Network Working Group A. Sajassi INTERNET-DRAFT Cisco Category: Standards Track R. Aggarwal N. Bitar Arktan Verizon W. Henderickx S. Boutros F. Balus K. Patel Alcatel-Lucent S. Salam Cisco Aldrin Isaac Bloomberg J. Drake R. Shekhar J. Uttaro Juniper Networks AT&T Expires: January 15, 2014 July 15, 2013 BGP MPLS Based Ethernet VPN draft-ietf-l2vpn-evpn-04 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 Copyright and License Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Sajassi, et al. Expires January 15, 2014 [Page 1] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 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. Abstract This document describes procedures for BGP MPLS based Ethernet VPNs (EVPN). Table of Contents 1. Specification of requirements . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. BGP MPLS Based EVPN Overview . . . . . . . . . . . . . . . . . 6 6. Ethernet Segment . . . . . . . . . . . . . . . . . . . . . . . 7 7. Ethernet Tag . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1 VLAN Based Service Interface . . . . . . . . . . . . . . . . 9 7.2 VLAN Bundle Service Interface . . . . . . . . . . . . . . . 9 7.2.1 Port Based Service Interface . . . . . . . . . . . . . . 10 7.3 VLAN Aware Bundle Service Interface . . . . . . . . . . . . 10 7.3.1 Port Based VLAN Aware Service Interface . . . . . . . . 10 8. BGP EVPN NLRI . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . . 11 8.2. MAC Advertisement Route . . . . . . . . . . . . . . . . . 12 8.3. Inclusive Multicast Ethernet Tag Route . . . . . . . . . . 12 8.4 Ethernet Segment Route . . . . . . . . . . . . . . . . . . . 13 8.5 ESI Label Extended Community . . . . . . . . . . . . . . . . 13 8.6 ES-Import Route Target . . . . . . . . . . . . . . . . . . . 14 8.7 MAC Mobility Extended Community . . . . . . . . . . . . . . 14 8.8 Default Gateway Extended Community . . . . . . . . . . . . . 15 9. Multi-homing Functions . . . . . . . . . . . . . . . . . . . . 15 9.1 Multi-homed Ethernet Segment Auto-Discovery . . . . . . . . 15 9.1.1 Constructing the Ethernet Segment Route . . . . . . . . 15 9.2 Fast Convergence . . . . . . . . . . . . . . . . . . . . . . 16 9.2.1 Constructing the Ethernet A-D Route per Ethernet Segment . . . . . . . . . . . . . . . . . . . . . . . . 16 9.2.1.1. Ethernet A-D Route Targets . . . . . . . . . . . . 17 9.3 Split Horizon . . . . . . . . . . . . . . . . . . . . . . . 17 9.3.1 ESI Label Assignment . . . . . . . . . . . . . . . . . . 18 9.3.1.1 Ingress Replication . . . . . . . . . . . . . . . . 18 Sajassi, et al. Expires January 15, 2014 [Page 2] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 9.3.1.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . . 19 9.4 Aliasing and Backup-Path . . . . . . . . . . . . . . . . . . 20 9.4.1 Constructing the Ethernet A-D Route per EVI . . . . . . 21 9.4.1.1 Ethernet A-D Route Targets . . . . . . . . . . . . . 22 9.5 Designated Forwarder Election . . . . . . . . . . . . . . . 22 9.6. Interoperability with Single-homing PEs . . . . . . . . . . 24 10. Determining Reachability to Unicast MAC Addresses . . . . . . 25 10.1. Local Learning . . . . . . . . . . . . . . . . . . . . . . 25 10.2. Remote learning . . . . . . . . . . . . . . . . . . . . . 26 10.2.1. Constructing the BGP EVPN MAC Address Advertisement . 26 10.2.2 Route Resolution . . . . . . . . . . . . . . . . . . . 28 11. ARP and ND . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11.1 Default Gateway . . . . . . . . . . . . . . . . . . . . . . 29 12. Handling of Multi-Destination Traffic . . . . . . . . . . . . 30 12.1. Construction of the Inclusive Multicast Ethernet Tag Route . . . . . . . . . . . . . . . . . . . . . . . . . . 31 12.2. P-Tunnel Identification . . . . . . . . . . . . . . . . . 31 13. Processing of Unknown Unicast Packets . . . . . . . . . . . . 32 13.1. Ingress Replication . . . . . . . . . . . . . . . . . . . 33 13.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . . . . . . 33 14. Forwarding Unicast Packets . . . . . . . . . . . . . . . . . . 34 14.1. Forwarding packets received from a CE . . . . . . . . . . 34 14.2. Forwarding packets received from a remote PE . . . . . . . 35 14.2.1. Unknown Unicast Forwarding . . . . . . . . . . . . . . 35 14.2.2. Known Unicast Forwarding . . . . . . . . . . . . . . . 35 15. Load Balancing of Unicast Frames . . . . . . . . . . . . . . . 36 15.1. Load balancing of traffic from an PE to remote CEs . . . . 36 15.1.1 Single-Active Redundancy Mode . . . . . . . . . . . . . 36 15.1.2 All-Active Redundancy Mode . . . . . . . . . . . . . . 37 15.2. Load balancing of traffic between an PE and a local CE . . 38 15.2.1. Data plane learning . . . . . . . . . . . . . . . . . 38 15.2.2. Control plane learning . . . . . . . . . . . . . . . . 39 16. MAC Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 39 16.1. MAC Duplication Issue . . . . . . . . . . . . . . . . . . 41 16.2. Sticky MAC addresses . . . . . . . . . . . . . . . . . . . 41 17. Multicast & Broadcast . . . . . . . . . . . . . . . . . . . . 41 17.1. Ingress Replication . . . . . . . . . . . . . . . . . . . 41 17.2. P2MP LSPs . . . . . . . . . . . . . . . . . . . . . . . . 42 17.2.1. Inclusive Trees . . . . . . . . . . . . . . . . . . . 42 18. Convergence . . . . . . . . . . . . . . . . . . . . . . . . . 42 18.1. Transit Link and Node Failures between PEs . . . . . . . . 42 18.2. PE Failures . . . . . . . . . . . . . . . . . . . . . . . 43 18.2. PE to CE Network Failures . . . . . . . . . . . . . . . . 43 19. Frame Ordering . . . . . . . . . . . . . . . . . . . . . . . . 43 20. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44 21. Security Considerations . . . . . . . . . . . . . . . . . . . 44 22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 23. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Sajassi, et al. Expires January 15, 2014 [Page 3] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 23.1 Normative References . . . . . . . . . . . . . . . . . . . 45 23.2 Informative References . . . . . . . . . . . . . . . . . . 45 24. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 45 Sajassi, et al. Expires January 15, 2014 [Page 4] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 1. Specification of requirements 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 [RFC2119]. 2. Terminology Bridge Domain: Broadcast Domain: CE: Customer Edge device e.g., host or router or switch EVI: An EVPN instance spanning across the PEs participating in that VPN MAC-VRF: A Virtual Routing and Forwarding table for MAC addresses on a PE for an EVI Ethernet Segment Identifier (ESI): If a CE is multi-homed to two or more PEs, the set of Ethernet links that attaches the CE to the PEs is an 'Ethernet segment'. Ethernet segments MUST have a unique non- zero identifier, the 'Ethernet Segment Identifier'. Ethernet Tag: An Ethernet Tag identifies a particular broadcast domain, e.g., a VLAN. An EVPN instance consists of one or more broadcast domains. Ethernet tag(s) are assigned to the broadcast domains of a given EVPN instance by the provider of that EVPN, and each PE in that EVPN instance performs a mapping between broadcast domain identifier(s) understood by each of its attached CEs and the corresponding Ethernet tag. LACP: Link Aggregation Control Protocol MP2MP: Multipoint to Multipoint P2MP: Point to Multipoint P2P: Point to Point Single-Active Mode: When a device or a network is multi-homed to two or more PEs and when only a single PE in such redundancy group can forward traffic to/from the multi-homed device or network for a given VLAN, then such multi-homing or redundancy is referred to as "Single- Active". Sajassi, et al. Expires January 15, 2014 [Page 5] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 All-Active Mode: When a device is multi-homed to two or more PEs and when all PEs in such redundancy group can forward traffic to/from the multi-homed device for a given VLAN, then such multi-homing or redundancy is referred to as "All-Active". 3. Introduction This document describes procedures for BGP MPLS based Ethernet VPNs (EVPN). The procedures described here are intended to meet the requirements specified in [EVPN-REQ]. Please refer to [EVPN-REQ] for the detailed requirements and motivation. EVPN requires extensions to existing IP/MPLS protocols as described in this document. In addition to these extensions EVPN uses several building blocks from existing MPLS technologies. 4. Contributors In addition to the authors listed above, the following individuals also contributed to this document: Quaizar Vohra Kireeti Kompella Apurva Mehta Nadeem Mohammad Juniper Networks Clarence Filsfils Dennis Cai Cisco 5. BGP MPLS Based EVPN Overview This section provides an overview of EVPN. An EVPN instance comprises CEs that are connected to PEs that form the edge of the MPLS infrastructure. A CE may be a host, a router or a switch. The PEs provide virtual Layer 2 bridged connectivity between the CEs. There may be multiple EVPN instances in the provider's network. The PEs may be connected by an MPLS LSP infrastructure which provides the benefits of MPLS technology such as fast-reroute, resiliency, etc. The PEs may also be connected by an IP infrastructure in which case IP/GRE tunneling or other IP tunneling can be used between the PEs. The detailed procedures in this version of this document are specified only for MPLS LSPs as the tunneling technology. However these procedures are designed to be extensible to IP tunneling as the Sajassi, et al. Expires January 15, 2014 [Page 6] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 PSN tunneling technology. In an EVPN, MAC learning between PEs occurs not in the data plane (as happens with traditional bridging) but in the control plane. Control plane learning offers greater control over the MAC learning process, such as restricting who learns what, and the ability to apply policies. Furthermore, the control plane chosen for advertising MAC reachability information is multi-protocol (MP) BGP (similar to IP VPNs (RFC 4364)). This provides greater scalability and the ability to preserve the "virtualization" or isolation of groups of interacting agents (hosts, servers, virtual machines) from each other. In EVPN, PEs advertise the MAC addresses learned from the CEs that are connected to them, along with an MPLS label, to other PEs in the control plane using MP-BGP. Control plane learning enables load balancing of traffic to and from CEs that are multi-homed to multiple PEs. This is in addition to load balancing across the MPLS core via multiple LSPs between the same pair of PEs. In other words it allows CEs to connect to multiple active points of attachment. It also improves convergence times in the event of certain network failures. However, learning between PEs and CEs is done by the method best suited to the CE: data plane learning, IEEE 802.1x, LLDP, 802.1aq, ARP, management plane or other protocols. It is a local decision as to whether the Layer 2 forwarding table on an PE is populated with all the MAC destination addresses known to the control plane, or whether the PE implements a cache based scheme. For instance the MAC forwarding table may be populated only with the MAC destinations of the active flows transiting a specific PE. The policy attributes of EVPN are very similar to those of IP-VPN. A EVPN instance requires a Route-Distinguisher (RD) which is unique per PE and one or more globally unique Route-Targets (RTs). A CE attaches to a MAC-VRF on an PE, on an Ethernet interface which may be configured for one or more Ethernet Tags, e.g., VLAN IDs. Some deployment scenarios guarantee uniqueness of VLAN IDs across EVPN instances: all points of attachment for a given EVPN instance use the same VLAN ID, and no other EVPN instance uses this VLAN ID. This document refers to this case as a "Unique VLAN EVPN" and describes simplified procedures to optimize for it. 6. Ethernet Segment If a CE is multi-homed to two or more PEs, the set of Ethernet links constitutes an "Ethernet Segment". An Ethernet segment may appear to the CE as a Link Aggregation Group (LAG). Ethernet segments have an identifier, called the "Ethernet Segment Identifier" (ESI) which is Sajassi, et al. Expires January 15, 2014 [Page 7] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 encoded as a ten octets integer. The following two ESI values are reserved: - ESI 0 denotes a single-homed CE. - ESI {0xFF} (repeated 10 times) is known as MAX-ESI and is reserved. In general, an Ethernet segment MUST have a non-reserved ESI that is unique network wide (e.g., across all EVPN instances on all the PEs). If the CE(s) constituting an Ethernet Segment is (are) managed by the network operator, then ESI uniqueness should be guaranteed; however, if the CE(s) is (are) not managed, then the operator MUST configure a network-wide unique ESI for that Ethernet Segment. This is required to enable auto-discovery of Ethernet Segments and DF election. The ESI can be assigned using various mechanisms: 1. If IEEE 802.1AX LACP is used between the PEs and CEs, then the ESI is determined from LACP by concatenating the following parameters: + CE LACP System Identifier comprised of two octets of System Priority and six octets of System MAC address, where the System Priority is encoded in the most significant two octets. The CE LACP identifier MUST be encoded in the high order eight octets of the ESI. + CE LACP two octets Port Key. The CE LACP port key MUST be encoded in the low order two octets of the ESI. As far as the CE is concerned, it would treat the multiple PEs that it is connected to as the same switch. This allows the CE to aggregate links that are attached to different PEs in the same bundle. This mechanism could be used only if it produces ESIs that satisfy the uniqueness requirement specified above. 2. In the case of indirectly connected hosts via a bridged LAN between the CEs and the PEs, the ESI is determined based on the Layer 2 bridge protocol as follows: If MST is used in the bridged LAN then the value of the ESI is derived by listening to BPDUs on the Ethernet segment. To achieve this the PE is not required to run MST. However the PE must learn the Root Bridge MAC address and Bridge Priority of the root of the Internal Spanning Tree (IST) by listening to the BPDUs. The ESI is constructed as follows: {Bridge Priority (16 bits) , Root Bridge MAC Address (48 bits)} Sajassi, et al. Expires January 15, 2014 [Page 8] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 This mechanism could be used only if it produces ESIs that satisfy the uniqueness requirement specified above. 3. The ESI may be configured. 7. Ethernet Tag An Ethernet Tag identifies a particular broadcast domain, e.g. a VLAN, in an EVPN Instance. An EVPN Instance consists of one or more broadcast domains (one or more VLANs). VLANs are assigned to a given EVPN Instance by the provider of the EVPN service. A given VLAN can itself be represented by multiple VLAN IDs (VIDs). In such cases, the PEs participating in that VLAN for a given EVPN instance are responsible for performing VLAN ID translation to/from locally attached CE devices. If a VLAN is represented by a single VID across all PE devices participating in that VLAN for that EVPN instance, then there is no need for VID translation at the PEs. Furthermore, some deployment scenarios guarantee uniqueness of VIDs across all EVPN instances; all points of attachment for a given EVPN instance use the same VID and no other EVPN instances use that VID. This allows the RT(s) for each EVPN instance to be derived automatically from the corresponding VID, as described in section 9.4.1.1.1 "Auto-Derivation from the Ethernet Tag ID". The following subsections discuss the relationship between broadcast domains (e.g., VLANs), Ethernet Tags (e.g., VIDs), and MAC-VRFs as well as the setting of the Ethernet Tag Identifier, in the various EVPN BGP routes (defined in section 8), for the different types of service interfaces described in [EVPN-REQ]. 7.1 VLAN Based Service Interface With this service interface, an EVPN instance consists of only a single broadcast domain (e.g., a single VLAN). Therefore, there is a one to one mapping between a VID on this interface and a MAC-VRF. Since a MAC-VRF corresponds to a single VLAN, it consists of a single bridge domain corresponding to that VLAN. If the VLAN is represented by different VIDs on different PEs, then each PE needs to perform VID translation for frames destined to its attached CEs. In such scenarios, the Ethernet frames transported over MPLS/IP network SHOULD remain tagged with the originating VID and a VID translation MUST be supported in the data path and MUST be performed on the disposition PE. The Ethernet Tag Identifier in all EVPN routes MUST be set to 0. 7.2 VLAN Bundle Service Interface Sajassi, et al. Expires January 15, 2014 [Page 9] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 With this service interface, an EVPN instance corresponds to several broadcast domains (e.g., several VLANs); however, only a single bridge domain is maintained per MAC-VRF which means multiple VLANs share the same bridge domain. This implies MAC addresses MUST be unique across different VLANs for this service to work. In other words, there is a many-to-one mapping between VLANs and a MAC-VRF, and the MAC-VRF consists of a single bridge domain. Furthermore, a single VLAN must be represented by a single VID - e.g., no VID translation is allowed for this service interface type. The MPLS encapsulated frames MUST remain tagged with the originating VID. Tag translation is NOT permitted. The Ethernet Tag Identifier in all EVPN routes MUST be set to 0. 7.2.1 Port Based Service Interface This service interface is a special case of the VLAN Bundle service interface, where all of the VLANs on the port are part of the same service and map to the same bundle. The procedures are identical to those described in section 7.2. 7.3 VLAN Aware Bundle Service Interface With this service interface, an EVPN instance consists of several broadcast domains (e.g., several VLANs) with each VLAN having its own bridge domain - e.g., multiple bridge domains (one per VLAN) is maintained by a single MAC-VRF corresponding to the EVPN instance. In the case where a single VLAN is represented by different VIDs on different CEs and thus tag (VID) translation is required, a normalized Ethernet Tag (VID) MUST be carried in the MPLS encapsulated frames and a tag translation function MUST be supported in the data path. This translation MUST be performed in data path on both the imposition as well as the disposition PEs (translating to normalized tag on imposition PE and translating to local tag on disposition PE). The Ethernet Tag Identifier in all EVPN routes MUST be set to the normalized Ethernet Tag assigned by the EVPN provider. 7.3.1 Port Based VLAN Aware Service Interface This service interface is a special case of the VLAN Aware Bundle service interface, where all of the VLANs on the port are part of the same service and map to the same bundle. The procedures are identical to those described in section 7.3. 8. BGP EVPN NLRI This document defines a new BGP NLRI, called the EVPN NLRI. Following is the format of the EVPN NLRI: Sajassi, et al. Expires January 15, 2014 [Page 10] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 +-----------------------------------+ | Route Type (1 octet) | +-----------------------------------+ | Length (1 octet) | +-----------------------------------+ | Route Type specific (variable) | +-----------------------------------+ The Route Type field defines encoding of the rest of the EVPN NLRI (Route Type specific EVPN NLRI). The Length field indicates the length in octets of the Route Type specific field of EVPN NLRI. This document defines the following Route Types: + 1 - Ethernet Auto-Discovery (A-D) route + 2 - MAC advertisement route + 3 - Inclusive Multicast Route + 4 - Ethernet Segment Route The detailed encoding and procedures for these route types are described in subsequent sections. The EVPN NLRI is carried in BGP [RFC4271] using BGP Multiprotocol Extensions [RFC4760] with an AFI of 25 (L2VPN) and a SAFI of 70 (EVPN). The NLRI field in the MP_REACH_NLRI/MP_UNREACH_NLRI attribute contains the EVPN NLRI (encoded as specified above). In order for two BGP speakers to exchange labeled EVPN NLRI, they must use BGP Capabilities Advertisement to ensure that they both are capable of properly processing such NLRI. This is done as specified in [RFC4760], by using capability code 1 (multiprotocol BGP) with an AFI of 25 (L2VPN) and a SAFI of 70 (EVPN). 8.1. Ethernet Auto-Discovery Route A Ethernet A-D route type specific EVPN NLRI consists of the following: Sajassi, et al. Expires January 15, 2014 [Page 11] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 +---------------------------------------+ | RD (8 octets) | +---------------------------------------+ |Ethernet Segment Identifier (10 octets)| +---------------------------------------+ | Ethernet Tag ID (4 octets) | +---------------------------------------+ | MPLS Label (3 octets) | +---------------------------------------+ For procedures and usage of this route please see section 9.2 "Fast Convergence" and section 9.4 "Aliasing". 8.2. MAC Advertisement Route A MAC advertisement route type specific EVPN NLRI consists of the following: +---------------------------------------+ | RD (8 octets) | +---------------------------------------+ |Ethernet Segment Identifier (10 octets)| +---------------------------------------+ | Ethernet Tag ID (4 octets) | +---------------------------------------+ | MAC Address Length (1 octet) | +---------------------------------------+ | MAC Address (6 octets) | +---------------------------------------+ | IP Address Length (1 octet) | +---------------------------------------+ | IP Address (4 or 16 octets) | +---------------------------------------+ | MPLS Label (3 octets) | +---------------------------------------+ For the purpose of BGP route key processing, only the Ethernet Tag ID, MAC Address Length, MAC Address, IP Address Length, and IP Address Address fields are considered to be part of the prefix in the NLRI. The Ethernet Segment Identifier and MPLS Label fields are to be treated as route attributes as opposed to being part of the "route". For procedures and usage of this route please see section 10 "Determining Reachability to Unicast MAC Addresses" and section 15 "Load Balancing of Unicast Packets". 8.3. Inclusive Multicast Ethernet Tag Route Sajassi, et al. Expires January 15, 2014 [Page 12] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 An Inclusive Multicast Ethernet Tag route type specific EVPN NLRI consists of the following: +---------------------------------------+ | RD (8 octets) | +---------------------------------------+ | Ethernet Tag ID (4 octets) | +---------------------------------------+ | IP Address Length (1 octet) | +---------------------------------------+ | Originating Router's IP Addr | | (4 or 16 octets) | +---------------------------------------+ For procedures and usage of this route please see section 12 "Handling of Multi-Destination Traffic", section 13 "Processing of Unknown Unicast Traffic" and section 17 "Multicast". 8.4 Ethernet Segment Route The Ethernet Segment Route is encoded in the EVPN NLRI using the Route Type value of 4. The Route Type Specific field of the NLRI is formatted as follows: +---------------------------------------+ | RD (8 octets) | +---------------------------------------+ |Ethernet Segment Identifier (10 octets)| +---------------------------------------+ | IP Address Length (1 octet) | +---------------------------------------+ | Originating Router's IP Addr | | (4 or 16 octets) | +---------------------------------------+ For procedures and usage of this route please see section 9.5 "Designated Forwarder Election". 8.5 ESI Label Extended Community This extended community is a new transitive extended community with the Type field is 0x06, and the Sub-Type of 0x01. It may be advertised along with Ethernet Auto-Discovery routes and it enables split-horizon procedures for multi-homed sites as described in section 9.3 "Split Horizon". Each ESI Label Extended Community is encoded as a 8-octet value as follows: Sajassi, et al. Expires January 15, 2014 [Page 13] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 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=0x01 | Flags (One Octet) |Reserved=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved = 0| ESI Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The low order bit of the flags octet is defined as the "Active- Standby" bit and may be set to 1. A value of 0 means that the multi- homed site is operating in All-Active mode; whereas, a value of 1 means that the multi-homed site is operating in Single-Active mode. The second low order bit of the flags octet is defined as the "Root- Leaf". A value of 0 means that this label is associated with a Root site; whereas, a value of 1 means that this label is associate with a Leaf site. The other bits must be set to 0. 8.6 ES-Import Route Target This is a new transitive Route Target extended community carried with the Ethernet Segment route. When used, it enables all the PEs connected to the same multi-homed site to import the Ethernet Segment routes. The value is derived automatically from the ESI by encoding the 6-byte MAC address portion of the ESI in the ES-Import Route Target. The format of this extended community is as follows: 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=0x02 | ES-Import | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ES-Import Cont'd | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This document expands the definition of the Route Target extended community to allow the value of high order octet (Type field) to be 0x06 (in addition to the values specified in rfc4360). The value of low order octet (Sub-Type field) of 0x02 indicates that this extended community is of type "Route Target". The new value for Type field of 0x06 indicates that the structure of this RT is a six bytes value (e.g., a MAC address). A BGP speaker that implements RT-Constrain (RFC4684) MUST apply the RT-Constrain procedures to the ES-import RT as-well. For procedures and usage of this attribute, please see section 9.1 "Redundancy Group Discovery". 8.7 MAC Mobility Extended Community Sajassi, et al. Expires January 15, 2014 [Page 14] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 This extended community is a new transitive extended community with the Type field of 0x06 and the Sub-Type of 0x00. It may be advertised along with MAC Advertisement routes. The procedures for using this Extended Community are described in section 16 "MAC Mobility". The MAC Mobility Extended Community is encoded as a 8-octet value as follows: 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=0x00 |Flags(1 octet)| Reserved=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The low order bit of the flags octet is defined as the "Sticky/static" flag and may be set to 1. A value of 1 means that the MAC address is static and cannot move. 8.8 Default Gateway Extended Community The Default Gateway community is an Extended Community of an Opaque Type (see 3.3 of rfc4360). It is a transitive community, which means that the first octet is 0x03. The value of the second octet (Sub- Type) is 0x030d (Default Gateway) as defined by IANA. The Value field of this community is reserved (set to 0 by the senders, ignored by the receivers). 9. Multi-homing Functions This section discusses the functions, procedures and associated BGP routes used to support multi-homing in EVPN. This covers both multi- homed device (MHD) as well as multi-homed network (MHN) scenarios. 9.1 Multi-homed Ethernet Segment Auto-Discovery PEs connected to the same Ethernet segment can automatically discover each other with minimal to no configuration through the exchange of the Ethernet Segment route. 9.1.1 Constructing the Ethernet Segment Route The Route-Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value field comprises an IP address of the MES (typically, the loopback address) followed by 0's. Sajassi, et al. Expires January 15, 2014 [Page 15] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 The Ethernet Segment Identifier MUST be set to the ten octet ESI identifier described in section 6. The BGP advertisement that advertises the Ethernet Segment route MUST also carry an ES-Import extended community attribute, as defined in section 8.6. The Ethernet Segment Route filtering MUST be done such that the Ethernet Segment Route is imported only by the PEs that are multi- homed to the same Ethernet Segment. To that end, each PE that is connected to a particular Ethernet segment constructs an import filtering rule to import a route that carries the ES-Import extended community, constructed from the ESI. 9.2 Fast Convergence In EVPN, MAC address reachability is learnt via the BGP control-plane over the MPLS network. As such, in the absence of any fast protection mechanism, the network convergence time is a function of the number of MAC Advertisement routes that must be withdrawn by the PE encountering a failure. For highly scaled environments, this scheme yields slow convergence. To alleviate this, EVPN defines a mechanism to efficiently and quickly signal, to remote PE nodes, the need to update their forwarding tables upon the occurrence of a failure in connectivity to an Ethernet segment. This is done by having each PE advertise an Ethernet A-D Route per Ethernet segment for each locally attached segment (refer to section 9.2.1 below for details on how this route is constructed). Upon a failure in connectivity to the attached segment, the PE withdraws the corresponding Ethernet A-D route. This triggers all PEs that receive the withdrawal to update their next-hop adjacencies for all MAC addresses associated with the Ethernet segment in question. If no other PE had advertised an Ethernet A-D route for the same segment, then the PE that received the withdrawal simply invalidates the MAC entries for that segment. Otherwise, the PE updates the next-hop adjacencies to point to the backup PE(s). 9.2.1 Constructing the Ethernet A-D Route per Ethernet Segment This section describes procedures to construct the Ethernet A-D route when a single such route is advertised by an PE for a given Ethernet Segment. This flavor of the Ethernet A-D route is used for fast convergence (as discussed above) as well as for advertising the ESI label used for split-horizon filtering (as discussed in section 9.3). Support of this route flavor is MANDATORY. Route-Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value Sajassi, et al. Expires January 15, 2014 [Page 16] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 field comprises an IP address of the PE (typically, the loopback address) followed by 0. The Ethernet Segment Identifier MUST be a ten octet entity as described in section "Ethernet Segment". This document does not specify the use of the Ethernet A-D route when the Segment Identifier is set to 0. The Ethernet Tag ID MUST be set to 0. The MPLS label in the NLRI MUST be set to 0. The "ESI Label Extended Community" MUST be included in the route. If all-Active multi-homing is desired, then the "Active-Standby" bit in the flags of the ESI Label Extended Community MUST be set to 0 and the MPLS label in that extended community MUST be set to a valid MPLS label value. The MPLS label in this Extended Community is referred to as an "ESI label". This label MUST be a downstream assigned MPLS label if the advertising PE is using ingress replication for receiving multicast, broadcast or unknown unicast traffic from other PEs. If the advertising PE is using P2MP MPLS LSPs for sending multicast, broadcast or unknown unicast traffic, then this label MUST be an upstream assigned MPLS label. The usage of this label is described in section 9.3. If the Ethernet Segment is connected to more than one PE and Single- Active multi-homing is desired, then the "Active-Standby" bit in the flags of the ESI Label Extended Community MUST be set to 1 and ESI label MUST be set to zero. 9.2.1.1. Ethernet A-D Route Targets The Ethernet A-D route MUST carry one or more Route Target (RT) attributes. These RTs MUST be the set of RTs associated with all the EVPN instances to which the Ethernet Segment, corresponding to the Ethernet A-D route, belongs. 9.3 Split Horizon Consider a CE that is multi-homed to two or more PEs on an Ethernet segment ES1 operating in All-Active mode. If the CE sends a broadcast, unknown unicast, or multicast (BUM) packet to one of the non-DF (Designated Forwarder) PEs, say PE1, then PE1 will forward that packet to all or subset of the other PEs in that EVPN instance including the DF PE for that Ethernet segment. In this case the DF PE that the CE is multi-homed to MUST drop the packet and not forward back to the CE. This filtering is referred to as "split horizon" filtering in this document. Sajassi, et al. Expires January 15, 2014 [Page 17] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 In order to achieve this split horizon function, every BUM packet originating from a non-DF PE is encapsulated with an MPLS label that identifies the Ethernet segment of origin (i.e. the segment from which the frame entered the EVPN network). This label is referred to as the ESI label, and MUST be distributed by all PEs when operating in All-Active multi-homing mode using the "Ethernet A-D route per Ethernet Segment" as per the procedures in section 9.2.1 above. This route is imported by the PEs connected to the Ethernet Segment and also by the PEs that have at least one EVPN instance in common with the Ethernet Segment in the route. As described in section 9.1.1, the route MUST carry an ESI Label Extended Community with a valid ESI label. The disposition DF PE rely on the value of the ESI label to determine whether or not a BUM frame is allowed to egress a specific Ethernet segment. It should be noted that if the BUM frame is originated from the DF PE operating in All-Active multi-homing mode, then the DF PE MAY not encapsulate the frame with the ESI label. Furthermore, if the multi-homed PEs operate in active/standby mode, then the packet MUST NOT be encapsulated with the ESI label and the label value MUST be set to zero in ESI Label Extended Community per section 9.2.1 above. 9.3.1 ESI Label Assignment The following subsections describe the assignment procedures for the ESI label, which differ depending on the type of tunnels being used to deliver multi-destination packets in the EVPN network. 9.3.1.1 Ingress Replication All PEs operating in an All-Active multi-homing mode that rely on ingress replication for the reception of BUM traffic, distribute to other PEs, that belong to the Ethernet segment, a downstream assigned "ESI label" in the Ethernet A-D route per ESI. This label MUST be programmed in the platform label space by the advertising PE. Further the forwarding entry for this label must result in NOT forwarding packets received with this label onto the Ethernet segment that the label was distributed for. Consider PE1 and PE2 that are multi-homed to CE1 on ES1 and operating in All-Active multi-homing mode. Further consider that PE1 is using P2P or MP2P LSPs to send packets to PE2. Consider that PE1 is the non-DF for VLAN1 and PE2 is the DF for VLAN1, and PE1 receives a BUM packet from CE1 on VLAN1 on ES1. In this scenario, PE2 distributes an Inclusive Multicast Ethernet Tag route for VLAN1 corresponding to an EVPN instance. So, when PE1 sends a BUM packet, that it receives from CE1, it MUST first push onto the MPLS label stack the ESI label that PE2 has distributed for ES1. It MUST then push on the MPLS label distributed by PE2 in the Inclusive Multicast Ethernet Tag route for Sajassi, et al. Expires January 15, 2014 [Page 18] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 VLAN1. The resulting packet is further encapsulated in the P2P or MP2P LSP label stack required to transmit the packet to PE2. When PE2 receives this packet, it determines the set of ESIs to replicate the packet to from the top MPLS label, after any P2P or MP2P LSP labels have been removed. If the next label is the ESI label assigned by PE2 for ES1, then PE2 MUST NOT forward the packet onto ES1. If the next label is an ESI label which has not been assigned by PE2, then PE2 MUST drop the packet. It should be noted that in this scenario, if PE2 receives a BUM traffic for VLAN1 from CE1, then it doesn't need to encapsulate the packet with an ESI label when sending it to the PE1 since PE1 can use its DF logic to filter the BUM packets and thus doesn't need to use split-horizon filtering for ES1. 9.3.1.2. P2MP MPLS LSPs The non-DF PEs operating in an All-Active multi-homing mode that is using P2MP LSPs for sending BUM traffic, distribute to other PEs, that belong to the Ethernet segment or have an EVPN instance in common with the Ethernet Segment, an upstream assigned "ESI label" in the Ethernet A-D route. This label is upstream assigned by the PE that advertises the route. This label MUST be programmed by the other PEs, that are connected to the ESI advertised in the route, in the context label space for the advertising PE. Further the forwarding entry for this label must result in NOT forwarding packets received with this label onto the Ethernet segment that the label was distributed for. This label MUST also be programmed by the other PEs, that import the route but are not connected to the ESI advertised in the route, in the context label space for the advertising PE. Further the forwarding entry for this label must be a POP with no other associated action. Consider PE1 and PE2 that are multi-homed to CE1 on ES1 and operating in All-Active multi-homing mode. Also consider PE3 belongs to one of the EVPN instances of ES1. Further, assume that PE1 which is the non-DF, using P2MP MPLS LSPs to send BUM packets. When PE1 sends a BUM packet, that it receives from CE1, it MUST first push onto the MPLS label stack the ESI label that it has assigned for the ESI that the packet was received on. The resulting packet is further encapsulated in the P2MP MPLS label stack necessary to transmit the packet to the other PEs. Penultimate hop popping MUST be disabled on the P2MP LSPs used in the MPLS transport infrastructure for EVPN. When PE2 receives this packet, it de-capsulates the top MPLS label and forwards the packet using the context label space determined by the top label. If the next label is the ESI label assigned by PE1 to ES1, then PE2 MUST NOT forward the packet onto ES1. When PE3 receives this packet, it de-capsulates the top MPLS label and forwards the packet using the context label space determined by the top label. If the next label is the ESI label assigned by PE1 to ES1 and PE3 is not Sajassi, et al. Expires January 15, 2014 [Page 19] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 connected to ES1, then PE3 MUST pop the label and flood the packet over all local ESIs in that EVPN instance. It should be noted that when PE2 sends a BUM frame over a P2MP LSP, it does not need to encapsulate the frame with an ESI label because it is the DF for that VLAN. 9.4 Aliasing and Backup-Path In the case where a CE is multi-homed to multiple PE nodes, using a LAG with All-Active redundancy, it is possible that only a single PE learns a set of the MAC addresses associated with traffic transmitted by the CE. This leads to a situation where remote PE nodes receive MAC advertisement routes, for these addresses, from a single PE even though multiple PEs are connected to the multi-homed segment. As a result, the remote PEs are not able to effectively load-balance traffic among the PE nodes connected to the multi-homed Ethernet segment. This could be the case, for e.g. when the PEs perform data- path learning on the access, and the load-balancing function on the CE hashes traffic from a given source MAC address to a single PE. Another scenario where this occurs is when the PEs rely on control plane learning on the access (e.g. using ARP), since ARP traffic will be hashed to a single link in the LAG. To alleviate this issue, EVPN introduces the concept of 'Aliasing'. Aliasing refers to the ability of a PE to signal that it has reachability to a given locally attached Ethernet segment, even when it has learnt no MAC addresses from that segment. The Ethernet A-D route per EVI is used to that end. Remote PEs which receive MAC advertisement routes with non-reserved ESI SHOULD consider the advertised MAC address as reachable via all PEs which have advertised reachability to the relevant Segment using: (1) Ethernet A-D routes per EVI with the same ESI (and Ethernet Tag if applicable) AND (2)Ethernet A-D routes per ESI with the same ESI and with the Active/Standby bit set to 0 in the ESI Label Extended Community. This flavor of Ethernet A-D route per EVI, associated with aliasing, can arrive at target PEs asynchronously relative to the flavor of Ethernet A-D route associated with split-horizon and mass-withdraw (i.e. per ESI). Therefore, if the Ethernet A-D route per EVI arrives ahead of the Ethernet A-D route per ESI, then the former must NOT be used for traffic forwarding till the latter arrives. This will take care of corner cases and race conditions where the Ethernet A-D route associated with mass-withdraw is withdrawn but a PE still receives the route associated with aliasing. Backup-Path is a closely related function, albeit it applies to the case where the redundancy mode is Active/Standby. In this case, the Sajassi, et al. Expires January 15, 2014 [Page 20] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 PE advertises that it has reachability to a given locally attached Ethernet Segment using the Ethernet A-D route as well. Remote PEs which receive the MAC advertisement routes, with non-reserved ESI, MUST consider the MAC address as reachable via the advertising PE. Furthermore, the remote PEs SHOULD install a Backup-Path, for said MAC, to the PE which had advertised reachability to the relevant Segment using (1) an Ethernet A-D routes per EVI with the same ESI (and Ethernet Tag if applicable) AND (2) Ethernet A-D routes per ESI with the same ESI and with the Active/Standby bit set to 1 in the ESI Label Extended Community. 9.4.1 Constructing the Ethernet A-D Route per EVI This section describes procedures to construct the Ethernet A-D route when one or more such routes are advertised by an PE for a given EVI. This flavor of the Ethernet A-D route is used for aliasing, and support of this route flavor is OPTIONAL. Route-Distinguisher (RD) MUST be set to the RD of the EVI that is advertising the NLRI. An RD MUST be assigned for a given EVI on an PE. This RD MUST be unique across all EVIs on an PE. It is RECOMMENDED to use the Type 1 RD [RFC4364]. The value field comprises an IP address of the PE (typically, the loopback address) followed by a number unique to the PE. This number may be generated by the PE. Or in the Unique VLAN EVPN case, the low order 12 bits may be the 12 bit VLAN ID, with the remaining high order 4 bits set to 0. The Ethernet Segment Identifier MUST be a ten octet entity as described in section "Ethernet Segment Identifier". This document does not specify the use of the Ethernet A-D route when the Segment Identifier is set to 0. The Ethernet Tag ID is the identifier of an Ethernet Tag on the Ethernet segment. This value may be a 12 bit VLAN ID, in which case the low order 12 bits are set to the VLAN ID and the high order 20 bits are set to 0. Or it may be another Ethernet Tag used by the EVPN. It MAY be set to the default Ethernet Tag on the Ethernet segment or to the value 0. Note that the above allows the Ethernet A-D route to be advertised with one of the following granularities: + One Ethernet A-D route for a given tuple per EVI. This is applicable when the PE uses MPLS-based disposition. + One Ethernet A-D route per (where the Ethernet Tag ID is set to 0). This is applicable when the PE uses Sajassi, et al. Expires January 15, 2014 [Page 21] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 MAC-based disposition, or when the PE uses MPLS-based disposition when no VLAN translation is required. The usage of the MPLS label is described in the section on "Load Balancing of Unicast Packets". The Next Hop field of the MP_REACH_NLRI attribute of the route MUST be set to the IPv4 or IPv6 address of the advertising PE. 9.4.1.1 Ethernet A-D Route Targets The Ethernet A-D route MUST carry one or more Route Target (RT) attributes. RTs may be configured (as in IP VPNs), or may be derived automatically. If an PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD advertise all such RTs using Route Target Constrains. The use of RT Constrains allows each Ethernet A-D route to reach only those PEs that are configured to import at least one RT from the set of RTs carried in the Ethernet A-D route. 9.4.1.1.1 Auto-Derivation from the Ethernet Tag ID The following is the procedure for deriving the RT attribute automatically from the Ethernet Tag ID associated with the advertisement: + The Global Administrator field of the RT MUST be set to the Autonomous System (AS) number that the PE belongs to. + The Local Administrator field of the RT contains a 4 octets long number that encodes the Ethernet Tag-ID. If the Ethernet Tag-ID is a two octet VLAN ID then it MUST be encoded in the lower two octets of the Local Administrator field and the higher two octets MUST be set to zero. For the "Unique VLAN EVPN" this results in auto-deriving the RT from the Ethernet Tag, e.g., VLAN ID for that EVPN. 9.5 Designated Forwarder Election Consider a CE that is a host or a router that is multi-homed directly to more than one PE in an EVPN instance on a given Ethernet segment. One or more Ethernet Tags may be configured on the Ethernet segment. In this scenario only one of the PEs, referred to as the Designated Forwarder (DF), is responsible for certain actions: Sajassi, et al. Expires January 15, 2014 [Page 22] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 - Sending multicast and broadcast traffic, on a given Ethernet Tag on a particular Ethernet segment, to the CE. - Flooding unknown unicast traffic (i.e. traffic for which an PE does not know the destination MAC address), on a given Ethernet Tag on a particular Ethernet segment to the CE, if the environment requires flooding of unknown unicast traffic. Note that this behavior, which allows selecting a DF at the granularity of for multicast, broadcast and unknown unicast traffic, is the default behavior in this specification. Note that a CE always sends packets belonging to a specific flow using a single link towards an PE. For instance, if the CE is a host then, as mentioned earlier, the host treats the multiple links that it uses to reach the PEs as a Link Aggregation Group (LAG). The CE employs a local hashing function to map traffic flows onto links in the LAG. If a bridged network is multi-homed to more than one PE in an EVPN network via switches, then the support of All-Active points of attachments, as described in this specification, requires the bridge network to be connected to two or more PEs using a LAG. In this case the reasons for doing DF election are the same as those described above when a CE is a host or a router. If a bridged network does not connect to the PEs using LAG, then only one of the links between the switched bridged network and the PEs must be the active link for a given Ethernet Tag. In this case, the Ethernet A-D route per Ethernet segment MUST be advertised with the "Active-Standby" flag set to one. Procedures for supporting All- Active points of attachments, when a bridge network connects to the PEs using LAG, are for further study. The default procedure for DF election at the granularity of is referred to as "service carving". With service carving, it is possible to elect multiple DFs per Ethernet Segment (one per EVI) in order to perform load-balancing of multi-destination traffic destined to a given Segment. The load-balancing procedures carve up the EVI space among the PE nodes evenly, in such a way that every PE is the DF for a disjoint set of EVIs. The procedure for service carving is as follows: 1. When a PE discovers the ESI of the attached Ethernet Segment, it advertises an Ethernet Segment route with the associated ES-Import extended community attribute. Sajassi, et al. Expires January 15, 2014 [Page 23] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 2. The PE then starts a timer (default value = 3 seconds) to allow the reception of Ethernet Segment routes from other PE nodes connected to the same Ethernet Segment. This timer value MUST be same across all PEs connected to the same Ethernet Segment. 3. When the timer expires, each PE builds an ordered list of the IP addresses of all the PE nodes connected to the Ethernet Segment (including itself), in increasing numeric value. Each IP address in this list is extracted from the "Originator Router's IP address" field of the advertised Ethernet Segment route. Every PE is then given an ordinal indicating its position in the ordered list, starting with 0 as the ordinal for the PE with the numerically lowest IP address. The ordinals are used to determine which PE node will be the DF for a given EVPN instance on the Ethernet Segment using the following rule: Assuming a redundancy group of N PE nodes, the PE with ordinal i is the DF for an EVPN instance with an associated Ethernet Tag value V when (V mod N) = i. In the case where multiple Ethernet Tags are associated with a single EVPN instance, then the numerically lowest Ethernet Tag value in that EVPN instance MUST be used in the modulo function. It should be noted that using "Originator Router's IP address" field in the Ethernet Segment route to get the PE IP address needed for the ordered list, allows for a CE to be multi-homed across different ASes if such need every arises. 4. The PE that is elected as a DF for a given EVPN instance will unblock traffic for the Ethernet Tags associated with that EVPN instance. Note that the DF PE unblocks multi-destination traffic in the egress direction towards the Segment. All non-DF PEs continue to drop multi-destination traffic (for the associated EVPN instances) in the egress direction towards the Segment. In the case of link or port failure, the affected PE withdraws its Ethernet Segment route. This will re-trigger the service carving procedures on all the PEs in the RG. For PE node failure, or upon PE commissioning or decommissioning, the PEs re-trigger the service carving. In case of a Single-Active multi-homing, when a service moves from one PE in the RG to another PE as a result of re-carving, the PE, which ends up being the elected DF for the service, must trigger a MAC address flush notification towards the associated Ethernet Segment. This can be done, for e.g. using IEEE 802.1ak MVRP 'new' declaration. 9.6. Interoperability with Single-homing PEs Let's refer to PEs that only support single-homed CE devices as Sajassi, et al. Expires January 15, 2014 [Page 24] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 single-homing PEs. For single-homing PEs, all the above multi-homing procedures can be omitted; however, to allow for single-homing PEs to fully inter-operate with multi-homing PEs, some of the multi-homing procedures described above SHOULD be supported even by single-homing PEs: - procedures related to processing Ethernet A-D route for the purpose of Fast Convergence (9.2 Fast Convergence), to let single-homing PEs benefit from fast convergence - procedures related to processing Ethernet A-D route for the purpose of Aliasing (9.4 Aliasing and Backup-path), to let single-homing PEs benefit from load balancing - procedures related to processing Ethernet A-D route for the purpose of Backup-path (9.4 Aliasing and Backup-path), to let single-homing PEs to benefit from the corresponding convergence improvement 10. Determining Reachability to Unicast MAC Addresses PEs forward packets that they receive based on the destination MAC address. This implies that PEs must be able to learn how to reach a given destination unicast MAC address. There are two components to MAC address learning, "local learning" and "remote learning": 10.1. Local Learning A particular PE must be able to learn the MAC addresses from the CEs that are connected to it. This is referred to as local learning. The PEs in a particular EVPN instance MUST support local data plane learning using standard IEEE Ethernet learning procedures. An PE must be capable of learning MAC addresses in the data plane when it receives packets such as the following from the CE network: - DHCP requests - ARP request for its own MAC. - ARP request for a peer. Alternatively PEs MAY learn the MAC addresses of the CEs in the control plane or via management plane integration between the PEs and the CEs. Sajassi, et al. Expires January 15, 2014 [Page 25] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 There are applications where a MAC address that is reachable via a given PE on a locally attached Segment (e.g. with ESI X) may move such that it becomes reachable via another PE on another Segment (e.g. with ESI Y). This is referred to as a "MAC Mobility". Procedures to support this are described in section "MAC Mobility". 10.2. Remote learning A particular PE must be able to determine how to send traffic to MAC addresses that belong to or are behind CEs connected to other PEs i.e. to remote CEs or hosts behind remote CEs. We call such MAC addresses as "remote" MAC addresses. This document requires an PE to learn remote MAC addresses in the control plane. In order to achieve this, each PE advertises the MAC addresses it learns from its locally attached CEs in the control plane, to all the other PEs in that EVPN instance, using MP-BGP and specifically the MAC Advertisement route. 10.2.1. Constructing the BGP EVPN MAC Address Advertisement BGP is extended to advertise these MAC addresses using the MAC Advertisement route type in the EVPN NLRI. The RD MUST be the RD of the EVI that is advertising the NLRI. The procedures for setting the RD for a given EVI are described in section 9.4.1. The Ethernet Segment Identifier is set to the ten octet ESI described in section "Ethernet Segment". The Ethernet Tag ID may be zero or may represent a valid Ethernet Tag ID. This field may be non-zero when there are multiple bridge domains in the MAC-VRF (e.g., the PE needs to perform qualified learning for the VLANs in that MAC-VRF). When the the Ethernet Tag ID in the NLRI is set to a non-zero value, for a particular bridge domain, then this Ethernet Tag may either be the Ethernet tag value associated with the CE, e.g., VLAN ID, or it may be the Ethernet Tag Identifier, e.g., VLAN ID assigned by the EVPN provider and mapped to the CE's Ethernet tag. The latter would be the case if the CE Ethernet tags, e.g., VLAN ID, for a particular bridge domain are different on different CEs. The MAC address length field is in bits and it is typically set to 48. However this specification enables specifying the MAC address as a prefix; in which case, the MAC address length field is set to the length of the prefix. This provides the ability to aggregate MAC Sajassi, et al. Expires January 15, 2014 [Page 26] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 addresses if the deployment environment supports that. The encoding of a MAC address MUST be the 6-octet MAC address specified by [802.1D-ORIG] [802.1D-REV]. If the MAC address is advertised as a prefix then the trailing bits of the prefix MUST be set to 0 to ensure that the entire prefix is encoded as 6 octets. The IP Address field is optional. By default, the IP Address Length field is set to 0 and the IP address field is omitted from the route. When a valid IP address or address prefix needs to be advertised (e.g., for ARP suppression purposes or for inter-subnet switching), it is then encoded in this route. The IP Address Length field is in bits and it is the length of the IP prefix. This provides the ability to advertise IP address prefixes when the deployment environment supports that. The encoding of an IP address MUST be either 4 octets for IPv4 or 16 octets for IPv6. When the IP address is advertised as a prefix, then the trailing bits of the prefix MUST be set to 0 to ensure that the entire prefix is encoded as either 4 or 16 octets. The length field of EVPN NLRI (which is in octets and is described in section 8) is sufficient to determine whether an IP address/prefix is encoded in this route and if so, whether the encoded IP address/prefix is IPV4 or IPv6. The MPLS label field carries a single label and it is encoded as 3 octets, where the high-order 20 bits contain the label value. The MPLS label MUST be the downstream assigned that is used by the PE to forward MPLS-encapsulated Ethernet frames, where the destination MAC address in the Ethernet frame is the MAC address advertised in the above NLRI. The forwarding procedures are specified in section "Forwarding Unicast Packets" and "Load Balancing of Unicast Packets". An PE may advertise the same single EVPN label for all MAC addresses in a given EVI. This label assignment methodology is referred to as a per EVI label assignment. Alternatively, an PE may advertise a unique EVPN label per combination. This label assignment methodology is referred to as a per label assignment. As a third option, an PE may advertise a unique EVPN label per MAC address. All of these methodologies have their tradeoffs. The choice of a particular label assignment methodology is purely local to the PE that originates the route. Per EVI label assignment requires the least number of EVPN labels, but requires a MAC lookup in addition to an MPLS lookup on an egress PE for forwarding. On the other hand, a unique label per or a unique label per MAC allows an egress PE to forward a packet that it receives from another PE, to the connected CE, after looking up only the MPLS labels without having to perform a MAC lookup. This includes the capability to perform appropriate VLAN Sajassi, et al. Expires January 15, 2014 [Page 27] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 ID translation on egress to the CE. The Next Hop field of the MP_REACH_NLRI attribute of the route MUST be set to the IPv4 or IPv6 address of the advertising PE. The BGP advertisement for the MAC advertisement route MUST also carry one or more Route Target (RT) attributes. RTs may be configured (as in IP VPNs), or may be derived automatically from the Ethernet Tag ID, in the Unique VLAN case, as described in section "Ethernet A-D Route per EVPN". It is to be noted that this document does not require PEs to create forwarding state for remote MACs when they are learnt in the control plane. When this forwarding state is actually created is a local implementation matter. 10.2.2 Route Resolution If the Ethernet Segment Identifier field in a received MAC Advertisement route is set to the reserved ESI value of 0 or MAX-ESI, then the receiving PE MUST install forwarding state for the associated MAC Address based on the MAC Advertisement route alone. If the Ethernet Segment Identifier field in a received MAC Advertisement route is set to a non-reserved ESI, and the receiving PE is locally attached to the same ESI, then the PE does not alter its forwarding state based on the received route. This ensures that local routes are preferred to remote routes. If the Ethernet Segment Identifier field in a received MAC Advertisement route is set to a non-reserved ESI, then the receiving PE MUST install forwarding state for a given MAC address only when both the MAC Advertisement route AND the associated Ethernet A-D route per ESI have been received. To illustrate this with an example, consider two PEs (PE1 and PE2) connected to a multi-homed Ethernet Segment ES1. All-Active redundancy mode is assumed. A given MAC address M1 is learnt by PE1 but not PE2. On PE3, the following states may arise: T1- When the MAC Advertisement Route from PE1 and the Ethernet A-D routes per ESI from PE1 and PE2 are received, PE3 can forward traffic destined to M1 to both PE1 and PE2. T2- If after T1, PE1 withdraws its Ethernet A-D route per ESI, then PE3 forwards traffic destined to M1 to PE2 only. T3- If after T1, PE2 withdraws its Ethernet A-D route per ESI, then Sajassi, et al. Expires January 15, 2014 [Page 28] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 PE3 forwards traffic destined to M1 to PE1 only. T4- If after T1, PE1 withdraws its MAC Advertisement route, then PE3 treats traffic to M1 as unknown unicast. Note, here, that had PE2 also advertised a MAC route for M1 before PE1 withdraws its MAC route, then PE3 would have continued forwarding traffic destined to M1 to PE2. 11. ARP and ND The IP address field in the MAC advertisement route may optionally carry one of the IP addresses associated with the MAC address. This provides an option which can be used to minimize the flooding of ARP or Neighbor Discovery (ND) messages over the MPLS network and to remote CEs. This option also minimizes ARP (or ND) message processing on end-stations/hosts connected to the EVPN network. An PE may learn the IP address associated with a MAC address in the control or management plane between the CE and the PE. Or, it may learn this binding by snooping certain messages to or from a CE. When an PE learns the IP address associated with a MAC address, of a locally connected CE, it may advertise this address to other PEs by including it in the MAC Advertisement route. The IP Address may be an IPv4 address encoded using four octets, or an IPv6 address encoded using sixteen octets. The IP Address length field MUST be set to 32 for an IPv4 address or to 128 for an IPv6 address. If there are multiple IP addresses associated with a MAC address, then multiple MAC advertisement routes MUST be generated, one for each IP address. For instance, this may be the case when there are both an IPv4 and an IPv6 address associated with the MAC address. When the IP address is dissociated with the MAC address, then the MAC advertisement route with that particular IP address MUST be withdrawn. When an PE receives an ARP request for an IP address from a CE, and if the PE has the MAC address binding for that IP address, the PE SHOULD perform ARP proxy by responding to the ARP request. 11.1 Default Gateway When a PE needs to perform inter-subnet forwarding where each subnet is represented by a different broadcast domain (e.g., different VLAN) the inter-subnet forwarding is performed at layer 3 and the PE that performs such function is called the default gateway. In this case when the PE receives an ARP Request for the IP address of the default gateway, the PE originates an ARP Reply. Each PE that acts as a default gateway for a given EVPN instance MAY Sajassi, et al. Expires January 15, 2014 [Page 29] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 advertise in the EVPN control plane its default gateway MAC address using the MAC advertisement route, and indicates that such route is associated with the default gateway. This is accomplished by requiring the route to carry the Default Gateway extended community defined in [Section 8.8 Default Gateway Extended Community]. The IP address field (4 octets for IPv4, 16 octets for IPv6) is set to zero when advertising the MAC route with the Default Gateway extended community. Both ESI and Ethernet Tag fields are also set to zero for this advertisement. Unless it is known a priori (by means outside of this document) that all PEs of a given EVPN instance act as a default gateway for that EVPN instance, the MPLS label MUST be set to a valid downstream assigned label. Furthermore, even if all PEs of a given EVPN instance do act as a default gateway for that EVPN instance, but only some, but not all, of these PEs have sufficient (routing) information to provide inter- subnet routing for all the inter-subnet traffic originated within the subnet associated with the EVPN instance, then when such PE advertises in the EVPN control plane its default gateway MAC address using the MAC advertisement route, and indicates that such route is associated with the default gateway, the route MUST carry a valid downstream assigned label. If all PEs of a given EVPN instance act as a default gateway for that EVPN instance, and the same default gateway MAC address is used across all gateway devices, then no such advertisement is needed. However, if each default gateway uses a different MAC address, then each default gateway needs to be aware of other gateways' MAC addresses and thus the need for such advertisement. This is called MAC address aliasing since a single default GW can be represented by multiple MAC addresses. Each PE that receives this route and imports it as per procedures specified in this document follows the procedures in this section when replying to ARP Requests that it receives if such Requests are for the IP address in the received EVPN route. Each PE that acts as a default gateway for a given EVPN instance that receives this route and imports it as per procedures specified in this document MUST create MAC forwarding state that enables it to apply IP forwarding to the packets destined to the MAC address carried in the route. 12. Handling of Multi-Destination Traffic Sajassi, et al. Expires January 15, 2014 [Page 30] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Procedures are required for a given PE to send broadcast or multicast traffic, received from a CE encapsulated in a given Ethernet Tag (VLAN) in an EVPN instance, to all the other PEs that span that Ethernet Tag (VLAN) in that EVPN instance. In certain scenarios, described in section "Processing of Unknown Unicast Packets", a given PE may also need to flood unknown unicast traffic to other PEs. The PEs in a particular EVPN instance may use ingress replication, P2MP LSPs or MP2MP LSPs to send unknown unicast, broadcast or multicast traffic to other PEs. Each PE MUST advertise an "Inclusive Multicast Ethernet Tag Route" to enable the above. The following subsection provides the procedures to construct the Inclusive Multicast Ethernet Tag route. Subsequent subsections describe in further detail its usage. 12.1. Construction of the Inclusive Multicast Ethernet Tag Route The RD MUST be the RD of the EVI that is advertising the NLRI. The procedures for setting the RD for a given EVPN instance on a PE are described in section 9.4.1. The Ethernet Tag ID is the identifier of the Ethernet Tag. It MAY be set to 0 or to a valid Ethernet Tag value. The Originating Router's IP address MUST be set to an IP address of the PE. This address SHOULD be common for all the EVIs on the PE (e.,g., this address may be PE's loopback address). The IP Address Length field is in bits. The Next Hop field of the MP_REACH_NLRI attribute of the route MUST be set to the same IP address as the one carried in the Originating Router's IP Address field. The BGP advertisement for the Inclusive Multicast Ethernet Tag route MUST also carry one or more Route Target (RT) attributes. The assignment of RTs described in the section on "Constructing the BGP EVPN MAC Address Advertisement" MUST be followed. 12.2. P-Tunnel Identification In order to identify the P-Tunnel used for sending broadcast, unknown unicast or multicast traffic, the Inclusive Multicast Ethernet Tag route MUST carry a "PMSI Tunnel Attribute" as specified in [BGP MVPN]. Depending on the technology used for the P-tunnel for the EVPN instance on the PE, the PMSI Tunnel attribute of the Inclusive Sajassi, et al. Expires January 15, 2014 [Page 31] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Multicast Ethernet Tag route is constructed as follows. + If the PE that originates the advertisement uses a P-Multicast tree for the P-tunnel for EVPN, the PMSI Tunnel attribute MUST contain the identity of the tree (note that the PE could create the identity of the tree prior to the actual instantiation of the tree). + An PE that uses a P-Multicast tree for the P-tunnel MAY aggregate two or more Ethernet Tags in the same or different EVIs present on the PE onto the same tree. In this case, in addition to carrying the identity of the tree, the PMSI Tunnel attribute MUST carry an MPLS upstream assigned label which the PE has bound uniquely to the Ethernet Tag for the EVI associated with this update (as determined by its RTs). If the PE has already advertised Inclusive Multicast Ethernet Tag routes for two or more Ethernet Tags that it now desires to aggregate, then the PE MUST re-advertise those routes. The re-advertised routes MUST be the same as the original ones, except for the PMSI Tunnel attribute and the label carried in that attribute. + If the PE that originates the advertisement uses ingress replication for the P-tunnel for EVPN, the route MUST include the PMSI Tunnel attribute with the Tunnel Type set to Ingress Replication and Tunnel Identifier set to a routable address of the PE. The PMSI Tunnel attribute MUST carry a downstream assigned MPLS label. This label is used to demultiplex the broadcast, multicast or unknown unicast EVPN traffic received over a MP2P tunnel by the PE. + The Leaf Information Required flag of the PMSI Tunnel attribute MUST be set to zero, and MUST be ignored on receipt. 13. Processing of Unknown Unicast Packets The procedures in this document do not require the PEs to flood unknown unicast traffic to other PEs. If PEs learn CE MAC addresses via a control plane protocol, the PEs can then distribute MAC addresses via BGP, and all unicast MAC addresses will be learnt prior to traffic to those destinations. However, if a destination MAC address of a received packet is not known by the PE, the PE may have to flood the packet. When flooding, one must take into account "split horizon forwarding" as follows: The principles behind the following procedures are borrowed from the split horizon forwarding rules in VPLS solutions [RFC4761] and Sajassi, et al. Expires January 15, 2014 [Page 32] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 [RFC4762]. When an PE capable of flooding (say PEx) receives an unknown destination MAC address, it floods the frame. If the frame arrived from an attached CE, PEx must send a copy of the frame to every other attached CE participating in that EVPN instance, on a different ESI than the one it received the frame on, as long as the PE is the DF for the egress ESI. In addition, the PE must flood the frame to all other PEs participating in that EVPN instance. If, on the other hand, the frame arrived from another PE (say PEy), PEx must send a copy of the packet only to attached CEs as long as it is the DF for the egress ESI. PEx MUST NOT send the frame to other PEs, since PEy would have already done so. Split horizon forwarding rules apply to unknown MAC addresses. Whether or not to flood packets to unknown destination MAC addresses should be an administrative choice, depending on how learning happens between CEs and PEs. The PEs in a particular EVPN instance may use ingress replication using RSVP-TE P2P LSPs or LDP MP2P LSPs for sending unknown unicast traffic to other PEs. Or they may use RSVP-TE P2MP or LDP P2MP for sending such traffic to other PEs. 13.1. Ingress Replication If ingress replication is in use, the P-Tunnel attribute, carried in the Inclusive Multicast Ethernet Tag routes for the EVPN instance, specifies the downstream label that the other PEs can use to send unknown unicast, multicast or broadcast traffic for that EVPN instance to this particular PE. The PE that receives a packet with this particular MPLS label MUST treat the packet as a broadcast, multicast or unknown unicast packet. Further if the MAC address is a unicast MAC address, the PE MUST treat the packet as an unknown unicast packet. 13.2. P2MP MPLS LSPs The procedures for using P2MP LSPs are very similar to VPLS procedures [VPLS-MCAST]. The P-Tunnel attribute used by an PE for sending unknown unicast, broadcast or multicast traffic for a particular EVPN instance is advertised in the Inclusive Ethernet Tag Multicast route as described in section "Handling of Multi- Destination Traffic". The P-Tunnel attribute specifies the P2MP LSP identifier. This is the equivalent of an Inclusive tree in [VPLS-MCAST]. Note that multiple Ethernet Tags, which may be in different EVPN instances, may use the same P2MP LSP, using upstream labels [VPLS-MCAST]. This is the Sajassi, et al. Expires January 15, 2014 [Page 33] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 equivalent of an Aggregate Inclusive tree in [VPLS-MCAST]. When P2MP LSPs are used for flooding unknown unicast traffic, packet re- ordering is possible. The PE that receives a packet on the P2MP LSP specified in the PMSI Tunnel Attribute MUST treat the packet as a broadcast, multicast or unknown unicast packet. Further if the MAC address is a unicast MAC address, the PE MUST treat the packet as an unknown unicast packet. 14. Forwarding Unicast Packets This section describes procedures for forwarding unicast packets by PEs, where such packets are received from either directly connected CEs, or from some other PEs. 14.1. Forwarding packets received from a CE When an PE receives a packet from a CE, on a given Ethernet Tag, it must first look up the source MAC address of the packet. In certain environments the source MAC address MAY be used to authenticate the CE and determine that traffic from the host can be allowed into the network. Source MAC lookup MAY also be used for local MAC address learning. If the PE decides to forward the packet, the destination MAC address of the packet must be looked up. If the PE has received MAC address advertisements for this destination MAC address from one or more other PEs or learned it from locally connected CEs, it is considered as a known MAC address. Otherwise, the MAC address is considered as an unknown MAC address. For known MAC addresses the PE forwards this packet to one of the remote PEs or to a locally attached CE. When forwarding to a remote PE, the packet is encapsulated in the EVPN MPLS label advertised by the remote PE, for that MAC address, and in the MPLS LSP label stack to reach the remote PE. If the MAC address is unknown and if the administrative policy on the PE requires flooding of unknown unicast traffic then: - The PE MUST flood the packet to other PEs. The PE MUST first encapsulate the packet in the ESI MPLS label as described in section 9.3. If ingress replication is used, the packet MUST be replicated one or more times to each remote PE with the outermost label being an MPLS label determined as follows: This is the MPLS label advertised by the remote PE in a PMSI Tunnel Attribute in the Inclusive Multicast Ethernet Tag route for an combination. The Ethernet Tag in the route must be the same as the Sajassi, et al. Expires January 15, 2014 [Page 34] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Ethernet Tag associated with the interface on which the ingress PE receives the packet. If P2MP LSPs are being used the packet MUST be sent on the P2MP LSP that the PE is the root of for the Ethernet Tag in the EVPN instance. If the same P2MP LSP is used for all Ethernet Tags, then all the PEs in the EVPN instance MUST be the leaves of the P2MP LSP. If a distinct P2MP LSP is used for a given Ethernet Tag in the EVPN instance, then only the PEs in the Ethernet Tag MUST be the leaves of the P2MP LSP. The packet MUST be encapsulated in the P2MP LSP label stack. If the MAC address is unknown then, if the administrative policy on the PE does not allow flooding of unknown unicast traffic: - The PE MUST drop the packet. 14.2. Forwarding packets received from a remote PE This section described the procedures for forwarding known and unknown unicast packets received from a remote PE. 14.2.1. Unknown Unicast Forwarding When an PE receives an MPLS packet from a remote PE then, after processing the MPLS label stack, if the top MPLS label ends up being a P2MP LSP label associated with an EVPN instance or in case of ingress replication the downstream label advertised in the P-Tunnel attribute, and after performing the split horizon procedures described in section "Split Horizon": - If the PE is the designated forwarder of BUM traffic on a particular set of ESIs for the Ethernet Tag, the default behavior is for the PE to flood the packet on these ESIs. In other words, the default behavior is for the PE to assume that for BUM traffic, it is not required to perform a destination MAC address lookup. As an option, the PE may perform a destination MAC lookup to flood the packet to only a subset of the CE interfaces in the Ethernet Tag. For instance the PE may decide to not flood an BUM packet on certain Ethernet segments even if it is the DF on the Ethernet segment, based on administrative policy. - If the PE is not the designated forwarder on any of the ESIs for the Ethernet Tag, the default behavior is for it to drop the packet. 14.2.2. Known Unicast Forwarding If the top MPLS label ends up being an EVPN label that was advertised in the unicast MAC advertisements, then the PE either forwards the packet based on CE next-hop forwarding information associated with Sajassi, et al. Expires January 15, 2014 [Page 35] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 the label or does a destination MAC address lookup to forward the packet to a CE. 15. Load Balancing of Unicast Frames This section specifies the load balancing procedures for sending known unicast frames to a multi-homed CE. 15.1. Load balancing of traffic from an PE to remote CEs Whenever a remote PE imports a MAC advertisement for a given in an EVI, it MUST examine all imported Ethernet A-D routes for that ESI in order to determine the load-balancing characteristics of the Ethernet segment. 15.1.1 Single-Active Redundancy Mode For a given ESI, if the remote PE has imported an Ethernet A-D route per Ethernet Segment from at least one PE, where the "Active-Standby" flag in the ESI Label Extended Community is set, then the remote PE MUST deduce that the Ethernet segment is operating in Single-Active redundancy mode. As such, the MAC address will be reachable only via the PE announcing the associated MAC Advertisement route - this is referred to as the primary PE. The set of other PE nodes advertising Ethernet A-D routes per Ethernet Segment for the same ESI serve as backup paths, in case the active PE encounters a failure. These are referred to as the backup PEs. It should be noted that the primary PE for a given is the DF for that . If the primary PE encounters a failure, it MAY withdraw its Ethernet A-D route for the affected segment prior to withdrawing the entire set of MAC Advertisement routes. In the case where only a single other backup PE in the network had advertised an Ethernet A-D route for the same ESI, the remote PE can then use the Ethernet A-D route withdrawal as a trigger to update its forwarding entries, for the associated MAC addresses, to point towards the backup PE. As the backup PE starts learning the MAC addresses over its attached Ethernet segment, it will start sending MAC Advertisement routes while the failed PE withdraws its own. This mechanism minimizes the flooding of traffic during fail-over events. In the case where multiple other backup PE in the network had advertised an Ethernet A-D route for the same ESI, the remote PE MUST then use the Ethernet A-D route withdrawal as a trigger to start flooding traffic destined to the associated MAC addresses (as long as flooding of unknown unicast is administratively allowed). It is not possible to select a single backup path in this case. Sajassi, et al. Expires January 15, 2014 [Page 36] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 15.1.2 All-Active Redundancy Mode If for the given ESI, none of the Ethernet A-D routes per Ethernet Segment imported by the remote PE have the "Active-Standby" flag set in the ESI Label Extended Community, then the remote PE MUST treat the Ethernet segment as operating in All-Active redundancy mode. The remote PE would then treat the MAC address as reachable via all of the PE nodes from which it has received both an Ethernet A-D route per Ethernet Segment as well as an Ethernet A-D route per EVI for the ESI in question. The remote PE MUST use the MAC advertisement and eligible Ethernet A-D routes to construct the set of next-hops that it can use to send the packet to the destination MAC. Each next-hop comprises an MPLS label stack that is to be used by the egress PE to forward the packet. This label stack is determined as follows: -If the next-hop is constructed as a result of a MAC route then this label stack MUST be used. However, if the MAC route doesn't exist, then the next-hop and MPLS label stack is constructed as a result of the Ethernet A-D routes. Note that the following description applies to determining the label stack for a particular next-hop to reach a given PE, from which the remote PE has received and imported Ethernet A-D routes that have the matching ESI and Ethernet Tag as the one present in the MAC advertisement. The Ethernet A-D routes mentioned in the following description refer to the ones imported from this given PE. -If an Ethernet A-D route per Ethernet Segment for that ESI exists, together with an Ethernet A-D route per EVI, then the label from that latter route must be used. The following example explains the above. Consider a CE (CE1) that is dual-homed to two PEs (PE1 and PE2) on a LAG interface (ES1), and is sending packets with MAC address MAC1 on VLAN1. A remote PE, say PE3, is able to learn that MAC1 is reachable via PE1 and PE2. Both PE1 and PE2 may advertise MAC1 in BGP if they receive packets with MAC1 from CE1. If this is not the case, and if MAC1 is advertised only by PE1, PE3 still considers MAC1 as reachable via both PE1 and PE2 as both PE1 and PE2 advertise a Ethernet A-D route per ESI for ES1 as well as an Ethernet A-D route per EVI for . The MPLS label stack to send the packets to PE1 is the MPLS LSP stack to get to PE1 and the EVPN label advertised by PE1 for CE1's MAC. The MPLS label stack to send packets to PE2 is the MPLS LSP stack to get to PE2 and the MPLS label in the Ethernet A-D route advertised by PE2 for , if PE2 has not advertised MAC1 in BGP. Sajassi, et al. Expires January 15, 2014 [Page 37] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 We will refer to these label stacks as MPLS next-hops. The remote PE (PE3) can now load balance the traffic it receives from its CEs, destined for CE1, between PE1 and PE2. PE3 may use N-Tuple flow information to hash traffic into one of the MPLS next-hops for load balancing of IP traffic. Alternatively PE3 may rely on the source MAC addresses for load balancing. Note that once PE3 decides to send a particular packet to PE1 or PE2 it can pick one out of multiple possible paths to reach the particular remote PE using regular MPLS procedures. For instance, if the tunneling technology is based on RSVP-TE LSPs, and PE3 decides to send a particular packet to PE1, then PE3 can choose from multiple RSVP-TE LSPs that have PE1 as their destination. When PE1 or PE2 receive the packet destined for CE1 from PE3, if the packet is a unicast MAC packet it is forwarded to CE1. If it is a multicast or broadcast MAC packet then only one of PE1 or PE2 must forward the packet to the CE. Which of PE1 or PE2 forward this packet to the CE is determined based on which of the two is the DF. If the connectivity between the multi-homed CE and one of the PEs that it is attached to fails, the PE MUST withdraw the Ethernet Tag A-D routes, that had been previously advertised, for the Ethernet Segment to the CE. When the MAC entry on the PE ages out, the PE MUST withdraw the MAC address from BGP. Note that to aid convergence, the Ethernet Tag A-D routes MAY be withdrawn before the MAC routes. This enables the remote PEs to remove the MPLS next-hop to this particular PE from the set of MPLS next-hops that can be used to forward traffic to the CE. For further details and procedures on withdrawal of EVPN route types in the event of PE to CE failures please section "PE to CE Network Failures". 15.2. Load balancing of traffic between an PE and a local CE A CE may be configured with more than one interface connected to different PEs or the same PE for load balancing, using a technology such as LAG. The PE(s) and the CE can load balance traffic onto these interfaces using one of the following mechanisms. 15.2.1. Data plane learning Consider that the PEs perform data plane learning for local MAC addresses learned from local CEs. This enables the PE(s) to learn a particular MAC address and associate it with one or more interfaces, if the technology between the PE and the CE supports multi-pathing. The PEs can now load balance traffic destined to that MAC address on the multiple interfaces. Sajassi, et al. Expires January 15, 2014 [Page 38] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Whether the CE can load balance traffic that it generates on the multiple interfaces is dependent on the CE implementation. 15.2.2. Control plane learning The CE can be a host that advertises the same MAC address using a control protocol on both interfaces. This enables the PE(s) to learn the host's MAC address and associate it with one or more interfaces. The PEs can now load balance traffic destined to the host on the multiple interfaces. The host can also load balance the traffic it generates onto these interfaces and the PE that receives the traffic employs EVPN forwarding procedures to forward the traffic. 16. MAC Mobility It is possible for a given host or end-station (as defined by its MAC address) to move from one Ethernet segment to another; this is referred to as 'MAC Mobility' or 'MAC move' and it is different from the multi-homing situation in which a given MAC address is reachable via multiple PEs for the same Ethernet segment. In a MAC move, there would be two sets of MAC Advertisement routes, one set with the new Ethernet segment and one set with the previous Ethernet segment, and the MAC address would appear to be reachable via each of these segments. In order to allow all of the PEs in the EVPN instance to correctly determine the current location of the MAC address, all advertisements of it being reachable via the previous Ethernet segment MUST be withdrawn by the PEs, for the previous Ethernet segment, that had advertised it. If local learning is performed using the data plane, these PEs will not be able to detect that the MAC address has moved to another Ethernet segment and the receipt of MAC Advertisement routes, with the MAC Mobility extended community attribute, from other PEs serves as the trigger for these PEs to withdraw their advertisements. If local learning is performed using the control or management planes, these interactions serve as the trigger for these PEs to withdraw their advertisements. In a situation where there are multiple moves of a given MAC, possibly between the same two Ethernet segments, there may be multiple withdrawals and re-advertisements. In order to ensure that all PEs in the EVPN instance receive all of these correctly through the intervening BGP infrastructure, it is necessary to introduce a sequence number into the MAC Mobility extended community attribute. An implementation MUST handle the scenarios where the sequence number Sajassi, et al. Expires January 15, 2014 [Page 39] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 wraps around to process mobility event correctly. Every MAC mobility event for a given MAC address will contain a sequence number that is set using the following rules: - A PE advertising a MAC address for the first time advertises it with no MAC Mobility extended community attribute. - A PE detecting a locally attached MAC address for which it had previously received a MAC Advertisement route with a different Ethernet segment identifier advertises the MAC address in a MAC Advertisement route tagged with a MAC Mobility extended community attribute with a sequence number one greater than the sequence number in the MAC mobility attribute of the received MAC Advertisement route. In the case of the first mobility event for a given MAC address, where the received MAC Advertisement route does not carry a MAC Mobility attribute, the value of the sequence number in the received route is assumed to be 0 for purpose of this processing. - A PE detecting a locally attached MAC address for which it had previously received a MAC Advertisement route with the same non-zero Ethernet segment identifier advertises it with: i. no MAC Mobility extended community attribute, if the received route did not carry said attribute. ii. a MAC Mobility extended community attribute with the sequence number equal to the highest of the sequence number(s) in the received MAC Advertisement route(s), if the received route(s) is (are) tagged with a MAC Mobility extended community attribute. - A PE detecting a locally attached MAC address for which it had previously received a MAC Advertisement route with the same zero Ethernet segment identifier (single-homed scenarios) advertises it with MAC mobility extended community attribute with the sequence number set properly. In case of single-homed scenarios, there is no need for ESI comparison. The reason ESI comparison is done for multi- homing, is to prevent false detection of MAC move among the PEs attached to the same multi-homed site. A PE receiving a MAC Advertisement route for a MAC address with a different Ethernet segment identifier and a higher sequence number than that which it had previously advertised, withdraws its MAC Advertisement route. If two (or more) PEs advertise the same MAC address with same sequence number but different Ethernet segment identifiers, a PE that receives these routes selects the route advertised by the PE with lowest IP address as the best route. Sajassi, et al. Expires January 15, 2014 [Page 40] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 16.1. MAC Duplication Issue A situation may arise where the same MAC address is learned by different PEs in the same VLAN because of two (or more hosts) being mis-configured with the same (duplicate) MAC address. In such situation, the traffic originating from these hosts would trigger continuous MAC moves among the PEs attached to these hosts. It is important to recognize such situation and avoid incrementing the sequence number (in the MAC Mobility attribute) to infinity. In order to remedy such situation, a PE that detects a MAC mobility event by way of local learning starts an M-second timer (default value of M = 5) and if it detects N MAC moves before the timer expires (default value for N = 3), it concludes that a duplicate MAC situation has occurred. The PE MUST alert the operator and stop sending and processing any BGP MAC Advertisement routes for that MAC address till a corrective action is taken by the operator. The values of M and N MUST be configurable to allow for flexibility in operator control. Note that the other PEs in the E-VPN instance will forward the traffic for the duplicate MAC address to one of the PEs advertising the duplicate MAC address. 16.2. Sticky MAC addresses There are scenarios in which it is desired to configure some MAC addresses as static so that they are not subjected to MAC move. In such scenarios, these MAC addresses are advertised with MAC Mobility Extended Community where static flag is set to 1 and sequence number is set to zero. If a PE receives such advertisements and later learns the same MAC address(es) via local learning, then the PE MUST alert the operator. 17. Multicast & Broadcast The PEs in a particular EVPN instance may use ingress replication or P2MP LSPs to send multicast traffic to other PEs. 17.1. Ingress Replication The PEs may use ingress replication for flooding BUM traffic as described in section "Handling of Multi-Destination Traffic". A given broadcast packet must be sent to all the remote PEs. However a given multicast packet for a multicast flow may be sent to only a subset of the PEs. Specifically a given multicast flow may be sent to only those PEs that have receivers that are interested in the multicast flow. Determining which of the PEs have receivers for a given multicast flow is done using explicit tracking described below. Sajassi, et al. Expires January 15, 2014 [Page 41] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 17.2. P2MP LSPs An PE may use an "Inclusive" tree for sending an BUM packet. This terminology is borrowed from [VPLS-MCAST]. A variety of transport technologies may be used in the SP network. For inclusive P-Multicast trees, these transport technologies include point-to-multipoint LSPs created by RSVP-TE or mLDP. 17.2.1. Inclusive Trees An Inclusive Tree allows the use of a single multicast distribution tree, referred to as an Inclusive P-Multicast tree, in the SP network to carry all the multicast traffic from a specified set of EVPN instances on a given PE. A particular P-Multicast tree can be set up to carry the traffic originated by sites belonging to a single EVPN instance, or to carry the traffic originated by sites belonging to different EVPN instances. The ability to carry the traffic of more than one EVPN instance on the same tree is termed 'Aggregation'. The tree needs to include every PE that is a member of any of the EVPN instances that are using the tree. This implies that an PE may receive multicast traffic for a multicast stream even if it doesn't have any receivers that are interested in receiving traffic for that stream. An Inclusive P-Multicast tree as defined in this document is a P2MP tree. A P2MP tree is used to carry traffic only for EVPN CEs that are connected to the PE that is the root of the tree. The procedures for signaling an Inclusive Tree are the same as those in [VPLS-MCAST] with the VPLS-AD route replaced with the Inclusive Multicast Ethernet Tag route. The P-Tunnel attribute [VPLS-MCAST] for an Inclusive tree is advertised in the Inclusive Multicast route as described in section "Handling of Multi-Destination Traffic". Note that an PE can "aggregate" multiple inclusive trees for different EVPN instances on the same P2MP LSP using upstream labels. The procedures for aggregation are the same as those described in [VPLS- MCAST], with VPLS A-D routes replaced by EVPN Inclusive Multicast routes. 18. Convergence This section describes failure recovery from different types of network failures. 18.1. Transit Link and Node Failures between PEs Sajassi, et al. Expires January 15, 2014 [Page 42] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 The use of existing MPLS Fast-Reroute mechanisms can provide failure recovery in the order of 50ms, in the event of transit link and node failures in the infrastructure that connects the PEs. 18.2. PE Failures Consider a host host1 that is dual homed to PE1 and PE2. If PE1 fails, a remote PE, PE3, can discover this based on the failure of the BGP session. This failure detection can be in the sub-second range if BFD is used to detect BGP session failure. PE3 can update its forwarding state to start sending all traffic for host1 to only PE2. It is to be noted that this failure recovery is potentially faster than what would be possible if data plane learning were to be used. As in that case PE3 would have to rely on re-learning of MAC addresses via PE2. 18.2. PE to CE Network Failures When an Ethernet segment connected to an PE fails or when a Ethernet Tag is decommissioned on an Ethernet segment, then the PE MUST withdraw the Ethernet A-D route(s) announced for the that are impacted by the failure or decommissioning. In addition, the PE MUST also withdraw the MAC advertisement routes that are impacted by the failure or decommissioning. The Ethernet A-D routes should be used by an implementation to optimize the withdrawal of MAC advertisement routes. When an PE receives a withdrawal of a particular Ethernet A-D route from an PE it SHOULD consider all the MAC advertisement routes, that are learned from the same as in the Ethernet A-D route, from the advertising PE, as having been withdrawn. This optimizes the network convergence times in the event of PE to CE failures. 19. Frame Ordering In a MAC address, bit-1 of the most significant byte is used for unicast/multicast indication and bit-2 is used for globally unique versus locally administered MAC address. If the value of the 2nd nibble (bits 4 thorough 8) of the most significant byte of the destination MAC address (which follows the last MPLS label) happens to be 0x4 or 0x6, then the Ethernet frame can be misinterpreted as an IPv4 or IPv6 packet by intermediate P nodes performing ECMP resulting in load balancing packets belonging to the same flow on different ECMP paths, thus subjecting them to different delays. Therefore, packets belonging to the same flow can arrive at the destination out of order. This out of order delivery can happen during steady state in absence of any failures resulting in significant impact to the Sajassi, et al. Expires January 15, 2014 [Page 43] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 network operation. In order to avoid any such mis-ordering, the usage of control word SHALL adhere to the following rules: - A PE MUST use the control world when sending EVPN encapsulated packets over a MP2P or a P2P LSP - A PE MUST NOT use the control world when sending EVPN encapsulated packets over a P2MP LSP The control word is defined as follows: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0| Reserved | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In the above diagram the first 4 bits MUST be set to 0. The rest of the first 16 bits are reserved for future use. They MUST be set to 0 when transmitting, and MUST be ignored upon receipt. The next 16 bits provide a sequence number that MUST also be set to zero by default. 20. Acknowledgements Special thanks to Yakov Rekhter for reviewing this draft several times and providing valuable comments and for his very engaging discussions on several topics of this draft that helped shape this document. We would also like to thank Pedro Marques, Kaushik Ghosh, Nischal Sheth, Robert Raszuk, Amit Shukla and Nadeem Mohammed for discussions that helped shape this document. We would also like to thank Han Nguyen for his comments and support of this work. We would also like to thank Steve Kensil and Reshad Rahman for their reviews. Last but not least, many thanks to Jakob Heitz for his help to improve several sections of this draft. 21. Security Considerations 22. IANA Considerations Sajassi, et al. Expires January 15, 2014 [Page 44] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 23. References 23.1 Normative References [RFC4364] "BGP/MPLS IP VPNs", Rosen, Rekhter, et. al., February 2006 [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, January 2007. [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007. [RFC4271] Y. Rekhter et. al., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006 [RFC4760] T. Bates et. al., "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007 23.2 Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [EVPN-REQ] A. Sajassi, R. Aggarwal et. al., "Requirements for Ethernet VPN", draft-ietf-l2vpn-evpn-req-04.txt, July 2013. [VPLS-MCAST] "Multicast in VPLS". R. Aggarwal et.al., draft-ietf- l2vpn-vpls-mcast-14.txt, July 2013. [RT-CONSTRAIN] P. Marques et. al., "Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684, November 2006 24. Author's Address Ali Sajassi Cisco Email: sajassi@cisco.com Rahul Aggarwal Email: raggarwa_1@yahoo.com Sajassi, et al. Expires January 15, 2014 [Page 45] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Wim Henderickx Alcatel-Lucent e-mail: wim.henderickx@alcatel-lucent.com Aldrin Isaac Bloomberg Email: aisaac71@bloomberg.net James Uttaro AT&T 200 S. Laurel Avenue Middletown, NJ 07748 USA Email: uttaro@att.com Nabil Bitar Verizon Communications Email : nabil.n.bitar@verizon.com Ravi Shekhar Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: rshekhar@juniper.net Florin Balus Alcatel-Lucent e-mail: Florin.Balus@alcatel-lucent.com Keyur Patel Cisco 170 West Tasman Drive San Jose, CA 95134, US Email: keyupate@cisco.com Sami Boutros Cisco 170 West Tasman Drive San Jose, CA 95134, US Email: sboutros@cisco.com Sajassi, et al. Expires January 15, 2014 [Page 46] INTERNET DRAFT BGP MPLS Based Ethernet VPN July 15, 2013 Samer Salam Cisco Email: ssalam@cisco.com John Drake Juniper Networks Email: jdrake@juniper.net Sajassi, et al. Expires January 15, 2014 [Page 47]