PIM DR Improvement
draft-ietf-pim-dr-improvement-02

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PIM WG                                                      Zheng. Zhang
Internet-Draft                                               Fangwei. Hu
Intended status: Standards Track                            BenChong. Xu
Expires: June 8, 2017                                    ZTE Corporation
                                                        December 5, 2016

                           PIM DR Improvement
                  draft-ietf-pim-dr-improvement-02.txt

Abstract

   PIM is worldly deployed multicast protocol.  This document will
   improve the stability of PIM protocol, decrease the lost of multicast
   packets when the PIM DR (Designed Router) is down.

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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   This Internet-Draft will expire on June 8, 2017.

Copyright Notice

   Copyright (c) 2016 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
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  PIM hello message format  . . . . . . . . . . . . . . . . . .   3
     3.1.  DR Address Option format  . . . . . . . . . . . . . . . .   3
     3.2.  BDR Address Option format . . . . . . . . . . . . . . . .   4
   4.  The Protocol Treatment  . . . . . . . . . . . . . . . . . . .   4
     4.1.  Election Algorithm  . . . . . . . . . . . . . . . . . . .   5
     4.2.  Sending Hello Messages  . . . . . . . . . . . . . . . . .   6
     4.3.  Receiving Hello Messages  . . . . . . . . . . . . . . . .   6
     4.4.  The treatment . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Deployment suggestion . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Multicast technology is used widely.  Many modern technology use PIM
   technology, such as IPTV, Net-Meeting, and so on.  There are many
   events that will influence the quality of multicast services.  The
   change of unicast routes will cause the lost of multicast packets.
   The change of DR cause the lost of multicast packets too.

   When a DR on a share-media LAN is down, other routers will elect a
   new DR until the expiration of Hello-Holdtime.  The default value of
   Hello-Holdtime is 105 seconds.  Although the value of Hello-Holdtime
   can be changed by manual, when the DR is down, there are still many
   multicast packets will be lost.  The quality of IPTV and Net-Meeting
   will be influenced.

                   \                                     /
                    \                                   /
                  -------                             -------
                  |  A  |                             |  B  |
                  -------                             -------
                     | DR                                |
                     |                                   |
                  -------                             -------
                  | SW  |-----------------------------| SW  |
                  -------                             -------
                     |                                   |
                   Figure 1: An example of multicast network

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   For example, there were two routers on one Ethernet.  RouterA was
   elected to DR.  When RouterA is down, the multicast packets are
   discarded until the RouterB is elected to DR and RouterB imports the
   multicast flows successfully.

   We suppose that there is only a RouterA in the Ethernet at first in
   Figure 1.  RouterA is the DR which is responsible for forwarding
   multicast flows.  When RouterB connects the Ethernet, RouterB will be
   elected to DR because a higher priority.  So RouterA will stop
   forwarding multicast packets.  The multicast flows will not recover
   until RouterB joins the multicast group after it is elected to DR.

2.  Terminology

   Backup Designated Router (BDR): A shared-media LAN like Ethernet may
   have multiple PIM-SM routers connected to it.  Except for DR, a
   router which will act on behalf of directly connected hosts with
   respect to the PIM-SM protocol.  But BDR will not forward the flows.
   When DR is down, the BDR will forward multicast flows immediately.  A
   single BDR is elected per interface like the DR.

3.  PIM hello message format

   In [RFC4601] and [RFC7761], the PIM hello message format was defined.
   In this document, we define two new option values which are including
   Type, Length, and Value.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        |                   Hello message format                      |
        |                                                             |
        +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        |         OptionType            +       OptionLength          |
        +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        |                       OptionValue                           |
        |                                                             |
        +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                   Figure 2: Hello message format

3.1.  DR Address Option format

   o  OptionType : The value is TBD.

   o  OptionLength: If the network is support IPv4, the OptionLength is
      4 octets.  If the network is support IPv6, the OptionLength is 16
      octets.

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   o  OptionValue: The OptionValue is IP address of DR.  If the network
      is support IPv4, the value is IPv4 address of DR.  If the network
      is support IPv6, the value is IPv6 address of DR.

3.2.  BDR Address Option format

   o  OptionType : The value is TBD.

   o  OptionLength: If the network is support IPv4, the OptionLength is
      4 octets.  If the network is support IPv6, the OptionLength is 16
      octets.

   o  OptionValue: The OptionValue is IP address of BDR.  If the network
      is support IPv4, the value is IPv4 address of BDR.  If the network
      is support IPv6, the value is IPv6 address of BDR.

4.  The Protocol Treatment

   A new router starts to send hello messages with the values of DR and
   BDR are all set to 0 after its interface is enabled in PIM on a
   share-media LAN.  When the router receives hello messages from other
   routers on the same share-media LAN, the router will check if the
   value of DR is filled.  If the value of DR is filled with IP address
   of router which is sending hello messages, the router will store the
   IP address as the DR address of this interface.

   Then the new router compare the priority and IP address itself to the
   stored IP address of DR and BDR according to the algorithm of
   [RFC4601] and [RFC7761].  If the new router notices that it is better
   to be DR than the existed DR or BDR.  The router will make itself the
   BDR, and send new hello messages with its IP address as BDR and
   existed DR.  If the router notices that the existed DR has the
   highest priority in the share-media LAN, but the existed BDR is set
   to 0x0 in the received hello messages, or the existed BDR is not
   better than the new router, the new router will elect itself to BDR.
   If the router notices that it is not better to be DR than existed DR
   and BDR, the router will respect the existed DR and BDR.

   When the new router becomes the new BDR, the router will join the
   existed multicast groups, import multicast flows from upstream
   routers.  But the BDR MUST not forward the multicast flows to avoid
   the duplicate multicast packets in the share-media LAN.  The new
   router will monitor the DR.  The method that BDR monitors the DR may
   be BFD technology or other ways that can be used to detect link/node
   failure quickly.  When the DR becomes unavailable because of the down
   or other reasons, the BDR will forward multicast flows immediately.

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4.1.  Election Algorithm

   The DR and BDR election is according the rules defined below, the
   algorithm is similar to the DR election definition in [RFC2328].

   (1) Note the current values for the network's Designated Router and
   Backup Designated Router.  This is used later for comparison
   purposes.

   (2) Calculate the new Backup Designated Router for the network as
   follows.  Those routers that have not declared themselves to be
   Designated Router are eligible to become Backup Designated Router.
   The one which have the highest priority will be chosen to be Backup
   Designed Router.  In case of a tie, the one having the highest Router
   ID is chosen.

   (3) Calculate the new Designated Router for the network as follows.
   If one or more of the routers have declared themselves Designated
   Router (i.e., they are currently listing themselves as Designated
   Router in their Hello Packets) the one having highest Router Priority
   is declared to be Designated Router.  In case of a tie, the one
   having the highest Router ID is chosen.  If no routers have declared
   themselves Designated Router, assign the Designated Router to be the
   same as the newly elected Backup Designated Router.

   (4) If Router X is now newly the Designated Router or newly the
   Backup Designated Router, or is now no longer the Designated Router
   or no longer the Backup Designated Router, repeat steps 2 and 3, and
   then proceed to step 5.  For example, if Router X is now the
   Designated Router, when step 2 is repeated X will no longer be
   eligible for Backup Designated Router election.  Among other things,
   this will ensure that no router will declare itself both Backup
   Designated Router and Designated Router.

   (5) As a result of these calculations, the router itself may now be
   Designated Router or Backup Designated Router.

   The reason behind the election algorithm's complexity is the desire
   for the DR stability.

   The above procedure may elect the same router to be both Designated
   Router and Backup Designated Router, although that router will never
   be the calculating router (Router X) itself.  The elected Designated
   Router may not be the router having the highest Router Priority.  If
   Router X is not itself eligible to become Designated Router, it is
   possible that neither a Backup Designated Router nor a Designated
   Router will be selected in the above procedure.  Note also that if
   Router X is the only attached router that is eligible to become

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   Designated Router, it will select itself as Designated Router and
   there will be no Backup Designated Router for the network.

4.2.  Sending Hello Messages

   According to Section 4.3.1 in [RFC4601] and [RFC7761], when a new
   router's interface is enabled in PIM protocol, the router send hello
   messages with the values of DR and BDR are filled with 0x0.  Then the
   interface is in waiting state and start the hold-timer which is like
   the neighbor hold-timer.  When the hold-timer is expired, the
   interface will elect the DR and BDR according to the DR election
   rules.

   When a new router sets itself BDR after receive hello messages from
   other routers, the router send hello messages with the value of DR is
   set to the IP address of existed DR and the value of BDR is set to
   the IP address of the router itself.

   When a existed BDR sets itself non DR and non BDR after receive hello
   messages from other routers, the router will send hello messages with
   the value of DR is set to existed DR and the value of BDR is set to
   new BDR.

                  DR                                newcomer
                   \                                  /
                    -----       -----           -----
                    | A |       | B |           | C |
                    -----       -----           -----
                      |           |               |
                      |           |               |
              ------------------------------------------- LAN
                               Figure 3

   For example, there is a stable LAN that include RouterA and RouterB.
   RouterA is the DR which has the best priority.  RouterC is a
   newcomer.  RouterC sends hello packet with the DR and BDR is all set
   to zero.

   If RouterC cannot send hello packet with the DR/BDR capability,
   Router C may send the hello packet according the rule defined
   in[RFC4601] and [RFC7761].

4.3.  Receiving Hello Messages

   When the values of DR and BDR which are carried by hello messages are
   received is all set to 0x0, the router MUST elect the DR due to the
   algorithm of [RFC4601] and [RFC7761] after the hold-timer expires.
   And elect a new BDR which are the best choice except DR.

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   In case the value of DR which is carried by received hello messages
   is not 0x0, and the value of BDR is set to 0x0, when the hold-timer
   expires there is no hello packet from other router is received, the
   router will elect itself to BDR.

   In case the values of DR and BDR that are carried by received hello
   messages are all larger than 0x0.  The router will mark the existed
   DR, and compare itself and the BDR in message.  When the router
   notice that it is better to be DR than existed BDR.  The router will
   elect itself to the BDR.

   When a router receives a new hello message with the values of DR and
   BDR are set to 0x0.  The router will compare the new router with
   existed information.  If the router noticed that the new router is
   better to be DR than itself, or the new router is better to be BDR
   than the existed BDR, the router will set the BDR to the new router.

   As illustrated in Figure 3, after RouterC sends hello packet, RouterC
   will not elect the DR until hold-timer expired.  During the period,
   RouterC should receive the hello packets from RouterA and RouterB.
   RouterC accepts the result that RouterA is the DR.  In case RouterC
   has the lowest priority than RouterA and RouterB, RouterC will also
   accept that Router B is the BDR.  In case RouterC has the
   intermediate priority among the three routers, RouterC will treat
   itself as new BDR after the hold-timer expired.  In case RouterC has
   the highest priority among the three routers, RouterC will treat
   RouterA which is the existed DR as DR, and RouterC will treat itself
   as new BDR.  If the network administrator thinks that RouterC should
   be new DR, the DR changing should be triggered manually.

   Exception: During the hold-timer period, RouterC receives only the
   hello packet from RouterA.  When the hold-timer expired, RouterC
   treats RouterA as DR. and RouterC treats itself as BDR.  In case
   RouterC only receives the hello packet from RouterB during the hold-
   timer period, RouterC will compare the priority between RouterB and
   itself to elect the new DR.  In these situations, some interfaces or
   links go wrong in the LAN.

4.4.  The treatment

   When all the routers on a shared-media LAN are start to work on the
   same time, the election result of DR is same as [RFC4601] and
   [RFC7761].  And all the routers will elect a BDR which is suboptimum
   to DR.  The routers in the network will store the DR and BDR.  The
   hello messages sent by all the routers are same with the value of DR
   and BDR are all set.

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   When a new router start to work on a shared-media LAN and receive
   hello messages from other routers that the value of DR is set.  The
   new router will not change the existed DR even if it is superior to
   the existed DR.  If the new router is superior to existed BDR, the
   new router will replace the existed BDR.

   When the routers receive hello message from a new router, the routers
   will compare the new router and all the other routers on the LAN.  If
   the new router is superior to existed BDR, the new router will be new
   BDR.  Then the old BDR will send prune message to upstream routers.

   As a result, the BDR is the one which has the highest priority except
   DR.  Once the DR is elected, the DR will not change until it fails or
   manually adjustment.  After the DR and BDR are elected, the routers
   in the network will store the address of DR and BDR.

5.  Compatibility

   If the LAN is a hybrid network that there are some routers which have
   DR/BDR capability and the other routers which have not DR/BDR
   capability.  In order to avoid duplicated multicast flows in the LAN,
   all the routers should go backward to use the algorithm defined in
   [RFC4601] and [RFC7761].

6.  Deployment suggestion

   If there are two and more routers on a share-media LAN, and the
   multicast services is sensitive to the lost of multicast packets, the
   function of DR and BDR defined in this document should be deployed.

7.  Security Considerations

   For general PIM Security Considerations.

8.  IANA Considerations

   IANA is requested to allocate OptionTypes in TLVs of hello message.
   Include DR and BDR.

9.  Normative References

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

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   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601,
              DOI 10.17487/RFC4601, August 2006,
              <http://www.rfc-editor.org/info/rfc4601>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <http://www.rfc-editor.org/info/rfc7761>.

Authors' Addresses

   Zheng(Sandy) Zhang
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: zhang.zheng@zte.com.cn

   Fangwei Hu
   ZTE Corporation
   No.889 Bibo Rd
   Shanghai
   China

   Email: hu.fangwei@zte.com.cn

   BenChong Xu
   ZTE Corporation
   No. 68 Zijinghua Road, Yuhuatai Distinct
   Nanjing
   China

   Email: xu.benchong@zte.com.cn

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