One document matched: draft-eastlake-trill-rbridge-dcb-01.txt
Differences from draft-eastlake-trill-rbridge-dcb-00.txt
TRILL Working Group Donald Eastlake 3rd
INTERNET-DRAFT Huawei
Intended status: Proposed Standard Manoj Wadekar
Updates: RFCtrill QLogic
Anoop Ghanwani
Brocade
Puneet Agarwal
Broadcom
Expires: November 17, 2011 May 18, 2011
RBridges: Support of IEEE 802.1Qbb, 802.1Qaz, and 802.1Qau
<draft-eastlake-trill-rbridge-dcb-01.txt>
Abstract
IEEE 802.1 is developing standards as part of its Data Center
Bridging (DCB) activity that amend the IEEE 802.1Q standard. These
include 802.1Qau, 802.1Qaz, and 802.1Qbb. The intent of these three
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 means to
allocate the available bandwidth on links to different classes of
traffic.
IEEE 802.1 is specifying theses standards and the behavior needed to
support them in bridges and end stations. This document briefly
explains the standards and discusses the support of these standards
in RBridges.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the authors or the TRILL working group mailing list:
<rbridge@postel.org>.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
D. Eastlake, et al [Page 1]
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http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
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Table of Contents
1. Introduction............................................4
1.1 Overview of These Standards............................5
1.2 Terminology............................................6
1.3 Additional Acronyms....................................6
2. Priority-Based Flow Control.............................7
3. Enhanced Transmission Selection.........................8
4. The DCB Exchange Protocol...............................8
5. Congestion Notification.................................9
5.1 Congestion Notification Domains.......................10
5.2 Congestion Notification Tag Details...................12
5.3 Congestion Notification Message Details...............12
5.4 Additions to TRILL for Congestion Notification........13
5.4.1 RBridge Ingress Details.............................14
5.4.2 Transit RBridge Details.............................17
5.4.2.1 Transit RBridge Input Port........................18
5.4.2.2 Transit RBridge Output Port.......................18
5.4.3 RBridge Egress Details..............................19
6. Management Considerations..............................20
7. IANA Considerations....................................20
8. Security Considerations................................20
9. References.............................................21
9.1 Normative References..................................21
9.2 Informative References................................21
Version History...........................................23
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1. Introduction
IEEE 802.1 is developing standards that amend IEEE [802.1Q] as part
of its Data Center Bridging (DCB) activity. These include 802.1Qau,
802.1Qaz, and 802.1Qbb. The intent of these three standards is (1) to
efficiently eliminate data loss due to queue overflow for selected
classes of traffic within Local Area Networks (LANs) having a limited
delay bandwidth product and meeting other conditions and (2) to
provide limited means to allocate the available bandwidth to
different classes of traffic. 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
802.1Q port level, no changes in the TRILL protocol are required to
support IEEE 802.1Qbb or 802.1Qaz. To support 802.1Qau, some minor
changes to TRILL, including an interworking function to handle one
corner case, are specified.
The existing optional PAUSE feature of IEEE 802.3 (Annex 31B of
[802.3]) can, with appropriate engineering, 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, require 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 comprises time critical network control frames, for
example BPDUs (Bridge Protocol Data Units). PAUSE is relatively
indiscriminant and pauses such frames, except for some MAC Control
frames such as PAUSE control frames themselves, along with pausing
the loss sensitive multi-hop traffic that we are primarily worried
about. This might compromise network 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. When that happens, 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
both P2 and P3, unnecessarily blocking traffic between those two
ports, to be sure it will not receive input on either of them for
P1. This can repeat in switches connected to S1, switches
connected to those switches, etc.
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1.1 Overview of These Standards
Overviews of the three DCB standards documents are given below. IEEE
802.1 is specifying theses standards and the behavior needed to
support them in bridges and end stations. This document discusses the
support of these standards in RBridges [RFCtrill].
IEEE [802.1Qbb], Priority-based Flow Control (PFC), DDS A refined
version of the Ethernet PAUSE feature in a priority based fashion 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 problems above. Traffic requiring
frame drops due to congestion can be assigned a priority for which
PFC is not enabled. And 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 only affect the priority or priorities
with PFC enabled.
IEEE [802.1Qaz] is a standards document that actually covers two
things. One, Enhanced Transmission Selection (ETS), allocates
bandwidth between traffic class groups indicated by priority. It is
described in Section 3. The 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.
IEEE [802.1Qau], Congestion Notification, enables switches to manage
congestion by signaling congestion on a per flow basis to end
stations. As a part of the standard, participating end stations are
required to implement per flow rate limiting that typically doesn't
exist in currently deployed end stations. 802.1Qau is enabled on a
per priority basis and, with appropriate engineering, minimizes frame
drops due to queue overflow in a LAN Congestion Notification Domain
within which all switches and end stations implement it. Thus
802.1Qau and 802.1bb Priority-Based Flow Control complement each
other, to help eliminate such frame drops. 802.1Qau tries to reduce
congestion by proactively reducing frame ingress rates at the source
end station(s). For some congestion cases this may be insufficient to
stop buffer overflow at the congestions point. PFC provides an
emergency brake for such cases and avoids frame loss. 802.1Qau
eliminates the first problem listed above for PAUSE in that frames
that require congestion drops can be assigned a priority for which
802.1Qau is not enabled. It avoids the second problem because it is
not normally used to limit priorities 6 and 7, which are typically
used for time sensitive control frames. And it avoids the third
problem listed above for PAUSE because it acts by restraining end
station flow sources rather than blocking transmission on
intermediate switch ports. Section 5 below provides additional
information on 802.1Qau and specifies additions to the TRILL protocol
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to support it.
These three DCB standards may be implemented independently or in any
combination except that implementation of any of them implies
implementation of DCBX, specified in IEEE 802.1Qaz.
1.2 Terminology
The terminology and acronyms of [RFCtrill] are used in this document.
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].
1.3 Additional Acronyms
The following acronyms are used in this document in addition to those
defined in [RFCtrill].
AVB - Audio-Visual Bridging
CNM - Congestion Notification Message
CNtag - Congestion Notification tag
DCB - Data Center Bridging
DCBX - DCB Exchange protocol
ETS - Enhanced Transmission Selection (IEEE 802.1Qaz)
FCoE - Fiber Channel over Ethernet
LLDP - Link Layer Discovery Protocol (IEEE 802.1AB)
PFC - Priority-based Flow Control (IEEE 802.1Qbb, 802.3bd)
PHY - Physical layer
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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, on a physical
link, pausing and unpausing the traffic of each of the eight
available frame priority levels. The actual priority-based pause
Ethernet control frame is being specified in [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 [RFCtrill].
LLDP/DCBX is used in PFC discovery and agreement with peers as
described in Section 4. A station implementing the PFC standard MUST
implement DCBX, signaling PFC support and configuration. Guarantee of
lossless handling of frames with a particular priority in an RBridge
campus requires implementation and enablement of PFC for that
priority at all end stations that originate frames and all RBridges
and bridges in that campus as well as meeting the PFC engineering
requirements specified 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 is specifying an algorithm in
connection with precise frame timing (AVB), but we are only concerned
with the default DCB 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 [RFCtrill]. An RBridge
implementing the ETS standard MUST 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.
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,
RBridges ignore intervening bridges, but for the purposes of LLDP and
DCBX all stations, including RBridges, 802.1 bridges, and end
stations are considered peers.
RBridges implementing any of the three DCB protocols MUST also
implement DCBX.
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5. Congestion Notification
Congestion Notification, IEEE [802.1Qau], can limit flows to minimize
frame loss by having congestion points that detect congestion and
send congestion notification messages back to reaction points in end
stations that can limit flows. See [802.1Qau] for the specification
of the algorithms to perform at congestion and reaction points.
Congestion Notification is designed to operate best in minimizing
frame loss of unicast flows in a LAN composed of point-to-point
physical links where all switches have implemented Congestion
Notification.
An RBridge that implements Congestion Notification may act as an end
point, for example when sourcing or sinking SNMP management frames,
and thus may contain one or more reaction points, as well as
implementing congestion points at its output queues.
Reaction points are in end stations where flows originate and are the
mechanism to limit flows. The granularity of reaction points is
beyond the scope of IEEE 802.1Qau and this document but cannot be
larger than a priority at a MAC address. If the granularity is
smaller and there are multiple reaction points in an end station for
a given priority, then the end station must label outgoing frames
with a Congestion Notification tag (CNtag) that includes an end
station flow ID. This flow ID is an opaque field to the rest or the
network. Reaction points are typically implemented within the native
frame origination logic of an end station.
+-----------------------------------------------+
| Ethernet Header (possibly including VLAN Tag) |
+-----------------------------------------------+
| Optional CNtag |
+-----------------------------------------------+
| Ethernet Payload |
+-----------------------------------------------+
| Ethernet FCS |
+-----------------------------------------------+
Figure 1: Native Ethernet Frame in a Congestion Notification Domain
Congestion points are at queues in forwarding devices, normally port
output queues. The functions of a congestion point are (1) to
conditionally send Congestion Notification Messages (CNMs) to the
source of a frame and (2) to conditionally strip Congestion
Notification tags (CNtags) out of a frame being forwarded, for
example if it is being forwarded out of a congestion notifiation
domain.
When a frame is to be inserted into an output queue with a congestion
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point, the procedures specified in IEEE 802.1Qau are used to
determine if a CNM should be sent to the frame's source and if so to
determine various fields in that CNM. When a frame is to be inserted
into an output queue with a congestion point, the congestion point
may remove any CNtag in the frame as discussed in Section 5.1.
Congestion points are implemented within the logic associated with a
port and require no changes to the TRILL protocol for the output of
native frames, as TRILL is implemented above such port logic as
described in [RFCtrill]; however, when outputting a TRILL data frame,
any CNM generated needs to be for the TRILL encapsulated frame rather
than for the entire TRILL data frame and the CNM needs to be TRILL
encapsulated. Thus there are some differences between the details of
the creation of a CNM at an RBridge output port and at a bridge
output port.
+-----------------------------------------------+
| Ethernet Header (possibly including VLAN Tag) |
+-----------------------------------------------+
| CNtag |
+-----------------------------------------------+
| Congestion Notification Message Fixed Fields |
+ - - - - - - - - - - - - - - - - - - - - - - -+
| Initial bytes of frame causing CNM |
+-----------------------------------------------+
| Ethernet FCS |
+-----------------------------------------------+
Figure 2: Native CNM
Within a contiguous part of the campus where Congestion Notification
is enabled (see Section 5.1), you would see the same frames with the
same tags as in a similar bridged LAN except that those frames will
be TRILL encapsulated as shown in Figures 3 and 4. The exception is
when a TRILL-ignorant bridge within the campus produces a CNM in
response to a TRILL data frame as shown in Figure 6. The resulting
CNM is adjusted by the first RBridge it encounters, which will be the
previous-hop RBridge.
5.1 Congestion Notification Domains
IEEE 802.1Qau reduces frame drops due to output queue overflow in a
Congestion Notification Domain. There could be many such domains,
each limited to a specific priority value and contiguous set of
network stations (end stations, RBridges, or 802.1 bridges), within
an RBridge campus. For example, two Congestion Notification Domains,
one at priority X and one at priority Y, could cover the same set of
contiguous stations, overlapping but different sets of such stations,
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or completely disjoint sets of such stations, in a campus.
IEEE 802.1Qau includes mechanisms to "defend" Congestion Notification
Domains, that is, make sure only congestion managed flows of frames
enter congestion point queues. The edge of a domain, i.e. the set of
station ports in the domain connected by a physical link to a station
not in the domain, is determined by a combination of auto-detection
using LLDP (see Section 4) and management configuration. Bridges that
implement Congestion Notification defend a domain by (1) prohibiting
priority mapping inside the domain, (2) mapping the priority of any
frame entering the domain from a station outside the domain to a
priority that is not a congestion managed priority, and (3)
prohibiting the mapping of the priority of any frame entering the
domain from a station outside the domain to the domain's priority.
Note that, because of item 2 in the previous paragraph, a station can
be a member of no more than 7 different Congestion Notification
Domains because there must be at least one priority that is not
congestion managed for use as the mapped priority of entering frames
from outside the domain and which are therefore not part of a
congestion managed flow. As a practical matter, it is unlikely that a
station would be a member of more than 4 or 5 different Congestion
Notification Domains as priorities 6 and 7 are normally used for high
priority control frames and are not congestion controlled and at
least one low priority is kept not congestion managed for mapping as
above.
The per port per priority state of a switch or end station will be
one of the following four values, which have the effects indicated:
o Disabled:
- On native frame input, frame priority can be mapped to or from
this priority.
- If this is an end-station output port, CNtags are not added.
- If this is a switch output port, CNtags are not stripped.
o Edge:
- On native frame input, a frame with this priority is mapped to
a non-congestion control priority and no native frame can be
mapped to this priority, regardless of the priority-mapping
table at the port. For TRILL Data frames, this also applies to
the Inner.VLAN priority.
- If this is an end-station output port, CNtags are not added.
- If this is a switch output port, CNtags are stripped including
any CNtag in the encapsulated frames if a TRILL Data frame is
being output.
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o Interior:
- On frame input, a frame in this priority is not mapped to
another priority and no frame can be mapped to this priority,
regardless of the priority-mapping table at this port. For
TRILL Data frames, this also applies to the Inner.VLAN
priority.
- If this is an end-station output port, CNtags are not added.
- If this is a switch output port, CNtags are strippedd including
any CNtag in the encapsulated frames if a TRILL Data frame is
being output.
o InteriorReady:
- On frame input, a frame in this priority is not mapped to
another priority and no frame can be mapped to this priority,
regardless of the priority-mapping table at this port. For
TRILL Data frames, this also applies to the Inner.VLAN
priority.
- If this is an end-station output port, CNtags may be added.
- If this is a switch output port, CNtags are not stripped.
Note that when the priority of a TRILL encapsulated frame is mapped,
the priority field in the Inner.VLAN tag MUST be changed.
5.2 Congestion Notification Tag Details
An end station originating a native frame may add a Congestion
Notification tag (CNtag), if the end station and the next hop device
are part of a Congestion Domain, to identify the reaction point in
that end station that controls the end station flow to which that
native frame belongs. A CNtag is 4 bytes long, consisting of a 2
bytes Ethertype (0x22E9) followed by a 2 bytes flow ID, and appears
after any VLAN tag but before the frame body. The inclusion of a
CNtag is optional as the originating end station may be able to
identify the corresponding reaction point from other information
returned in a Congestion Notification Message such as the priority.
As described in Section 5.3, CNtags are always added to Congestion
Notification Messages (CNM) when they are created.
5.3 Congestion Notification Message Details
A Congestion Notification Message (CNM) is, under certain
circumstances, created by a congestion point, as described in IEEE
802.1Qau, for frame is entered into the queue associated with that
congestion point. The complete CNM frame always includes a Congestion
Notification tag (CNtag, see Section 5.2). The CNtag includes a zero
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flow id if the frame provoking the CNM did not have a CNtag. The body
of the CNM itself, after the CNtag, starts with the CNM Ethertype
(0x22E7) followed by the information below:
- CNM version information, currently zero
- Quantized congestion feedback information as specified in IEEE
802.1Qau
- An 8 byte opaque ID of the congestion point generating the CNM
- The priority of the frame causing the CNM
- The destination MAC address of the frame causing the CNM
- The number of bytes included from the beginning of the body of
the frame causing the CNM
- The first up to 64 bytes of the body of the frame causing the
CNM
Except that input bytes/frame counters are not incremented, a CNM
generated at an output queue for a port is treated as if it had been
received on that port above the EISS. CNMs are considered to be in
the same VLAN as the frame that provoked them and have configurable
priority that defaults to priority 6.
It is undesirable, but not an error, for a CNM to be sent in response
to a CNM frame which encounters congestion. This is normally avoided
by sending CNM frames with a priority which does not have congestion
notification enabled.
As described in Section 5.4.1.3 below, when a CNM is generated by an
RBridge when queuing a TRILL data frame, it is generated for the
enclosed frame, not for the entire TRILL data frame. This will cause
the CNM to be addressed to the source end station of the data.
5.4 Additions to TRILL for Congestion Notification
The figure below is used in the discussion in this section. The
assumption is that a frame is generated at End Station "a" (ESa)
destined for End Station "b" (ESb) and this frame is forwarded
through the sequence of 802.1 bridges (Bn) and RBridges (RBn) shown.
For native frames from ESa, RB1 acts as the ingress RBridge,
encapsulating and directing them to egress RBridge RB3 for
decapsulation and delivery to ESb. The arrows indicate the flow of a
data frame. Any resulting CNM will flow in the opposite direction.
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+-----+ +-----+ +-----+ +-----+
| ESa +-->--+ B1 | + RB3 |-->--+ B3 +
+-----+ +--+--+ +--+--+ +--+--+
| | |
V ^ V
| | |
+--+--+ +-----+ +--+--+ +--+--+
| RB1 +-->--+ RB2 +-->--+ B2 + | ESb |
+-----+ +-----+ +-----+ +-----+
Figure 5: Example Frame Path
TRILL can make no difference to the actions at any reaction points in
ESa or any congestion points at the output queues of B1, B2, or B3,
since they are not RBridges, although any Congestion Notification
Message (CNM) generated at B2 will be in response to a TRILL frame
and will need adjustment at the previous hop RBridge. The situation
at the output queue of RB3 is actually the same as B3 since, as
egress, RB3 will have decapsulated any traffic for ESb before it
tries to insert it in an output queue. Thus the frame RB3 is
enqueuing will be a native frame, a congestion point at the RB3
output can act, for such a frame, exactly as an 802.1 bridge
congestion point, and any CNM generated in the RB3 output from that
native frame will be treated as if it was received by the RB3 port.
A CNM created at the RB1 or RB2 output queue is straightforward.
Assume the CNM is created in response to TRILL frame 1 (TF1) and the
TF1 encapsulates native frame 1 (NF1). The CNM would be created as a
TRILL encapsulated CNM with the ingress RBridge of TF1 as its egress.
The Inner.MacDA would be ESa. The Inner.MacSA would be the MAC
address of the port on which the TRILL encapsulated CNM was initially
sent, that is, the same as the Outer.MacSA. The encapsulated CNM
itself would be filled in as if in response to NF1, not TF1.
Similarly, a CNM created at B3 would have ESa as its destination
address and would be encapsulated when it arrived at RB3 as RB3 would
be its ingress RBridge.
5.4.1 RBridge Ingress Details
This section specifies special actions for Congestion Notification at
an RBridge input port receiving a native frame, that is, the RBridge
ingress function. The usual 802.1Q processing on the priority of the
input TRILL data frame, modified as described in Section 5.1, is
done. Special actions are required only when the native frame
received is a CNM.
The ingress process at an RBridge, say RB2, supporting Congestion
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Notification MUST detect the case of a native CNM created by a bridge
in response to a TRILL frame, say by B2 in Figure 5, and transform or
discard it as described below. If such a CNM was generated in
response to a TRILL control (IS-IS) frame, it is discarded. No other
changes are needed in the RBridge ingress process.
Such a native CNM requiring special actions is easily recognized as
it's MAC destination address will be the RBridge and it will have the
CNM Ethertype. (A CNM not addressed to the RBridge must have been
generated in response to an unencapsulated native frame, for example
at B3 in the diagram above, and can be encapsulated and generally
forwarded by transit Rbridges in the same way as other native frame.)
Such a native CNM resulting from a TRILL data frame at B2 has the
contents generally shown in Figure 6 and listed further below.
+-----------------------------------------------+
| Ethernet Header (possibly including VLAN Tag} |
+-----------------------------------------------+
| CNtag |
+-----------------------------------------------+
| Congestion Notification Message Fixed Fields |
+ - - - - - - - - - - - - - - - - - - - - - - -+
| Up to 64 initial bytes of the following: |
| +-----------------------------------------+ |
| | TRILL Ethertype and Header | |
| +-----------------------------------------+ |
| | Inner Ethernet Header incl. VLAN Tag | |
| +-----------------------------------------+ |
| | Optional CNtag | |
| +-----------------------------------------+ |
| | Ethernet Payload | |
| +-----------------------------------------+ |
| |
+-----------------------------------------------+
| Ethernet FCS |
+-----------------------------------------------+
Figure 6: Native CNM Caused by a TRILL Data Frame
1 + Outer.MacDA, MAC address of RB2
2 + Outer.MacSA, MAC address of port on which B2, the bridge
generating this CNM, sent the CNM
3 + Outer.VLAN tag for the designated VLAN on the RB2 to RB3 link
with the priority configured at B2 for CNMs (default priority 6)
4 + CNtag (CNtag Ethertype 0x22E9 followed by Flow ID of zero)
+ CNM
5 o CNM Ethertype 0x22E7
6 o CNM version information, quantized congestion feedback
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information, and an 8 byte opaque ID of the congestion
point generating the CNM
7 o The priority of the TRILL encapsulation frame causing the
CNM
8 o The destination MAC address of the TRILL encapsulation
frame causing the CNM, RB3 in this case
9 o The number of bytes included below from the beginning of
the body of the TRILL encapsulation frame causing the CNM
+ Initial bytes of body of TRILL encapsulation Data frame causing
the CNM
o TRILL Header of the frame causing the CNM
10 - TRILL Ethertype 0x22F3
11 - Flags, hop count, options length
12 - Egress nickname, RB3 in this case
13 - Ingress nickname, RB1 in this case
14 - Options, if any
15 o Inner.MacDA, MAC address of ESb
16 o Inner.MacSA, MAC address of ESa
17 o Inner.VLAN tag of the TRILL encapsulated frame causing the
CNM
18 o Optional CNtag
19 o Encapsulated native frame body
The ingressing RBridge RB2 transforms this CNM above into the
following TRILL encapsulated CNM.
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+ Outer.MacDA, MAC address of next hop RBridge (RB1) toward
originating end station
+ Outer.MacSA, MAC address of RB2 port on which this TRILL
encapsulated CNM frame is to be sent
+ Outer.VLAN tag for the designated VLAN on the RB2 to RB1 link
with priority copied from incoming Outer.VLAN, field #3 above
+ TRILL Header to get the CNM to the right end station
o TRILL Ethertype 0x22F3
o Flags, hop count, options length
o Egress nickname, RB1 in this case, from ingress nickname in
the TRILL header in the received CNM, field #13 above
o Ingress nickname, RB2 in this case, the nickname of the
RBridge doing this transformation
o Options, if any
+ Inner.MacDA, MAC address of ESa, field #16 above
+ Inner.MacSA, MAC address of B2, field #2 above
+ Inner.VLAN Tag with VLAN ID from field #17 above and priority
from field #3 above
+ CNtag, with flow ID from field #18 above, if #18 is present,
otherwise flow ID of zero
+ CNM
o CNM Ethertype 0x22E7
o CNM version information, quantized congestion feedback
information, and an 8 byte opaque ID of the congestion
point generating the CNM, field #6 above
o The priority of the native frame who's encapsulated form
caused the CNM, from Inner.VLAN, field #17 above
o The destination MAC address of the frame whose encapsulated
form caused the CNM, the Inner.MacDA, field #15 above
o The number of bytes included below from the beginning of
the body of the frame whose encapsulated form caused the
CNM. This will be 24 smaller (but not less than zero) than
the same field (#9) in the CNM tag received due to dropping
the TRILL Header (8 bytes), MAC addresses (12 bytes), and
Inner.VLAN (4 bytes).
+ Initial bytes of the body of the frame whose encapsulated form
caused the CNM, field #19 above
Because of the reduction in the number of bytes of the body of the
frame that would have caused the CNM if it weren't encapsulated, it
is RECOMMENDED that bridges and RBridges implementing Congestion
Notification in a campus be configured to include the maximum (64)
number of bytes when generating a CNM.
5.4.2 Transit RBridge Details
The subsections below describe transit RBridge support of Congestion
Notification at input and output ports. As this is considering an
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RBridge in its transit role, only the handling of TRILL data frames
is discussed. If the RBridge is receiving a native frame, it will be
an ingress as described in Section 5.4.2 and if it is sending a
native frame, it will be an egress as described in Section 5.4.3.
However, this section does apply to the output of an encapsulated
frame that was ingressed at an RBridge and to the input, in TRILL
encapsulated form, of a frame to be egressed at the RBridge.
5.4.2.1 Transit RBridge Input Port
The usual 802.1Q processing on the priority of the input TRILL data
frame, modified as described in Section 5.1, is done.
5.4.2.2 Transit RBridge Output Port
As discussed in Section 5.1, a CNtag is stripped under some
circumstances; however, such a CNtag will appear as part of the
encapsulated frame, not on the outside of the TRILL data frame, so
the CNtag is stripped from deeper in the frame. When there is a
Congestion Point enabled at an RBridge output queue a CNM is not
generated as the result of trying to queue a TRILL control (IS-IS)
frame for output at an RBridge. A TRILL encapsulated CNM is generated
in response to a TRILL Data frame composed as below, when to do so is
specified by 802.1Qau. The TRILL Data frame causing the CNM is
referred to as TF1 and its encapsulated native frame as NF1.
+ Outer.MacDA - MAC address of the next hop RBridge towards the
egress nickname used in the TRILL Header (see below)
+ Outer.MacSA - MAC address of the output port on which the TRILL
encapsulated CNM is to be sent
+ Outer.VLAN - Designated VLAN of the link on which the TRILL
encapsulated CNM is to be sent
+ TRILL Header
o TRILL Ethertype 0x22F3
o Flags, hop count, options length
o Egress nickname, from ingress nickname in TF1
o Ingress nickname, a nickname of the RBridge generating the
CNM
o Options, if any
+ Inner.MacDA - set to the Inner.MacSA of TF1, that is, the source
MAC address of NF1
+ Inner.MacSA - same as Outer.MacSA of TF1
+ Inner.VLAN - same as the Inner.VLAN of TF1, that is, the VLAN
tag of NF1
+ CNtag - with flow ID from the CNtag of NF1 or zero if NF1 did
not have a CNtag
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+ CNM - message generated for NF1
5.4.3 RBridge Egress Details
After decapsulation, processing of the decapsulated native frame is
the same as at an 802.1 bridge output port. As discussed in Section
5.1, any CNtag present is stripped under some circumstances. If the
output queue is congested, then a native CNM may be generated in
response to the decapsulated native frame. This native CNM will then
be treated as if it had been received on the port.
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6. Management Considerations
---TBD---
7. IANA Considerations
This document requires no IANA actions. This section should be
deleted by the RFC Editor before publication.
8. Security Considerations
See [RFCtrill] for general RBridge Security Considerations.
---more TBD---
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9. References
Normative and informational references for this document are given
below.
9.1 Normative References
[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-2005, 19 May 2006.
[802.1Qau] - "IEEE Standard for Local and metropolitan area networks
/ Virtual Bridged Local Area Networks / Amendment 13:
Congestion Notification", IEEE 802.1Qau-2010, 23 April 2010.
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
[RFCtrill] - R. Perlman, D. Eastlake, D. Dutt, S. Gai, and A.
Ghanwani, "RBridges: Base Protocol Specification", draft-ietf-
trill-rbridge-protocol-16.txt, in RFC Editor queue.
9.2 Informative References
[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", Work in Progress, 4 August 2010.
[802.1Qbb] - IEEE, "Draft Standard for Local and Metropolitan Area
Networks / Virtual Bridged Local Area Networks / Amendment:
Priority-based Flow Control", Work in Progress, 25 May 2010.
[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, "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",
Work in Progress, 14 July 2010.
[FCoE] - http://fcoe.com/
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Version History
Changes from -00 to -01.
1. Minor editorial changes.
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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
Brocade Communications Systems
130 Holger Way
San Jose, CA 95134 USA
Phone: +1-408-333-7149
Email: anoop@brocade.com
Puneet Agarwal
Broadcom
Phone: +1-949-926-5000
Email: pagarwal@broadcom.com
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Copyright, Disclaimer, and Additional IPR Provisions
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D. Eastlake, et al [Page 25]
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