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rfc:rfc6847

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.

Melman, et al. Informational [Page 1] RFC 6847 FCoE over TRILL January 2013

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

Melman, et al. Informational [Page 2] RFC 6847 FCoE over TRILL January 2013

 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

Melman, et al. Informational [Page 3] RFC 6847 FCoE over TRILL January 2013

 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

Melman, et al. Informational [Page 4] RFC 6847 FCoE over TRILL January 2013

 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.

Melman, et al. Informational [Page 5] RFC 6847 FCoE over TRILL January 2013

                        +-------------------+
                        |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

Melman, et al. Informational [Page 6] RFC 6847 FCoE over TRILL January 2013

 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

Melman, et al. Informational [Page 7] RFC 6847 FCoE over TRILL January 2013

 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

Melman, et al. Informational [Page 8] RFC 6847 FCoE over TRILL January 2013

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.

Melman, et al. Informational [Page 9] RFC 6847 FCoE over TRILL January 2013

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

Melman, et al. Informational [Page 10] RFC 6847 FCoE over TRILL January 2013

 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.

Melman, et al. Informational [Page 11] RFC 6847 FCoE over TRILL January 2013

 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.

Melman, et al. Informational [Page 12] 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: davidme@marvell.com
 Tal Mizrahi
 Marvell
 6 Hamada St.
 Yokneam, 20692 Israel
 EMail: talmi@marvell.com
 Donald Eastlake 3rd
 Huawei USA R&D
 155 Beaver Street
 Milford, MA 01757 USA
 Phone: +1-508-333-2270
 EMail: d3e3e3@gmail.com

Melman, et al. Informational [Page 13]

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