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Versions: (draft-sajassi-l2vpn-evpn-etree) 00 draft-ietf-bess-evpn-etree

L2VPN Workgroup                                              Ali Sajassi
INTERNET-DRAFT                                               Samer Salam
Intended Status: Standards Track                            Sami Boutros
                                                                   Cisco

Wim Henderickx                                                Jim Uttaro
Jorge Rabadan                                                       AT&T
Alcatel-Lucent
                                                            Aldrin Isaac
                                                               Bloomberg

Expires: April 27, 2015                                 October 27, 2014


                   E-TREE Support in EVPN & PBB-EVPN
                    draft-sajassi-bess-evpn-etree-00


Abstract

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree).  [ETREE-FMWK]
   proposes a solution framework for supporting this service in MPLS
   networks. This document discusses how those functional requirements
   can be easily met with EVPN.


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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html




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Copyright and License Notice

   Copyright (c) 2013 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
   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
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  E-Tree Scenarios and EVPN / PBB-EVPN Support  . . . . . . . . .  3
     2.1 Scenario 1: Leaf OR Root site(s) per PE  . . . . . . . . . .  3
     2.2 Scenario 2: Leaf AND Root site(s) per PE . . . . . . . . . .  4
     2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment . . .  4
   3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  5
     3.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.3 E-TREE Traffic Flows for EVPN  . . . . . . . . . . . . . . .  7
       3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . .  7
       3.3.2 E-Tree without MAC Learning  . . . . . . . . . . . . . .  8
   4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . .  8
     4.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  9
     4.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . .  9
   5  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 10
   6  Security Considerations . . . . . . . . . . . . . . . . . . . . 10
   7  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
   8  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1  Normative References  . . . . . . . . . . . . . . . . . . . 10
     8.2  Informative References  . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10










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1  Introduction

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree). In an E-Tree
   service, endpoints are labeled as either Root or Leaf sites. Root
   sites can communicate with all other sites. Leaf sites can
   communicate with Root sites but not with other Leaf sites.

   [ETREE-FMWK] proposes the solution framework for supporting E-Tree
   service in MPLS networks. The document identifies the functional
   components of the overall solution to emulate E-Tree services in
   addition to Ethernet LAN (E-LAN) services on an existing MPLS
   network.

   [EVPN] is a solution for multipoint L2VPN services, with advanced
   multi-homing capabilities, using BGP for distributing customer/client
   MAC address reach-ability information over the MPLS/IP network. [PBB-
   EVPN] combines the functionality of EVPN with [802.1ah] Provider
   Backbone Bridging for MAC address scalability.

   This document discusses how the functional requirements for E-Tree
   service can be easily met with EVPN and PBB-EVPN.

1.1  Terminology

   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 [KEYWORDS].


2  E-Tree Scenarios and EVPN / PBB-EVPN Support

   In this section, we will categorize support for E-Tree into three
   different scenarios, depending on the nature of the site association
   (Root/Leaf) per PE or per Ethernet Segment:

   - Leaf OR Root site(s) per PE

   - Leaf AND Root site(s) per PE

   - Leaf AND Root site(s) per Ethernet Segment


2.1 Scenario 1: Leaf OR Root site(s) per PE

   In this scenario, a PE may have Root sites OR Leaf sites for a given
   VPN instance, but not both concurrently. The PE may have both Root
   and Leaf sites albeit for different VPNs. Every Ethernet Segment



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   connected to the PE is uniquely identified as either a Root or a Leaf
   site.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  | MPLS |  |  |   +--+----ES2-----+CE2|
    +---+    (Root)  |  | E |  |  |  /IP |  |  | E |  |   (Leaf)   +---+
                     |  | V |  |  |      |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                     +---------+            +---------+

   Figure 1: Scenario 1


2.2 Scenario 2: Leaf AND Root site(s) per PE

   In this scenario, a PE may have a set of one or more Root sites AND a
   set of one or more Leaf sites for a given VPN instance. Every
   Ethernet Segment connected to the PE is uniquely identified as either
   a Root or a Leaf site.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+----ES2-----+CE2|
    +---+    (Leaf)  |  | E |  |  | MPLS |  |  | E |  |   (Leaf)   +---+
                     |  | V |  |  |  /IP |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Root)   +---+
                     +---------+            +---------+

   Figure 2: Scenario 2

2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment

   In this scenario, a PE may have a set of one or more Root sites AND a
   set of one or more Leaf sites for a given VPN instance. An Ethernet
   Segment connected to the PE may be identified as both a Root and a
   Leaf site concurrently.








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                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+----ES2-----+CE2|
    +---+ (Leaf/Root)|  | E |  |  | MPLS |  |  | E |  | (Leaf/Root)+---+
                     |  | V |  |  |  /IP |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                     +---------+            +---------+

   Figure 3: Scenario 3


3 Operation for EVPN

   [EVPN] defines the notion of an Ethernet Segment which can be readily
   used to identify a Root and/or Leaf site in E-TREE services. In other
   words, [EVPN] has inherent capability to support E-TREE services
   without defining any new BGP routes. It only requires a  minor
   modification to the existing procedures and a modification to a BGP
   attribute as shown in this section.

   The following procedures are used consistently for all the scenarios
   highlighted in the previous section.

3.1 Known Unicast Traffic

   For known unicast traffic, the PE must advertise a Root/Leaf
   indication along with each MAC Advertisement route, to indicate
   whether the associated MAC address was learnt from a Root or a Leaf.
   This enables remote PEs to perform ingress filtering for known
   unicast traffic: On the ingress PE, the MAC destination address
   lookup yields, in addition to the forwarding adjacency, a flag which
   indicates whether the target MAC is associated with a Root or a Leaf
   site. The ingress PE cross-checks this flag with the status of the
   originating site, and if both are a Leaf, then the packet is not
   forwarded.

   The PE places all Leaf Ethernet Segments of a given bridge domain in
   a single split-horizon group in order to prevent intra-PE forwarding
   among Leaf segments. This split-horizon function applies to BUM
   traffic as well.

   To support the above ingress filtering functionality, a new Root/Leaf
   indication flag will added to the Tunnel Encapsulation Type Extended
   Community [RFC5512]. This extended community will be advertised with
   each EVPN MAC Advertisement route.



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3.2 BUM Traffic

   For BUM traffic, it is not possible to perform filtering on the
   ingress PE, as is the case with known unicast, because of the multi-
   destination nature of the traffic. As such, the solution relies on
   egress filtering. In order to apply the proper egress filtering,
   which varies based on whether a packet is sent from a Root or a Leaf,
   the MPLS-encapsulated frames MUST be tagged with an indication of
   whether they originated from a Root or a Leaf Ethernet Segment. This
   can be achieved in EVPN through the use of the ESI MPLS label, since
   this label identifies the Ethernet Segment of origin of a given
   frame. The egress PE determines whether or not to forward a
   particular frame to an Ethernet Segment depending on the split-
   horizon rule defined in [EVPN]:

   - If the ESI Label indicates that the source Ethernet Segment is a
   Root, then the frame can be forwarded on a segment granted that it
   passes the split-horizon check.

   - If the ESI Label indicates that the source Ethernet Segment is a
   Leaf, then the frame can be forwarded only on a Root segment, granted
   that it passes the split-horizon check.

   When advertising the ESI MPLS label for a given Ethernet Segment, a
   PE must indicate whether the corresponding ESI is a Root or a Leaf
   site. This can be done by encoding the Root or Leaf indication in the
   Flags field of the ESI MPLS label Extended Community attribute
   ([EVPN] Section 8) to indicate Root/Leaf status.

   In the case where a multi-homed Ethernet Segment has both Root and
   Leaf sites attached, two ESI MPLS labels are allocated and
   advertised: one ESI MPLS label denotes Root and the other denotes
   Leaf. The ingress PE imposes the right ESI MPLS label depending on
   whether the Ethernet frame originated from the Root or Leaf site on
   that Ethernet Segment. The mechanism by which the PE identifies
   whether a given frame originated from a Root or Leaf site on the
   segment is based on the Ethernet Tag associated with the frame. Other
   mechanisms of identification, beyond the Ethernet Tag, are outside
   the scope of this document. It should be noted that support for both
   Root and Leaf sites on a single Ethernet Segment requires that the PE
   performs the Ethernet Segment split-horizon check on a per Ethernet
   Tag basis. In the case where a multi-homed Ethernet Segment has
   either Root or Leaf sites attached, then a single ESI MPL label is
   allocated and advertised.

   Furthermore, a PE advertises two special ESI MPLS labels: one for
   Root and another for Leaf. These are used by remote PEs for traffic
   originating from single-homed segments and for multi-homed segments



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   that are not connected to the advertising PE. Note that these special
   labels are advertised on a per PE basis (i.e. each PE advertises only
   two such special labels).

   In addition to egress filtering (which is a MUST requirement), an
   EVPN PE implementation MAY provide topology constraint among the PEs
   belonging to the same EVI associated with an E-TREE service. The
   purpose of this topology constraint is to avoid having PEs with only
   host Leaf sites importing and processing BGP MAC routes from each
   other, thereby unnecessarily exhausting their RIB tables. However, as
   soon as a Root site is added to a Leaf PE, then that PE needs to
   process MAC routes from all other Leaf PEs and add them to its
   forwarding table. To support such topology constrain in EVPN, two BGP
   Route-Targets (RTs) are used for every EVPN Instance (EVI): one RT is
   associated with the Root sites and the other is associated with the
   Leaf sites. On a per EVI basis, every PE exports the single RT
   associated with its type of site(s). Furthermore, a PE with Root
   site(s) imports both Root and Leaf RTs, whereas a PE with Leaf
   site(s) only imports the Root RT. If for a given EVI, the PEs can
   eventually have both Leaf and Root sites attached, even though they
   may start as  Root-only or Leaf-only PEs, then it is recommended to
   use a single RT per EVI and avoid additional configuration and
   operational overhead. If the number of EVIs is very large (e.g., more
   than 32K or 64K), then RT type 0 as defined in [RFC4360] SHOULD be
   used; otherwise, RT type 2 is sufficient.

3.3 E-TREE Traffic Flows for EVPN

   Per [ETREE-FMWK], a generic E-Tree service supports all of the
   following traffic flows:

        - Ethernet Unicast from Root to Roots & Leaf
        - Ethernet Unicast from Leaf to Root
        - Ethernet Broadcast/Multicast from Root to Roots & Leafs
        - Ethernet Broadcast/Multicast from Leaf to Roots

   A particular E-Tree service may need to support all of the above
   types of flows or only a select subset, depending on the target
   application. In the case where unicast flows need not be supported,
   the L2VPN PEs can avoid performing any MAC learning function.

   In the subsections that follow, we will describe the operation of
   EVPN to support E-Tree service with and without MAC learning.


3.3.1 E-Tree with MAC Learning

   The PEs implementing an E-Tree service must perform MAC learning when



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   unicast traffic flows must be supported from Root to Leaf or from
   Leaf to Root sites. In this case, the PE with Root sites performs MAC
   learning in the data-path over the Ethernet Segments, and advertises
   reachability in EVPN MAC Advertisement routes. These routes will be
   imported by PEs that have Leaf sites as well as by PEs that have Root
   sites, in a given EVI. Similarly, the PEs with Leaf sites perform MAC
   learning in the data-path over their Ethernet Segments, and advertise
   reachability in EVPN MAC Advertisement routes which are imported only
   by PEs with at least one Root site in the EVI. A PE with only Leaf
   sites will not import these routes. PEs with Root and/or Leaf sites
   may use the Ethernet A-D routes for aliasing (in the case of multi-
   homed segments) and for mass MAC withdrawal.

   To support multicast/broadcast from Root to Leaf sites, either a P2MP
   tree rooted at the PE(s) with the Root site(s) or ingress replication
   can be used. The multicast tunnels are set up through the exchange of
   the EVPN Inclusive Multicast route, as defined in [EVPN].

   To support multicast/broadcast from Leaf to Root sites, ingress
   replication should be sufficient for most scenarios where there is a
   single Root or few Roots. If the number of Roots is large, a P2MP
   tree rooted at the PEs with Leaf sites may be used.

3.3.2 E-Tree without MAC Learning

   The PEs implementing an E-Tree service need not perform MAC learning
   when the traffic flows between Root and Leaf sites are multicast or
   broadcast. In this case, the PEs do not exchange EVPN MAC
   Advertisement routes. Instead, the Ethernet A-D routes are used to
   exchange the EVPN labels.

   The fields of the Ethernet A-D route are populated per the procedures
   defined in [EVPN], and the route import rules are as described in
   previous sections.

4 Operation for PBB-EVPN

   In PBB-EVPN, the PE must advertise a Root/Leaf indication along with
   each MAC Advertisement route, to indicate whether the associated B-
   MAC address corresponds to a Root or a Leaf site. Similar to the EVPN
   case, this flag will be added to the Tunnel Encapsulation Type
   Extended Community [RFC5512], and advertised with each MAC
   Advertisement route.

   In the case where a multi-homed Ethernet Segment has both Root and
   Leaf sites attached, two B-MAC addresses are allocated and
   advertised: one B-MAC address denotes Root and the other denotes
   Leaf. The ingress PE uses the right B-MAC source address depending on



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   whether the Ethernet frame originated from the Root or Leaf site on
   that Ethernet Segment. The mechanism by which the PE identifies
   whether a given frame originated from a Root or Leaf site on the
   segment is based on the Ethernet Tag associated with the frame. Other
   mechanisms of identification, beyond the Ethernet Tag, are outside
   the scope of this document. It should be noted that support for both
   Root and Leaf sites on a single Ethernet Segment requires that the PE
   performs the Ethernet Segment split-horizon check on a per Ethernet
   Tag basis. In the case where a multi-homed Ethernet Segment has
   either Root or Leaf sites attached, then a single B-MAC address is
   allocated and advertised per segment.

   Furthermore, a PE advertises two global B-MAC addresses: one for Root
   and another for Leaf, and tags them as such in the MAC Advertisement
   routes. These B-MAC addresses are used as source addresses for
   traffic originating from single-homed segments.

4.1 Known Unicast Traffic

   For known unicast traffic, the PEs perform ingress filtering: On the
   ingress PE, the C-MAC destination address lookup yields, in addition
   to the target B-MAC address and forwarding adjacency, a flag which
   indicates whether the target B-MAC is associated with a Root or a
   Leaf site. The ingress PE cross-checks this flag with the status of
   the originating site, and if both are a Leaf, then the packet is not
   forwarded.

   The PE places all Leaf Ethernet Segments of a given bridge domain in
   a single split-horizon group in order to prevent intra-PE forwarding
   among Leaf segments. This split-horizon function applies to BUM
   traffic as well.

4.2 BUM Traffic

   For BUM traffic, the PEs must perform egress filtering. When a PE
   receives a MAC advertisement route, it updates its Ethernet Segment
   egress filtering function (based on the B-MAC source address), as
   follows:

   - If the MAC Advertisement route indicates that the advertised B-MAC
   is a Leaf, and the local Ethernet Segment is a Leaf as well, then the
   source B-MAC address is added to the B-MAC filtering list.

   - Otherwise, the B-MAC filtering list is not updated.

   When the egress PE receives the packet, it examines the B-MAC source
   address to check whether it should filter or forward the frame. Note
   that this uses the same filtering logic as baseline [PBB-EVPN] and



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   does not require any additional flags in the data-plane.


5  Acknowledgement

   We would like to thank Sami Boutros and Dennis Cai for their
   comments.

6  Security Considerations

   Same security considerations as [EVPN].

7  IANA Considerations

   Allocation of Extended Community Type and Sub-Type for EVPN.

8  References

8.1  Normative References

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



   [RFC4360] S. Sangli et al, ""BGP Extended Communities Attribute",
              February, 2006.

              [RFC5512] Mohapatra, P. and E. Rosen, "The BGP
              Encapsulation Subsequent Address Family Identifier (SAFI)
              and the BGP Tunnel Encapsulation Attribute", RFC 5512,
              April 2009.

8.2  Informative References

   [ETREE-FMWK] Key et al., "A Framework for E-Tree Service over MPLS
   Network", draft-ietf-l2vpn-etree-frwk-03, work in progress, September
   2013.

   [EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
   l2vpn-evpn-04.txt, work in progress, July, 2013.

   [PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
   05.txt, work in progress, October, 2013.



Authors' Addresses



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   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com


   Samer Salam
   Cisco
   Email: ssalam@cisco.com


   Wim Henderickx
   Alcatel-Lucent
   Email: wim.henderickx@alcatel-lucent.com


   Jim Uttaro
   AT&T
   Email: ju1738@att.com


   Aldrin
   Bloomberg Issac
   Email: aisaac71@bloomberg.net


   Sami Boutros
   Cisco
   Email: sboutros@cisco.com























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