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Network Virtualization Overlays Working                           L. Xia
Group                                                              Q. Wu
Internet-Draft                                                    Huawei
Intended status: Standards Track                           June 28, 2013
Expires: December 30, 2013


      Tenant system information discovery approaches Gap analysis
                   draft-wu-nvo3-mac-learning-arp-03

Abstract

   This document analyzes various protocol solutions for tenant system
   information (e.g.  MAC, IP, etc) discovery in the virtualization
   environment (e.g.,MAC in MAC, MAC in IP, IP in IP) and identifies the
   gap against NVO3 control plane and data plane requirements.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 30, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  4
   3.  Overview of tenant system information discovery in the
       virtualization domain using NVO3 . . . . . . . . . . . . . . .  5
     3.1.  Issues with tenant system information discovery in the
           virtualization domain using NVO3 . . . . . . . . . . . . .  6
   4.  Related work for Tenant system information discovery . . . . .  8
     4.1.  SPB and TRILL  . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  ARMD and SARP  . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  BGP/MPLS IP VPNs - Distributed control plane
           distribution . . . . . . . . . . . . . . . . . . . . . . .  9
     4.4.  BGP/MPLS Ethernet VPNs and PBB-EVPN  . . . . . . . . . . . 10
     4.5.  VPLS - ARP + data plane learning . . . . . . . . . . . . . 10
     4.6.  LISP - Centralized control plane distribution  . . . . . . 11
   5.  Gap Analysis and Discuss . . . . . . . . . . . . . . . . . . . 13
   6.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20





























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1.  Introduction

   The tenant system information in this document is referred to as L2
   address and L3 address of VM.  As described in [I.D-ietf-nvo3-
   framework], for an L2 NVE, the NVE needs to be able to determine MAC
   addresses of the tenant system.  For an L3 NVE, the NVE needs to be
   able to determine IP addresses of the tenant system.

   This can be achieved mainly in 3 ways: data plane learning; ARP;
   control plane distribution (e.g. by BGP or IS-IS).  This document
   analyzes various protocol solutions for tenant system information
   (e.g.  MAC, IP, etc) discovery in the virtualization environment
   (e.g.,MAC in MAC, MAC in IP, IP in IP) and identifies the gap against
   NVO3 control plane and data plane requirements.





































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2.  Conventions 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 [RFC2119].














































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3.  Overview of tenant system information discovery in the
    virtualization domain using NVO3

   Tenant system information discovery can be achieved either using
   dynamic data plane learning or ARP or control plane distribution.
   This document addresses how tenant system information discovery works
   in the overlay network enviroment.  Figure 1 shows the NVO3 reference
   architecture for tenant system information discovery.  The reference
   architecture assumes that:

   o  Tenant system A in DC site X wants to establish communication with
      tenant system B in the DC site Y.

   o  Tenant system A is connecting to VN by attaching to NVE X. Tenant
      System A knows IP address of Tenant System B using out of band
      means but does not know MAC address of Tenant System B.

   o  Tenant system B is connecting to VN by attaching to NVE Y. Tenant
      System B knows IP address of Tenant System A using out of band
      means but does not know MAC address of Tenant System A.

   o  NVE X associated with tenant system A doesn't know IP address and
      MAC address of tenant system B.

   o  NVE Y associated with tenant system B doesn't know IP address and
      MAC address of tenant system A.

























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                               ,---------.
                             ,'  Backend  `.
                            (      NVA       )
                             `.           ,'
                               `-+------+'
                               |         |
                          .--..--. .--. ..
                         (    '           '.--.
                      .-.'        L3          '
                     (          Overlay       )
                      (                     '-'
                           .'--'._.'.-._.'.-._)
           NVE X =       //                \\    NVE Y =
     (MAC_X,IP_X) +------+              +-------+(MAC_Y,IP_Y)
                .-|NVE X |              | NVE Y |
              (   +------+--.         ( +-------+.--.
            .-.'              '     .-.'              '
           (    DC Site X     )    (    DC Site Y     )
            (             .'-'      (             .'-'
             '--'._.'.    )          '--'._.'.    )
                     '--'              /     '--'
                  /     \             /       \
               __/_      \           /_       _\__
        '--------'   '--------'   '--------'   '--------'
        : Tenant :   : Tenant :   : Tenant :   : Tenant :
        : SystemA:   : SystemC:   : SystemD:   : SystemB:
        '--------'   '--------'   '--------'   '--------'
          TSID=                                  TSID=
      (VNID,MAC_A,IP_A)                      (VNID,MAC_B,IP_B)

    Figure 1: Example of NVO3 reference architecture for tenant system
                           information discovery

3.1.  Issues with tenant system information discovery in the
      virtualization domain using NVO3

   Here we give an example of tenant system information discovery in
   large layer 2 domain using NVO3 using traditional approach for MAC
   address learning.  The packet flow and control plane operation are as
   follows:

   1.  Tenant system A sends a broadcast ARP message to discover the MAC
       address of Tenant system B. The message contains IP_B in the ARP
       message payload.

   2.  The ARP proxy [RFC1027] in NVE X, receiving the ARP message and
       knowing source and destination are in the different subnet will
       encapsulate it with overlay header and outer header and flood it



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       on the overlay network for TSID = <VNID,IP_B,*>.  VNID is
       included in the overlay header.

   3.  The ARP message will be processed by NVE Y which maintains
       mapping table matching TSID = <VNID,IP_B,*>.  NVE Y, will forward
       the ARP message to tenant system B. Tenant System B sends ARP
       reply to tenant system A containing MAC_B.

   4.  NVE X processes ARP reply message and populates the mapping table
       with the received entry, then sends it to Tenant System A that
       includes MAC_B and IP_B of Tenant System B.

   5.  Tenant system A learns MAC_B from the ARP rely message and can
       now send a packet to Tenant system B by including MAC_B, and
       IP_B, as destination addresses.

   The issues with tenant system information discovery are as follows:

   o  The demand on the forwarding table capacity at each NVE is
      increased compared to non-virtualized environments since layer 2
      network is no longer constrained to small local network and has a
      need for millions of hosts.

   o  If Address resolution protocol is used for control plane learning,
      it may cause excessive flooding since ARP packets need to be
      flooded over the whole overlay network. the ARP/ND processing load
      imposes great challenge on L2/L3 boundary routers.

   o  Dynamic data plane learning implies that flooding of unknown
      destinations be supported and hence implies that broadcast and/or
      multicast be supported or that ingress replication, which may
      cause excessive flooding issue and lead to significant scalability
      limitations.

   o  A control plane protocol (e.g., BGP) that carries both MAC and IP
      addresses eliminates the need for ARP, however some NVEs or DC
      Gateways may not support complex control plane protocol, for
      example, BGP protocol.













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4.  Related work for Tenant system information discovery

   Currently, 3 main solutions or their combination can be used to
   perform the tenant system information discovery.  They are dynamic
   data plane learning, ARP, control plane distribution (including two
   options: centralized or distributed).  Additionally, the ARP proxy
   [RFC1027] mechanism can be used for preventing the ARP flooding in
   the core network and limiting the MAC table size of NVEs and hosts.
   Here is a brief analysis of them and the associated protocols are
   discussed.

4.1.  SPB and TRILL

   Shortest Path Bridging (SPB) [SPB] and TRILL [TRILL] are two
   different methods of IS-IS based overlay that operates over L2
   Ethernets.  They all use the MAC in MAC encapsulation and have the
   same default MAC address learning method:

   o  Using IS-IS extension for outer MAC address distribution over the
      SPB area or TRILL campus network;

   o  Using ARP or data plane snooping for inner MAC address learning of
      locally attached hosts.

   o  In addition, the TRILL maybe use
      [draft-ietf-trill-directory-framework] distributes the inner MAC
      address between all the RBriges

   In the centralized approach, TRILL may use TRILL ESADI to distribute
   the inner MAC address between all the RBridges however SPB doesn't
   support ESADI distribution mechanism.  In the distributed approach,
   SPB and TRILL may use combination of the above 3 methods.

4.2.  ARMD and SARP

   The ARMD WG examined data center scaling issues with a focus on
   address resolution and developed a problem statement document
   [RFC6820].  In this document, the scaling issues of MAC address
   learning related to the overlay-based approach are listed as
   followed:

      ARP processing on Routers: This issue mainly concerns about the
      significant amount of ARP traffic or BUM packets traffic in large
      L2 broadcast domains and its impact to the routers.  Finally, some
      optimized method are proposed;

      IPv6 Neighbor Discovery has the similar issue as ARP processing on
      router;



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      MAC Address Table Size Limitations at Switches: This issue mainly
      concerns on the MAC Address Table Size Limitations when the VM
      number is very large in the Virtualized data center environment.

   In order to tackle the above problems, SARP [SARP] seamlessly
   supports Layer 2 network virtualization services over the overlay
   network and significantly reduces their complexity in terms of table
   size and performance.  The overlay networks are only required to map
   MAC addresses of the SARP proxies, instead of MAC address of the
   destination end host, to the correct tunnel.

4.3.  BGP/MPLS IP VPNs - Distributed control plane distribution

   BGP/MPLS IP VPNs [RFC4364] provides IP Virtual Private Networks
   (VPNs) for its customers and support VPN traffic isolation, address
   overlapping and separation between customer networks.  The BGP/MPLS
   control plane is used to distribute both the VPN labels and the
   tenant system IP addresses that are used to identify the customer.
   However BGP/MPLS IP VPN doesn't support interconnection with Data
   Center (DC) overlay networks and provide a virtual end to end tenant
   network service to tenant systems in the BGP/MPLS IPVPN.It also has
   the scalability related problems when IP addresses of a large number
   of VMs need to be propagated in control plane in the Virtualized data
   center environments.

   For an L3 overlay node, the overlay node only needs to determine IP
   addresses of the tenant system but doesn't need to know the MAC
   address of the destination system since overlay tunnels the L3
   traffic from the tenant system in an encapsulated format to the final
   destination and doesn't care about the MAC address of destination end
   system for the inner L3 packet.  Therefore overlay node can answer
   any address resolution query with its own MAC address or one virtual
   MAC address.  In [I.D-ietf-l3vpn-end-system], NVE uses XMPP to
   exchange information with the tenant system and answer the address
   resolution query from tenant system with a virtual router MAC
   address.

   In order to propagate tenant system information to the whole overlay
   network environment, [I.D-ietf-l3vpn-end-system]use Route Server to
   gather VPN membership on each Forwarder and IP addresses that are
   currently associated with each virtual interface of tenant system and
   advertise them to the BGP speaker.  In addition, BGP speaker also can
   interact with Route Server to generate tenant system information
   update to the upstream end systems.







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4.4.  BGP/MPLS Ethernet VPNs and PBB-EVPN

   Ethernet Virtual Private Networks (E-VPNs) [I-D.ietf-l2vpn-evpn]
   provide an emulated L2 service in which each tenant has its own
   Ethernet network over a common IP or MPLS infrastructure.  PBB-EVPN
   [I-D.ietf -l2vpn-pbb-evpn] is a combined solution of PBB and E-VPN.
   They all use BGP for MAC address distribution over the core MPLS/IP
   network, and use ARP or data plane snooping for MAC address learning
   of locally attached hosts.  In other words, the mapping table
   information <VNID,IP_A,NVE_X> should be distributed to all the remote
   overlay nodes that belong to the same VN.  After that,the tenant
   system information<VNID,IP_A, MAC_X> is distributed from remote
   overlay nodes to all the remote tenant system.  When all the tenant
   system information is populated, overlay nodes will process the
   packet from each tenant system and perform a lookup operation in its
   map table for the destination TSID=<VNID,IP_B> and determine which
   tunnel the packet needs to be sent to.

   The analysis of their MAC address learning methods is as followed:

   Pros:

   o  ARP broadcast Suppression: They all construct ARP caches on the
      PEs and synchronize them either via BGP or data plane snooping.
      The PEs act as ARP proxies for locally attached hosts, thereby
      preventing repeated ARP broadcast over the core MPLS/IP network;

   o  Comparing E-VPN, PBB-EVPN reduces the number of BGP MAC
      advertisement routes, provide C-MAC address mobility, confine the
      scope of C-MAC address learning to only active flows, offer per
      site policies and avoid C-MAC address flushing on topology
      changes.


   Con: An E-VPN PE sends a BGP MAC Advertisement Route per customer/
   client MAC (C-MAC) address.  This will raise the scalability related
   problems in the case of Virtualized data center environments where
   the number of virtual machines (VMs) is very large.

4.5.  VPLS - ARP + data plane learning

   VPLS is an L2 VPN technology.  VPLS uses the ARP and data plane
   learning for L2 tenant system information discovery, and not
   advertised and distributed via a BGP/LDP control plane.  The analysis
   of this method is as followed:

   Pros:




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   o  Reducing complexity and work burden of the control plane by
      decreasing the control packets;

   o  MAC address learning based on active flows can save the space of
      MAC mapping table.


   Cons:

   o  PE will learn all active MACs over the associated PW by BUM
      flooding of data plane.  But, some active MACs is not destined to
      the PE;

   o  Unlike the active MAC withdraw mechanism in control plane, PE
      cannot flush MAC address real-time in data plane, when host MACs
      behind the PE are changed.

4.6.  LISP - Centralized control plane distribution

   LISP[RFC6830] essentially provides an IP over IP overlay where the
   internal addresses are end station Identifiers and the outer IP
   addresses represent the location of the end station within the core
   IP network topology. [draft-maino-nvo3-lisp-cp-02] discusses L2 over
   L3 LISP Encapsulation and proposes a LISP Mapping System for ARP
   resolution to eliminate the flooding of ARP traffic and further
   reduce the need for multicast in the underlay network.  This system
   relies on mapping system for tenant system information distribution
   and involves MAP-request/MAP-Response message exchange between
   overlay node and mapping system.  With introduced LISP Mapping
   system, the scalability is improved for tenant system information
   discovery. the packet flow and control plane operation are as
   follows:

   o  Tenant System A sends a broadcast ARP message to discover the MAC
      address of Tenant system B. The message contains IP_B in the ARP
      message payload.

   o  NVE X as an ARP proxy, receiving the ARP message and knowing
      source and destination are in the different subnet[RFC1027], but
      rather than flooding it on the overlay network, sends a Map-
      Request(i.e.,LISP signaling) to the backend LISP mapping system
      (i.e.,NVA) that maintains mapping information for entire overlay
      network for TSID = <VNID,IP_B,*>.

   o  The Map-Request is reflected by the backend LISP Mapping system to
      NVE Y, that will send a Map-Reply back to NVE X containing the
      mapping TSID=<VNID,IP_B,MAC_B>.  Alternatively, depending on the
      Backend LISP Mapping system configuration, the backend LISP



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      Mapping system may send directly a Map-Reply to NVE X.

   o  NVE X populates the mapping table with the received entry, and
      sends an ARP-Agent Reply to Tenant System A that includes MAC_B
      and IP_B.

   o  Tenant system A learns MAC_B from the ARP message and can now send
      a packet to Tenant system B by including MAC_B, and IP_B, as
      destination addresses.










































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5.  Gap Analysis and Discuss

   The following table compares several tenant system information
   discovery methods from different aspects under the same network
   topology and scale.

   +-----------+-------------+--------------+-------------+------------+
   |   TS      |  Forwarding |   Packets    |Control plane| Directory  |
   | Discovery |     table   |  flooding    |Distribution    Support   |
   |  method   |     size    |   impact     |  support    |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   |   SPB     |             |              |             | Trill:Yes  |
   | &TRILL    |   Mediaum   |     Medium   |    Yes      | SPB:No     |
   |           |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   |           |             |              |             |            |
   | ARMD&SARP |   Small     |     Medium   |    No       |   No       |
   |           |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   |   LISP    |             |              |             |LISP Mapping|
   |    +      |   Medium    |     Medium   |   Yes       |   System   |
   + ARP proxy |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   | BGP/MPLS  |             |              |             |            |
   |    IP     |   Large     |     Large    |   Yes       |   No       |
   |   VPN     |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   |  BGP/MPLS |             |              |             |            |
   |  Ethernet |   Large     |     Large    |   Yes       |   No       |
   |    VPN    |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
   |           |             |              |             |            |
   |   VPLS    |             |              |             |            |
   |    +      |   Medium    |     Small    |   Yes       |   No       |
   | ARP proxy |             |              |             |            |
   |           |             |              |             |            |
   +-----------+-------------+--------------+-------------+------------+
     Table 1: The comparison between several tenant system



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               information discovery methods


















































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6.  Conclusion

   There are three ways for tenant system information discovery, data
   plane learning and control plane ARP learning and control plane
   distribution.  In large layer 2 domain, the MAC address can not be
   simply learnt by looking at the outer layer 2 header, instead, Deeper
   parsing inner Ethernet header is required.  However it also
   introduces a lot of processing overhead.  In order to address this
   issue, the control plane distribution is proposed, and used to carry
   both MAC address and IP address and eliminate the above data plane
   learning issue.  However distribution protocol is needed.  How
   distribution protocol is used to propagate tenant system information
   and mapping table information in large scale and in a more efficient
   way is still under study.





































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7.  IANA Considerations

   This document has no actions for IANA.
















































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8.  Security Considerations

   TBC.
















































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9.  Normative References

   [ESADI]    Eastlake, D., "TRILL (Transparent Interconnection of Lots
              of Links): ESADI (End Station Address Distribution
              Information) Protocol", ID draft-ietf-trill-esadi-02,
              February 2013.

   [I-D.ietf-l2vpn-evpn]
              Sajassi, A. and R. Aggarwal, "BGP MPLS Based Ethernet
              VPN", ID draft-ietf-l2vpn-evpn-03, February 2013.

   [I-D.ietf-l2vpn-pbb-evpn]
              Sajassi, A., "PBB-EVPN", ID draft-ietf-l2vpn-pbb-evpn-04,
              April 2013.

   [I-D.ietf-trill-directory-framework]
              Dunbar, L. and D. Eastlake, "TRILL (Transparent
              Interconnection of Lots of Links): Edge Directory
              Assistance Framework",
              ID draft-ietf-trill-directory-framework-05, April 2013.

   [I.D-ietf-l3vpn-end-system]
              Marques, P., "BGP-signaled end-system IP/VPNs",
              ID draft-maino-nvo3-lisp-cp-02, April 2013.

   [I.D-ietf-nvo3-framework]
              Lasserre, M., "Framework for DC Network Virtualization",
              ID draft-ietf-nvo3-framework-00, September 2012.

   [RFC1027]  Carl-Mitchell, S., "Using ARP to Implement Transparent
              Subnet Gateways", October 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [RFC4364]  Rosen, E., "BGP/MPLS IP Virtual Private Networks (VPNs)",
              February 2006.

   [RFC6325]  Perlman, R., "RBridges: Base Protocol Specification",
              July 2011.

   [RFC6820]  Farinacci, D., "The Locator/ID Separation Protocol
              (LISP)", January 2013.

   [RFC6830]  Farinacci, D., "The Locator/ID Separation Protocol
              (LISP)", January 2013.

   [SARP]     Dunbar, L. and I. Yerushalmi, "Scaling the Address



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              Resolution Protocol for Large Data Centers (SARP)",
              ID draft-nachum-sarp-04, February 2013.

   [SPB]      "IEEE standard for local and metropolitan area networks:
              Media access control (MAC) bridges and virtual bridged
              local area networks -- Amendment 20: Shortest path
              bridging", IEEE 802.1aq, June 2012.

   [draft-maino-nvo3-lisp-cp]
              Maino, F. and R. Aggarwal, "LISP Control Plane for Network
              Virtualization Overlays", ID draft-maino-nvo3-lisp-cp-02,
              April 2013.







































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Authors' Addresses

   Liang Xia
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: frank.xialiang@huawei.com


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: bill.wu@huawei.com

































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