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BESS Workgroup                                                   J. Chen
Internet Draft
Intended status: Standards Track                                     H3C


Expires: May 20, 2018                                       Nov 27, 2017




                  EVPN DF Election Algorithm Selection
             draft-chen-bess-evpn-df-algorithm-selection-00

Abstract

   This document describes a new EVPN Designated Forwarder Election (DF)
   method which can be used to select a proper DF Election algorithm.


Status of this Memo

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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



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   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
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2. Specification of Requirements . . . . . . . . . . . . . . . . .  3
   3. Solution requirements  . . . . . .  . . . . . . . . . . . . . .  3
   4. EVPN BGP Attributes for DF Election . . . . . . . . . . . . . .  3
   5. Solution description  . . . . . . . . . . . . . . . . . . . . .  4
     5.1 Use of the DF Type Priority  . . . . . . . . . . . . . . . .  4
   6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  5
   7. Security Considerations . . . . . . . . . . . . . . . . . . . .  5
   8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  5
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     9.1 Normative References . . . . . . . . . . . . . . . . . . . .  5
     9.2 Informative References . . . . . . . . . . . . . . . . . . .  6
   Authors' Addresses  .  . . . . . . . . . . . . . . . . . . . . . .  6




1. Introduction

   IN RFC7432, the Designated Forwarder (DF) in (PBB-)EVPN networks is
   the PE responsible for ccertain actions:

   o Sending multicast and broadcast traffic, on a given Ethernet tag on
   a particular Ethernet segment, to the CE.

   o Flooding unknown unicast traffic (i.e., traffic for which a PE does
   not know the destination MAC address), on a given Ethernet tag on a
   particular Ethernet segment to the CE, if the environment requires
   flooding of unknown unicast traffic.

   The DF is selected out of a candidate list of PEs at the granularity
   of <ES, VLAN> or <ES, VLAN bundle> as the default procedure. This is
   refereed to as "service carving".

   Besides 'service-carving', there are also many other efficient and
   automated way of selecting the DF.



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   This document proposes an extension to the current RFC7432 DF
   election procedures to select a proper way for DF election.

2. Specification of Requirements

   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].

3. Solution requirements

   This document proposes an extension for 'service-carving' with the
   following requirements:

   a) An administrative priority option provided for controlling the
   order of candidate DF Election Algorithms MAY be used.

4. EVPN BGP Attributes for DF Election

   This solution reuses and extends the DF Election Extended Community
   defined in [EVPN-HRW-DF] that is advertised along with the ES route:


   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(TBD) |   DF Type     | Reserved = 0  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | DF Type Prio  |  Reserved = 0 |    Reserved = 0               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o The definition of DF Type is outside the scope of this document and
   can have the following values :

   - Type 0 - Default, mod based DF election as per RFC7432.
   - Type 1 - HRW algorithm as per [EVPN-HRW-DF]
   - Type 2 and so on - To be determined

   o DF Type Prio or DF Type Priority defines a 1-octect value indicates
     the priority that PE uses the DF Type. The allowed values are
     within the range 0-255 inclusive, and default value MUST be 0. This
     value stands for lowest priority. If PEs advertise different
     priority for one ES, the minimum will be used.









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5. Solution description

   Figure 1 gives an example that will be used in the description of the
   solution.


            +-------------------+
            |                +-------+
            |                |  PE1  | <---ESI1, DF type 1, Priority 100
            |                |       | <---ESI1, DF type 2, Priority 200
            |                |       |
        +-----+              |       |
   CEs--+PEs  |              +-------+
        +-----+                 |
            |                   |
            |                 +-----+
            |                 | PE2 | <---ESI1, DF type 1, Priority 50
            |                 +-----+ <---ESI1, DF type 2, Priority 100
            |                   |
            |                 +-----+
            |                 | PE3 + <---ESI1, DF type 1, Priority 100
            |                 +-----+
            --------------------+

                  Figure 1 DF Election Method

   Figure 1 shows three PEs that are connecting to the same ES in the
   EVPN network.

   If all the PEs use the DF election method described in this document,
   DF type 1 will become the DF election algorithm. The following
   sections provide some examples of the new defined procedures and how
   they are applied in the use-case in Figure 1.


5.1 Use of the DF Type Priority

   Assuming the operator wants to control globally - in a flexible way -
   what DF election algorithm to be used for a given ES . The following
   procedure may be used:

   a) PEs (or ES1 in PEs) are now configurable with two optional
      parameters that are signaled in the DF Election extended
      community. These parameters are the DF algorithm type and
      Priority. We will represent these parameters as [(DF Type, DF Type
      Priority), (DF Type, DF Type Priority) ...]. Let's assume PE1 is
      configured as [(1, 100), (2, 200)], [(1, 50), (2, 100)] in PE2 and
      [(1, 100)] in PE3.



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   b) The PEs will advertise an ES route for each ES (here ESI 1),
      including the 2 parameters in one or more DF Election Extended
      Community. Each DF type needs one DF Election Extended Community
      except the DF type 0 with the priority 0.

   c) According to RFC7432, each PE will wait for the DF timer to expire
      before running the DF election algorithm. After the timer expires,
      each PE runs the DF election method as follows:

      o Each PE builds a list of candidate DF election algorithms that
        are supported by all PEs, ordered based on the Priority. E.g.
        PE1 will build a list of candidate DF election algorithms for
        ESI1 by the Priority, from high to low: (DF type 1, 50), (DF
        type 0, 0). Hence the DF type 1 will be used as DF election
        algorithm.

      o Each PE uses the selected DF election algorithm to elect a
        proper DF for ESI1.

   d) In case of equal Priority for two or more DF types, the tie-
      breakers will be the highest DF type number in that order. For
      instance:

      o If the DF list is [(2, 50), (1, 50), (0, 0)], DF type 2 will be
        used.

   e) The DF type and Priority are administrative options that may be
      configured on a per-ES/per-device basis from the management plane
      or fixed by device capability. The definition of the actual local
      policies is out of scope of this document.

6. IANA Considerations

   This document solicits the addition of DFT Priority field in the
   registry created by [EVPN-HRW-DF].

7. Security Considerations

   This section will be added in future versions.

8. Acknowledgments

   TBD.

9. References

9.1 Normative References




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   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac,
   A.,Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet
   VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015, <http://www.rfc-
   editor.org/info/rfc7432>.

   [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>.

9.2 Informative References

   [EVPN-HRW-DF] Mohanty S. et al. "A new Designated Forwarder Election
   for the EVPN", draft-mohanty-bess-evpn-df-election-02, work-in-
   progress, October 19, 2015.

   [EVPN-PREF-DF] Rabadan J., Ed. et al. "Preference-based EVPN DF
   Election", draft-ietf-bess-evpn-pref-df-00, work-in- progress, June
   21, 2017.

Authors' Addresses
   Jian Chen
   H3C
   Email: jian_chen@h3c.com




























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