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Network Working Group                                              X. Xu
Internet-Draft                                                    Huawei
Intended status: Standards Track                            E. Auerswald
Expires: November 3, 2017                                       fgn GmbH
                                                                 L. Fang
                                                                    ebay
                                                             J. Tantsura
                                                              Individual
                                                             May 2, 2017


                    IS-IS Flooding Reduction in MSDC
              draft-xu-isis-flooding-reduction-in-msdc-01

Abstract

   IS-IS is commonly used as an underlay routing protocol for MSDC
   (Massively Scalable Data Center) networks.  For a given IS-IS router
   within the CLOS topology, it would receive multiple copies of exactly
   the same LSP from multiple IS-IS neighbors.  In addition, two IS-IS
   neighbors may send each other the same LSP simultaneously.  The
   unneccessary link-state information flooding wastes the precious
   process resource of IS-IS routers greatly due to the fact that there
   are too many IS-IS neighbors for each IS-IS router within the CLOS
   topology.  This document proposes some extensions to IS-IS so as to
   reduce the IS-IS flooding within MSDC networks greatly.  The
   reduction of the IS-IS flooding is much beneficial to improve the
   scalability of MSDC networks.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 3, 2017.






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Copyright Notice

   Copyright (c) 2017 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Modifications to Current IS-IS Behaviors  . . . . . . . . . .   4
     3.1.  IS-IS Routers as Non-DIS  . . . . . . . . . . . . . . . .   4
     3.2.  Controllers as DIS  . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IS-IS is commonly used as an underlay routing protocol for Massively
   Scalable Data Center (MSDC) networks where CLOS is the most popular
   toplogy.  For a given IS-IS router within the CLOS topology, it would
   receive multiple copies of exactly the same LSP from multiple IS-IS
   neighbors.  In addition, two IS-IS neighbors may send each other the
   same LSP simultaneously.  The unnecessary link-state information
   flooding wastes the precious process resource of IS-IS routers
   greatly and therefore IS-IS could not scale very well in MSDC
   networks.

   To simplify the network management task, centralized controllers are
   becoming fundamental network elements in most MSDCs.  One or more
   controllers are usually connected to all routers within the MSDC
   network via a Local Area Network (LAN) which is dedicated for network
   management purpose (called management LAN), as shown in Figure 1.



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           +----------+                  +----------+
           |Controller|                  |Controller|
           +----+-----+                  +-----+----+
                |DIS                           |Candidate DIS
                |                              |
                |                              |
   ---+---------+---+----------+-----------+---+---------+-Management LAN
      |             |          |           |             |
      |Non-DIS      |Non-DIS   |Non-DIS    |Non-DIS      |Non-DIS
      |             |          |           |             |
      |         +---+--+       |       +---+--+          |
      |         |Router|       |       |Router|          |
      |         *------*-      |      /*---/--*          |
      |        /     \   --    |    //    /    \         |
      |        /     \     --  |  //      /    \         |
      |       /       \      --|//       /      \        |
      |       /        \      /*-       /        \       |
      |      /          \   // | --    /         \       |
      |      /          \ //   |   --  /          \      |
      |     /           /X     |     --           \      |
      |     /         //  \    |     / --          \     |
      |    /        //    \    |     /   --         \    |
      |    /      //       \   |    /      --       \    |
      |   /     //          \  |   /         --      \   |
      |   /   //             \ |  /            --     \  |
      |  /  //               \ |  /              --   \  |
    +-+- //*                +\\+-/-+               +---\-++
    |Router|                |Router|               |Router|
    +------+                +------+               +------+

                              Figure 1

   With the assistance of a controller acting as IS-IS Designated
   Intermediate System (DIS) for the management LAN, IS-IS routers
   within the MSDC network don't need to exchange any IS-IS Protocl
   Datagram Units (PDUs) other than Hello packets among them.  In order
   to obtain the full topology information (i.e., the fully synchronized
   link-state database) of the MSDC's network, these IS-IS routers would
   exchange the link-state information with the controller being elected
   as IS-IS DIS for the management LAN instead.

   To further suppress the flooding of multicast IS-IS PDUs originated
   from IS-IS routers over the management LAN, IS-IS routers would not
   send multicast IS-IS Hello packets over the management LAN.
   Insteads, they just wait for IS-IS Hello packets originated from the
   controller being elected as IS-IS DIS initially.  Once an IS-IS DIS
   for the management LAN has been discovered, they start to send IS-IS
   Hello packets directly (as unicasts) to the IS-IS DIS periodically.



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   In addition, IS-IS routers would send IS-IS PDUs to the IS-IS DIS for
   the management LAN as unicasts as well.  In contrast, the controller
   being elected as IS-IS DIS would send IS-IS PDUs as before.  As a
   result, IS-IS routers would not receive IS-IS PDUs from one another
   unless these IS-IS PDUs are forwarded as unknown unicasts over the
   management LAN.  Through the above modifications to the current IS-IS
   router behaviors, the IS-IS flooding is greatly reduced, which is
   much beneficial to improve the scalability of MSDC networks.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  Terminology

   This memo makes use of the terms defined in [RFC1195].

3.  Modifications to Current IS-IS Behaviors

3.1.  IS-IS Routers as Non-DIS

   After the bidirectional exchange of IS-IS Hello packets among IS-IS
   routers, IS-IS routers would originate Link State PDUs (LSPs)
   accordingly.  However, these self-originated LSPs need not to be
   exchanged directly among them anymore.  Instead, these LSPs just need
   to be sent solely to the controller being elected as IS-IS DIS for
   the management LAN.

   To further reduce the flood of multicast IS-IS PDUs over the
   management LAN, IS-IS routers SHOULD send IS-IS PDUs as unicasts.
   More specifically, IS-IS routers SHOULD send unicast IS-IS Hello
   packets periodically to the controller being elected as IS-IS DIS.
   In other words, IS-IS routers would not send any IS-IS Hello packet
   over the management LAN until they have found an IS-IS DIS for the
   management LAN.  Note that IS-IS routers SHOULD NOT be elected as IS-
   IS DIS for the management LAN (This is done by setting the DIS
   Priority of those IS-IS routers to zero).  As a result, IS-IS routers
   would not see each other over the management LAN.  In other word, IS-
   IS routers would not establish adjacencies with one other.
   Furthermore, IS-IS routers SHOULD send all the types of IS-IS PDUs to
   the controller being elected as IS-IS DIS as unicasts as well.

   To advoid the data traffic from being forwarded across the management
   LAN, the cost of all IS-IS routers' interfaces to the management LAN
   SHOULD be set to the maximum value.




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   When a given IS-IS router lost its connection to the management LAN,
   it SHOULD actively establish adjacency with all of its IS-IS
   neighbors within the CLOS network.  As such, it could obtain the full
   LSDB of the CLOS network while flooding its self-originated LSPs to
   the remaining part of the whole CLOS network through these IS-IS
   neighbor.

3.2.  Controllers as DIS

   The controller being elected as IS-IS DIS would send IS-IS PDUs as
   multicasts or unicasts as before.  And it SHOULD accept and process
   those unicast IS-IS PDUs originated from IS-IS routers.  Upon
   receiving any new LSP from a given IS-IS router, the controller being
   elected as DIS MUST flood it immediately to the management LAN for
   two purposes: 1) implicitly acknowledging the receipt of that LSP; 2)
   synchronizing that LSP to all the other IS-IS routers.

   Furthermore, to decrease the frequency of advertising Complete
   Sequence Number PDU (CSNP) on the controller being elected as DIS,
   it's RECOMMENDED that IS-IS routers SHOULD send an explicit
   acknowledgement with a Partial Sequence Number PDU (PSNP) upon
   receiving a new LSP from the controller being elected as DIS.

4.  Acknowledgements

   The authors would like to thank Peter Lothberg for his valuable comments
   and suggestions on this document.

5.  IANA Considerations

   TBD.

6.  Security Considerations

   TBD.

7.  References

7.1.  Normative References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <http://www.rfc-editor.org/info/rfc1195>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.



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7.2.  Informative References

   [RFC4136]  Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction
              in Stable Topologies", RFC 4136, DOI 10.17487/RFC4136,
              July 2005, <http://www.rfc-editor.org/info/rfc4136>.

Authors' Addresses

   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com


   Erik Auerswald
   fgn GmbH

   Email: auerswald@fg-networking.de


   Luyuan Fang
   ebay

   Email: lufang@ebay.com


   Jeff Tantsura
   Individual

   Email: jefftant@gmail.com





















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