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Versions: 00 01

BESS Working Group                                           Yisong Liu
Internet Draft                                               Individual
Intended status: Standards Track                             M. McBride
Expires: May 26, 2020                                         Futurewei
                                                           Nov 26, 2019



       Multicast DF Election for EVPN based on bandwidth or quantity
            draft-liu-bess-evpn-mcast-bw-quantity-df-election-01


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   Section 4.e of the Trust Legal Provisions and are provided without
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Abstract

   Ethernet Virtual Private Network (EVPN, RFC7432) is becoming
   prevalent in Data Centers, Data Center Interconnect (DCI) and
   Service Provider VPN applications. When multi-homing from a CE to
   multiple PEs, including links in an EVPN instance on a given
   Ethernet Segment, in an all-active redundancy mode, [RFC7432]
   describes a basic mechanism to elect a Designated Forwarder (DF),
   and [RFC8584] improves basic DF election by a HRW algorithm. [I-
   D.ietf-bess-evpn-per-mcast-flow-df-election] enhances the HRW
   algorithm for the multicast flows to perform DF election at the
   granularity of (ESI, VLAN, Mcast flow). This document specifies a
   new algorithm, based on multicast bandwidth utilization and
   multicast state quantity, in order for the multicast flows to elect
   a DF.

Table of Contents


   1. Introduction ................................................ 2
      1.1. Requirements Language .................................. 3
      1.2. Terminology ............................................ 4
   2. Solution .................................................... 4
      2.1. DF Election Based on Bandwidth ......................... 5
      2.2. DF Election Based on State Qunatity .................... 5
      2.3. Inconsistent Timing between Multi-homed PEs ............ 5
      2.4. Increase or Decrease of Multi-homed PEs ................ 6
         2.4.1. Decrease of Multi-homed PEs ....................... 6
         2.4.2. Increase of Multi-homed PEs ....................... 6
   3. BGP Encoding ................................................ 7
      3.1. DF Election Extended Community ......................... 7
      3.2. Multicast DF Extended Community ........................ 8
   4. Security Considerations  .................................... 8
   5. IANA Considerations ......................................... 8
   6. References .................................................. 9
      6.1. Normative References ................................... 9
      6.2. Informative References ................................. 9
   7. Acknowledgments ............................................. 9
   Authors? Addresses ............................................ 11

1. Introduction

   Ethernet Virtual Private Network (EVPN [RFC7432]) solutions are
   becoming prevalent in Data Centers, Data Center Interconnect (DCI)
   and Service Provider VPN applications. When multi-homing from a CE

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   to multiple PEs, with links in an EVPN instance on a given Ethernet
   Segment (ES), in an all-active redundancy mode, [RFC7432] defines
   the role of Designated Forwarder (DF) as the node that is
   responsible to forward multicast flows.

   Per [RFC7432], the basic method of DF election is specified. The
   same ES is sorted in ascending order according to the IP address of
   the EVPN peer. The PE set is generated, and then the number of PEs
   is modulo according to the VLAN. The modulo value is equal to the
   position of the PE in the PE set. The election is the primary DF of
   the corresponding VLAN, and the other PEs are elected as standby.

   [RFC8584] defines extended community attributes for DF elections,
   which can be extended to use different DF election algorithms and
   would be used for PEs in a redundancy group to reach a consensus as
   to which DF election procedure is desired. A PE can notify other
   participating PEs in a redundancy group about its DF election
   algorithm by signaling a DF election extended community along with
   the ES route. The document also improves the basic DF election by a
   HRW algorithm.

   [I-D.ietf-bess-evpn-per-mcast-flow-df-election] proposes a method
   for DF election by enhancing the HRW algorithm, adding the source
   and group address of the multicast flow as hash factors, and
   extending the types 4 and 5 of the extended community of the DF
   election for (S, G) and (*, G) types for different multicast flows.
   The source and group address is introduced as new elements to HRW
   algorithm, and the PE with the largest weight is selected as the DF
   of the multicast flow.

   However, the relationship between the bandwidth of the multicast
   flows and the link capacity of different PEs, to the same CE device,
   is not considered in any of the current DF election algorithms. This
   may result in severe bandwidth utilization of different links due to
   different bandwidth usage of multicast flows. This document
   specifies a new algorithm for multicast flow DF election based on
   multicast bandwidth or multicast state quantity and extends the
   existing extended community defined in [I-D.ietf-bess-evpn-df-
   election-framework].

1.1. Requirements Language

   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.


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1.2. Terminology

   CE: Customer Edge equipment

   PE: Provider Edge device

   EVPN: Ethernet Virtual Private Network

   Ethernet Segment (ES): When a customer site (device or network) is
   connected to one or more PEs via a set of Ethernet links, then that
   set of links is referred to as an 'Ethernet segment'.

   IGMP: Internet Group Management Protocol

   MLD: Multicast Listener Discovery

   PIM: Protocol Independent Multicast

2. Solution

   In the DF election calculation, the bandwidth weight of each multi-
   homed link of the PE is added, and the bandwidth occupation of the
   multicast flows is calculated and divided into two scenarios:

   * The specific bandwidth value of the multicast flow exists, and the
   ratio of the current multicast flow bandwidth value to the link
   bandwidth weight is calculated according to the bandwidth weight of
   each multi-homed link, and the link with the smallest ratio is
   elected as the new multicast flow DF.

   * The specific bandwidth value of the multicast flow does not exist,
   and the ratio of the current multicast flow state quantity to the
   link bandwidth weight is calculated according to the bandwidth
   weight of each multi-homed link, and the link with the smallest
   ratio is elected as the new multicast flow DF.

   In particular, if there are multiple PEs with the same calculated
   ratio, the DF is elected according to the method of maximum
   bandwidth weight of the link or maximum IP address of the EVPN peer.

   Since [I-D.ietf-idr-link-bandwidth] defines the link bandwidth
   extended community, it can be reused to transfer the link bandwidth
   value of the local ES to other multi-homed PEs, so that each PE can
   calculate the bandwidth weight ratio of each link of the ES in
   advance.




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2.1. DF Election Based on Bandwidth

   Each PE obtains the link bandwidth values of the other multi-homed
   PEs in the same EVPN instance on a given ES according to the
   extended community of the Link bandwidth, and calculates the link
   bandwidth weight ratio, for example W1:W2:...:Wn for N multi-homed
   PEs.

   When the CE sends an IGMP or PIM join to one of the PEs, like PE1,
   PE1 advertises the PE2, PE3, ... and PEn by the EVPN IGMP/PIM Join
   Synch route defined in [I-D.ietf-bess-evpn-igmp-mld-proxy] and [I-
   D.skr-bess-evpn-pim-proxy]. If PE2, PE3, ... or PEn receives an IGMP
   or PIM join, the procedure will be the same.

   Each PE calculates the ratio of the current multicast flows
   bandwidth to the link bandwidth weight. The one PE in PE1, PE2, ...
   and PEn, which has the smallest ratio, is elected as the DF of the
   new multicast flow. When the smallest ratios of more than one PE are
   the same, the PE with the maximum bandwidth weight of the link or
   the maximum EVPN peer IP address is elected as the DF.

2.2. DF Election Based on State Qunatity

   The procedure is almost the same as described in section 2.1. The
   only difference is that each PE calculates the ratio of the current
   number of multicast states instead of the bandwidth to the link
   bandwidth weight because of lacking specific bandwidth value of the
   multicast flows.

2.3. Inconsistent Timing between Multi-homed PEs

   As a result of the same multicast join, only one of the multi-homed
   PEs can receive the multicast join message and advertise the EVPN
   Join Synch route (Type 7). The other PEs need to install the new
   multicast join state according to the received Synch route.

   The inconsistent processing timing of the same multicast group
   joining process between PEs may cause electing different DFs. For
   example:

   * Multicast group G1, G2, and G3 join packets are sent from the CE
   to PE1, PE2 and PE3.

   * PE1 calculates the DF of G1, while PE2 calculates the DF of G2,
   and PE calculates the DF of G3, and at this moment each PE has not
   received the EVPN Join Synch route.



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   * PE1, PE2 and PE3 select the link on the same ES to the CE using
   the algorithm as described in section 2.1 or 2.2, and the same DF
   may be elected for G1, G2, and G3.

   * After receiving the EVPN Join Synch route sent by PE2, PE1 may
   calculate the DF of G2 as PE3, which is inconsistent with the
   calculation result of PE2.

   The DF calculation results of the PEs are inconsistent, which may
   result in multiple flows or traffic interruptions of the same
   multicast flow state. Therefore, EVPN Join Synch routes need to
   carry elected DF information in the route advertisement as the
   extended community called Multicast DF Extended Community, which can
   make the DF information for a given multicast flow state between PEs
   consistent. The actual effect is that the PE that receives the
   multicast join packet completes the calculation of the DF election
   and notifies other PEs on the same ES.

2.4. Increase or Decrease of Multi-homed PEs

2.4.1. Decrease of Multi-homed PEs

   When one of the multi-homed PEs on the same ES fails or is shut down
   for maintenance reasons, because the other PEs have received the
   synch routes of all the multicast flows, the multicast flows
   destined to the failed PE need to be in a specific order (for
   example, the group and source address ascending order) to reassign
   the DF. The DF election calculation based on the multicast flows
   bandwidth, or the number of multicast states, is completed by one of
   the specified multi-homing PEs, and the specified calculated PE can
   be selected according to the link bandwidth weight value or the IP
   address of the EVPN peer. The specified PE needs to advertise each
   DF election result of the multicast flow that belongs to the
   original faulty PE to the other multi-homed PEs that belong to the
   same ES by the EVPN Join Synch route carrying the Multicast DF
   Extended Community.

   If a new multicast join is received in the above calculation
   process, the DF election calculation of the new multicast flow is
   still completed by the PE receiving the multicast join packet.
   Similarly, the PE needs to advertise the DF information to other
   multi-homed PEs belonging to the same ES by the EVPN Join Synch
   route carrying the Multicast DF Extended Community.

2.4.2. Increase of Multi-homed PEs

   One multi-homing PE of the same ES is added, and no active
   adjustment can be performed. The DF of the subsequent new multicast

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   flow is elected according to the algorithm of this document. The new
   multicast flow must be preferentially assigned to the new PE, and
   finally the multicast flows on the PEs of the same ES are
   approximately equalized.

   If active adjustment is required, consider calculating the ratio
   using the algorithm as described in section 2.1 and 2.2. Each time
   the multicast entries in the PE, whose ratio of the existing multi-
   homed PE is the largest, are migrated to the new PE. The multicast
   entries are migrated in descending order of multicast flow bandwidth
   or in ascending order of the group and source address until the
   ratio of the new PE is greater than the existing smallest ratio of
   other multi-homed PEs.

   The calculation of the active adjustment is still performed by one
   specific PE among the multi-homed PEs. The specified calculated PE
   can be selected according to the link bandwidth weight value or the
   IP address of the EVPN peer.

   After the new PE is started, in the synchronization process of all
   the multicast entries of other multi-homed PEs, the existing
   multicast join packet may be received on the new PE. To avoid having
   the existing multicast join appear as a new multicast join, and
   recalculating the DF and notifying the other PEs belonging to the
   same ES, it is necessary to start a timer to suppress the
   synchronization process from the new PE to other existing PE's. The
   timer range should also be configured.

3. BGP Encoding

3.1. DF Election Extended Community

   [RFC8584] defines an extended community, which would be used for
   multi-homed PEs to reach a consensus as to which DF election
   procedure is desired. A PE can notify other participating PEs its DF
   election capability by signaling a DF election extended community
   along with Ethernet-Segment Route (Type-4). The current document
   extends the existing extended community defined in [RFC8584]. This
   document defines a new DF type.

   o  DF type (1 octet) - Encodes the DF Election algorithm values
   (between 0 and 255) that the advertising PE desires to use for the
   ES.

   *  Type TBD1: Based on bandwidth of multicast flow DF
   election(detailed in this document)



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   *  Type TBD2: Based on quantity of multicast flow state DF
   election(detailed in this document)

3.2. Multicast DF Extended Community



   This document defines a new extended community in EVPN Type 7 route
   to notify other multi-homed PEs the elected DF of a given multicast
   flow. The new extended community is called Multicast DF Extended
   Community and it belongs to the transitive extended community. The
   type is to be assigned. It is used to carry DF information of a
   given (S,G) or (*,G) multicast flow selection. The role of this
   extended community has been described in sections 2.3 and 2.4.



       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type=0x06   | Sub-Type=TBD3 |    Reserved   |  DF Length    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  DF IP Address(Variable)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o Type is 0x06 as registered with IANA for EVPN Extended Communities

   o Sub-Type: TBD3

   o DF Length: the length of the DF IP Address field, 4 octets for
   IPv4 address, 16 octets for IPv6 address

   o DF IP Address: the elected DF IP address of the given (S,G) or
   (*,G) route in the EVPN type 7 route

4. Security Considerations

   For general EVPN Security Considerations, see [RFC7432].

   TBD

5. IANA Considerations

   TBD




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6. References

6.1. Normative References

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

   [RFC7432] A. Sajassi, Ed., R. Aggarwal, N. Bitar, A. Isaac, J.
             Uttaro, J. Drake, and W. Henderickx, "BGP MPLS-Based
             Ethernet VPN", RFC 7432, February 2015

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
             2119 Key Words", BCP 14, RFC 8174, May 2017

   [RFC8584] J. Rabadan Ed., S. Mohanty, Ed., A. Sajassi, J. Drake, K.
             Nagaraj and S. Sathappan, " Framework for Ethernet VPN
             Designated Forwarder Election Extensibility ", RFC8584,
             April 2019.

   [I-D.ietf-bess-evpn-per-mcast-flow-df-election] Ali Sajassi,
             Mankamana Mishra, Samir Thoria, Jorge Rabadan and John
             Drake, " Per multicast flow Designated Forwarder Election
             for EVPN ", November 2019, work-in-progress, draft-ietf-
             bess-evpn-per-mcast-flow-df-election-02.

   [I-D.ietf-idr-link-bandwidth] P. Mohapatra and R. Fernando, " BGP
             Link Bandwidth Extended Community ", March 2018, expired,
             draft-ietf-idr-link-bandwidth-07.

   [I-D.ietf-bess-evpn-igmp-mld-proxy] Ali Sajassi, Samir Thoria, Keyur
             Patel, John Drake and Wen Lin, "IGMP and MLD
             Proxy for EVPN", September 2019, work-in-progress, draft-
             ietf-bess-evpn-igmp-mld-proxy-04.

   [I-D.skr-bess-evpn-pim-proxy] J. Rabadan, Ed., J. Kotalwar, S.
             Sathappan, Z. Zhang and A. Sajassi, "PIM Proxy in EVPN
             Networks", October 2017, expired, draft-skr-evpn-bess-pim-
             proxy-01.

6.2. Informative References

   TBD

7. Acknowledgments

   The authors would like to thank the following for their valuable
   contributions of this document:


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   TBD














































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Authors' Addresses

   Yisong Liu
   Individual

   Email: liuyisong.ietf@gmail.com


   Mike McBride
   Futurewei Inc.

   Email: michael.mcbride@futurewei.com




































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