TRILL Working Group Donald Eastlake
INTERNET-DRAFT Huawei
Intended status: Informational Manoj Wadekar
QLogic
Anoop Ghanwani
Dell
Puneet Agarwal
Broadcom
Tal Mizrahi
Marvell
Expires: July 1, 2013 January 2, 2013
TRILL: Support of IEEE 802.1 Priority-based Flow Control
and Enhanced Transmission Selection
<draft-eastlake-trill-pfc-ets-00.txt>
Abstract
This document briefly explains the IEEE 802.1 Priority-based Flow
Control and Enhanced Transmission standards and discusses the support
of these standards in TRILL switches (devices that implement the IETF
TRILL protocol standard).
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Table of Contents
1. Introduction............................................3
1.1 Overview of PFC and ETS................................4
1.2 Terminology............................................4
2. Priority-Based Flow Control.............................6
3. Enhanced Transmission Selection.........................7
4. The DCB Exchange Protocol...............................8
5. Management Considerations...............................9
6. IANA Considerations.....................................9
7. Security Considerations.................................9
8. References.............................................10
8.1 Normative References..................................10
8.2 Informative References................................10
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1. Introduction
IEEE 802.1 has developed various standards as part of its Data Center
Bridging (DCB) activity. The intent of these standards is (1) to
efficiently minimize data loss due to queue overflow for selected
classes of traffic within Local Area Networks (LANs) meeting certain
conditions and (2) to provide limited means to allocate the available
bandwidth to different classes of traffic. Those standardes are
Priority Based Flow Control (the IEEE [802.1Qbb] standard), Enhanced
Tramission Selection (the IEEE [802.1Qaz] standard), and the
Congestion Notification (CN) feature in the IEEE [802.1Q] standard.
Intended uses include the support of loss sensitive services, such as
Fiber Channel over Ethernet [FCoE], in data centers.
Because they are primarily implemented at the port level, no changes
in the TRILL protocol are required to support PFC or ETS which are
discussed in this document. CN support by TRILL may be considered in
a separate document.
The existing optional PAUSE feature of IEEE 802.3 (Annex 31B of
[802.3]) can, with appropriate engineering, also provide Ethernet
service without loss of frames due to queue overflow. However, PAUSE
has problems as follows:
1. Traffic for some protocols, for example TCP [RFC793], requires
frame losses to signal congestion for flow control. Elimination of
frame drops due to congestion would prevent TCP flow control,
unless some other mechanism were added.
2. Some traffic consists of time critical network control frames, for
example IS-IS Hellos [IS-IS]. PAUSE is relatively indiscriminant
and pauses such frames, except for some MAC Control frames such as
PAUSE control frames themselves, along with less critical traffic.
Pausing such critical network control frames can compromise
transport connectivity.
3. PAUSE can result in intermittent waves of spreading traffic
paralysis, crippling network throughput, as follows: When a switch
S1 receives a PAUSE on a port P1 and can no longer transmit frames
out that port it is likely that output queues to P1 will fill up
quickly. As soon as one output queue to P1 is full or almost so
then, to avoid frame loss, S1 must send PAUSE frames out on each
of its ports that might receive a frame for output to P1. For
example, it might have to PAUSE input on P2 through P9,
unnecessarily blocking traffic between any pair of those ports, to
be sure it will not receive input on any of them for P1. This can
repeat in switches connected to S1, switches connected to switches
connected to S1, etc.
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1.1 Overview of PFC and ETS
Overviews of the PFC and ETS standards covered herein are given
below. IEEE 802.1 has specified these standards and the behavior
needed to support them in bridges and end stations. This document
discusses the support of these standards in TRILL switches [RFC6325].
IEEE [802.1Qbb], Priority-based Flow Control (PFC), provides a frame
priority based refinement of the Ethernet PAUSE feature as described
in Section 2. To the extent that a switch implements separate queues
for different priorities at each port, this can eliminate the first
and second of the PAUSE problems listed above. Traffic requiring
frame drops due to congestion can be assigned a priority for which
PFC is not enabled. PFC is not normally enabled for the two highest
priorities, 6 and 7, which are typically used for time sensitive
control frames. PFC also reduces the third problem as any congestion
spreading would affect only priorities with PFC enabled.
IEEE [802.1Qaz] is a standard covering two things: One, Enhanced
Transmission Selection (ETS), allocates bandwidth between traffic
class groups indicated by priority. It is described in Section 3.
Second, [802.1Qaz] contains the specification of the Data Center
Bridging Exchange Protocol (DCBX) for discovering and configuring the
three standards that this document covers, as described in Section 4.
PFC and ETS may be implemented independently or in any combination
except that implementation of either of them implies implementation
of DCBX, specified in IEEE [802.1Qaz].
1.2 Terminology
The following acronyms are used in this document in addition to those
defined in [RFC6325].
AVB - Audio-Visual Bridging
CN - Congestion Notification [802.1Q]
DCB - Data Center Bridging [802.1Qaz]
DCBX - DCB Exchange protocol [802.1Qaz]
ETS - Enhanced Transmission Selection [802.1Qaz]
FCoE - Fiber Channel over Ethernet [FCoE]
LLDP - Link Layer Discovery Protocol (IEEE 802.1AB)
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PFC - Priority-based Flow Control [802.1Qbb] [802.3bd]
RBridge - "Routing Bridge", an alternative name for a TRILL switch
[RFC6325]
TRILL Switch - A device implementing the TRILL protocol [RFC6325]
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2. Priority-Based Flow Control
IEEE [802.1Qbb], Priority-Based Flow Control (PFC), refines the IEEE
[802.3] PAUSE feature to permit separately requesting the pausing and
unpausing the traffic of each of the eight available frame priority
levels. The actual priority-based pause control frame is specified in
IEEE [802.3bd].
Such queue pausing occurs within the transmission logic associated
with a port and requires no changes to the TRILL protocol, which is
implemented above such port logic, as described in [RFC6325].
LLDP/DCBX is used in PFC discovery and agreement with peers as
described in Section 4. A TRILL switch implementing the PFC standard
should implement DCBX, signaling PFC support and configuration.
Guarantee of lossless handling of frames with a particular priority
in a TRILL campus requires implementation and enablement of PFC for
that priority at all end stations that originate frames and all TRILL
switches and bridges in that campus as well as meeting the PFC
engineering requirements in [802.1Qbb].
The PFC control frames specified in [802.3bd] are MAC control frames
that are not VLAN tagged. Their transmission normally bypasses the
output queue at a port so they are transmitted immediately, or as
soon as the frame currently being transmitted is sent, so as to meet
the timing requirements of PFC.
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3. Enhanced Transmission Selection
Enhanced Transmission Selection (ETS), specified in IEEE [802.1Qaz],
allocates bandwidth, between traffic classes, through each of the
ports of a switch or end station. (To be more precise, it modifies
the algorithm used to select, from multiple priority-based output
queues at a port, the next frame to transmit. Provision is made for
proprietary algorithms and 802.1 has also specified an algorithm in
connection with precise frame timing (AVB), but we are only concerned
with the default algorithm.)
Transmission selection occurs within the logic associated with a port
and requires no changes to the TRILL protocol, which is implemented
above such port logic, as described in [RFC6325]. A TRILL switch
implementing the ETS standard should implement DCBX (see Section 4)
signaling of ETS support and configuration. For ETS to be effective,
traffic in different ETS groups cannot share an output queue.
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4. The DCB Exchange Protocol
The DCB Exchange Protocol (DCBX) is specified in IEEE [802.1Qaz],
which also specifies ETS as described in Section 3.
DCBX is built on the Link Layer Discovery Protocol (LLDP), which is
specified in IEEE [802.1AB]. DCBX is used for the discovery of DCB
capabilities of peer switches, for the detection of inconsistent
configuration of DCB features between peer switches, and for the
propagation of DCB features to switches configured to accept
configuration via DCBX. For purposes of TRILL protocol peering, TRILL
switches ignore intervening bridges, but for the purposes of LLDP and
DCBX all stations, including TRILL switches, 802.1 bridges, and end
stations are considered peers.
TRILL switches implementing PFC or ETS should also implement DCBX.
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5. Management Considerations
---TBD---
6. IANA Considerations
This document requires no IANA actions. This section should be
deleted by the RFC Editor before publication.
7. Security Considerations
See [RFC6325] for general RBridge Security Considerations.
---more TBD---
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8. References
Normative and informational references for this document are given
below.
8.1 Normative References
As this is an informational document, there are no normative
references.
8.2 Informative References
[IS-IS] - ISO/IEC, "Intermediate system to Intermediate system
routeing information exchange protocol for use in conjunction
with the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002.
[802.1AB] - IEEE, "IEEE Standard for Local and metropolitan area
networks / Station and Media Access Control Connectivity
Discovery", IEEE 802.1AB-2009, 17 September 2009.
[802.1Q] - IEEE, "IEEE Standard for Local and metropolitan area
networks / Virtual Bridged Local Area Networks", IEEE
802.1Q-2011, May 2011.
[802.1Qaz] - IEEE, "Draft Standard for Local and Metropolitan Area
Networks / Virtual Bridged Local Area Networks / Amendment XX:
Enhanced Transmission Selection for Bandwidth Sharing Between
Traffic Classes", IEEE Std 802.1Qaz-2011, June 2011.
[802.1Qbb] - IEEE, "Draft Standard for Local and Metropolitan Area
Networks / Virtual Bridged Local Area Networks / Amendment:
Priority-based Flow Control", IEEE Std 802.1Qbb-2011, June
2011.
[802.3] IEEE, "IEEE Standard for Information technology /
Telecommunications and information exchange between systems /
Local and metropolitan area networks / Specific requirements
Part 3: Carrier sense multiple access with collision detection
(CSMA/CD) access method and physical layer specifications",
IEEE 802.3-2008, 26 December 2008.
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[802.3bd] - IEEE 802.3, "Draft Standard for Information technology /
Telecommunications and information exchange between systems /
Local and Metropolitan Area Networks / Specific requirements
Part 3: Carrier Sense Multiple Access with Collision Detection
(CSMA/CD) Access Method and Physical Layer Specifications /
Amendment: MAC Control Frame for Priority-based Flow Control",
IEEE Std 802.3bd-2011, June 2011.
[FCoE] - http://fcoe.com/
[RFC793] - Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981
[RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
D. Eastlake, et al [Page 11]
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Authors' Addresses
Donald Eastlake 3rd
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Tel: +1-508-333-2270
Email: d3e3e3@gmail.com
Manoj Wadekar
QLogic Corporation
26650 Aliso Viejo Pkwy
Aliso Viejo, CA 92656 USA
Tel: +1-949-389-6000
Email: manoj.wadekar@qlogic.com
Anoop Ghanwani
Dell
350 Holger Way
San Jose, CA 95134 USA
Phone: +1-408-571-3500
Email: anoop@alumni.duke.edu
Puneet Agarwal
Broadcom
3975 Freedom Circle
Santa Clara, CA 95054 USA
Phone: +1-949-926-5000
Email: pagarwal@broadcom.com
Tal Mizrahi
Marvell
6 Hamada Street
Yokneam, 20692 Israel
Email: talmi@marvell.com
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