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Versions: 00 01 02 draft-ietf-bess-evpn-pref-df

BESS Workgroup                                           J. Rabadan, Ed.
Internet Draft                                              S. Sathappan
Intended status: Standards Track                          Alcatel-Lucent

                                                           T. Przygienda
                                                                Ericsson

                                                                  W. Lin
                                                                T. Singh
                                                        Juniper Networks

                                                              A. Sajassi
                                                              S. Mohanty
                                                           Cisco Systems

Expires: May 28, 2016                                  November 25, 2015




                   Preference-based EVPN DF Election
                   draft-rabadan-bess-evpn-pref-df-00

Abstract

   RFC7432 defines the Designated Forwarder (DF) in (PBB-)EVPN networks
   as the PE responsible for sending broadcast, multicast and unknown
   unicast traffic (BUM) to a multi-homed device/network in the case of
   an all-active multi-homing ES, or BUM and unicast in the case of
   single-active multi-homing.

   The DF is selected out of a candidate list of PEs that advertise the
   Ethernet Segment Identifier (ESI) to the EVPN network, according to
   the 'service-carving' algorithm.

   While 'service-carving' provides an efficient and automated way of
   selecting the DF across different EVIs or ISIDs in the ES, there are
   some use-cases where a more 'deterministic' and user-controlled
   method is required. At the same time, Service Providers require an
   easy way to force an on-demand DF switchover in order to carry out
   some maintenance tasks on the existing DF or control whether a new
   active PE can preempt the existing DF PE.

   This document proposes an extension to the current RFC7432 DF
   election procedures so that the above requirements can be met.


Status of this Memo



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Table of Contents

   1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Solution requirements . . . . . . . . . . . . . . . . . . . . .  3
   3. EVPN BGP Attributes for Deterministic DF Election . . . . . . .  4
   4. Solution description  . . . . . . . . . . . . . . . . . . . . .  5
     4.1 Use of the Preference algorithm  . . . . . . . . . . . . . .  5
     4.2 Use of the Preference algorithm in RFC7432
         Ethernet-Segments  . . . . . . . . . . . . . . . . . . . . .  7
     4.3 The Non-Revertive option . . . . . . . . . . . . . . . . . .  7



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   5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   11. Conventions used in this document  . . . . . . . . . . . . . .  9
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     15.1 Normative References  . . . . . . . . . . . . . . . . . . . 10
     15.2 Informative References  . . . . . . . . . . . . . . . . . . 10
   16. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   17. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
   17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10




1. Problem Statement

   RFC7432 defines the Designated Forwarder (DF) in (PBB-)EVPN networks
   as the PE responsible for sending broadcast, multicast and unknown
   unicast traffic (BUM) to a multi-homed device/network in the case of
   an all-active multi-homing ES or BUM and unicast traffic to a multi-
   homed device or network.

   The DF is selected out of a candidate list of PEs that advertise the
   Ethernet Segment Identifier (ESI) to the EVPN network and according
   to the 'service-carving' algorithm.

   While 'service-carving' provides an efficient and automated way of
   selecting the DF across different EVIs or ISIDs in the ES, there are
   some use-cases where a more 'deterministic' and user-controlled
   method is required. At the same time, Service Providers require an
   easy way to force an on-demand DF switchover in order to carry out
   some maintenance tasks on the existing DF or control whether a new
   active PE can preempt the existing DF PE.

   This document proposes an extension to the current RFC7432 DF
   election procedures so that the above requirements can be met.


2. Solution requirements

   This document proposes an extension of the RFC7432 'service-carving'
   DF election algorithm motivated by the following requirements:

   a) The solution MUST provide an administrative preference option so
      that the user can control in what order the candidate PEs may
      become DF, assuming they are all operationally ready to take over.

   b) This extension MUST work for RFC7432 Ethernet Segments (ES) and



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      virtual ES, as defined in [vES].

   c) The user MUST be able to force a PE to preempt the existing DF for
      a given EVI/ISID without re-configuring all the PEs in the ES.

   d) The solution SHOULD allow an option to NOT preempt the current DF,
      even if the former DF PE comes back up after a failure. This is
      also known as "non-revertive" behavior, as opposed to the RFC7432
      DF election procedures that are always revertive.

   e) The solution MUST work for single-active and all-active multi-
      homing Ethernet Segments.


3. EVPN BGP Attributes for Deterministic 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     |DP| Reserved=0 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Reserved = 0                 |    DF Preference (2 octets)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Where the following fields are re-defined as follows:

   o DF Type 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 - Preference algorithm (this document)

   o DP or 'Don't Preempt' bit, determines if the PE advertising the ES
     route requests the remote PEs in the ES not to preempt it as DF.
     The default value is DP=0, which is compatible with the current
     'preempt' or 'revertive' behavior in RFC7432. The DP bit SHOULD be
     ignored if the DF Type is different than 2.

   o DF Preference defines a 2-octet value that indicates the PE
     preference to become the DF in the ES. The default value MUST be
     32767. This value is the midpoint in the allowed Preference range
     of values, which gives the operator the flexibility of choosing a
     significant number of values, above or below the default
     Preference.



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4. Solution description

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


                 EVPN network
            +-------------------+
            |                +-------+  ENNI    Aggregation
            |   <---ESI1,500 |  PE1  |   /\  +----Network---+
            | <-----ESI2,100 |       |===||===              |
            |                |       |===||== \      vES1   |  +----+
        +-----+              |       |   \/  |\----------------+CE1 |
   CE3--+ PE4 |              +-------+       | \   ------------+    |
        +-----+                 |            |  \ /         |  +----+
            |                   |            |   X          |
            |   <---ESI1,255  +-----+============ \         |
            | <-----ESI2,200  | PE2 |==========    \ vES2   | +----+
            |                 +-----+        | \    ----------+CE2 |
            |                   |            |  --------------|    |
            |                 +-----+   ----------------------+    |
            | <-----ESI2,300  | PE3 +--/     |              | +----+
            |                 +-----+        +--------------+
            --------------------+

                  Figure 1 ES and Deterministic DF Election

   Figure 1 shows three PEs that are connecting EVCs coming from the
   Aggregation Network to their EVIs in the EVPN network. CE1 is
   connected to vES1 - that spans PE1 and PE2 - and CE2 is connected to
   vES2, that is defined in PE1, PE2 and PE3.

   If the algorithm chosen for vES1 and vES2 is type 2, i.e. Preference-
   based, the PEs may become DF irrespective of their IP address and
   based on an administrative Preference value. The following sections
   provide some examples of the new defined procedures and how they are
   applied in the use-case in Figure 1.


4.1 Use of the Preference algorithm

   Assuming the operator wants to control - in a flexible way - what PE
   becomes the DF for a given vES and the order in which the PEs become
   DF in case of multiple failures, the following procedure may be used:

   a) vES1 and vES2 are now configurable with three optional parameters
      that are signaled in the DF Election extended community. These
      parameters are the Preference, Preemption option (or "Don't



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      Preempt Me" option) and DF algorithm type. We will represent these
      parameters as [Pref,DP,type]. Let's assume vES1 is configured as
      [500,0,Pref] in PE1, and [255,0,Pref] in PE2. vES2 is configured
      as [100,0,Pref], [200,0,Pref] and [300,0,Pref] in PE1, PE2 and PE3
      respectively.

   b) The PEs will advertise an ES route for each vES, including the 3
      parameters in the DF Election Extended Community.

   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 Preference-based DF election algorithm as
      follows:

      o The PE will check the DF type in each ES route, and assuming all
        the ES routes are consistent in this DF type and the value is 2
        (Preference-based), the PE will run the new extended procedure.
        Otherwise, the procedure will fall back to RFC7432 'service-
        carving'.

      o In this extended procedure, each PE builds a list of candidate
        PEs, ordered based on the Preference. E.g. PE1 will build a list
        of candidate PEs for vES1 ordered by the Preference, from high
        to low: PE1>PE2. Hence PE1 will become the DF for vES1. In the
        same way, PE3 becomes the DF for vES2.

   d) Note that, by default, the Highest-Preference is chosen for each
      ES or vES, however the ES configuration can be changed to the
      Lowest-Preference algorithm as long as this option is consistent
      in all the PEs in the ES. E.g. vES1 could have been explicitly
      configured as type Preference-based with Lowest-Preference, in
      which case, PE2 would have been the DF.

   e) Assuming some maintenance tasks had to be executed on PE3, the
      operator could set vES2's preference to e.g. 50 so that PE2 is
      forced to take over as DF for vES2. Once the maintenance on PE3 is
      over, the operator could decide to leave the existing preference
      or configure the old preference back.

   f) In case of equal Preference in two or more PEs in the ES, the tie-
      breakers will be the DP bit and the lowest IP PE in that order.
      For instance:

      o If vES1 parameters were [500,0,Pref] in PE1 and [500,1,Pref] in
        PE2, PE2 would be elected due to the DP bit.

      o If vES1 parameters were [500,0,Pref] in PE1 and [500,0,Pref] in
        PE2, PE1 would be elected, assuming PE1's IP address is lower



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        than PE2's.

   g) The Preference is an administrative option that MUST be configured
      on a per-ES basis from the management plane, but MAY also be
      dynamically changed based on the use of local policies. For
      instance, on PE1, ES1's Preference can be lowered from 500 to 100
      in case the bandwidth on the ENNI port is decreased a 50% (that
      could happen if e.g. the 2-port LAG between PE1 and the
      Aggregation Network loses one port). Policies MAY also trigger
      dynamic Preference changes based on the PE's bandwidth
      availability in the core, of specific ports going operationally
      down, etc. The definition of the actual local policies is out of
      scope of this document. The default Preference value is 32767.


4.2 Use of the Preference algorithm in RFC7432 Ethernet-Segments

   While the Preference-based DF type described in section 4.1 is
   typically used in virtual ES scenarios where there is normally an
   individual EVI per vES, the existing RFC7432 definition of ES allows
   potentially up to thousands of EVIs on the same ES. If this is the
   case, and the operator still wants to control who the DF is for a
   given EVI, the use of the Preference-based DF type can also provide
   the desired level of load balancing.

   In this type of scenarios, the ES is configured with an
   administrative Preference value, but then a range of EVI/ISIDs can be
   defined to use the Highest-Preference or the Lowest-Preference
   depending on the desired behavior. With this option, the PE will
   build a list of candidate PEs ordered by the Preference, however the
   DF for a given EVI/ISID will be determined by the local
   configuration.

   For instance:

   o Assuming ES3 is defined in PE1 and PE2, PE1 may be configured as
     [500,0,Preference] for ES3 and PE2 as [100,0,Preference].

   o In addition, assuming vlan-based service interfaces, the PEs will
     be configured with (vlan/ISID-range,high_or_low), e.g. (1-
     2000,high) and (2001-4000, low).

   o This will result in PE1 being DF for EVI/ISIDs 1-2000 and PE2 being
     DF for EVI/ISIDs 2001-4000.

4.3 The Non-Revertive option

   As discussed in section 2(d), an option to NOT preempt the existing



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   DF for a given EVI/ISID is required and therefore added to the DF
   Election extended community. This option will allow a non-revertive
   behavior in the DF election.

   Note that, when a given PE in an ES is taken down for maintenance
   operations, before bringing it back, the Preference may be changed in
   order to provide a non-revertive behavior. The DP bit and the
   mechanism explained in this section will be used for those cases when
   a former DF comes back up without any controlled maintenance
   operation, and the non-revertive option is desired in order to avoid
   service impact.

   In Figure 1, we assume that based on the Highest-Pref, PE3 is the DF
   for ESI2.

   If PE3 has a link, EVC or node failure, PE2 would take over as DF.
   If/when PE3 comes back up again, PE3 will take over, causing some
   unnecessary packet loss in the ES.

   The following procedure avoids preemption upon failure recovery
   (please refer to Figure 1):

   1) A new "Don't Preempt Me" parameter is defined on a per-PE per-ES
      basis. If "Don't Preempt Me" is disabled (default behavior) the
      advertised DP bit will be 0. If "Don't Preempt Me" is enabled on a
      PE, the ES route will be advertised with DP=1 ("Don't Preempt Me")
      once the DF timer is expired and the DF elected.

   2) Assuming we want to avoid 'preemption', the three PEs are
      configured with the "Don't Preempt Me" option. Note that each PE
      individually MAY be configured with different preemption value. In
      this example, we assume ESI2 is configured as 'DP=disabled' in PE1
      but 'DP=enabled' in PE2 and PE3.

   3) When ES2 is enabled in the three PEs, and after the DF timer, the
      PEs (due to the Highest-Pref type) select PE3 as DF for EVI1. Only
      after the timer and the DF election, the PEs will check the 'DP'
      configuration and since it is enabled on PE2 and PE3, these two
      PEs will send an ES route update, now with DP=1. This update will
      not cause any change in the existing DFs since there is no change
      in the Preference value.

   4) If PE3's vES2 goes down (due to EVC failure - detected by OAM, or
      port failure or node failure), PE2 will become the DF for
      ESI2/EVI1.

   5) When PE3's vES2 comes back up, PE3 will start a boot-timer (if
      booting up) or hold-timer (if the port or EVC recovers). That



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      timer will allow some time for PE3 to receive the ES routes from
      PE1 and PE2. PE3 will then check its own
      [Pref,DP,type]=[300,1,Pref] and if its Pref is higher than any of
      the other PE's Pref, then PE3 will send the ES route with an 'in-
      use' Preference equal to the highest received Preference. In this
      case, since PE2 advertised [Pref,DP,type]=[200,1,Pref], PE3 will
      then send [200,0,Pref].

      Note that, a PE will always send DP=0 the first time it advertises
      an ES route after the ES becomes active, and irrespective of the
      configuration. Also a PE will always send DP=0 as long as the
      advertised Pref is the 'in-use' Pref (as opposed to the 'admin'
      Pref).

      This ES route update sent by PE3 (with [200,0,Pref]) will not
      cause any changes in the DF election and PE2 will continue being
      DF. This is because the DP bit will be used as a tie-breaker in
      the DF election. That is, if a PE has two candidate PEs with the
      same Pref, it will pick up the one with DP=1.

   6) Only in case of PE2's failure, PE3 will become DF again (assuming
      it wins the DF election to PE1), and will resend the ES route with
      the admin Pref (as opposed to the 'in-use' Pref) and the DP bit
      that corresponds to its configuration.


5. Conclusions

   Service Providers are seeking for options where the DF election can
   be controlled by the user in a deterministic way and with a non-
   revertive behavior. This document defines the use of a Preference
   algorithm that can be configured and used in a flexible manner to
   achieve those objectives.


11. Conventions used in this document

   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].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

   In this document, the characters ">>" preceding an indented line(s)
   indicates a compliance requirement statement using the key words
   listed above. This convention aids reviewers in quickly identifying



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   or finding the explicit compliance requirements of this RFC.

12. Security Considerations

   This section will be added in future versions.

13. IANA Considerations

   This document solicits the allocation of DF type = 2 in the registry
   created by [vES] for the DF type field.

15. References

15.1 Normative References


   [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>.



15.2 Informative References

   [vES] Sajassi et al. "EVPN Virtual Ethernet Segment", draft-sajassi-
   bess-evpn-virtual-eth-segment-01, work-in-progress, July 6, 2015.

   [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.

16. Acknowledgments


17. Contributors

   In addition to the authors listed, the following individuals also
   contributed to this document:

   Vinod Prabhu, ALU
   Kiran Nagaraj, ALU
   John Drake, Juniper
   Selvakumar Sivaraj, Juniper


17. Authors' Addresses




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   Jorge Rabadan
   Alcatel-Lucent
   777 E. Middlefield Road
   Mountain View, CA 94043 USA
   Email: jorge.rabadan@alcatel-lucent.com

   Senthil Sathappan
   Alcatel-Lucent
   Email: senthil.sathappan@alcatel-lucent.com

   Tony Przygienda
   Ericsson
   Email: antoni.przygienda@ericsson.com

   Tapraj Singh
   Juniper Networks, Inc.
   Email: tsingh@juniper.net

   Wen Lin
   Juniper Networks, Inc.
   Email: wlin@juniper.net

   Ali Sajassi
   Cisco Systems, Inc.
   Email: sajassi@cisco.com

   Satya Ranjan Mohanty
   Cisco Systems, Inc.
   Email: satyamoh@cisco.com






















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