INTERNET-DRAFT                                              Linda Dunbar
Intended status: Proposed Standard                       Donald Eastlake
                                                           Radia Perlman
Expires: May 26, 2018                                  November 27, 2017

                 Directory Assisted TRILL Encapsulation


   This draft describes how data center networks can benefit from non-
   RBridge nodes performing TRILL encapsulation with assistance from a
   directory service.

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

      1. Introduction............................................3
      2. Conventions Used in This Document.......................4

      3. Directory Assistance to Non-RBridge.....................5
      4. Source Nickname in Encapsulation by Non-RBridge Nodes...8

      5. Benefits of Non-RBridge Performing TRILL Encapsulation..9
      5.1. Avoid Nickname Exhaustion Issue.......................9
      5.2. Reduce MAC Tables for Switches on Bridged LANs........9

      6. Manageability Considerations...........................11
      7. Security Considerations................................11

      8. IANA Considerations....................................12

      Normative References......................................13
      Informative References....................................13

      Authors' Addresses........................................14

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1. Introduction

   This document describes how data center networks can benefit from
   non-RBridge nodes performing TRILL encapsulation with assistance from
   directory service and specifies a method for them to do so.

   [RFC7067] and [RFC8171] describe the framework and methods for edge
   RBridges to get MAC&VLAN <-> Edge RBridge mapping from a directory
   service instead of flooding unknown DAs across TRILL domain. If it
   has the needed directory information, any node, even a non-RBridge
   node, can perform the TRILL data packet encapsulation.  This draft is
   to describe the benefits of and a scheme for non-RBridge nodes
   performing TRILL encapsulation.

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2. Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   AF:       Appointed Forwarder RBridge port [RFC8139]

   Bridge:   IEEE 802.1Q compliant device. In this draft, Bridge is used
             interchangeably with Layer 2 switch.

   DA:       Destination Address

   ES-IS:    End System to Intermediate Systems [RFC8171]

   Host:     Application running on a physical server or a virtual
             machine. A host usually has at least one IP address and at
             least one MAC address.

   IS-IS:. Intermediate System to Intermediate System [RFC7176]

   SA:       Source Address

   TRILL-EN: TRILL Encapsulating node. It is a node that performs the
             TRILL encapsulation but doesn't participate in RBridge's
             IS-IS routing.

   VM:       Virtual Machines

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3. Directory Assistance to Non-RBridge

   With directory assistance [RFC7067] [RFC8171], a non-RBridge node can
   be informed if a data packet needs to be forwarded across the RBridge
   domain and if so the corresponding egress RBridge. Suppose the
   RBridge domain boundary starts at network switches (not virtual
   switches embedded on servers), a directory can assist Virtual
   Switches embedded on servers to encapsulate with a proper TRILL
   header by providing the nickname of the egress RBridge edge to which
   the destination is attached. The other information needed to
   encapsulate can be either learned by listening to TRILL ES-IS Hellos
   [RFC8171], which will indicate the MAC address and nickname of
   appropriate edge RBridges, or by configuration.

   If a destination is not shown as attached to one or more RBridge edge
   nodes, based on the directory, the non-RBridge node can forward the
   data frames natively, i.e. not encapsulating with any TRILL header.
   Or, if the directory is known to be complete, the non-RBridge node
   can discard such data frames.

          \              +-------+         +------+ TRILL Domain/
           \           +/------+ |       +/-----+ |            /
            \          | Aggr11| + ----- |AggrN1| +           /
             \         +---+---+/        +------+/           /
              \         /     \            /      \         /
               \       /       \          /        \       /
                \   +---+    +---+      +---+     +---+   /
                 \- |T11|... |T1x|      |T21| ..  |T2y|---
                    +---+    +---+      +---+     +---+
                      |        |          |         |
                    +-|-+    +-|-+      +-|-+     +-|-+
                    |   |... | V |      | V | ..  | V |<- vSwitch
                    +---+    +---+      +---+     +---+
                    |   |... | V |      | V | ..  | V |
                    +---+    +---+      +---+     +---+
                    |   |... | V |      | V | ..  | V |
                    +---+    +---+      +---+     +---+

           Figure 1. TRILL domain in typical Data Center Network

   When a TRILL encapsulated data packet reaches the ingress RBridge,
   the ingress RBridge simply forwards the pre-encapsulated packet to
   the RBridge that is specified by the egress nickname field of the
   TRILL header of the data frame.  When the ingress RBridge receives a
   native Ethernet frame, it handles it as usual and may drop it if it
   has complete directory information indicating that the target is not
   attached to the TRILL campus. In such an environment with complete
   directory information, the ingress RBridge doesn't flood or forward
   the received data frames when the DA in the Ethernet data frames is

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   When all nodes attached to an ingress RBridge can pre-encapsulate
   with a TRILL header for traffic across the TRILL domain, the ingress
   RBridge don't need to encapsulate any native Ethernet frames to the
   TRILL domain. The attached nodes can be connected to multiple edge
   RBridges by having multiple ports or by an bridged LAN.  All RBridge
   edge ports connected to one bridged LAN can receive and forward pre-
   encapsulated traffic, which can greatly improve the overall network
   utilization. However, it is still necessary to designate AF ports.
   For example, to be sure that multi-destination packets from the TRILL
   campus are only egressed through one RBridge.

   The TRILL base protocol specification [RFC6325] Section 4.6.2 Bullet
   8 specifies that an RBridge port can be configured to accept TRILL
   encapsulated frames from a neighbor that is not an RBridge.

   When a TRILL frame arrives at an RBridge whose nickname matches the
   destination nickname in the TRILL header of the frame, the processing
   is exactly same as normal, i.e. as specified in [RFC6325] the RBridge
   decapsulates the received TRILL frame and forwards the decapsulated
   frame to the target attached to its edge ports.  When the DA of the
   decapsulated Ethernet frame is not in the egress RBridge's local MAC
   attachment tables, the egress RBridge floods the decapsulated frame
   to all attached links in the frame's VLAN, or drops the frame (if the
   egress RBridge is configured with that policy).

   We call a node that, as specified herein, only performs the TRILL
   encapsulation, but doesn't participate in RBridge's IS-IS routing, a
   TRILL Encapsulating node (TRILL-EN). The TRILL Encapsulating Node can
   get the MAC&VLAN <-> Edge RBridge mapping pulled from directory
   servers [RFC8171]. In order to do this, a TRILL-EN MUST support TRILL
   ES-IS [RFC8171].

   Upon receiving a native Ethernet frame, the TRILL-EN checks the
   MAC&VLAN <-> Edge RBridge mapping, and perform the corresponding
   TRILL encapsulation if the mapping entry is found. If the destination
   address and VLAN of the received Ethernet frame doesn't exist in the
   mapping table and there is no positive reply from pulling requests to
   a directory, the Ethernet frame is dropped or forwarded in native
   form to an edge RBridge.

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       |OuterEtherHd|TRILL HD| InnerDA | InnerSA |..|Payload|FCS|
               |             |<Inner Ether Header>  |
               |      +-------+  TRILL    +------+
               |      |  R1   |-----------|  R2  |  Decapsulate
               |      +---+---+  domain   +------+  TRILL header
               |          |                   |
               +----------|                   |
                          |                   |
                       +-----+             +-----+
      Non-RBridge node:|T12  |             | T22 |
      Encapsulate TRILL+-----+             +-----+
      Header for data
      Frames to traverse
      TRILL domain.

                   Figure 2.  Data frames from TRILL-EN

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4. Source Nickname in Encapsulation by Non-RBridge Nodes

   The TRILL header includes a Source RBridge's Nickname (ingress) and
   Destination RBridge's Nickname (egress). When a TRILL header is added
   to a data packet by TRILL-EN, the Ingress RBridge nickname field in
   the TRILL header is set to a nickname of the AF for the data packet's
   VLAN. The TRILL-EN determines the AF by listening to IS-IS Hellos
   from the edge RBridges on the link with the TRILL-EN in the same way
   that the RBridges on the link determine the AF [RFC8139]. TRILL-EN is
   free to send the encapsulated data frame to any of the edge RBridges
   on its link.

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5. Benefits of Non-RBridge Performing TRILL Encapsulation

5.1. Avoid Nickname Exhaustion Issue

   For a large Data Center with hundreds of thousands of virtualized
   servers, setting the TRILL boundary at the servers' virtual switches
   will create a TRILL domain with hundreds of thousands of RBridge
   nodes, which has issues of TRILL Nicknames exhaustion and challenges
   to IS-IS. On the other hand, setting the TRILL boundary at
   aggregation switches that have many virtualized servers attached can
   limit the number of RBridge nodes in a TRILL domain, but introduce
   the issues of very large MAC&VLAN <-> Edge RBridge mapping table to
   be maintained by RBridge edge nodes.

   Allowing Non-RBridge nodes to pre-encapsulate data frames with TRILL
   header makes it possible to have a TRILL domain with a reasonable
   number of RBridge nodes in a large data center. All the TRILL-ENs
   attached to one RBridge are represented by one TRILL nickname, which
   can avoid the Nickname exhaustion problem.

5.2. Reduce MAC Tables for Switches on Bridged LANs

   When hosts in a VLAN (or subnet) span across multiple RBridge edge
   nodes and each RBridge edge has multiple VLANs enabled, the switches
   on the bridged LANs attached to the RBridge edge are exposed to all
   MAC addresses among all the VLANs enabled.

   For example, for an Access switch with 40 physical servers attached,
   where each server has 100 VMs, there are 4000 hosts under the Access
   Switch. If indeed hosts/VMs can be moved anywhere, the worst case for
   the Access Switch is when all those 4000 VMs belong to different
   VLANs, i.e. the access switch has 4000 VLANs enabled. If each VLAN
   has 200 hosts, this access switch's MAC table potentially has
   200*4000 = 800,000 entries.

   If the virtual switches on servers pre-encapsulate the data frames
   destined for hosts attached to other RBridge Edge nodes, the outer
   MAC DA of those TRILL encapsulated data frames will be the MAC
   address of a local RBridge edge, i.e.  the ingress RBridge.
   Therefore, the switches on the local bridged LAN don't need to keep
   the MAC entries for remote hosts attached to other edge RBridges.

   But the traffic from nodes attached to other RBridges is decapsulated
   and has the true source and destination MACs. One simple way to
   prevent local bridges from learning remote hosts' MACs and adding to
   their MAC tables, if that is a problem, is to disable this data plane

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   learning on local bridges. The local bridges can be pre-configured
   with MAC addresses of local hosts with the assistance of a directory.
   The local bridges can always send frames with unknown Destination to
   the ingress RBridge. In an environment where a large number of VMs
   are instantiated in one server, the number of remote MAC addresses
   could be very large. If it is not feasible to disable learning and
   pre- configure MAC tables for local bridges, one effective method to
   minimize local bridges' MAC table size is to use the server's MAC
   address to hide MAC addresses of the attached VMs. I.e., the server
   acting as an edge node uses its own MAC address in the Source Address
   field of the packets originated from a host (or VM) embedded. When
   the Ethernet frame arrives at the target edge node (the egress), the
   target edge node can send the packet to the corresponding destination
   host based on the packet's IP address. Very often, the target edge
   node communicates with the embedded VMs via a layer 2 virtual switch.
   In this case, the target edge node can construct the proper Ethernet
   header with the assistance of the directory.  The information from
   the directory includes the proper host IP to MAC mapping information.

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6. Manageability Considerations

   It requires directory assistance [RFC8171] to make it possible for a
   non-TRILL node to pre-encapsulate packets destined towards remote

7. Security Considerations

   For Pull Directory and TRILL ES-IS security considerations, see

   For general TRILL security considerations, see [RFC6325].

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8. IANA Considerations

   This document requires no IANA actions. RFC Edtior: please remove
   this section before publication.

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Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
          March 1997, <>.

   [RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
          Ghanwani, "Routing Bridges (RBridges): Base Protocol
          Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,

   [RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt, D.,
          and A. Banerjee, "Transparent Interconnection of Lots of Links
          (TRILL) Use of IS-IS", RFC 7176, DOI 10.17487/RFC7176, May
          2014, <>.

   [RFC8139] Eastlake 3rd, D., Li, Y., Umair, M., Banerjee, A., and F.
          Hu, "Transparent Interconnection of Lots of Links (TRILL):
          Appointed Forwarders", RFC 8139, DOI 10.17487/RFC8139, June
          2017, <>.

   [RFC8171] Eastlake 3rd, D., Dunbar, L., Perlman, R., and Y. Li,
          "Transparent Interconnection of Lots of Links (TRILL): Edge
          Directory Assistance Mechanisms", RFC 8171, DOI
          10.17487/RFC8171, June 2017, <https://www.rfc-

Informative References

   [RFC7067] Dunbar, et, al "Directory Assistance Problem and High-Level
          Design Proposal", RFC7067, November 2013.


   The followiing are thanked for their contributions:

      Igor Gashinsky

   The document was prepared in raw nroff. All macros used were defined
   within the source file.

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Authors' Addresses

      Linda Dunbar
      Huawei Technologies
      5340 Legacy Drive, Suite 175
      Plano, TX 75024, USA

      Phone: +1-469-277-5840

      Donald Eastlake
      Huawei Technologies
      155 Beaver Street
      Milford, MA 01757 USA

      Phone: +1-508-333-2270

      Radia Perlman
      2010 256th Avenue NE, #200
      Bellevue, WA 98007 USA


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