PIM DR Improvement
draft-ietf-pim-dr-improvement-09

Document Type Active Internet-Draft (pim WG)
Last updated 2019-10-25
Stream IETF
Intended RFC status Proposed Standard
Formats plain text pdf htmlized bibtex
Stream WG state Submitted to IESG for Publication
Document shepherd Stig Venaas
Shepherd write-up Show (last changed 2019-10-27)
IESG IESG state Publication Requested
Consensus Boilerplate Yes
Telechat date
Responsible AD Alvaro Retana
Send notices to Stig Venaas <stig@venaas.com>
PIM WG                                                      Zheng. Zhang
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                             Fangwei. Hu
Expires: April 27, 2020                                       Individual
                                                            Benchong. Xu
                                                         ZTE Corporation
                                                       Mankamana. Mishra
                                                           Cisco Systems
                                                        October 25, 2019

                           PIM DR Improvement
                  draft-ietf-pim-dr-improvement-09.txt

Abstract

   Protocol Independent Multicast - Sparse Mode (PIM-SM) is widely
   deployed multicast protocol.  As deployment for PIM protocol is
   growing day by day, user expects lower traffic loss and faster
   convergence in case of any network failure.  This document provides
   an extension to the existing protocol which would improve the
   stability of the PIM protocol with respect to traffic loss and
   convergence time when the PIM DR role changes.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 27, 2020.

Copyright Notice

   Copyright (c) 2019 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

Zhang, et al.            Expires April 27, 2020                 [Page 1]
Internet-Draft             PIM DR Improvement               October 2019

   (https://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.  Code Components extracted from this document must
   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.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  PIM hello message format  . . . . . . . . . . . . . . . . . .   4
     3.1.  DR Address Option format  . . . . . . . . . . . . . . . .   4
     3.2.  BDR Address Option format . . . . . . . . . . . . . . . .   4
   4.  Protocol Specification  . . . . . . . . . . . . . . . . . . .   5
     4.1.  Deployment Choice . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Election Algorithm  . . . . . . . . . . . . . . . . . . .   6
     4.3.  Sending Hello Messages  . . . . . . . . . . . . . . . . .   7
     4.4.  Receiving Hello Messages  . . . . . . . . . . . . . . . .   8
     4.5.  The treatment . . . . . . . . . . . . . . . . . . . . . .   9
     4.6.  Sender side . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Multicast technology is used widely.  Many modern technologies, such
   as IPTV, Net-Meeting, use PIM-SM to facilitate multicast service.
   There are many events that will influence the quality of multicast
   services.  Like the change of unicast routes, the change of the PIM-
   SM DR may cause the loss of multicast packets too.

   After a DR on a shared-media LAN goes down, other routers will elect
   a new DR after the expiration of Hello-Holdtime.  The default value
   of Hello-Holdtime is 105 seconds.  Although the minimum Hello
   interval can be adjusted to 1 second, the Hello-Holdtime is 3.5 times
   Hello interval.  Thus, the detection of DR Down event cannot be
   guaranteed in less than 3.5 seconds.  And it is too long for modern
   multicast services.  Still, many multicast packets will be lost.  The
   quality of IPTV and Net-Meeting will be influenced.

Zhang, et al.            Expires April 27, 2020                 [Page 2]
Internet-Draft             PIM DR Improvement               October 2019

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

   For example, there are two routers on one LAN.  Two SWs (Layer 2
   switches) provide shared-media LAN connection.  RouterA is elected as
   DR.  When RouterA goes 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 LAN at first in
   Figure 1.  RouterA is the DR which is responsible for forwarding
   multicast flows.  When RouterB connects to the LAN, RouterB will be
   elected as DR because of its higher priority.  RouterA will stop
   forwarding multicast packets.  The multicast flows will not recover
   until RouterB pulls the multicast flows after it is elected to DR.

   So if we want to increase the stability of DR, carrying DR/ BDR role
   information in PIM hello packet is a feasible way to show the DR/ BDR
   roles explicitly.  It avoids the confusion caused by newcomers which
   have a higher priority.

1.1.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   Backup Designated Router (BDR): Like DR (Designated Router), a BDR
   which acts on behalf of directly connected hosts in a shared-media
   LAN.  But BDR must not forward the flows when DR works normally.
   When DR goes down, the BDR will forward multicast flows immediately.
   A single BDR MUST be elected per interface like the DR.

Zhang, et al.            Expires April 27, 2020                 [Page 3]
Internet-Draft             PIM DR Improvement               October 2019

   Designated Router Other (DROther): A router which is neither DR nor
   BDR.

3.  PIM hello message format

   The PIM hello message format is defined in [RFC7761].  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 TBD1.

   o  OptionLength: If the IP version of PIM message is IPv4, the
      OptionLength is 4 octets.  If the IP version of PIM message is
      IPv6, the OptionLength is 16 octets.

   o  OptionValue: The OptionValue is IP address of DR.  If the IP
      version of PIM message is IPv4, the value is the IPv4 address of
      DR.  If the IP version of PIM message is IPv6, the value is the
      IPv6 address of DR.

3.2.  BDR Address Option format

   o  OptionType : The value is TBD2.

   o  OptionLength: If the IP version of PIM message is IPv4, the
      OptionLength is 4 octets.  If the IP version of PIM message is
      IPv6, the OptionLength is 16 octets.

   o  OptionValue: The OptionValue is IP address of BDR.  If the IP
      version of PIM message is IPv4, the value is the IPv4 address of
      BDR.  If the IP version of PIM message is IPv6, the value is the
      IPv6 address of BDR.

Zhang, et al.            Expires April 27, 2020                 [Page 4]
Internet-Draft             PIM DR Improvement               October 2019

4.  Protocol Specification

   Carrying DR/ BDR role information in PIM hello packet is a feasible
   way to keep the stability of DR.  It avoids the confusion caused by
   newcomers which have a higher priority.  So there are some changes in
   PIM hello procedure and interface state machine.

   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
   shared-media LAN.  When the router receives hello messages from other
   routers on the same shared-media LAN, the router will check if the
   value of DR is filled.  If the value of DR is filled with IP address
   of the router which is sending hello messages, the router will store
   the IP address as the DR address of this interface.

   Then the new router compares the priority and IP address itself to
   the stored information of DR and BDR according to the algorithm of
   [RFC7761].  If the new router notices that it is better to be DR than
   the current DR or BDR, the new router will make itself the BDR, and
   send new hello messages with its IP address as BDR and current DR.
   If the router notices that the current DR has the highest priority in
   the shared-media LAN, but the current BDR is set to 0.0.0.0 if IPv4
   addresses are in use or 0:0:0:0:0:0:0:0/128 if IPv6 addresses are in
   use in the received hello messages (To simplify, we use 0x0 in
   abbreviation in following parts of the draft), or the current 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
   current DR and BDR, the router will follow the current DR and BDR.

   When the new router becomes the new BDR, the router will join the
   current multicast groups, and import multicast flows from upstream
   routers.  But the BDR must not forward the multicast flows to avoid
   the duplicate multicast packets in the shared-media LAN.  The new
   router will monitor the DR.  The method that BDR monitors the DR may
   be Bidirectional Forwarding Detection (BFD) for Multi-point Networks
   and Protocol Independent Multicast [I-D.ietf-pim-bfd-p2mp-use-case]
   technology, BFD (Bidirectional Forwarding Detection) [RFC5880]
   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.

   BFD for PIM function defined in [I-D.ietf-pim-bfd-p2mp-use-case], or
   asynchronous mode defined in BFD [RFC5880] are suggested to be used
   for the DR failure detection.  BDR monitors DR after the BFD session
   between DR and BDR is established.  For example, an aggressive BFD
   session that achieves a detection time of 300 milliseconds, by using
   a transmit interval of 100 milliseconds and a detect multiplier of 3.
   So BDR can replace DR to forward flows when DR goes down within sub

Zhang, et al.            Expires April 27, 2020                 [Page 5]
Internet-Draft             PIM DR Improvement               October 2019

   second.  The other BFD modes can also be used to monitor the failure
   of DR, the network administrator should choose the most suitable
   function.

4.1.  Deployment Choice

   DR / BDR election SHOULD be handled in two ways.  Selection of which
   procedure to use would be totally dependent on deployment scenario.

   1.  The algorithm defined in [RFC7761] should be used if it is ok to
   adopt with new DR as and when they are available, and the loss caused
   by DR changing is acceptable.

   2.  If the deployment requirement is to have minimum packets loss
   when DR changing, the mechanism defined in this draft should be used.
   That is, if the new router notices that it is better to be DR than
   the current DR or BDR, the new router will make itself the BDR, and
   send new hello message with its IP address as BDR and current DR.

   According to section 4.9.2 defined in [RFC7761], the device receives
   unknown options Hello packet will ignore it.  So the new extension
   defined in this draft will not influence the stability of neighbor.
   But if the router which has the ability defined in this draft
   receives non-DR/BDR capable Hello messages defined in [RFC7761], the
   router MAY stop sending DR/BDR capable Hello messages in the LAN and
   go back to use the advertisement and election algorithm defined in
   [RFC7761].

4.2.  Election Algorithm

   The DR and BDR election is according to the rules defined below, the
   algorithm is similar to the DR election defined 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.  The router that has not declared itself to be Designated
   Router is eligible to become Backup Designated Router.  The one which
   has the highest priority will be chosen to be Backup Designated
   Router.  In case of a tie, the one having the highest primary address
   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

Zhang, et al.            Expires April 27, 2020                 [Page 6]
Internet-Draft             PIM DR Improvement               October 2019

   is declared to be Designated Router.  In case of a tie, the one
   having the highest primary address 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
   Designated Router, it will select itself as Designated Router and
   there will be no Backup Designated Router for the network.

4.3.  Sending Hello Messages

   According to Section 4.3.1 in [RFC7761], when a new router's
   interface is enabled in PIM protocol, the router sends Hello messages
   with the values of DR and BDR are filled with 0x0.  Then the
   interface is in Waiting state and starts the hold-timer which is
   equal to the Neighbor Liveness Timer.  When the 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 receives hello messages from
   other routers, the router sends hello messages with the value of DR
   is set to the IP address of current DR and the value of BDR is set to
   the IP address of the router itself.

   A current BDR MUST set itself DROther after it receives Hello
   messages from other router which is eligible to be BDR/DR, the router

Zhang, et al.            Expires April 27, 2020                 [Page 7]
Internet-Draft             PIM DR Improvement               October 2019

   will send hello messages with the value of DR is set to current DR
   and the value of BDR is set to the new BDR.

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

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

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

   If deployment requirement is to adopt with a new DR when it is
   available, a new router with the highest priority or the highest IP
   address sends hello packet with DR and BDR are all set to zero at
   first.  It sends hello packet with itself set to DR after it finish
   join all the existing multicast groups.  Then current DR compares
   with the new router, the new router will be the final DR.

4.4.  Receiving Hello Messages

   When the values of DR and BDR which are carried by hello messages
   received are all set to 0x0, the router MUST elect the DR using
   procedure defined in DR election algorithm after the hold-timer
   expires.  And elect a new BDR which is the best choice except DR.
   The election cases can be executed as follows:

   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 either of the values of DR and BDR that are carried by
   received hello messages is greater than 0x0.  The router will mark
   the current DR, and compare itself with the BDR in the message.  When
   the router notices that it is better to be DR than the current BDR.
   The router will elect itself to the BDR.

Zhang, et al.            Expires April 27, 2020                 [Page 8]
Internet-Draft             PIM DR Improvement               October 2019

   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
   current 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 current BDR, the router will set the BDR to the new router.

   When current DR receives hello packet with the value of DR is set
   larger than zero, the algorithm defined in section 4.2 can be used to
   select the final DR.

   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 current DR as DR, and RouterC will treat itself
   as the new BDR.  If the network administrator thinks that RouterC
   should be the new DR, the DR changing should be triggered manually.
   That is RouterC will be elected as DR after it sends hello message
   with DR is set to RouterC itself.

   Exception: In case RouterC receives only the hello packet from
   RouterA during the hold-timer period, 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.

4.5.  The treatment

   If all the routers on a shared-media LAN have started working at the
   same time, then the election result of DR is same as the definition
   in [RFC7761].  And all the routers will elect a BDR which is next
   best to DR.  The routers in the network MUST store the DR and BDR.
   The hello messages sent by all the routers are the same with the
   value of DR and BDR are all set.  When a new router is activated on
   the shared-media LAN and receives hello messages from other routers
   with the value of DR is already set.  The new router will not change
   the current DR even if it is superior to the current DR.  If the new
   router is superior to current BDR, the new router will replace the
   current BDR.

Zhang, et al.            Expires April 27, 2020                 [Page 9]
Internet-Draft             PIM DR Improvement               October 2019

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

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

4.6.  Sender side

   DR/BDR function is also used in source side that multiple routers and
   source is in a same shared-media LAN.  The algorithm is the same as
   the receiver side.  Only the BDR need not build multicast tree from a
   downstream router.

5.  Compatibility

   If the LAN is a hybrid network that there are some routers which
   support DR/BDR capability and the other routers which do not support
   DR/BDR capability.  All the routers MUST go backward to use the
   election algorithm defined in [RFC7761].  And the values of DR and
   BDR carried in hello message MUST be set to zero.  That is once a
   router sends hello messages with no DR/BDR options, the DR election
   MUST go backward to the definition in [RFC7761].

   If the routers find that all the routers in the LAN support DR/BDR
   capability by the hello messages with DR/BDR options set, they MUST
   elect DR and BDR according the algorithm defined in this document.
   And the routers MUST send hello messages with correct DR/BDR options
   set.

   In case there is only one router which does not support DR/BDR
   capability in a shared-media LAN, the other routers in the LAN send
   hello messages with the values of DR and BDR are set to zero, the
   router which does not support DR/BDR capability ignores the options.
   All the routers elect DR according to the algorithm defined in
   [RFC7761].  When the router which does not support DR/BDR capability
   goes away, the routers in the LAN MUST elect DR/BDR according to the
   algorithm defined in this document, and send hello messages with
   correct DR/BDR options set.

   This draft allows DR election to be sticky by not unnecessarily
   changing the DR when routers go down or come up.  This is done by
   introducing new PIM Hello options.  Both this draft, and the draft
   [I-D.mankamana-pim-bdr], introduce a backup DR.  The latter draft

Zhang, et al.            Expires April 27, 2020                [Page 10]
Internet-Draft             PIM DR Improvement               October 2019

   does this without introducing new options, but does not consider the
   sticky behavior.

6.  Security Considerations

   If an attacker which has the highest priority participates in the DR
   election when a shared-media LAN starts to work, it will be elected
   as DR, but it may not forward flows to receivers.  And the attacker
   remains DR position even if a legal router which has a higher
   priority joins the LAN.

   If an attacker is a newcomer which has a higher priority than the
   existed BDR, it will be elected as the new BDR, but it may not
   monitor DR, import multicast flows and forward flows to receiver when
   DR is down.

   In order to avoid these situations, source authentication should be
   used to identify the validity of the DR/BDR candidates.
   Authentication methods mentioned in section 6 RFC7761 can be used.

   And the network administrator should consider the potential BFD
   session attack if BFD is used between BDR and DR for DR failure
   detection.  The security function mentioned in section 9 RFC5880 can
   be used.

7.  IANA Considerations

   IANA is requested to allocate two new code points from the "PIM-Hello
   Options" registry within the Protocol Independent Multicast (PIM)
   Parameters;

               +------+--------------------+---------------+
               | Type | Description        | Reference     |
               +------+--------------------+---------------+
               | TBD1 | DR Address Option  | This Document |
               | TBD2 | BDR Address Option | This Document |
               +------+--------------------+---------------+

                                  Table 1

8.  Acknowledgements

   The authors would like to thank Greg Mirsky, Jake Holland, Stig
   Venaas for their valuable comments and suggestions.

Zhang, et al.            Expires April 27, 2020                [Page 11]
Internet-Draft             PIM DR Improvement               October 2019

9.  References

9.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [I-D.ietf-pim-bfd-p2mp-use-case]
              Mirsky, G. and J. Xiaoli, "Bidirectional Forwarding
              Detection (BFD) for Multi-point Networks and Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Use Case",
              draft-ietf-pim-bfd-p2mp-use-case-02 (work in progress),
              July 2019.

   [I-D.mankamana-pim-bdr]
              mishra, m., Goh, J., and G. Mishra, "PIM Backup Designated
              Router Procedure", draft-mankamana-pim-bdr-03 (work in
              progress), October 2019.

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

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

Authors' Addresses

Zhang, et al.            Expires April 27, 2020                [Page 12]
Internet-Draft             PIM DR Improvement               October 2019

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

   Email: zhang.zheng@zte.com.cn

   Fangwei Hu
   Individual
   Shanghai
   China

   Email: hufwei@gmail.com

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

   Email: xu.benchong@zte.com.cn

   Mankamana Mishra
   Cisco Systems
   821 Alder Drive,
   MILPITAS, CALIFORNIA 95035
   UNITED STATES

   Email: mankamis@cisco.com

Zhang, et al.            Expires April 27, 2020                [Page 13]