L2VPN Workgroup Ali Sajassi INTERNET-DRAFT Samer Salam Intended Status: Standards Track Sami Boutros Cisco Wim Henderickx Jorge Rabadan Jim Uttaro Alcatel-Lucent AT&T John Drake Aldrin Isaac Wen Lin Bloomberg Juniper Expires: December 10, 2015 June 10, 2015 E-TREE Support in EVPN & PBB-EVPN draft-ietf-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 (PBB-)EVPN and how (PBB-)EVPN offers a more efficient implementation of these functions. 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 Sajassi et al. Expires December 10, 2015 [Page 1] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 http://www.ietf.org/shadow.html 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. 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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 . . . . . . . . . . . . . . . 8 3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 8 3.3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . 9 4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 9 4.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 9 4.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 10 5 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 10 6 Security Considerations . . . . . . . . . . . . . . . . . . . . 10 7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1 Normative References . . . . . . . . . . . . . . . . . . . 10 8.2 Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Sajassi et al. Expires December 10, 2015 [Page 2] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 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 (PBB-)EVPN and how (PBB-)EVPN offers a more efficient implementation of these functions. 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 Sajassi et al. Expires December 10, 2015 [Page 3] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 and Leaf sites albeit for different VPNs. Every Ethernet Segment 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. Sajassi et al. Expires December 10, 2015 [Page 4] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 +---------+ +---------+ | 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 new BGP Extended Community for leaf indication as shown later in this document. 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 Leaf indication along with each MAC Advertisement route, to indicate that the associated MAC address was learnt from a Leaf Attachment Circuit (AC). The lack of a Leaf indication, indicates the MAC address is learnt from a root AC. In other words, a default mode of operation in an EVPN is that all ACs are root (can transmit and receive traffic to/from other ACs in an EVI) unless the AC is explicitly identified as a leaf. Tagging MAC addresses with a leaf indication when they are associated with a leaf AC, enables remote PEs to perform ingress filtering for known unicast traffic - i.e., 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 Leaf site or not. The ingress PE cross-checks this flag with the status of the originating AC, and if both are a Leaf, then the packet is not forwarded. The PE places all Leaf Ethernet Segments (ACs) of a given bridge domain in a single split-horizon group in order to prevent intra-PE Sajassi et al. Expires December 10, 2015 [Page 5] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 forwarding among Leaf ACs (segments). This split-horizon function applies to BUM traffic as well. To support the above ingress filtering functionality, a new Extended Community with a Leaf indication flag will be introduced [section xxx]. This new Extended Community will be advertised with each EVPN MAC/IP Advertisement route. 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 for a given frame. For multi-homing use cases where BUM traffic uses P2MP LSP, the egress PE can determine 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 achieved by advertising the Ethernet A-D per ES route with with the ESI MPLS label Extended Community along with the new Extended Community defined in section [xxx] that has a Leaf indication flag. 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 default ESI MPLS label that denotes Root and another ESI MPLS label with Leaf indication that 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 Sajassi et al. Expires December 10, 2015 [Page 6] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 originated from a Root or Leaf site on the segment is based on the Ethernet Tag associated with the frame (e.g., whether the frame come from a leaf or a root AC). 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 only either Root or Leaf sites attached, then a single ESI MPL label is allocated and advertised. Furthermore, a PE advertises a special per-PE Leaf MPLS label to indicate Leaf. For traffic originated from single-homed segments, this label can be either upstream assigned or downstream assigned (depending on whether BUM traffic uses P2MP LSP or ingress replication). However, for traffic originated from multi-homed segments, this label is downstream assigned as ingress replication is assumed to be used for BUM traffic. Furthermore, this label is used for traffic originating from a multi-homed segments that are not part of the same redundancy group (same ES) as the advertising PE. This label indicates to the egress PE that the BUM traffic is originated from a Leaf AC. Note that this special label is advertised on a per PE basis (i.e. each PE advertises only a single such special label). It should be noted that this per-PE Leaf label is not used for multi- homed segments when P2MP LSP is used for BUM traffic or when ingress replication is destined to a PE that shares the same multi-homed ES - i.e., in such scenarios, the color-coded per-ES ESI MPLS label is used (indicating leaf or root). This per-PE Leaf MPLS label is advertised along with the Leaf indication flag with the Ethernet A-D per ES route. 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, when 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 Sajassi et al. Expires December 10, 2015 [Page 7] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 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 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 Sajassi et al. Expires December 10, 2015 [Page 8] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 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 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 Sajassi et al. Expires December 10, 2015 [Page 9] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 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 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 Sajassi et al. Expires December 10, 2015 [Page 10] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 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 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 Sajassi et al. Expires December 10, 2015 [Page 11] INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN June 10, 2015 Aldrin Bloomberg Issac Email: aisaac71@bloomberg.net Sami Boutros Cisco Email: sboutros@cisco.com Sajassi et al. 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