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Versions: 00 01 02 03 04 draft-ietf-bess-evpn-mh-pa

BESS Working Group                                     Patrice Brissette
INTERNET-DRAFT                                               Ali Sajassi
Intended Status: Proposed Standard                         Cisco Systems

                                                                 Bin Wen
                                                                 Comcast

                                                           Edward Leyton
                                                        Verizon Wireless

                                                           Jorge Rabadan
                                                                   Nokia

Expires: May 3, 2020                                    October 31, 2019


              EVPN multi-homing port-active load-balancing
                  draft-brissette-bess-evpn-mh-pa-04

Abstract

   The Multi-Chassis Link Aggregation Group (MC-LAG) technology enables
   the establishment of a logical link-aggregation connection with a
   redundant group of independent nodes. The purpose of multi-chassis
   LAG is to provide a solution to achieve higher network availability,
   while providing different modes of sharing/balancing of traffic. EVPN
   standard defines EVPN based MC-LAG with single-active and all-active
   multi-homing load-balancing mode. The current draft expands on
   existing redundancy mechanisms supported by EVPN and introduces
   support of port-active load-balancing mode. In the current document,
   port-active load-balancing mode is also referred to as per interface
   active/standby.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   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."




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   The list of current Internet-Drafts can be accessed at
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Copyright and License Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
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   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2. Multi-Chassis Ethernet Bundles  . . . . . . . . . . . . . . . .  4
   3. Port-active load-balancing procedure  . . . . . . . . . . . . .  4
   4. Algorithm to elect per port-active PE . . . . . . . . . . . . .  5
     4.1 Capability Flag  . . . . . . . . . . . . . . . . . . . . . .  5
     4.2 Modulo-based Designated Forwarder Algorithm  . . . . . . . .  6
     4.3 HRW Algorithm  . . . . . . . . . . . . . . . . . . . . . . .  6
     4.4 Preferred-DF Algorithm . . . . . . . . . . . . . . . . . . .  6
   5. Convergence considerations  . . . . . . . . . . . . . . . . . .  6
   6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7. Overall Advantages  . . . . . . . . . . . . . . . . . . . . . .  7
   8  Security Considerations . . . . . . . . . . . . . . . . . . . .  8
   9  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  8
   10  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     10.1  Normative References . . . . . . . . . . . . . . . . . . .  8
     10.2  Informative References . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9







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1  Introduction

   EVPN, as per [RFC7432], provides all-active per flow load balancing
   for multi-homing. It also defines single-active with service carving
   mode, where one of the PEs, in redundancy relationship, is active per
   service.

   While these two multi-homing scenarios are most widely utilized in
   data center and service provider access networks, there are scenarios
   where active-standby per interface multi-homing redundancy is useful
   and required. The main consideration for this mode of redundancy is
   the determinism of traffic forwarding through a specific interface
   rather than statistical per flow load balancing across multiple PEs
   providing multi-homing. The determinism provided by active-standby
   per interface is also required for certain QOS features to work.
   While using this mode, customers also expect minimized convergence
   during failures. A new term of load-balancing mode "port-active load-
   balancing" is then defined.

   This draft describes how that new redundancy mode can be supported
   via EVPN.

                 +-----+
                 | PE3 |
                 +-----+
              +-----------+
              |  MPLS/IP  |
              |  CORE     |
              +-----------+
            +-----+   +-----+
            | PE1 |   | PE2 |
            +-----+   +-----+
               |         |
               I1       I2
                 \     /
                  \   /
                  +---+
                  |CE1|
                  +---+

         Figure 1. MC-LAG topology

   Figure 1 shows a MC-LAG multi-homing topology where PE1 and PE2 are
   part of the same redundancy group providing multi-homing to CE1 via
   interfaces I1 and I2. Interfaces I1 and I2 are Bundle-Ethernet
   interfaces running LACP protocol. The core, shown as IP or MPLS
   enabled, provides wide range of L2 and L3 services. MC-LAG multi-
   homing functionality is decoupled from those services in the core and



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   it focuses on providing multi-homing to CE. With per-port
   active/standby redundancy, only one of the two interface I1 or I2
   would be in forwarding, the other interface will be in standby. This
   also implies that all services on the active interface are in active
   mode and all services on the standby interface operate in standby
   mode.

1.1  Terminology

   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
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2. Multi-Chassis Ethernet Bundles

   When a CE is multi-homed to a set of PE nodes using the [802.1AX]
   Link Aggregation Control Protocol (LACP), the PEs must act as if they
   were a single LACP speaker for the Ethernet links to form a bundle,
   and operate as a Link Aggregation Group (LAG). To achieve this, the
   PEs connected to the same multi-homed CE must synchronize LACP
   configuration and operational data among them. InterChassis
   Communicated-based Protocol (ICCP) has been used for that purpose.
   EVPN LAG simplifies greatly that solution. Along with the
   simplification comes few assumptions:

   - CE device connected to Multi-homing PEs may has a single LAG with
   all its active links i.e. Links in the Ethernet Bundle operate in
   all-active load-balancing mode.

   - Same LACP parameters MUST be configured on peering PEs such as
   system id, port priority and port key.

   Any discrepancies from this list is left for future study.
   Furthermore, mis-configuration and mis-wiring detection across
   peering PEs are also left for further study.

3. Port-active load-balancing procedure

   Following steps describe the proposed procedure with EVPN LAG to
   support port-active load-balancing mode:

   1- The Ethernet-Segment Identifier (ESI) MUST be assigned per access
   interface as described in [RFC7432], which may be auto derived or
   manually assigned. Access interface MAY be a Layer-2 or Layer3
   interface. The usage of ESI over L3 interfce is newly described in
   this document.



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   2- Ethernet-Segment MUST be configured in port-active load-balancing
   mode on peering PEs for specific access interface

   3- Peering PEs MAY exchange only Ethernet-Segment route (Route Type-
   4) when ESI is configured on a Layer3 interface.

   4- PEs in the redundancy group leverage the DF election defined in
   [RFC8584] to determine which PE keeps the port in active mode and
   which one(s) keep it in standby mode.  While the DF election defined
   in [RFC8584] is per <ES, Ethernet Tag> granularity, for port-active
   mode of multi-homing, the DF election is done per <ES>.  The details
   of this algorithm are described in Section 4.

   5- DF router MUST keep corresponding access interface in up and
   forwarding active state for that Ethernet-Segment

   6- Non-DF routers MAY bring and keep peering access interface
   attached to it in operational down state. If the interface is running
   LACP protocol, then the non-DF PE MAY also set the LACP state to OOS
   (Out of Sync) as opposed to interface state down. This allows for
   better convergence on standby to active transition.

   7- For EVPN-VPWS service, the usage of primary/backup bits of EVPN
   Layer2 attributes extended community [RFC8214] is highly recommended
   to achieve better convergence.

4. Algorithm to elect per port-active PE

   The ES routes, running in port-active load-balancing mode, are
   advertised with a new capability in the DF Election Extended
   Community as defined in [RFC8584]. Moreover, the ES associated to the
   port leverages existing procedure of single-active, and signals
   single-active bit along with Ethernet-AD per-ES route. Finally, as in
   RFC7432, the ESI-label based split-horizon procedures should be used
   to avoid transient echo'ed packets when L2 circuits are involved.

4.1 Capability Flag

   [RFC8584] defines a DF Election extended community, and a Bitmap
   field to encode "capabilities" to use with the DF election algorithm
   in the DF algorithm field. Bitmap (2 octets) is extended by the
   following value:

                         1 1 1 1 1 1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |D|A|     |P|                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   Figure 2 - Amended Bitmap field in the DF Election Extended Community

    - Bit 0: 'Don't Preempt' bit, as explained in [PREF-DF].

    - Bit 1: AC-Influenced DF Election, as explained in [RFC8584].

    - Bit 5: (corresponds to Bit 25 of the DF Election Extended
             Community and it is defined by this document):
             P bit or 'Port Mode' bit (P hereafter), determines
             that the DF-Algorithm should be modified to consider
             the port only and not the Ethernet Tags.

4.2 Modulo-based Designated Forwarder Algorithm

   The default DF Election algorithm, or modulus-based algorithm as in
   [RFC7432] and updated by [RFC8584], is used here, at the granularity
   of <ES> only. Given the fact, ES-Import RT community inherits from
   ESI only byte 1-7, many deployments differentiate ESI within these
   bytes only. For Modulo calculation, bytes [3-7] are used to determine
   the designated forwarder using Modulo-based DF assignment.

4.3 HRW Algorithm

   Highest Random Weight (HRW) algorithm defined in [RFC8584] MAY also
   be used and signaled, and modified to operate at the granularity of
   <ES> rather than per <ES, VLAN>.

   [RFC8584] describes computing a 32 bit CRC over the concatenation of
   Ethernet Tag and ESI. For port-active load-balancing mode, the
   Ethernet Tag is simply removed from the CRC computation.

4.4 Preferred-DF Algorithm

   When the new capability 'Port-Mode' is signaled, the algorithm is
   modified to consider the port only and not any associated Ethernet
   Tags. Furthermore, the "port-based" capability MUST be compatible
   with the 'DP' capability (for non-revertive). The AC-DF bit MUST be
   set to zero. When an AC (sub-interface) goes down, it does not
   influence the DF election.

5. Convergence considerations

   To improve the convergence, upon failure and recovery, when port-
   active load-balancing mode is used, some advanced synchronization
   between peering PEs may be required. Port-active is challenging in a
   sense that the "standby" port is in down state. It takes some time to
   bring a "standby" port in up-state and settle the network. For IRB
   and L3 services, ARP / ND cache may be synchronized. Moreover,



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   associated VRF tables may also be synchronized. For L2 services, MAC
   table synchronization may be considered.

   Finally, for Bundle-Ethernet interface where LACP is running the
   ability to set the "standby" port in "out-of-sync" state aka "warm-
   standby" can be leveraged.

6. Applicability

   A common deployment is to provide L2 or L3 service on the PEs
   providing multi-homing. The services could be any L2 EVPN such as
   EVPN VPWS, EVPN [RFC7432], etc. L3 service could be in VPN context
   [RFC4364] or in global routing context. When a PE provides first hop
   routing, EVPN IRB could also be deployed on the PEs. The mechanism
   defined in this draft is used between the PEs providing the L2 and/or
   L3 service, when the requirement is to use per port active.

   A possible alternate solution is the one described in this draft is
   MC-LAG with ICCP [RFC7275] active-standby redundancy. However, ICCP
   requires LDP to be enabled as a transport of ICCP messages. There are
   many scenarios where LDP is not required e.g. deployments with VXLAN
   or SRv6. The solution defined in this draft with EVPN does not
   mandate the need to use LDP or ICCP and is independent of the
   underlay encapsulation.

7. Overall Advantages

   The use of port-active multi-homing brings the following benefits to
   EVPN networks:

   - Open standards based per interface single-active redundancy
   mechanism that eliminates the need to run ICCP and LDP.

   - Agnostic of underlay technology (MPLS, VXLAN, SRv6) and associated
   services (L2, L3, Bridging, E-LINE, etc).

   - Provides a way to enable deterministic QOS over MC-LAG attachment
   circuits

   - Fully compliant with [RFC7432], does not require any new protocol
   enhancement to existing EVPN RFCs.

   - Can leverage various DF election algorithms e.g. modulo, HRW, etc.

   - Replaces legacy MC-LAG ICCP-based solution, and offers following
   additional benefits:

      - Efficiently supports 1+N redundancy mode (with EVPN using BGP



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      RR) where as ICCP requires full mesh of LDP sessions among PEs in
      redundancy group

      - Fast convergence with mass-withdraw is possible with EVPN, no
      equivalent in ICCP

   - Customers want per interface single-active redundancy, but don't
   want to enable LDP (e.g. they may be running VXLAN or SRv6 in the
   network). Currently there is no alternative to this.

8  Security Considerations

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

9  IANA Considerations

   This document solicits the allocation of the following values:

      o Bit 5 in the [RFC8584] DF Election Capabilities registry,
        with name "P"(port mode load-balancing) Capability" for
        port-active ES.


10  References

10.1  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, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
              Rabadan, "Virtual Private Wire Service Support in Ethernet
              VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
              <https://www.rfc-editor.org/info/rfc8214>.

   [RFC8584]  Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
              VPN Designated Forwarder Election Extensibility",
              RFC 8584, DOI 10.17487/RFC8584, April 2019,
              <https://www.rfc-editor.org/info/rfc8584>.


10.2  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate



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              Requirement Levels", BCP 14, RFC 2119, DOI
              10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.

   [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>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC7275]  Martini, L., Salam, S., Sajassi, A., Bocci, M.,
              Matsushima, S., and T. Nadeau, "Inter-Chassis
              Communication Protocol for Layer 2 Virtual Private Network
              (L2VPN) Provider Edge (PE) Redundancy", RFC 7275, DOI
              10.17487/RFC7275, June 2014, <https://www.rfc-
              editor.org/info/rfc7275>.

   [PREF-DF]  Rabadan et al. "Preference-based EVPN DF Election",
              draft-ietf-bess-evpn-pref-df, work-in-progress, June,
              2019.

Authors' Addresses


   Patrice Brissette
   Cisco Systems
   EMail: pbrisset@cisco.com

   Ali Sajassi
   Cisco Systems
   EMail: sajassi@cisco.com

   Luc Andre Burdet
   Cisco Systems
   EMail: lburdet@cisco.com

   Samir Thoria
   Cisco Systems
   EMail: sthoria@cisco.com

   Jorge Rabadan
   Nokia
   Email: jorge.rabadan@nokia.com

   Bin Wen



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   Comcast
   Email: Bin_Wen@comcast.com

   Edward Leyton
   Verizon
   Email: edward.leyton@verizonwireless.com













































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