Independent Submission D. Melman

Independent Submission D. Melman
Request for Comments: 6847 T. Mizrahi
Category: Informational Marvell
ISSN: 2070-1721 D. Eastlake 3rd
Huawei
January 2013

Fibre Channel over Ethernet (FCoE) over
Transparent Interconnection of Lots of Links (TRILL)

Abstract

Fibre Channel over Ethernet (FCoE) and Transparent Interconnection of
Lots of Links (TRILL) are two emerging standards in the data center
environment. While these two protocols are seemingly unrelated, they
have a very similar behavior in the forwarding plane, as both perform
hop-by-hop forwarding over Ethernet, modifying the packet's Media
Access Control (MAC) addresses at each hop. This document describes
an architecture for the integrated deployment of these two protocols.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6847.

Copyright Notice

Copyright (c) 2013 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.

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Table of Contents

1. Introduction ................................................. 2
2. Abbreviations ................................................ 3
3. FCoE over TRILL .............................................. 4
3.1. FCoE over a TRILL Cloud ................................. 4
3.2. FCoE over an RBridge .................................... 5
3.2.1. FCRB ............................................... 5
3.2.2. Topology ........................................... 7
3.2.3. The FCRB Flow ..................................... 8
3.2.3.1. Example - ENode to ENode ..................... 8
3.2.3.1.1. Forwarding from A to C in Dense Mode .... 9
3.2.3.1.2. Forwarding from A to C in Sparse Mode ... 9
3.2.3.2. Example - ENode to Native FC Node ............ 10
3.2.3.3. Example - ENode to ENode with Non-FCRB EoR ... 10
3.2.3.4. Example - FCoE Control Traffic through an FCRB 11
4. Security Considerations ..................................... 12
5. Acknowledgments ............................................. 12
6. References .................................................. 12
6.1. Normative References ................................... 12
6.2. Informative References ................................. 12

1. Introduction

Data center networks are rapidly evolving towards a consolidated
approach, in which Ethernet is used as the common infrastructure for
all types of traffic. Storage traffic was traditionally dominated by
the Fibre Channel (FC) protocol suite. At the intersection between
these two technologies a new technology was born, Fibre Channel over
Ethernet (FCoE), in which native FC packets are encapsulated with an
FCoE encapsulation over an Ethernet header. FCoE is specified in
[FC-BB-5]. (A future version of FCoE is under development and is
expected to be specified in a document to be referred to as FC-BB-6;
however, this is a work in progress and is beyond the scope of this
document.)

Traffic between two FCoE end nodes (ENodes) is forwarded through one
or more FCoE Forwarders (FCFs). An FCF takes a forwarding decision
based on the Fibre Channel destination ID (D_ID), and enforces
security policies between ENodes, also known as zoning. Once an FCF
takes a forwarding decision, it modifies the source and destination
MAC addresses of the packet, to reflect the path to the next-hop FCF
or ENode. An FCoE virtual link is an Ethernet link between an ENode
and an FCF, or between two FCFs. An FCoE virtual link may traverse
one or more Layer 2 bridges. FCFs use a routing protocol called
Fabric Shortest Path First (FSPF) to find the optimal path to each

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destination. An FCF typically has one or more native Fibre Channel
interfaces, allowing it to communicate with native Fibre Channel
devices, e.g., storage arrays.

TRILL [TRILL] is a protocol for transparent least-cost routing, where
Routing Bridges (RBridges) forward traffic to their destination based
on a least-cost route, using a TRILL encapsulation header. RBridges
route TRILL-encapsulated packets based on the egress RBridge nickname
in the TRILL header. An RBridge routes a TRILL-encapsulated packet
after modifying its MAC addresses to reflect the path to the next-hop
RBridge and decrementing a Hop Count field.

TRILL and FCoE bear a strong resemblance in their forwarding planes.
Both protocols take a routing decision based on protocol addresses
above Layer 2, and both modify the Ethernet MAC addresses on a per-
hop basis. Each of the protocols uses its own routing protocol
rather than using any type of bridging protocol, such as the spanning
tree protocol [802.1Q] or the Shortest Path Bridging protocol
[802.1Q].

FCoE and TRILL are both targeted at the data center environment, and
their concurrent deployment is self-evident. This document describes
an architecture for the integrated deployment of these two protocols.

2. Abbreviations

DCB Data Center Bridging

ENode FCoE Node such as server or storage array

EoR End of Row

FC Fibre Channel

FCF FCoE Forwarder

FCoE Fibre Channel over Ethernet

FCRB FCF over RBridge

FIP FCoE Initialization Protocol

FSPF Fabric Shortest Path First

LAN Local Area Network

RBridge Routing Bridge

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SAN Storage Area Network

ToR Top of Rack

TRILL Transparent Interconnection of Lots of Links

WAN Wide Area Network

3. FCoE over TRILL

3.1. FCoE over a TRILL Cloud

The simplest approach for running FCoE traffic over a TRILL network
is presented in Figure 1. The figure illustrates a TRILL-enabled
network, in which FCoE traffic is transparently forwarded over the
TRILL cloud. The figure illustrates two ENodes, a Server and an FCoE
Storage Array, an FCF, and a native Fibre Channel SAN connected to
the FCF.

FCoE traffic between the two ENodes is sent from the first ENode over
the TRILL cloud to the FCF, and then back through the TRILL cloud to
the second ENode.

+---+
| |_________
| | \ ___ _
+---+ \/ \_/ \__ _ __
FCoE Storage _/ \ / \_/ \_
Array / TRILL / +---+ \_ \
(ENode A) \_ Cloud /________| |____/ SAN _/
/ \ | | \__ _/
\__/\_ ___/ +---+ \_/
+---+ / \_/ FCF
| |________/
| |
+---+
Server
(ENode B)

Figure 1. The "Separate Cloud" Approach

The configuration in Figure 1 separates the TRILL cloud(s) and the
FCoE cloud(s). The TRILL cloud routes FCoE traffic as standard
Ethernet traffic, and appears to the ENodes and FCF as an Ethernet
LAN. FCoE traffic routed over the TRILL cloud includes FCoE data
frames, as well as FCoE control traffic, including FCoE

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Initialization Protocol (FIP) frames. To eliminate frame loss due to
queue overflow, the switches in any TRILL Cloud used with FCoE would
likely implement and use the relevant DCB protocols [TRILLPFC]
[TRILLCN].

The main drawbacks of the Separate Cloud approach are that RBridges
and FCFs are separate nodes in the network, resulting in more cabling
and boxes, and that communication between ENodes usually requires
traversing the TRILL cloud twice, so there are twice as many hops.
As mentioned above, data center networking is converging towards a
consolidated and cost-effective approach, where the same
infrastructure and equipment are used for both data and storage
traffic, and where high efficiency and minimal number of hops are
important factors when designing the network topology.

The Separate Cloud approach is presented as background to clarify the
motivation to develop an alternative approach with a higher level of
integration.

3.2. FCoE over an RBridge

3.2.1. FCRB

Rather than using the Separate Cloud approach discussed in Section
3.1, an alternate approach is presented, where each switch
incorporates both an FCF entity and an RBridge entity. This
consolidated entity is referred to as FCoE-forwarder-over-RBridge
(FCRB).

Figure 2 illustrates an FCRB and its main building blocks. An FCRB
can be functionally viewed as two independent entities:

o An FCoE Forwarder (FCF) entity.

o An RBridge entity.

The FCF entity is connected to one of the ports of the RBridge, and
appears to the RBridge as a native Ethernet host. A detailed
description of the interaction between the layers is presented in
Section 3.2.3.

Note: In this document, the term "FCF" is used slightly differently
than defined in [FC-BB-5] to emphasize the concept that an FCRB is
logically similar to an RBridge cascaded to an FCF. In the
terminology defined in [FC-BB-5], an FCRB would be referred to as an
FCF, and the FCF building block in Figure 2 would be referred to as
an FC switching element.

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+-------------------+
|FCRB |
| +-----------+ | Native FC
| | FCF |------ Interface
| +-----+-----+ |
| | |
| +-----+-----+ |
| | RBridge | |
| +-+-+---+-+-+ |
| | | | | |
+-----|-|---|-|-----+
FCoE/ / | | |
+---+ Ethernet / / | | FCoE / Ethernet
| |___________________/ / | | over TRILL ___ _
| | / | | / \_/ \__
+---+ / | \_____________ _/ \
FCoE Storage / \_______________/ TRILL /
Array / \_ Cloud /
(ENode A) / / \
/ \__/\_ ___/
+---+ / \_/
| |______________/
| |
+---+
Server
(ENode B)

Figure 2. FCRB Entity in the Network

The FCRB entity maintains layer independence between the TRILL and
FCoE protocols, while enabling both protocols on the same network.

Note that FCoE traffic is always forwarded through an FCF and cannot
be forwarded directly between two ENodes. Thus, FCoE traffic between
ENodes A and B in the topology in Figure 1 is forwarded through the
path

ENode A-->TRILL cloud-->FCF-->TRILL cloud-->ENode B

As opposed to the topology in Figure 1, the FCF in Figure 2 is
adjacent to ENodes A and B. In Figure 2, the FCRB is connected to
ENodes A and B, and functions as the edge RBridge that connects these
two nodes to the TRILL cloud, as well as the FCF that forwards
traffic between these two nodes. Thus, traffic between ENodes A and
B in the topology in Figure 2 is forwarded through the path

ENode A-->FCRB-->ENode B

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Hence, the usage of FCRB entities allows TRILL and FCoE to use common
infrastructure and equipment, as opposed to requiring separate
infrastructure as shown in the Separate Cloud topology presented in
Figure 1.

3.2.2. Topology

The network configuration illustrated in Figure 3 shows a typical
topology of a data center network. Servers are hierarchically
connected through Top-of-Rack (ToR) switches, also known as access
switches, and each set of racks is aggregated through an End-of-Row
(EoR) switch. The EoR switches are aggregated to the core switches,
which may be connected to other clouds, such as an external WAN or a
native FC SAN.
_ __ _ __
/ \_/ \_ / \_/ \_
\_ \ \_ \ ....
/ SAN _/ / WAN _/
\__ _/ \__ _/
\_/ \_/
| |
| |
+------+ +------+
Core | | | |
FCoE over | | | |
RBridge | | | |
(FCRB) +------+ +------+
| \___ ___/ |
| \ / |
| \/ |
EoR +----+_______/\_______+----+
FCoE over | | | |
RBridge | | | |
(FCRB) +----+ +----+
/ \ / \
/ \ / \
ToR +---+ +---+ +---+ +---+
FCoE over | | | | | | | |
RBridge | | | | | | | |
(FCRB) +---+ +---+ +---+ +---+
/ \ / \ / \ / \
/ \ / \ / \ / \
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
Servers/ | | | | | | | | | | | | | | | |
ENodes +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
A B C D E F G H

Figure 3. FCoE over RBridge Topology

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Note that in the example in Figure 3, all the ToR, EoR, and core
switches are FCRB entities, but it is also possible for some of the
network nodes to be pure RBridges, creating a topology in which FCRBs
are interconnected through TRILL clouds.

3.2.3. The FCRB Flow

3.2.3.1. Example - ENode to ENode

FCoE traffic sent between the two ENodes A and B in Figure 3 is
transmitted through the ToR FCRB, since A and B are connected to the
same ToR. Traffic between ENodes A and C must be forwarded through
the EoR FCRB.

The FCoE jargon distinguishes between two deployment modes:

o Sparse mode: an FCoE packet sent between two FCFs may be forwarded
over several hops of a Layer 2 network, allowing the underlying
Layer 2 network to determine the path between the two FCFs.

o Dense mode: each node along the path between two FCFs is also an
FCF, and the network is configured such that the forwarding
decision at each hop is taken at the FCF layer, allowing the path
between the two FCFs to be based on the FSPF routing protocol.

Figure 4 illustrates the traffic between ENodes A and C, which are
not connected to the same ToR. The following two subsections
describe the forwarding procedure in the Dense mode and in the Sparse
mode, respectively.

+--------+ +--------+ +--------+ +--------+ +--------+
| FCoE |.....| FCF |.....| FCF |.....| FCF |.....| FCoE |
| ENode | +--------+ +--------+ +--------+ | ENode |
| | |RBridge |.....|RBridge |.....|RBridge | | |
+--------+ +--------+ +--------+ +--------+ +--------+
|Ethernet|<===>|Ethernet|<===>|Ethernet|<===>|Ethernet|<===>|Ethernet|
+--------+ +--------+ +--------+ +--------+ +--------+
Server ToR 1 EoR ToR 2 FCoE Storage
ENode A FCRB FCRB FCRB Array
ENode C

Figure 4. Traffic between two ENodes - Example

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3.2.3.1.1. Forwarding from A to C in Dense Mode

o FCoE traffic from A is sent to ToR 1 over the Ethernet interface.
The destination MAC address is the address of the FCF entity at
ToR 1.

o ToR 1:

o The packet is forwarded to the FCF entity at the ToR. Thus,
forwarding between ENode A and the FCF at the ToR is
analogous to forwarding between two Ethernet hosts.

o The FCF entity at the ToR takes a forwarding decision based
on the FC addresses. This decision is based on the FSPF
routing protocol at the FCF layer. The FCF entity at the
ToR forwards the packet to the FCF entity in the EoR.

o The FCF then updates the destination MAC address of the
packet to the address of the EoR FCF.

o The packet is forwarded to the RBridge entity, where it is
encapsulated in a TRILL header, and sent to the RBridge at
the EoR over a single hop of the TRILL network.

o The RBridge entity in the EoR FCRB, acting as the egress RBridge,
decapsulates the TRILL header and forwards the FCoE packet to the
FCF entity. From this point, the forwarding process is similar to
the one described above for the ToR.

o A similar forwarding process takes place at the next-hop ToR FCRB,
where the FCRB finally forwards the FCoE packet to the target,
ENode C.

3.2.3.1.2. Forwarding from A to C in Sparse Mode

o Traffic is forwarded to ToR 1, as described in Section 3.2.3.1.1.

o The FCF in ToR 1, based on an FSPF forwarding decision, forwards
the packet to the FCF in ToR 2. The destination MAC address of
the FCoE packet is updated, reflecting the FCF in ToR 2. The
RBridge entity in ToR 2 adds a TRILL encapsulation, with an egress
RBridge nickname representing ToR 2.

o The packet reaches the EoR. The RBridge entity in the EoR routes
the packet to the RBridge entity in ToR 2.

o The packet reaches ToR 2. From this point on, the process is
identical to the one described in Section 3.2.3.1.1.

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3.2.3.2. Example - ENode to Native FC Node

+--------+ +--------+ +--------+ +---------+ +--------+
| FCoE |.....| FCF |.....| FCF |.....| FCF |.....| FC |
| ENode | +--------+ +--------+ +----+----+ |protocol|
| | |RBridge |.....|RBridge |.....| RB | | | stack |
+--------+ +--------+ +--------+ +----+ FC | | |
|Ethernet|<===>|Ethernet|<===>|Ethernet|<===>|Eth | |<===>| |
+--------+ +--------+ +--------+ +----+----+ +--------+
Server ToR EoR Core Native FC
ENode FCRB FCRB FCRB Storage Array

Figure 5. Example of Traffic between an
ENode and a Native FC Storage Array

Figure 5 illustrates a second example, where traffic is sent between
an ENode and an FC Storage Array, based on the network topology in
Figure 3.

o FCoE traffic from the ENode is sent to the ToR over the Ethernet
interface. The forwarding process through the ToR FCRB and
through the EoR is similar to the corresponding steps in Section
3.2.3.1.

o When the packet reaches the core FCRB, the egress RBridge entity
decapsulates the TRILL header and forwards the FCoE packet to the
FCF entity. The packet is then forwarded as a native FC packet
through the FC interface to the native FC node.

3.2.3.3. Example - ENode to ENode with Non-FCRB EoR

The example illustrated in Figure 6 is similar to the one shown in
Figure 4, except that the EoR is an RBridge rather than an FCRB.

+--------+ +--------+ +--------+ +--------+
| FCoE |.....| FCF |....................| FCF |.....| FCoE |
| ENode | +--------+ +--------+ +--------+ | ENode |
| | |RBridge |.....|RBridge |.....|RBridge | | |
+--------+ +--------+ +--------+ +--------+ +--------+
|Ethernet|<===>|Ethernet|<===>|Ethernet|<===>|Ethernet|<===>|Ethernet|
+--------+ +--------+ +--------+ +--------+ +--------+
Server ToR 1 EoR ToR 2 FCoE Storage
ENode A FCRB FCRB FCRB Array
ENode C

Figure 6. Example of Traffic between Two ENodes

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An FCoE packet sent from ENode A to C is forwarded as follows:

o The packet is sent to the FCF in ToR 1, as in the previous
example.

o The FCF in ToR 1 takes a forwarding decision based on the FC
addresses and forwards the packet to the next-hop FCF, which
resides in ToR 2. This forwarding decision is taken at the FCF
layer and is based on the FSPF routing protocol.

o The packet is then forwarded to the RBridge entity in ToR 1, where
it is encapsulated in a TRILL encapsulation, and forwarded to the
RBridge at ToR 2. The packet is routed over the TRILL cloud
through the RBridge at the EoR. The path through the TRILL cloud
is determined by TRILL's IS-IS routing protocol.

o Once the packet reaches ToR 2, it is forwarded in a similar manner
to the description in Section 3.2.3.1.

This example demonstrates that it is possible to have a hybrid
network, in which some of the nodes are FCRBs and some of the nodes
are RBridges. The forwarding procedure in this example is somewhat
similar to the sparse-mode forwarding described in Section 3.2.3.1.2.

3.2.3.4. Example - FCoE Control Traffic through an FCRB

The previous subsections focused on the data plane, i.e., storage
data exchanges transported over an FCoE encapsulation. FCoE also
requires control and management traffic that is used for initializing
sessions (i.e., FIP), distributing routing information (i.e., FSPF),
and administering and managing fabric.

The FCoE Initialization Protocol (FIP) uses Ethernet frames with a
dedicated Ethertype, allowing the FCF to distinguish these frames
from other traffic. FIP uses both unicast and multicast traffic.
The following example describes the forwarding scheme of a multicast
FIP packet sent through the network depicted in Figure 4:

o ENode A generates a multicast frame to a multicast MAC address
that represents all the FCFs (All-FCF-MAC).

o The packet is forwarded to the ToR FCRB node. The RBridge entity
forwards a copy of the packet to its FCF entity, and also sends
the packet through the TRILL cloud as a multicast TRILL
encapsulated packet.

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o Each of the FCRBs then receives the packet, forwards a copy to its
FCF entity, and forwards the packet through the TRILL network,
allowing all the FCFs to receive the packet.

While FIP packets have a dedicated Ethertype and frame format, other
types of FCoE control and management frames use the same FCoE
encapsulation as FCoE data traffic. Thus, the forwarding scheme for
such control traffic is similar to the examples described in the
previous subsections, with the exception that these frames can be
sent between ENodes, between FCFs, or between ENodes and FCFs.

4. Security Considerations

For general TRILL security considerations, see [TRILL].

For general FCoE security considerations, see Annex D of [FC-BB-5].

There are no additional security implications imposed by this
document.

5. Acknowledgments

The authors gratefully acknowledge Ayandeh Siamack and David Black
for their helpful comments. The authors also thank the T11 committee
for reviewing the document, and in particular Pat Thaler and Joe
White for their useful input.

6. References

6.1. Normative References

[TRILL] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.

[FC-BB-5] ANSI INCITS 462: "Information Technology - Fibre Channel -
Backbone - 5 (FC-BB-5)", May 2010.

6.2. Informative References

[802.1Q] "IEEE Standard for Local and metropolitan area networks -
Media Access Control (MAC) Bridges and Virtual Bridged
Local Area Networks", IEEE Std 802.1Q(tm), 2012 Edition,
October 2012.

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RFC 6847 FCoE over TRILL January 2013

[TRILLPFC] Eastlake 3rd, D., Wadekar, M., Ghanwani, A., Agarwal, P.,
and T. Mizrahi, "TRILL: Support of IEEE 802.1 Priority-
based Flow Control and Enhanced Transmission Selection",
Work in Progress, January 2013.

[TRILLCN] Eastlake 3rd, D., Wadekar, M., Ghanwani, A., Agarwal, P.,
and T. Mizrahi, "TRILL: Support of IEEE 802.1 Congestion
Notification", Work in Progress, January 2013.

Authors' Addresses

David Melman
Marvell
6 Hamada St.
Yokneam, 20692 Israel

EMail: [email protected]

Tal Mizrahi
Marvell
6 Hamada St.
Yokneam, 20692 Israel

EMail: [email protected]

Donald Eastlake 3rd
Huawei USA R&D
155 Beaver Street
Milford, MA 01757 USA

Phone: +1-508-333-2270
EMail: [email protected]

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