Tunnel Congestion Feedback
draft-ietf-tsvwg-tunnel-congestion-feedback-00
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|---|---|---|---|
| Authors | Xinpeng Wei , Lei Zhu , Lingli Deng | ||
| Last updated | 2015-09-16 | ||
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draft-ietf-tsvwg-tunnel-congestion-feedback-00
Internet Engineering Task Force X. Wei
INTERNET-DRAFT Huawei Technologies
Intended Status: Informational L.Zhu
Expires: March 19, 2016 Huawei Technologies
L.Deng
China Mobile
September 16, 2015
Tunnel Congestion Feedback
draft-ietf-tsvwg-tunnel-congestion-feedback-00
Abstract
This document describes a mechanism to calculate congestion of a
tunnel segment based on RFC 6040 recommendations, and a feedback
protocol by which to send the measured congestion of the tunnel from
egress to ingress . A basic model for measuring tunnel congestion
and feedback is described, and a protocol for carrying the feedback
data is outlined.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright and License Notice
Copyright (c) 2015 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
(http://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
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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Congestion Information Feedback Models . . . . . . . . . . . . 4
3.1 Direct Model . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Centralized Model . . . . . . . . . . . . . . . . . . . . . 4
4. Congestion Level Measurement . . . . . . . . . . . . . . . . . 5
5. Congestion Information Delivery . . . . . . . . . . . . . . . . 7
5.1 IPFIX Extentions . . . . . . . . . . . . . . . . . . . . . . 7
5.1.1 ce-cePacketTotalCount . . . . . . . . . . . . . . . . . 7
5.1.2 ect0-nectPacketTotalCount . . . . . . . . . . . . . . . 8
5.1.3 ect1-nectPacketTotalCount . . . . . . . . . . . . . . . 8
5.1.4 ce-nectPacketTotalCount . . . . . . . . . . . . . . . . 8
5.1.5 ce-ect0PacketTotalCount . . . . . . . . . . . . . . . . 9
5.1.6 ce-ect1PacketTotalCount . . . . . . . . . . . . . . . . 9
5.1.7 ect0-ect0PacketTotalCount . . . . . . . . . . . . . . . 9
5.1.8 ect1-ect1PacketTotalCount . . . . . . . . . . . . . . . 10
6. Congestion Management . . . . . . . . . . . . . . . . . . . . . 10
7. Security . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1 Normative References . . . . . . . . . . . . . . . . . . . 11
9.2 Informative References . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
In IP network, persistent congestion (or named congestion collapse)
lowers transport throughput, leading to waste of network resource.
Appropriate congestion control mechanisms are therefore critical to
prevent the network from falling into the persistent congestion
state. Currently, transport protocols such as TCP, SCTP, DCCP, have
their built-in congestion control mechanisms, and even for certain
single transport protocol like TCP there can be a couple of different
congestion control mechanisms to choose from. All these congestion
control mechanisms are implemented on host side, and there are
reasons that only host side congestion control is not sufficient for
the whole network to keep away from persistent congestion. For
example, (1) some protocol's congestion control scheme may have
internal design flaws; (2) improper software implementation of
protocol; (3) some transport protocols do not even provide congestion
control at all.
In order to have a better control on network congestion status, it's
necessary for the network side to do certain kind of traffic control.
For example, ConEx [ConEx] provides a method for network operator to
learn about traffic's congestion contribution information, and then
congestion management action can be taken based on this information.
Tunnels are widely deployed in various networks including public
Internet, datacenter network, and enterprise network etc. A tunnel
consists of ingress, an egress and a set of interior routers. For the
tunnel scenario, a tunnel-based mechanism which is different from
ConEx is introduced for network traffic control to keep the network
from persistent congestion. Here, tunnel ingress will implement
congestion management function to control the traffic entering the
tunnel.
In order to perform congestion management at ingress, the ingress
must first obtain the inner tunnel congestion level information. Yet
the ingress cannot use the locally visible traffic rates, because it
would require additional knowledge of downstream capacity and
topology, as well as cross traffic that does not pass through this
ingress.
This document provides a mechanism of feeding back inner tunnel
congestion level to the ingress. Using this mechanism the egress can
feed the tunnel congestion level information it collects back to the
ingress. After receiving this information the ingress will be able to
perform congestion management according to network management policy.
2. Conventions
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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 RFC 2119 [RFC2119]
3. Congestion Information Feedback Models
According to specific network deployment, there are two kinds of
feedback model: direct model and centralized model.
3.1 Direct Model
Feedback
|-----------------------------------------|
| |
| |
| V
+----------+ tunnel +-----------+
|Egress |========================== |Inress |
|(Exporter)| |(Collector)|
+----------+ +-----------+
(a) Direct Feedback Model.
Direct model means egress feeds information directly to ingress. In
this model, egress collects network congestion level information and
feedback the information to the ingress for congestion management.
The ingress here will act as both the decision point that decides how
to do congestion management and the action point that implements
congestion management decision.
3.2 Centralized Model
Feedback +-----------+
--------->|Controller |#####################
| |(Collector)| #
| +-----------+ #
| #
+----------+ tunnel +-----V-+
|Egress | ===========================|Ingress|
|(Exporter)| +-------+
+----------+
(b) Centralized Feedback Model
In the centralized model, the ingress only takes the role of action
point, and it implements traffic control decision from another entity
named "controller". Here, after egress has collected network
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congestion level information, it feeds back the information to a
controller instead of the ingress. Then the controller makes
congestion management decision and sends the decision to the ingress
to implement.
4. Congestion Level Measurement
This section describes how to measure congestion level in a tunnel.
There may be different approaches to packet loss detection for
different tunneling protocol scenarios. For instance, if there is a
sequence field in the tunneling protocol header, it will be easy for
egress to detect packet loss through the gaps in sequence number
space. Another approach is to compare the number of packets entering
ingress and the number of packets arriving at egress over the same
span of packets. This document will focus on the latter one which is
a more general approach.
If the routers support Explicit Congestion Notification (ECN), after
router's queue length is over a predefined threshold, the routers
will marks the ECN-capable packets as Congestion Experienced (CE) or
drop not-ECT packets with the probability proportional to queue
length; if the queue overflows all packets will be dropped. If the
routers do not support ECN, after router's queue length is over a
predefined threshold, the routers will drop both the ECN-capable
packets and the not-ECT packets with the probability proportional to
the queue length. It's assumed all routers in the tunnel support ECN.
Faked ECN-capable transport (ECT) is used at ingress to defer packet
loss to egress. The basic idea of faked ECT is that, when
encapsulating packets, ingress first marks tunnel outer header
according to RFC6040, and then remarks outer header of Not-ECT packet
as ECT, there will be three kinds of combination of outer header ECN
field and inner header ECN field: CE|CE, ECT|N-ECT, ECT|ECT (in the
form of outer ECN| inner ECN).
In case all interior routers support ECN, the network congestion
level could be indicated through the ratio of CE-marked packet and
the ratio of packet drop, the relationship between these two kinds of
indicator is complementary. If the congestion level in tunnel is not
high enough, the packets would be marked as CE instead of being
dropped, and then it is easy to calculate congestion level according
to the ratio of CE-marked packets. If the congestion level is so high
that ECT packet will be dropped, then the packet loss ratio could be
calculated by comparing total packets entering ingress and total
packets arriving at egress over the same span of packets, if packet
loss is detected, it could be assumed that severe congestion has
occurred in the tunnel. Because loss is only ever a sign of serious
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congestion, so it doesn't need to measure loss ratio accurately.
The basic procedure of congestion level measurement is as follows:
+-------+ +------+
|Ingress| |Egress|
+-------+ +------+
| |
+----------------+ |
|cumulative count| |
+----------------+ |
| |
| <node id-i, ECN counts> |
|------------------------>|
|<node id-e, ECN counts> |
|<------------------------|
| |
| |
(a) Direct model feedback procedure
+----------+ +-------+ +------+
|Controller| |Ingress| |Egress|
+----------+ +-------+ +------+
| | |
| +----------------+ |
| |cumulative count| |
| +----------------+ |
| | |
| | <node id-i, ECN counts> |
| |------------------------>|
| | |
| |
| |
| <node id-i, ECN counts> |
| <node id-e, ECN counts> |
|<---------------------------------------|
| |
| |
| |
(b) Centralized model feedback procedure
Ingress encapsulates packets and marks outer header according to
faked ECT as described above. Ingress cumulatively counts packets for
three types of ECN combination (CE|CE, ECT|N-ECT, ECT|ECT) and then
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the ingress regularly sends cumulative packet counts message of each
type of ECN combination to the egress. When each message arrives, the
egress cumulatively counts packets coming from the ingress and adds
its own packet counts of each type of ECN combination (CE|CE, ECT|N-
ECT, CE|N-ECT, CE|ECT, ECT|ECT) to the message and either returns the
whole message to the ingress, or to a central controller.
The counting of packets can be at the granularity of the all traffic
from the ingress to the egress to learn about the overall congestion
status of the path between the ingress and the egress. The counting
can also be at the granularity of individual customer's traffic or a
specific set of flows to learn about their congestion contribution.
5. Congestion Information Delivery
As described above, the tunnel ingress needs to convey message of
cumulative packet counts of each type of ECN combination to tunnel
egress, and the tunnel egress also needs to feed the message of
cumulative packet counts of each type of ECN combination to the
ingress or central collector. This section describes how the messages
could be conveyed.
The message can travel along the same path with network data traffic,
referred as in band signal; or go through a different path from
network data traffic, referred as out of band signal. Because out of
band scheme needs additional separate path which might limit its
actual deployment, the in band scheme will be discussed here.
Because the message is transmitted in band, so the message packet may
get lost in case of network congestion. To cope with the situation
that the message packet gets lost, the packet counts values are sent
as cumulative counters. Then if a message is lost the next message
will recover the missing information.
IPFIX [RFC7011] is selected as a choice of candidate protocol. IPFIX
is preferred to use SCTP as transport. SCTP allows partially reliable
delivery [RFC3758], which ensures the feedback message will not be
blocked in case of packet loss due to network congestion.
When sending message from ingress to egress, the ingress acts as
IPFIX exporter and egress acts as IPFIX collector; when sending
message from egress to ingress or controller, the egress acts as
IPFIX exporter and ingress or controller acts as IPFIX collector.
5.1 IPFIX Extentions
5.1.1 ce-cePacketTotalCount
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Description: The total number of incoming packets with CE|CE ECN
marking combination for this Flow at the Observation Point since the
Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD1
Statues: current
Units: packets
5.1.2 ect0-nectPacketTotalCount
Description: The total number of incoming packets with ECT(0)|N-ECT
ECN marking combination for this Flow at the Observation Point since
the Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD2
Statues: current
Units: packets
5.1.3 ect1-nectPacketTotalCount
Description: The total number of incoming packets with ECT(1)|N-ECT
ECN marking combination for this Flow at the Observation Point since
the Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD3
Statues: current
Units: packets
5.1.4 ce-nectPacketTotalCount
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Description: The total number of incoming packets with CE|N-ECT ECN
marking combination for this Flow at the Observation Point since the
Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD4
Statues: current
Units: packets
5.1.5 ce-ect0PacketTotalCount
Description: The total number of incoming packets with CE|ECT(0) ECN
marking combination for this Flow at the Observation Point since the
Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD5
Statues: current
Units: packets
5.1.6 ce-ect1PacketTotalCount
Description: The total number of incoming packets with CE|ECT(1) ECN
marking combination for this Flow at the Observation Point since the
Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD6
Statues: current
Units: packets
5.1.7 ect0-ect0PacketTotalCount
Description: The total number of incoming packets with ECT(0)|ECT(0)
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ECN marking combination for this Flow at the Observation Point since
the Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD7
Statues: current
Units: packets
5.1.8 ect1-ect1PacketTotalCount
Description: The total number of incoming packets with ECT(1)|ECT(1)
ECN marking combination for this Flow at the Observation Point since
the Metering Process (re-)initialization for this Observation Point.
Abstract Data Type: unsigned64
Data Type Semantics: totalCounter
ElementId: TBD8
Statues: current
Units: packets
6. Congestion Management
After tunnel ingress (or controller) receives congestion level
information, then congestion management actions could be taken based
on the information, e.g. if the congestion level is higher than a
predefined threshold, then action could be taken to reduce the
congestion level.
The design of network side congestion management SHOULD take host
side e2e congestion control mechanism into consideration, which means
the congestion management needs to avoid the impacts on e2e
congestion control. For instance, congestion management action must
be delayed by more than a worst-case global RTT, otherwise tunnel
traffic management will not give normal e2e congestion control enough
time to do its job, and the system could go unstable.
The detailed description of congestion management is out of scope of
this document, as examples, congestion management such as circuit
breaker [CB] and congestion policing [CP] could be applied. Circuit
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breaker is an automatic mechanism to estimate congestion, and to
terminate flow(s) when persistent congestion is detected to prevent
network congestion collapse; Congestion policing is used in data
center to limit the amount of congestion any tenant can cause
according to the congestion information in the tunnels.
7. Security
This document describes the tunnel congestion calculation and
feedback. For feeding back congestion, security mechanisms of IPFIX
are expected to be sufficient. No additional security concerns are
expected.
8. IANA Considerations
This document defines a set of new IPFIX Information Elements (IE).
New registry for these IE identifiers is needed.
TBD1~TBD8.
9. References
9.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, September 2001, <http://www.rfc-
editor.org/info/rfc3168>.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004,
<http://www.rfc-editor.org/info/rfc3758>.
[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, November 2010, <http://www.rfc-
editor.org/info/rfc6040>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, September 2013, <http://www.rfc-
editor.org/info/rfc7011>.
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9.2 Informative References
[CONEX] Matt Mathis, Bob Briscoe. "Congestion Exposure (ConEx)
Concepts, Abstract Mechanism and Requirements", draft-
ietf-conex-abstract-mech-13, October 24, 2014
[CB] G. Fairhurst. "Network Transport Circuit Breakers", draft-ietf-
tsvwg-circuit-breaker-01, April 02, 2015
[CP] Bob Briscoe, Murari Sridharan. "Network Performance Isolation
in Data Centres using Congestion Policing", draft-briscoe-
conex-data-centre-02, February 14, 2014
10. Acknowledgements
Thanks Bob Briscoe for his insightful suggestions on the basic
mechanisms of congestion information collection and many other useful
comments. Thanks David Black for his useful technical suggestions.
Also, thanks Anthony Chan and John Kaippallimalil for their careful
reviews.
Authors' Addresses
Xinpeng Wei
Beiqing Rd. Z-park No.156, Haidian District,
Beijing, 100095, P. R. China
E-mail: weixinpeng@huawei.com
Zhu Lei
Beiqing Rd. Z-park No.156, Haidian District,
Beijing, 100095, P. R. China
E-mail:lei.zhu@huawei.com
Lingli Deng
Beijing, 100095, P. R. China
E-mail: denglingli@gmail.com
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