draft-ietf-tsvwg-le-phb-01.txt   draft-ietf-tsvwg-le-phb-02.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 6, 2017 Obsoletes: 3662 (if approved) June 30, 2017
Updates: 4594 (if approved) Updates: 4594 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: August 10, 2017 Expires: January 1, 2018
A Lower Effort Per-Hop Behavior (LE PHB) A Lower Effort Per-Hop Behavior (LE PHB)
draft-ietf-tsvwg-le-phb-01 draft-ietf-tsvwg-le-phb-02
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
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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This Internet-Draft will expire on August 10, 2017. This Internet-Draft will expire on January 1, 2018.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Deployment Considerations . . . . . . . . . . . . . . . . 4 1.2. Deployment Considerations . . . . . . . . . . . . . . . . 5
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.3. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 5 2. PHB Description . . . . . . . . . . . . . . . . . . . . . . . 6
3. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 5 3. Traffic Conditioning Actions . . . . . . . . . . . . . . . . 7
4. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 6 4. Recommended DS Codepoint . . . . . . . . . . . . . . . . . . 7
5. Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . . 6 5. Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . . 7
6. Changes to RFC 4594 . . . . . . . . . . . . . . . . . . . . . 7 6. Changes to RFC 4594 . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 9 Appendix A. History of the LE PHB . . . . . . . . . . . . . . . 11
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 9 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 11
Appendix C. Change History . . . . . . . . . . . . . . . . . . . 10 Appendix C. Change History . . . . . . . . . . . . . . . . . . . 11
Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 10 Appendix D. Note to RFC Editor . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
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 of
sufficiently low urgency, in which all other traffic takes precedence sufficiently low urgency that all other traffic takes precedence over
over LE traffic in consumption of network link bandwidth. Low LE traffic in consumption of network link bandwidth. Low urgency
urgency traffic has got a low priority in time, which does not traffic has a low priority for timely forwarding, which does not
necessarily imply that it is generally of minor importance. From 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. This is distinct from "best- network traffic is strictly limited ("no harm" property). This is
effort" (BE) traffic since the network makes no commitment to deliver distinct from "best- effort" (BE) traffic since the network makes no
LE packets. In contrast, BE traffic receives an implied "good faith" commitment to deliver LE packets. In contrast, BE traffic receives
commitment of at least some available network resources. This an implied "good faith" commitment of at least some available network
document proposes a Lower Effort Differentiated Services per-hop resources. This document proposes a Lower Effort Differentiated
behavior (LE PHB) for handling this "optional" traffic in a Services per-hop behavior (LE PHB) for handling this "optional"
differentiated services node. traffic in a differentiated services node.
1.1. Applicability 1.1. Applicability
A Lower Effort PHB is applicable for most elastic applications that A Lower Effort PHB is applicable for many applications that otherwise
otherwise use best-effort delivery. More specifically, it is use best-effort delivery. More specifically, it is suitable for
suitable for traffic and services accepting strongly varying traffic and services that can tolerate strongly varying throughput
throughput for their data flows, especially with respect to periods for their data flows, especially periods of very low throughput or
of very low throughput or even starvation (i.e., long interruptions even starvation (i.e., long interruptions due to significant or even
due to excessive packet loss). Therefore, an application sending an complete packet loss). Therefore, an application sending an LE
LE marked flow must be able to tolerate short or (even very) long marked flow must 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 should be an
expectation that packets of the LE PHB may be excessively delayed or expectation that packets of the LE PHB may be excessively delayed or
dropped when any other traffic is present. The LE PHB is suitable 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. Since LE traffic may be
starved completely for a longer period of time, transport protocols starved completely for a longer period of time, transport protocols
or applications (and their related congestion control mechanisms) or applications (and their related congestion control mechanisms)
SHOULD be able to detect and react to such a situation and should SHOULD be able to detect and react to such a situation and should
resume the transfer as soon as possible. Congestion control is not resume the transfer as soon as possible. Congestion control is not
only useful to let the flows within the LE behavior aggregate adapt only useful to let the flows within the LE behavior aggregate adapt
to the available bandwidth that may be highly fluctuating, but also to the available bandwidth that may be highly fluctuating, but also
in case that LE traffic is mapped to the default PHB (e.g., due to in case that LE traffic is mapped to the default PHB in DS domains
DSCP bleaching). 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 used as a traffic nor should packets be "downgraded" to the LE PHB instead of
substitute for dropping packets that ought simply to be dropped as being dropped, particularly when the packets are unauthorized
unauthorized. The LE PHB is expected to have applicability in traffic. The LE PHB is expected to have applicability in networks
networks that have at least some unused capacity at some times of that have at least some unused capacity at certain periods.
day.
The LE PHB allows networks to protect themselves from selected types The LE PHB allows networks to protect themselves from selected types
of traffic rather than giving a selected traffic aggregate of traffic as a complement to giving preferential treatment to other
preferential treatment. Moreover, the LE PHB may also exploit all selected traffic aggregates. LE should not be used for the general
unused resources from other PHBs. case of downgraded traffic, but may be used by design, e.g., to
protect an internal network from untrusted external traffic sources.
In this case there is no way for attackers to preempt internal (non
LE) traffic by flooding. Another use case in this regard is
forwarding of multicast traffic from untrusted sources. Multicast
forwarding is currently enabled within domains only for specific
sources within a domain, but not for sources from anywhere in the
Internet. A main problem is that multicast routing creates traffic
sources at (mostly) unpredictable branching points within a domain,
potentially leading to congestion and packet loss. In case multicast
packets from untrusted sources are forwarded as LE traffic, they will
not harm traffic from non-LE behavior aggregates. A further related
use case is mentioned in [RFC3754]: preliminary 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 tool for administrators in engineering networks. For an additional traffic engineering tool for network administrators.
instance, it can be used for filling up protection capacity of For instance, it can be used to fill protection capacity of
transmission links which is otherwise unused. Some network providers transmission links that is otherwise unused. Some network providers
keep link utilization below 50% in order to being able carrying all keep link utilization below 50% to ensure that all traffic is
traffic without loss in case of rerouting due to 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
capacity is required for all other traffic. Ideally, applications capacity is required for all other traffic. Ideally, applications
mark their packets as LE traffic, since they know the urgency of mark their packets as LE traffic, since they know the urgency of
flows. flows.
Example uses for the LE PHB comprise: Example uses for the LE PHB:
o For traffic caused by world-wide web search engines while they o For traffic caused by world-wide web search engines while they
gather information from web servers. gather information from web servers.
o For software updates or dissemination of new releases of operating o For software updates or dissemination of new releases of operating
systems. systems.
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 Netnews and other "bulk mail" of the Internet. o For Netnews 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 or the overall
network. LE should not be used for the general case of downgraded network.
traffic, but may be used by design, e.g., to protect an internal
network from untrusted external traffic sources. In this case o For multicast traffic from untrusted (e.g., non-local) sources.
there is no way for attackers to preempt internal (non LE) traffic
by flooding. Another use case is mentioned in [RFC3754]: non-
admitted multicast traffic.
1.2. Deployment Considerations 1.2. 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 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 Internet-wide deployment of the LE PHB is eased by the following
properties: properties:
o No harm to other traffic: since the LE PHB has got the lowest o No harm to other traffic: since the LE PHB has the lowest
forwarding priority it does not consume resources from other PHBs. forwarding priority it does not consume resources from other PHBs.
Deployment across different provider domains causes no trust Deployment across different provider domains with LE support
issues or attack vectors to existing traffic. 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 parameters or configuration: the LE PHB requires no parameters o No PHB parameters or configuration of traffic profiles: the LE PHB
and no configuration of traffic profiles and so on. 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 o No traffic conditioning mechanisms: the LE PHB requires no traffic
meters, droppers, or shapers. 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 DS domains that cannot or do not want to support the LE PHB should be
NOT drop LE marked packets, but rather map them to the default PHB aware that they violate the "no harm" property of LE. DS domains
and keep the LE DSCP. See also Section 5 for further discussion of without LE PHB support SHOULD NOT drop LE marked packets, but rather
forwarding LE traffic with the default PHB instead. 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 1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. PHB Description 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 case of congestion,
LE marked traffic SHOULD be dropped prior to dropping any default PHB LE marked traffic SHOULD be dropped prior to dropping any default PHB
traffic. Ideally, LE packets SHOULD be forwarded only if no best- traffic. Ideally, LE packets SHOULD be forwarded only if no packet
effort packet is waiting for its transmission. 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, may 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
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
sojourn time thresholds are exceeded.
Since congestion control is also useful within the LE traffic class,
Explicit Congestion Notification [RFC3168] SHOULD be used for LE
packets, too.
3. Traffic Conditioning Actions 3. Traffic Conditioning Actions
As for most other PHBs an initial classification and marking would If possible, packets SHOULD be pre-marked in DS-aware end systems by
usually be performed at the first DS boundary node. If possible, applications due to their specific knowledge about the particular
packets SHOULD be pre-marked in DS-aware end systems by applications precedence of packets. There is no incentive for DS domains to
due to their specific knowledge about the particular precedence of distrust this initial marking, because letting LE traffic enter a DS
packets. There is no incentive for DS domains to distrust this domain causes no harm. Thus, any policing such as limiting the rate
initial marking, because letting LE traffic enter a DS domain causes of LE traffic is not necessary at the DS boundary.
no harm. In the worst case it evokes the same effect as it would
have been marked with the default PHB, i.e., as best-effort traffic.
Usually, the amount of LE traffic is implicitly limited by queueing
mechanisms and related discard actions of the PHB. Thus, any
policing such as limiting the rate of LE traffic is not necessary at
the DS boundary.
Non-LE traffic (e.g., BE traffic) SHOULD not be remarked to LE on a As for most other PHBs an initial classification and marking can be
regular basis without consent or knowledge of the user. also performed at the first DS boundary node according to the DS
domain's own policies (e.g., as protection measure against untrusted
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
user. See also remarks with respect to downgrading in Section 1.1.
4. Recommended DS Codepoint 4. Recommended DS Codepoint
The RECOMMENDED codepoint for the LE PHB is '000010'. The RECOMMENDED codepoint for the LE PHB is '000010'.
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 '000010' whenever therefore use the unambiguous LE codepoint '000010' whenever
possible. possible.
5. Remarking to other DSCPs/PHBs 5. 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. In case DS domains do not support the LE PHB, they SHOULD traffic (no harm property). In case DS domains do not support the LE
treat LE marked packets with the default PHB instead (by mapping the PHB, they SHOULD treat LE marked packets with the default PHB instead
LE DSCP to the default PHB), but they SHOULD do so without remarking (by mapping the LE DSCP to the default PHB), but they SHOULD do so
to DSCP '000000'. The reason for this is that later traversed DS without remarking to DSCP '000000'. The reason for this is that
domains may then have still the possibility to treat such packets later traversed DS domains may then have still the possibility to
according the LE PHB. However, operators of DS domains that forward treat such packets according the LE PHB. However, operators of DS
LE traffic within the BE aggregate should be aware of the domains that forward LE traffic within the BE aggregate should be
implications, i.e., induced congestion situations and quality-of- aware of the implications, i.e., induced congestion situations and
service degradation of the original BE traffic. In this case, the LE quality-of-service degradation of the original BE traffic. In this
property of not harming other traffic is no longer fulfilled. In case, the LE property of not harming other traffic is no longer
order to limit the impact in such cases, traffic policing of the LE fulfilled. In order to limit the impact in such cases, traffic
aggregate may be used. 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. One possible solution for a clear affect the original BE aggregate. In some cases users want to be
distinction in such cases would be to use two different codepoints, sure that their LE marked traffic actually fulfills the "no harm"
"LE-min = LE, better treatment allowed", "LE-strict = LE, better property.
treatment NOT allowed". However, since DSCPs are a scarce resource,
applications that want to ensure the lower precedence compared to BE One possible solution for a clear distinction in such cases would be
traffic SHOULD use additionally a corresponding Lower-than-Best- to use two different codepoints, "LE-min = LE, better treatment
Effort transport protocol [RFC6297], e.g., LEDBAT [RFC6817]. allowed", "LE-strict = LE, better treatment NOT allowed". However,
since DSCPs are a scarce resource, applications that want to ensure
the lower precedence compared to BE traffic SHOULD use additionally a
corresponding Lower-than-Best-Effort transport protocol [RFC6297],
e.g., LEDBAT [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 '000010' definition in [RFC3662]) MUST remark traffic to the LE DSCP '000010'
at the egress to the next DS domain. This increases the probability at the egress to the next DS domain. This increases the probability
that the DSCP is preserved end-to-end, whereas a CS1 marked packet that the DSCP is preserved end-to-end, whereas a CS1 marked packet
may be remarked by the default DSCP if the next domain is applying may be remarked by the default DSCP if the next domain is applying
DiffServ-intercon [I-D.ietf-tsvwg-diffserv-intercon]. DiffServ-intercon [RFC8100].
6. Changes to RFC 4594 6. Changes 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.
skipping to change at page 8, line 9 skipping to change at page 9, line 21
o [RFC4594] recommended to remark Low-Priority Data to DSCP '000001' o [RFC4594] recommended to remark Low-Priority Data to DSCP '000001'
inside a DS domain that uses IP precedence marking. By using the inside a DS domain that uses IP precedence marking. By using the
herein defined LE DSCP such remarking is not necessary, so even if herein defined LE DSCP such remarking is not necessary, so even if
Low-Priority Data is unsupported (i.e., mapped to the default PHB) Low-Priority Data is unsupported (i.e., mapped to the default PHB)
the LE DSCP should be kept across the domain as RECOMMENDED in the LE DSCP should be kept across the domain as RECOMMENDED in
Section 5. Section 5.
7. IANA Considerations 7. IANA Considerations
This memo includes a request to assign a Differentiated Services This document assigns the Differentiated Services Field Codepoint
Field Codepoint (DSCP) '000010' from the Differentiated Services (DSCP) '000010' from the Differentiated Services Field Codepoints
Field Codepoints (DSCP) registry https://www.iana.org/assignments/ (DSCP) registry (https://www.iana.org/assignments/dscp-registry/dscp-
dscp-registry/dscp-registry.xml registry.xml) to the LE PHB. IANA is requested to update the
registry as follows:
o Name: LE
o Value (Binary): 000010
o Value (Decimal): 2
o Reference: [RFC number of this memo]
8. Security Considerations 8. 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, other traffic may be defines a new class of low forwarding priority, remarking other
downgraded to this LE PHB in case it is remarked as LE traffic. See traffic as LE traffic may lead to quality-of-service degradation of
the general security considerations in [RFC2474] and [RFC2475]. 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
security considerations in [RFC2474] and [RFC2475].
9. References 9. References
9.1. Normative References 9.1. 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>.
skipping to change at page 9, line 5 skipping to change at page 10, line 24
<http://www.rfc-editor.org/info/rfc2475>. <http://www.rfc-editor.org/info/rfc2475>.
9.2. Informative References 9.2. 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-diffserv-intercon] [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
Geib, R. and D. Black, "Diffserv-Interconnection classes of Explicit Congestion Notification (ECN) to IP",
and practice", draft-ietf-tsvwg-diffserv-intercon-14 (work RFC 3168, DOI 10.17487/RFC3168, September 2001,
in progress), December 2016. <http://www.rfc-editor.org/info/rfc3168>.
[RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
Per-Domain Behavior (PDB) for Differentiated Services", Per-Domain Behavior (PDB) for Differentiated Services",
RFC 3662, DOI 10.17487/RFC3662, December 2003, RFC 3662, DOI 10.17487/RFC3662, December 2003,
<http://www.rfc-editor.org/info/rfc3662>. <http://www.rfc-editor.org/info/rfc3662>.
[RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated [RFC3754] Bless, R. and K. Wehrle, "IP Multicast in Differentiated
Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754, Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754,
April 2004, <http://www.rfc-editor.org/info/rfc3754>. April 2004, <http://www.rfc-editor.org/info/rfc3754>.
skipping to change at page 9, line 33 skipping to change at page 11, line 5
[RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort [RFC6297] Welzl, M. and D. Ros, "A Survey of Lower-than-Best-Effort
Transport Protocols", RFC 6297, DOI 10.17487/RFC6297, June Transport Protocols", RFC 6297, DOI 10.17487/RFC6297, June
2011, <http://www.rfc-editor.org/info/rfc6297>. 2011, <http://www.rfc-editor.org/info/rfc6297>.
[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind, [RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
"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>.
[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <http://www.rfc-editor.org/info/rfc8100>.
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].
Appendix B. Acknowledgments Appendix B. Acknowledgments
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. Ruediger Geib provided helpful comments Nichols and Klaus Wehrle. David Black and Ruediger Geib provided
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 02:
o Applied many editorial suggestions from David Black
o Added Multicast traffic use case
o Clarified what is required for deployment in section 1.2
(Deployment Considerations)
o Added text about implementations using AQMs and ECN usage
o Updated IANA section according to David Black's suggestions
o Revised text in the security section
o Changed copyright Notice to pre5378Trust200902
Changes in Version 01: Changes in Version 01:
o Now obsoletes RFC 3662. o Now obsoletes RFC 3662.
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.
 End of changes. 37 change blocks. 
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