specification updates the
DSCP recommended in RFC 4594 and RFC 8325 to use the DSCP assigned in
this specification.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 9, 2018. This Internet-Draft will expire on September 6, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 30 skipping to change at page 2, line 35
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
1.2. Deployment Considerations . . . . . . . . . . . . . . . . 5 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 6 4. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 5
2. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 6 5. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 6
3. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 7 6. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 6
4. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 7 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 7
5. Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . . 7 8. Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . . 7
6. Changes to RFC 4594 . . . . . . . . . . . . . . . . . . . . . 8 9. The Update to RFC 4594 . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 10. The Update to RFC 8325 . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 12. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 10 13.1. Normative References . . . . . . . . . . . . . . . . . . 11
Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 11 13.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 12 Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 13
Appendix C. Change History . . . . . . . . . . . . . . . . . . . 12 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 13
Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 13 Appendix C. Change History . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13 Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
This document defines a Differentiated Services per-hop behavior This document defines a Differentiated Services per-hop behavior
[RFC2474] called "Lower Effort" (LE) which is intended for traffic of [RFC2474] called "Lower Effort" (LE), which is intended for traffic
sufficiently low urgency that all other traffic takes precedence over of sufficiently low urgency that all other traffic takes precedence
LE traffic in consumption of network link bandwidth. Low urgency over the LE traffic in consumption of network link bandwidth. Low
traffic has a low priority for timely forwarding, which does not urgency traffic has a low priority for timely forwarding, which does
necessarily imply that it is generally of minor importance. From not necessarily imply that it is generally of minor importance. From
this viewpoint, it can be considered as a network equivalent to a this viewpoint, it can be considered as a network equivalent to a
background priority for processes in an operating system. There may background priority for processes in an operating system. There may
or may not be memory (buffer) resources allocated for this type of or may not be memory (buffer) resources allocated for this type of
traffic. traffic.
Some networks carry traffic for which delivery is considered Some networks carry traffic for which delivery is considered
optional; that is, packets of this type of traffic ought to consume optional; that is, packets of this type of traffic ought to consume
network resources only when no other traffic is present. network resources only when no other traffic is present.
Alternatively, the effect of this type of traffic on all other Alternatively, the effect of this type of traffic on all other
network traffic is strictly limited ("no harm" property). This is network traffic is strictly limited ("no harm" property). This is
distinct from "best- effort" (BE) traffic since the network makes no distinct from "best-effort" (BE) traffic since the network makes no
commitment to deliver LE packets. In contrast, BE traffic receives commitment to deliver LE packets. In contrast, BE traffic receives
an implied "good faith" commitment of at least some available network an implied "good faith" commitment of at least some available network
resources. This document proposes a Lower Effort Differentiated resources. This document proposes a Lower Effort Differentiated
Services per-hop behavior (LE PHB) for handling this "optional" Services per-hop behavior (LE PHB) for handling this "optional"
traffic in a differentiated services node. traffic in a differentiated services node.
1.1. Applicability 2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Applicability
A Lower Effort PHB is applicable for many applications that otherwise A Lower Effort PHB is applicable for many applications that otherwise
use best-effort delivery. More specifically, it is suitable for use best-effort delivery. More specifically, it is suitable for
traffic and services that can tolerate strongly varying throughput traffic and services that can tolerate strongly varying throughput
for their data flows, especially periods of very low throughput or for their data flows, especially periods of very low throughput or
even starvation (i.e., long interruptions due to significant or even even starvation (i.e., long interruptions due to significant or even
complete packet loss). Therefore, an application sending an LE complete packet loss). Therefore, an application sending an LE
marked flow must be able to tolerate short or (even very) long marked flow needs to be able to tolerate short or (even very) long
interruptions due to the presence of severe congestion conditions interruptions due to the presence of severe congestion conditions
during the transmission of the flow. Thus, there should be an during the transmission of the flow. Thus, there ought to be an
expectation that packets of the LE PHB may be excessively delayed or expectation that packets of the LE PHB could be excessively delayed
dropped when any other traffic is present. The LE PHB is suitable or dropped when any other traffic is present. The LE PHB is suitable
for sending traffic of low urgency across a Differentiated Services for sending traffic of low urgency across a Differentiated Services
(DS) domain or DS region. (DS) domain or DS region.
LE traffic SHOULD be congestion controlled. Since LE traffic may be LE traffic SHOULD be congestion controlled (i.e., use a congestion
starved completely for a longer period of time, transport protocols controlled transport or implement a congestion control method
or applications (and their related congestion control mechanisms) [RFC8085]). Since LE traffic could be starved completely for a
SHOULD be able to detect and react to such a situation and should longer period of time, transport protocols or applications (and their
resume the transfer as soon as possible. Congestion control is not related congestion control mechanisms) SHOULD be able to detect and
only useful to let the flows within the LE behavior aggregate adapt react to such a situation and ought to resume the transfer as soon as
to the available bandwidth that may be highly fluctuating, but also possible. Congestion control is not only useful to let the flows
in case that LE traffic is mapped to the default PHB in DS domains within the LE behavior aggregate adapt to the available bandwidth
that do not support LE. that may be highly fluctuating, but is also essential if LE traffic
is mapped to the default PHB in DS domains that do not support LE.
Use of the LE PHB might assist a network operator in moving certain Use of the LE PHB might assist a network operator in moving certain
kinds of traffic or users to off-peak times. Alternatively, or in kinds of traffic or users to off-peak times. Alternatively, or in
addition, packets can be designated for the LE PHB when the goal is addition, packets can be designated for the LE PHB when the goal is
to protect all other packet traffic from competition with the LE to protect all other packet traffic from competition with the LE
aggregate while not completely banning LE traffic from the network. aggregate while not completely banning LE traffic from the network.
An LE PHB SHOULD NOT be used for a customer's "normal internet" An LE PHB SHOULD NOT be used for a customer's "normal internet"
traffic nor should packets be "downgraded" to the LE PHB instead of traffic nor should packets be "downgraded" to the LE PHB instead of
being dropped, particularly when the packets are unauthorized being dropped, particularly when the packets are unauthorized
traffic. The LE PHB is expected to have applicability in networks traffic. The LE PHB is expected to have applicability in networks
that have at least some unused capacity at certain periods. that have at least some unused capacity at certain periods.
The LE PHB allows networks to protect themselves from selected types The LE PHB allows networks to protect themselves from selected types
of traffic as a complement to giving preferential treatment to other of traffic as a complement to giving preferential treatment to other
selected traffic aggregates. LE should not be used for the general selected traffic aggregates. LE ought not to be used for the general
case of downgraded traffic, but may be used by design, e.g., to case of downgraded traffic, but could be used by design, e.g., to
protect an internal network from untrusted external traffic sources. protect an internal network from untrusted external traffic sources.
In this case there is no way for attackers to preempt internal (non In this case there is no way for attackers to preempt internal (non
LE) traffic by flooding. Another use case in this regard is LE) traffic by flooding. Another use case in this regard is
forwarding of multicast traffic from untrusted sources. Multicast forwarding of multicast traffic from untrusted sources. Multicast
forwarding is currently enabled within domains only for specific forwarding is currently enabled within domains only for specific
sources within a domain, but not for sources from anywhere in the sources within a domain, but not for sources from anywhere in the
Internet. A main problem is that multicast routing creates traffic Internet. A main problem is that multicast routing creates traffic
sources at (mostly) unpredictable branching points within a domain, sources at (mostly) unpredictable branching points within a domain,
potentially leading to congestion and packet loss. In case multicast potentially leading to congestion and packet loss. In the case of
packets from untrusted sources are forwarded as LE traffic, they will multicast traffic packets from untrusted sources are forwarded as LE
not harm traffic from non-LE behavior aggregates. A further related traffic, they will not harm traffic from non-LE behavior aggregates.
use case is mentioned in [RFC3754]: preliminary forwarding of non- A further related use case is mentioned in [RFC3754]: preliminary
admitted multicast traffic. forwarding of non-admitted multicast traffic.
There is no intrinsic reason to limit the applicability of the LE PHB There is no intrinsic reason to limit the applicability of the LE PHB
to any particular application or type of traffic. It is intended as to any particular application or type of traffic. It is intended as
an additional traffic engineering tool for network administrators. an additional traffic engineering tool for network administrators.
For instance, it can be used to fill protection capacity of For instance, it can be used to fill protection capacity of
transmission links that is otherwise unused. Some network providers transmission links that is otherwise unused. Some network providers
keep link utilization below 50% to ensure that all traffic is keep link utilization below 50% to ensure that all traffic is
forwarded without loss after rerouting caused by a link failure. LE forwarded without loss after rerouting caused by a link failure. LE
marked traffic can utilize the normally unused capacity and will be marked traffic can utilize the normally unused capacity and will be
preempted automatically in case of link failure when 100% of the link preempted automatically in case of link failure when 100% of the link
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o For reporting errors or telemetry data from operating systems or o For reporting errors or telemetry data from operating systems or
applications. applications.
o For backup traffic or non-time critical synchronization or o For backup traffic or non-time critical synchronization or
mirroring traffic. mirroring traffic.
o For content distribution transfers between caches. o For content distribution transfers between caches.
o For preloading or prefetching objects from web sites. o For preloading or prefetching objects from web sites.
o For Network news and other "bulk mail" of the Internet. o For network news and other "bulk mail" of the Internet.
o For "downgraded" traffic from some other PHB when this does not o For "downgraded" traffic from some other PHB when this does not
violate the operational objectives of the other PHB or the overall violate the operational objectives of the other PHB.
network.
o For multicast traffic from untrusted (e.g., non-local) sources. o For multicast traffic from untrusted (e.g., non-local) sources.
1.2. Deployment Considerations 4. PHB Description
In order to enable LE support, DS nodes typically only need
o A BA classifier (Behavior Aggregate classifier, see [RFC2475])
that classifies packets according to the LE DSCP
o A dedicated LE queue
o A suitable scheduling discipline, e.g., simple priority queueing
Alternatively, implementations may use active queue management
mechanisms instead of a dedicated LE queue, e.g., dropping all
arriving LE packets when certain queue length or sojourn time
thresholds are exceeded.
Internet-wide deployment of the LE PHB is eased by the following
properties:
o No harm to other traffic: since the LE PHB has the lowest
forwarding priority it does not consume resources from other PHBs.
Deployment across different provider domains with LE support
causes no trust issues or attack vectors to existing (non LE)
traffic. Thus, providers can trust LE markings from end-systems,
i.e., there is no need to police or remark incoming LE traffic.
o No PHB parameters or configuration of traffic profiles: the LE PHB
itself possesses no parameters that need to be set or configured.
Similarly, since LE traffic requires no admission or policing, it
is not necessary to configure traffic profiles.
o No traffic conditioning mechanisms: the LE PHB requires no traffic
meters, droppers, or shapers. See also Section 3 for further
discussion.
DS domains that cannot or do not want to support the LE PHB should be
aware that they violate the "no harm" property of LE. DS domains
without LE PHB support SHOULD NOT drop LE marked packets, but rather
map them to the default PHB and keep the LE DSCP. See also Section 5
for further discussion of forwarding LE traffic with the default PHB
instead.
1.3. Requirements Language
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. PHB Description
The LE PHB is defined in relation to the default PHB (best-effort). The LE PHB is defined in relation to the default PHB (best-effort).
A packet forwarded with the LE PHB SHOULD have lower precedence than A packet forwarded with the LE PHB SHOULD have lower precedence than
packets forwarded with the default PHB, i.e., in case of congestion, packets forwarded with the default PHB, i.e., in the case of
LE marked traffic SHOULD be dropped prior to dropping any default PHB congestion, LE marked traffic SHOULD be dropped prior to dropping any
traffic. Ideally, LE packets SHOULD be forwarded only if no packet default PHB traffic. Ideally, LE packets SHOULD be forwarded only if
with any other PHB is awaiting transmission. no packet with any other PHB is awaiting transmission.
A straightforward implementation could be a simple priority scheduler A straightforward implementation could be a simple priority scheduler
serving the default PHB queue with higher priority than the lower- serving the default PHB queue with higher priority than the lower-
effort PHB queue. Alternative implementations may use scheduling effort PHB queue. Alternative implementations may use scheduling
algorithms that assign a very small weight to the LE class. This, algorithms that assign a very small weight to the LE class. This,
however, may sometimes cause better service for LE packets compared however, could sometimes cause better service for LE packets compared
to BE packets in cases when the BE share is fully utilized and the LE to BE packets in cases when the BE share is fully utilized and the LE
share not. share not.
If a dedicated LE queue is not available, an active queue management If a dedicated LE queue is not available, an active queue management
mechanism within a common BE/LE queue could also be used. This could mechanism within a common BE/LE queue could also be used. This could
drop all arriving LE packets as soon as certain queue length or drop all arriving LE packets as soon as certain queue length or
sojourn time thresholds are exceeded. sojourn time thresholds are exceeded.
Since congestion control is also useful within the LE traffic class, Since congestion control is also useful within the LE traffic class,
Explicit Congestion Notification [RFC3168] SHOULD be used for LE Explicit Congestion Notification [RFC3168] SHOULD be used for LE
packets, too. packets, too.
3. Traffic Conditioning Actions 5. Traffic Conditioning Actions
If possible, packets SHOULD be pre-marked in DS-aware end systems by If possible, packets SHOULD be pre-marked in DS-aware end systems by
applications due to their specific knowledge about the particular applications due to their specific knowledge about the particular
precedence of packets. There is no incentive for DS domains to precedence of packets. There is no incentive for DS domains to
distrust this initial marking, because letting LE traffic enter a DS distrust this initial marking, because letting LE traffic enter a DS
domain causes no harm. Thus, any policing such as limiting the rate domain causes no harm. Thus, any policing such as limiting the rate
of LE traffic is not necessary at the DS boundary. of LE traffic is not necessary at the DS boundary.
As for most other PHBs an initial classification and marking can be As for most other PHBs an initial classification and marking can be
also performed at the first DS boundary node according to the DS also performed at the first DS boundary node according to the DS
domain's own policies (e.g., as protection measure against untrusted domain's own policies (e.g., as protection measure against untrusted
sources). However, non-LE traffic (e.g., BE traffic) SHOULD NOT be sources). However, non-LE traffic (e.g., BE traffic) SHOULD NOT be
remarked to LE on a regular basis without consent or knowledge of the remarked to LE on a regular basis without consent or knowledge of the
user. See also remarks with respect to downgrading in Section 1.1. user. See also remarks with respect to downgrading in Section 3.
4. Recommended DS Codepoint 6. Recommended DS Codepoint
The RECOMMENDED codepoint for the LE PHB is '000001'. The RECOMMENDED codepoint for the LE PHB is '000001'.
Earlier specifications [RFC4594] recommended to use CS1 as codepoint Earlier specifications [RFC4594] recommended to use CS1 as codepoint
(as mentioned in [RFC3662]). This is problematic since it may cause (as mentioned in [RFC3662]). This is problematic since it may cause
a priority inversion in DiffServ domains that treat CS1 as originally a priority inversion in DiffServ domains that treat CS1 as originally
proposed in [RFC2474], resulting in forwarding LE packets with higher proposed in [RFC2474], resulting in forwarding LE packets with higher
precedence than BE packets. Existing implementations SHOULD precedence than BE packets. Existing implementations SHOULD
therefore use the unambiguous LE codepoint '000001' whenever transition to use the unambiguous LE codepoint '000001' whenever
possible. possible.
This particular codepoint was chosen due to measurements on the This particular codepoint was chosen due to measurements on the
currently observable DSCP remarking behavior in the Internet. Since currently observable DSCP remarking behavior in the Internet. Since
some network domains set the former IP precedence bits to zero, it is some network domains set the former IP precedence bits to zero, it is
possible that some other standardized DSCPs get mapped to the LE PHB possible that some other standardized DSCPs get mapped to the LE PHB
DSCP if it were taken from the DSCP standards action pool 1 (xxxxx0). DSCP if it were taken from the DSCP standards action pool 1 (xxxxx0).
5. Remarking to other DSCPs/PHBs 7. Deployment Considerations
In order to enable LE support, DS nodes typically only need
o A BA classifier (Behavior Aggregate classifier, see [RFC2475])
that classifies packets according to the LE DSCP
o A dedicated LE queue
o A suitable scheduling discipline, e.g., simple priority queueing
Alternatively, implementations could use active queue management
mechanisms instead of a dedicated LE queue, e.g., dropping all
arriving LE packets when certain queue length or sojourn time
thresholds are exceeded.
Internet-wide deployment of the LE PHB is eased by the following
properties:
o No harm to other traffic: since the LE PHB has the lowest
forwarding priority it does not consume resources from other PHBs.
Deployment across different provider domains with LE support
causes no trust issues or attack vectors to existing (non LE)
traffic. Thus, providers can trust LE markings from end-systems,
i.e., there is no need to police or remark incoming LE traffic.
o No PHB parameters or configuration of traffic profiles: the LE PHB
itself possesses no parameters that need to be set or configured.
Similarly, since LE traffic requires no admission or policing, it
is not necessary to configure traffic profiles.
o No traffic conditioning mechanisms: the LE PHB requires no traffic
meters, droppers, or shapers. See also Section 5 for further
discussion.
Operators of DS domains that cannot or do not want to support the LE
PHB should be aware that they violate the "no harm" property of LE.
DS domains that do not offer support for the LE PHB support SHOULD
NOT drop packets marked with the LE DSCP. They SHOULD map packets
with this DSCP to the default PHB and SHOULD preserve the LE DSCP
marking. See also Section 8 for further discussion of forwarding LE
traffic with the default PHB instead.
8. Remarking to other DSCPs/PHBs
"DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is "DSCP bleaching", i.e., setting the DSCP to '000000' (default PHB) is
NOT RECOMMENDED for this PHB. This may cause effects that are in NOT RECOMMENDED for this PHB. This may cause effects that are in
contrast to the original intent in protecting BE traffic from LE contrast to the original intent in protecting BE traffic from LE
traffic (no harm property). In case DS domains do not support the LE traffic (no harm property). In the case that a DS domain does not
PHB, they SHOULD treat LE marked packets with the default PHB instead support the LE PHB, its nodes SHOULD treat LE marked packets with the
(by mapping the LE DSCP to the default PHB), but they SHOULD do so default PHB instead (by mapping the LE DSCP to the default PHB), but
without remarking to DSCP '000000'. The reason for this is that they SHOULD do so without remarking to DSCP '000000'. The reason for
later traversed DS domains may then have still the possibility to this is that later traversed DS domains may then have still the
treat such packets according the LE PHB. However, operators of DS possibility to treat such packets according the LE PHB.
domains that forward LE traffic within the BE aggregate should be
aware of the implications, i.e., induced congestion situations and Operators of DS domains that forward LE traffic within the BE
quality-of-service degradation of the original BE traffic. In this aggregate need to be aware of the implications, i.e., induced
case, the LE property of not harming other traffic is no longer congestion situations and quality-of-service degradation of the
fulfilled. In order to limit the impact in such cases, traffic original BE traffic. In this case, the LE property of not harming
policing of the LE aggregate may be used. other traffic is no longer fulfilled. To limit the impact in such
cases, traffic policing of the LE aggregate MAY be used.
In case LE marked packets are effectively carried within the default In case LE marked packets are effectively carried within the default
PHB (i.e., forwarded as best-effort traffic) they get a better PHB (i.e., forwarded as best-effort traffic) they get a better
forwarding treatment than expected. For some applications and forwarding treatment than expected. For some applications and
services, it is favorable if the transmission is finished earlier services, it is favorable if the transmission is finished earlier
than expected. However, in some cases it may be against the original than expected. However, in some cases it may be against the original
intention of the LE PHB user to strictly send the traffic only if intention of the LE PHB user to strictly send the traffic only if
otherwise unused resources are available, i.e., LE traffic may otherwise unused resources are available, i.e., LE traffic may
compete with BE traffic for the same resources and thus adversely compete with BE traffic for the same resources and thus adversely
affect the original BE aggregate. In some cases users want to be affect the original BE aggregate. In some cases users want to be
sure that their LE marked traffic actually fulfills the "no harm" sure that their LE marked traffic actually fulfills the "no harm"
property. Applications that want to ensure the lower precedence property. Applications that want to ensure the lower precedence
compared to BE traffic SHOULD use additionally a corresponding Lower- compared to BE traffic SHOULD use additionally a corresponding Lower-
than-Best-Effort transport protocol [RFC6297], e.g., LEDBAT than-Best-Effort transport protocol [RFC6297], e.g., LEDBAT
[RFC6817]. [RFC6817].
A DS domain that still uses DSCP CS1 for marking LE traffic A DS domain that still uses DSCP CS1 for marking LE traffic
(including Low Priority-Data as defined in [RFC4594] or the old (including Low Priority-Data as defined in [RFC4594] or the old
definition in [RFC3662]) MUST remark traffic to the LE DSCP '000001' definition in [RFC3662]) SHOULD remark traffic to the LE DSCP
at the egress to the next DS domain. This increases the probability '000001' at the egress to the next DS domain. This increases the
that the DSCP is preserved end-to-end, whereas a CS1 marked packet probability that the DSCP is preserved end-to-end, whereas a CS1
may be remarked by the default DSCP if the next domain is applying marked packet may be remarked by the default DSCP if the next domain
DiffServ-intercon [RFC8100]. is applying DiffServ-intercon [RFC8100].
6. Changes to RFC 4594 9. The Update to RFC 4594
[RFC4594] recommended to use CS1 as codepoint in section 4.10, [RFC4594] recommended to use CS1 as codepoint in section 4.10,
whereas CS1 was defined in [RFC2474] to have a higher precedence than whereas CS1 was defined in [RFC2474] to have a higher precedence than
CS0, i.e., the default PHB. Consequently, DiffServ domains CS0, i.e., the default PHB. Consequently, DiffServ domains
implementing CS1 according to [RFC2474] will cause a priority implementing CS1 according to [RFC2474] will cause a priority
inversion for LE packets that contradicts with the original purpose inversion for LE packets that contradicts with the original purpose
of LE. Therefore, every occurrence of the CS1 DSCP is replaced by of LE. Therefore, every occurrence of the CS1 DSCP is replaced by
the LE DSCP. the LE DSCP.
Changes: Changes:
o The Low-Priority Data row in Figure 3 is updated as follows: o This update to RFC 4594 removes the following entry from figure 3:
|---------------+---------+-------------+--------------------------|
| Low-Priority | CS1 | 001000 | Any flow that has no BW |
| Data | | | assurance |
------------------------------------------------------------------
and replaces this by the following entry:
|---------------+---------+-------------+--------------------------| |---------------+---------+-------------+--------------------------|
| Low-Priority | LE | 000001 | Any flow that has no BW | | Low-Priority | LE | 000001 | Any flow that has no BW |
| Data | | | assurance | | Data | | | assurance |
------------------------------------------------------------------ ------------------------------------------------------------------
o The Low-Priority Data row in Figure 4 is updated as follows: o This update to RFC 4594 removes the following entry from figure 4:
|---------------+------+-------------------+---------+--------+----|
| Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes|
| Data | | | | | |
------------------------------------------------------------------
and replaces this by the following entry:
|---------------+------+-------------------+---------+--------+----| |---------------+------+-------------------+---------+--------+----|
| Low-Priority | LE | Not applicable | RFCXXXX | Rate | Yes| | Low-Priority | LE | Not applicable | RFCXXXX | Rate | Yes|
| Data | | | | | | | Data | | | | | |
------------------------------------------------------------------ ------------------------------------------------------------------
o Section 4.10: The RECOMMENDED DSCP marking is LE (Lower Effort). o Section 2.3 of [RFC4594] specifies: "In network segments that use
IP precedence marking, only one of the two service classes can be
supported, High-Throughput Data or Low-Priority Data. We
RECOMMEND that the DSCP value(s) of the unsupported service class
be changed to 000xx1 on ingress and changed back to original
value(s) on egress of the network segment that uses precedence
marking. For example, if Low-Priority Data is mapped to Standard
service class, then 000001 DSCP marking MAY be used to distinguish
it from Standard marked packets on egress." This document removes
this recommendation, because by using the herein defined LE DSCP
such remarking is not necessary. So even if Low-Priority Data is
unsupported (i.e., mapped to the default PHB) the LE DSCP should
be kept across the domain as RECOMMENDED in Section 8.
o [RFC4594] recommended to remark Low-Priority Data to DSCP '000001' o This document removes the following line of RFC 4594,
inside a DS domain that uses IP precedence marking. By using the Section 4.10: "The RECOMMENDED DSCP marking is CS1 (Class Selector
herein defined LE DSCP such remarking is not necessary, so even if 1)." and replaces this with the following text: "The RECOMMENDED
Low-Priority Data is unsupported (i.e., mapped to the default PHB) DSCP marking is LE (Lower Effort)."
the LE DSCP should be kept across the domain as RECOMMENDED in
Section 5.
7. IANA Considerations 10. The Update to RFC 8325
Section 4.2.10 of RFC 8325 [RFC8325] specifies "therefore, it is
RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to UP 1"
which is updated to ""therefore, it is RECOMMENDED to map Low-
Priority Data traffic marked with LE DSCP or CS1 DSCP to UP 1
This update to RFC 8325 removes the following entry from figure 1:
+---------------+------+----------+-------------+--------------------+
| Low-Priority | CS1 | RFC 3662 | 1 | AC_BK (Background) |
| Data | | | | |
+--------------------------------------------------------------------+
and replaces this by the following entry:
+---------------+------+----------+-------------+--------------------+
| Low-Priority | LE | RFCXXXX | 1 | AC_BK (Background) |
| Data | | | | |
+--------------------------------------------------------------------+
11. IANA Considerations
This document assigns the Differentiated Services Field Codepoint This document assigns the Differentiated Services Field Codepoint
(DSCP) '000001' from the Differentiated Services Field Codepoints (DSCP) '000001' from the Differentiated Services Field Codepoints
(DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp- (DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp-
registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to registry.xhtml) (Pool 3, Codepoint Space xxxx01, Standards Action) to
the LE PHB. This document suggests to use a DSCP from Pool 3 in the LE PHB. This document suggests to use a DSCP from Pool 3 in
order to avoid problems for other PHB marked flows to become order to avoid problems for other PHB marked flows to become
accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching. accidentally remarked as LE PHB, e.g., due to partial DSCP bleaching.
See [I-D.ietf-tsvwg-iana-dscp-registry] for the request to re- See [I-D.ietf-tsvwg-iana-dscp-registry] for the request to re-
classify Pool 3 for Standards Action. classify Pool 3 for Standards Action.
skipping to change at page 9, line 48 skipping to change at page 10, line 48
IANA is requested to update the registry as follows: IANA is requested to update the registry as follows:
o Name: LE o Name: LE
o Value (Binary): 000001 o Value (Binary): 000001
o Value (Decimal): 1 o Value (Decimal): 1
o Reference: [RFC number of this memo] o Reference: [RFC number of this memo]
8. Security Considerations 12. Security Considerations
There are no specific security exposures for this PHB. Since it There are no specific security exposures for this PHB. Since it
defines a new class of low forwarding priority, remarking other defines a new class of low forwarding priority, remarking other
traffic as LE traffic may lead to quality-of-service degradation of traffic as LE traffic may lead to quality-of-service degradation of
such traffic. Thus, any attacker that is able to modify the DSCP of such traffic. Thus, any attacker that is able to modify the DSCP of
a packet to LE may carry out a downgrade attack. See the general a packet to LE may carry out a downgrade attack. See the general
security considerations in [RFC2474] and [RFC2475]. security considerations in [RFC2474] and [RFC2475].
With respect to privacy, an attacker could use the information from With respect to privacy, an attacker could use the information from
the DSCP to infer that the transferred (probably even encrypted) the DSCP to infer that the transferred (probably even encrypted)
content is considered of low priority or low urgency by a user, in content is considered of low priority or low urgency by a user, in
case the DSCP was set on the user's request. However, this disclosed case the DSCP was set on the user's request. However, this disclosed
information is only useful if some form of identification happened at information is only useful if some form of identification happened at
the same time, see [RFC6973] for further details on general privacy the same time, see [RFC6973] for further details on general privacy
threats. threats.
9. References 13. References
9.1. Normative References 13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>. <http://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<http://www.rfc-editor.org/info/rfc2475>. <http://www.rfc-editor.org/info/rfc2475>.
9.2. Informative References 13.2. Informative References
[draft-bless-diffserv-lbe-phb-00] [draft-bless-diffserv-lbe-phb-00]
Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop
Behavior", draft-bless-diffserv-lbe-phb-00 (work in Behavior", draft-bless-diffserv-lbe-phb-00 (work in
progress), September 1999, <https://tools.ietf.org/html/ progress), September 1999, <https://tools.ietf.org/html/
draft-bless-diffserv-lbe-phb-00>. draft-bless-diffserv-lbe-phb-00>.
[I-D.ietf-tsvwg-iana-dscp-registry] [I-D.ietf-tsvwg-iana-dscp-registry]
Fairhurst, G., "IANA Assignment of DSCP Pool 3 (xxxx01) Fairhurst, G., "IANA Assignment of DSCP Pool 3 (xxxx01)
Values to require Publication of a Standards Track or Best Values to require Publication of a Standards Track or Best
skipping to change at page 11, line 39 skipping to change at page 12, line 39
"Low Extra Delay Background Transport (LEDBAT)", RFC 6817, "Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
DOI 10.17487/RFC6817, December 2012, DOI 10.17487/RFC6817, December 2012,
<http://www.rfc-editor.org/info/rfc6817>. <http://www.rfc-editor.org/info/rfc6817>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013, <https://www.rfc- DOI 10.17487/RFC6973, July 2013, <https://www.rfc-
editor.org/info/rfc6973>. editor.org/info/rfc6973>.
[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>.
[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection [RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100, Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <http://www.rfc-editor.org/info/rfc8100>. March 2017, <http://www.rfc-editor.org/info/rfc8100>.
[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>.
[RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to
IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February
2018, <https://www.rfc-editor.org/info/rfc8325>.
Appendix A. History of the LE PHB Appendix A. History of the LE PHB
A first version of this PHB was suggested by Roland Bless and Klaus A first version of this PHB was suggested by Roland Bless and Klaus
Wehrle in 1999 [draft-bless-diffserv-lbe-phb-00]. After some Wehrle in 1999 [draft-bless-diffserv-lbe-phb-00]. After some
discussion in the DiffServ Working Group Brian Carpenter and Kathie discussion in the DiffServ Working Group Brian Carpenter and Kathie
Nichols proposed a bulk handling per-domain behavior and believed a Nichols proposed a bulk handling per-domain behavior and believed a
PHB was not necessary. Eventually, Lower Effort was specified as PHB was not necessary. Eventually, Lower Effort was specified as
per-domain behavior and finally became [RFC3662]. More detailed per-domain behavior and finally became [RFC3662]. More detailed
information about its history can be found in Section 10 of information about its history can be found in Section 10 of
[RFC3662]. [RFC3662].
skipping to change at page 12, line 17 skipping to change at page 13, line 32
Since text is borrowed from earlier Internet-Drafts and RFCs the co- Since text is borrowed from earlier Internet-Drafts and RFCs the co-
authors of previous specifications are acknowledged here: Kathie authors of previous specifications are acknowledged here: Kathie
Nichols and Klaus Wehrle. David Black and Ruediger Geib provided Nichols and Klaus Wehrle. David Black and Ruediger Geib provided
helpful comments and suggestions. helpful comments and suggestions.
Appendix C. Change History Appendix C. Change History
This section briefly lists changes between Internet-Draft versions This section briefly lists changes between Internet-Draft versions
for convenience. for convenience.
Changes in Version 04:
o Several editorial changes according to review from Gorry Fairhurst
o Changed the section structure a bit (moved subsections 1.1 and 1.2
into own sections 3 and 7 respectively)
o updated section 2 on requirements language
o added updates to RFC 8325
o tried to be more explicit what changes are required to RFCs 4594
and 8325
Changes in Version 03: Changes in Version 03:
o Changed recommended codepoint to 000001 o Changed recommended codepoint to 000001
o Added text to explain the reasons for the DSCP choice o Added text to explain the reasons for the DSCP choice
o Removed LE-min,LE-strict discussion o Removed LE-min,LE-strict discussion
o Added one more potential use case: reporting errors or telemetry o Added one more potential use case: reporting errors or telemetry
data from OSs data from OSs
o Added privacy considerations to the security section (not worth an o Added privacy considerations to the security section (not worth an
own section I think) own section I think)
o Changed IANA considerations section o Changed IANA considerations section
Changes in Version 02: Changes in Version 02:
skipping to change at page 13, line 15 skipping to change at page 14, line 43
o Tried to be more precise in section 1.1 (Applicability) according o Tried to be more precise in section 1.1 (Applicability) according
to R. Geib's suggestions, so rephrased several paragraphs. Added to R. Geib's suggestions, so rephrased several paragraphs. Added
text about congestion control text about congestion control
o Change section 2 (PHB Description) according to R. Geib's o Change section 2 (PHB Description) according to R. Geib's
suggestions. suggestions.
o Added RFC 2119 language to several sentences. o Added RFC 2119 language to several sentences.
o Detailed the description of remarking implications and o Detailed the description of remarking implications and
recommendations in Section 5. recommendations in Section 8.
o Added Section 6 to explicitly list changes with respect to RFC o Added Section 9 to explicitly list changes with respect to RFC
4594, because this document will update it. 4594, because this document will update it.
Appendix D. Note to RFC Editor Appendix D. Note to RFC Editor
This section lists actions for the RFC editor during final This section lists actions for the RFC editor during final
formatting. formatting.
o Please replace the occurrence of RFCXXXX in Section 6 with the o Please replace the occurrences of RFCXXXX in Section 9 and
assigned RFC number for this document. Section 10 with the assigned RFC number for this document.
o Delete Appendix C. o Delete Appendix C.
o Delete this section. o Delete this section.
Author's Address Author's Address
Roland Bless Roland Bless
Karlsruhe Institute of Technology (KIT) Karlsruhe Institute of Technology (KIT)
Kaiserstr. 12 Kaiserstr. 12
 End of changes. 43 change blocks. 
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