BESS Workgroup                                           J. Rabadan Rabadan, Ed.
Internet Draft                                                K. Nagaraj
                                                            S. Sathappan
Intended status: Informational                                 V. Prabhu
                                                           W. Henderickx

                                                                  A. Liu

                                                                  W. Lin
                                                        Juniper Networks

Expires: April 14, July 22, 2018                                  January 18, 2018                                 October 11, 2017

          AC-Influenced Designated Forwarder Election for EVPN


   The Designated Forwarder (DF) in EVPN networks is the PE responsible
   for sending multicast, broadcast and unknown unicast traffic to a
   multi-homed CE, on a given Ethernet Tag on a particular Ethernet
   Segment (ES). The DF is selected based on the list of PEs that
   advertise the Ethernet Segment Identifier (ESI) to the EVPN network.
   While PE node or link failures trigger the DF re-election for a given
   <ESI, EVI>, individual Attachment Circuit (AC) or MAC-VRF failures do
   not trigger such DF re-election and the traffic may therefore be
   permanently impacted, even though there is an alternative path. This
   document improves the DF election algorithm so that the AC status can
   influence the result of the election and this type of "logical"
   failures can be protected too.

Status of this Memo

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Table of Contents

   1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Solution Description  . . . . . . . . . . . . . . . . . . . . .  4
     2.1. Current DF Election Procedure And AC Failures . . . . . . .  5
     2.2. The Attachment Circuit (AC) Influenced DF Election  . . . .  6
     2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services  .  7
   3. Solution benefits . . . . . . . . . . . . . . . . . . . . . . .  8
   4. Conventions used in this document . . . . . . . . . . . . . . .  8
   5. Security Considerations . . . . . . . . . . . . . . . . . . . .  8  9
   6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  8  9
   7. References  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1. Normative References  . . . . . . . . . . . . . . . . . . .  9
     7.2. Informative References  . . . . . . . . . . . . . . . . . .  9
   8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  9
   9. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9 10

1. Problem Statement

   [RFC7432] defines the Designated Forwarder (DF) as the EVPN PE
   responsible for:

   o Flooding Broadcast, Unknown unicast and Multicast traffic (BUM), on
     a given Ethernet Tag on a particular Ethernet Segment (ES), to the
     CE. This is valid for single-active and all-active EVPN

   o Sending unicast traffic on a given Ethernet Tag on a particular ES
     to the CE. This is valid for single-active multi-homing.

   The default DF election algorithm defined by [RFC7432] is called
   service-carving and, for a given ES, is based on a (V mod N)= i
   function that provides a local DF election of a PEi at <ESI, EVI>
   level. V is the Ethernet Tag associated to the EVI (the numerically
   lowest Ethernet Tag value in case of multiple Ethernet Tags), whereas
   N is the number of PEs for which ES routes have been successfully
   imported. In other words, EVPN's service-carving takes into account
   only two variables in the DF election for a given ESI: the existence
   of the PE's IP address on the candidate list and the locally
   provisioned Ethernet Tags.

   If the DF for an <ESI, EVI> fails (due to physical link/node
   failures) an ES route withdrawn will make the Non-DF (NDF) PEs re-
   elect the DF for that <ESI, EVI> and the service will be recovered.

   However the current DF election procedure does not provide a
   protection against "logical" failures or human errors that may occur
   at service level on the DF, while the list of active PEs for a given
   ES does not change. These failures may have an impact not only on the
   local PE where the issue happens, but also on the rest of the PEs of
   the ES. Some examples of such logical failures are listed below:

   a) A given individual Attachment Circuit (AC) defined in an ES is
      accidentally shutdown or even not provisioned yet (hence the
      Attachment Circuit Status - ACS - is DOWN), while the ES is
      operationally active (since the ES route is active).

   b) A given MAC-VRF - with an ES defined - is shutdown or not
      provisioned yet, while the ES is operationally active (since the
      ES route is active). In this case, the ACS of all the AC defined
      in that MAC-VRF is considered to be DOWN.

   Neither (a) nor (b) will trigger the DF re-election on the remote PEs
   for a given ES since the ACS is not taken into account in the DF
   election procedures. While the ACS is used as a DF election tie-
   breaker and trigger in [VPLS-MH], there is no procedure defined in
   [RFC7432] to trigger the DF re-election based on the ACS change on
   the DF.

   This document improves the [RFC7432] service-carving procedure so
   that the ACS may be taken into account as a variable in the DF
   election, and therefore EVPN can provide protection against logical

2. Solution Description

   The ACS for a given Ethernet Tag on an ES is implicitly conveyed in
   the corresponding EVPN A-D per EVI route for that given <ESI,
   Ethernet Tag>. This section describes how to use the A-D per EVI
   routes to improve the DF election algorithm.

   Figure 1 illustrates an example EVPN network that will be used to
   describe the proposed solution.

   EVI-1 is defined in PE-1, PE-2, PE-3 and PE-4. CE12 is a multi-homed
   CE connected to ESI12 in PE-1 and PE-2. Similarly CE23 is multi-homed
   to PE-2 and PE-3 using ESI23. Both, CE12 and CE23, are connected to
   EVI-1 through VLAN-based service interfaces: CE12-VID 1 (VLAN ID 1 on
   CE12) is associated to AC1 and AC2 in EVI-1, whereas CE23-VID 1 is
   associated to AC3 and AC4 in EVI-1. Note that there are other ACs
   defined on these ES mapped to different EVIs.

                            PE-4 |
           +---------------|  +-----+  |---------------+
           |               |  |EVI-1|  |               |
           |               +-----------+               |
           |                                           |
           |                   EVPN                    |
           |                                           |
           | PE-1              PE-2               PE-3 |
           | (NDF)             (DF)               (NDF)|
       +-----------+       +-----------+       +-----------+
       |  |EVI-1|  |       |  |EVI-1|  |       |  |EVI-1|  |
       |  +-----+  |-------|  +-----+  |-------|  +-----+  |
       +-----------+       +-----------+       +-----------+
              AC1\   ESI12  /AC2  AC3\   ESI23  /AC4
                  \        /          \        /
                   \      /            \      /
                    +----+              +----+
                    |CE12|              |CE23|
                    +----+              +----+

                       Figure 1 EVPN network example

2.1. Current DF Election Procedure And AC Failures

   After running the service-carving DF election algorithm, PE-2 turns
   out to be the DF for ESI12 and ESI23 in EVI-1. The following two
   examples illustrate the issues with the existing defined procedure in

   a) If AC2 is accidentally shutdown or even not configured, CE12
   traffic will be impacted. In case of all-active multi-homing, only the BUM
   traffic to CE12 will be impacted, "black-holed", whereas for single-active
   multi-homing all the traffic to/from CE12 will be discarded. This is
   due to the fact that a logical failure in PE-2 AC2 may not trigger an
   ES route withdrawn for ESI12 (since there are still other ACs active
   on ESI12) and therefore PE-1 will not re-run the DF election

   b) If EVI-1 is administratively shutdown or even not configured yet
   on PE-2, CE12 and CE23 will both be impacted: BUM traffic to both CEs
   will be discarded in case of all-active multi-homing and all traffic
   will be discarded to/from the CEs in case of single-active
   multi-homing. This is due to the fact that PE-1 and PE-3 will not
   re-run the DF election procedures and will keep assuming PE-2 is the

   According to [RFC7432], "when an Ethernet tag is decommissioned on an
   Ethernet segment, then the PE MUST withdraw the Ethernet A-D per EVI
   route(s) announced for the <ESI, Ethernet tags> that are impacted by
   the decommissioning", however, while this A-D per EVI route
   withdrawal is used at the remote PEs performing aliasing or backup
   procedures, it is not used to influence the DF election for the
   affected EVIs.

2.2. The Attachment Circuit (AC) Influenced DF Election

   Modifying the service-carving DF election procedure in the following
   way solves the issue:

   1. When PE-1 and PE-2 discover ESI12, they advertise an ES route for
      ESI12 with the associated ES-import extended community, starting a
      timer at the same time. Likewise, PE-2 and PE-3 advertise an ES
      route for ESI23 and start a timer.

   2. Similarly, PE-1 and PE-2 advertise an Ethernet A-D per ES route
      for ESI12, and PE-2/PE-3 advertise an Ethernet A-D per ES route
      for ESI23.

   3. In addition, PE-1/PE-2/PE-3 advertise an Ethernet A-D per EVI
      route for AC1, AC2, AC3 and AC4 as soon as the ACs are enabled.
      Note that the AC can be associated to a single customer VID (e.g.
      VLAN-based service interfaces) or a bundle of customer VIDs (e.g.
      VLAN-bundle service interfaces).

   4. When the timer expires, each PE builds an ordered "candidate" list
      of the IP addresses of all the PE nodes connected to the Ethernet
      Segment (including itself), in increasing numeric order. The
      candidate list is based on the Originator Router's IP addresses of
      the ES routes, excluding all the PEs for which no Ethernet A-D per
      ES route has been received.

   5. When electing the DF for a given EVI, a PE will not be considered
      candidate until an Ethernet A-D per EVI route has been received
      from that PE. In other words, the ACS on the ESI for a given PE
      must be UP so that the PE is considered as candidate for a given
      EVI. For example, PE-1 will not consider PE-2 as candidate for DF
      election for <ESI12, EVI-1> until an Ethernet A-D per EVI route is
      received from PE-2 for <ESI12, EVI-1>.

   6. Once the PEs with ACS = DOWN for a given EVI have been eliminated
      from the candidate list, the (V mod N) = i function can be applied
      for the remaining N candidates, as per [RFC7432].

   Note that this procedure does not modify the existing EVPN control
   plane whatsoever. It only modifies the candidate list of PEs taken
   into account for the DF election algorithm defined in [RFC7432].

   In addition to the procedure described above, the following events
   SHALL modify the candidate PE list and trigger the DF re-election in
   a PE for a given <ESI,EVI>:

   a) Local ES going DOWN due to a physical failure or reception of an
      ES route withdraw for that ESI.

   b) Local ES going UP due to its detection/configuration or reception
      of a new ES route update for that ESI.

   c) Local AC going DOWN/UP.

   d) Reception of a new Ethernet A-D per EVI update/withdraw for the
      <ESI, EVI>.

   e) Reception of a new Ethernet A-D per ES update/withdraw for the

   This procedure is backwards compatible with the DF election
   procedures described in [RFC7432] since it does not add any new
   extension in the control plane, however, a PE not supporting the
   procedures in this document SHOULD NOT share a multi-homed ES with a
   PE following this solution since both PEs may end up with an
   inconsistent view on who the DF is. The AC influenced DF election
   procedures SHOULD be enabled by an administrative option and only
   used when all the PEs in the ES support it.

   The procedure discussed in this section is applicable to the DF
   Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire
   Services [RFC8214].

2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services

   The procedure described section 2.2 works for VLAN-based and VLAN-
   bundle service interfaces since, for those service types, a PE
   advertises only one Ethernet A-D per EVI route per <ESI,EVI>. The
   withdrawal of such route means that the PE cannot forward traffic on
   that particular <ESI,EVI>.

   In VLAN-aware bundle services, the PE advertises multiple Ethernet A-
   D per EVI routes per <ESI,EVI> (one route per Ethernet Tag). The
   withdrawal of an individual route only indicates the unavailability
   of a specific AC but not necessarily all the ACs in the <ESI,EVI>.

   For the specific case of VLAN-aware bundle services, the DF election
   will be influenced by the update/withdraw of any of the Ethernet A-D
   per EVI routes in the <ESI,EVI>.

   For example, assuming three bridge tables in PE-1 for the same MAC-
   VRF (each one associated to a different Ethernet Tag), PE-1 will
   advertise three Ethernet A-D per EVI routes for <ESI12,EVI1>. Each of
   the three routes will indicate the status of each AC in <ESI12,EVI1>.
   PE-1 will be considered as a valid candidate PE for DF election as
   long as the three routes are active. If PE-1 withdraws one or more of
   the Ethernet A-D per EVI routes for <ESI12,EVI1>, the PEs in ESI12
   will not consider PE-1 as a suitable DF candidate for <ESI12,EVI1>.

3. Solution benefits

   The solution described in this document provides the following

   a) Improves the DF election procedures for EVPN so that failures due
      to human errors, logical failures or even delay in provisioning of
      Attachment Circuits can be protected by multi-homing.

   b) It does not modify or add any BGP new attributes or NLRI changes.

   c) It is backwards compatible with the procedures defined in RFC7432.

4. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
   or finding the explicit compliance requirements of this RFC.

5. Security Considerations

   The same Security Considerations described in [RFC7432] are valid for
   this document.

6. IANA Considerations

   There are no new IANA considerations in this document.

7. References

7.1. Normative References

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
   R., Patel, K., and J. Guichard, "Constrained Route Distribution for
   Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
   Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684,
   DOI 10.17487/RFC4684, November 2006, <http://www.rfc->.

   [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->.

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., Rabadan,
   J., "Virtual Private Wire Service Support in Ethernet VPN", RFC 8214,
   DOI 10.17487/RFC8214, August 2017, <http://www.rfc->.

7.2. Informative References

   [VPLS-MH] Kothari, Henderickx et al., "BGP based Multi-homing in
   Virtual Private LAN Service", draft-ietf-bess-vpls-multihoming-
   01.txt, work in progress, January, 2016.

8. Acknowledgments

   Will be added.

   The authors want to thank Sriram Venkateswaran, Laxmi Padakanti,
   Ranganathan Boovaraghavan and Ali Sajassi for their review and

9. Contributors

   In addition to the authors listed on the front page, the following
   coauthors have also contributed to this document:

   Wim Henderickx
   Patrice Brissette
   Cisco Systems

Authors' Addresses

   Jorge Rabadan
   777 E. Middlefield Road
   Mountain View, CA 94043 USA

   Kiran Nagaraj

   Senthil Sathappan

   Vinod Prabhu

   Wim Henderickx

   Autumn Liu

   Wen Lin
   Juniper Networks, Inc.