Internet Working Group Ali Sajassi, Ed. Internet Draft Samer Salam Category: Standards Track Cisco Nabil Bitar Verizon Aldrin Isaac Bloomberg Wim Henderickx Alcatel-Lucent Lizhong Jin ZTE Expires: December 18, 2014 June 18, 2014 PBB-EVPN draft-ietf-l2vpn-pbb-evpn-07 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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Abstract This document discusses how Ethernet Provider Backbone Bridging [802.1ah] can be combined with EVPN in order to reduce the number of BGP MAC advertisement routes by aggregating Customer/Client MAC (C- MAC) addresses via Provider Backbone MAC address (B-MAC), provide client MAC address mobility using C-MAC aggregation and B-MAC sub- netting, confine the scope of C-MAC learning to only active flows, offer per site policies and avoid C-MAC address flushing on topology changes. The combined solution is referred to as PBB-EVPN. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. MAC Advertisement Route Scalability . . . . . . . . . . . 5 4.2. C-MAC Mobility with MAC Summarization . . . . . . . . . . 5 4.3. C-MAC Address Learning and Confinement . . . . . . . . . . 5 4.4. Per Site Policy Support . . . . . . . . . . . . . . . . . 6 4.5. Avoiding C-MAC Address Flushing . . . . . . . . . . . . . 6 5. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6 6. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . 7 6.2. BGP MAC Advertisement Route . . . . . . . . . . . . . . . 8 6.3. Inclusive Multicast Ethernet Tag Route . . . . . . . . . . 8 6.4. Ethernet Segment Route . . . . . . . . . . . . . . . . . . 8 6.5. ESI Label Extended Community . . . . . . . . . . . . . . . 9 6.6. ES-Import Route Target . . . . . . . . . . . . . . . . . . 9 6.7. MAC Mobility Extended Community . . . . . . . . . . . . . 9 6.8. Default Gateway Extended Community . . . . . . . . . . . . 9 7. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. MAC Address Distribution over Core . . . . . . . . . . . . 9 7.2. Device Multi-homing . . . . . . . . . . . . . . . . . . . 9 Sajassi et al. Expires December 18, 2014 [Page 2] INTERNET DRAFT PBB-EVPN June 18, 2014 7.2.1 Flow-based Load-balancing . . . . . . . . . . . . . . . 10 7.2.1.1 PE B-MAC Address Assignment . . . . . . . . . . . . 10 7.2.1.2. Automating B-MAC Address Assignment . . . . . . . 12 7.2.1.3 Split Horizon and Designated Forwarder Election . . 12 7.2.2 I-SID Based Load-balancing . . . . . . . . . . . . . . . 13 7.2.2.1 PE B-MAC Address Assignment . . . . . . . . . . . . 13 7.2.2.2 Split Horizon and Designated Forwarder Election . . 13 7.2.2.3 Handling Failure Scenarios . . . . . . . . . . . . . 13 7.3. Network Multi-homing . . . . . . . . . . . . . . . . . . . 14 7.4. Frame Forwarding . . . . . . . . . . . . . . . . . . . . . 15 7.4.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . 15 7.4.2. Multicast/Broadcast . . . . . . . . . . . . . . . . . 15 8. Minimizing ARP Broadcast . . . . . . . . . . . . . . . . . . . 16 9. Seamless Interworking with IEEE 802.1aq/802.1Qbp . . . . . . . 16 9.1 B-MAC Address Assignment . . . . . . . . . . . . . . . . . . 16 9.2 IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route . . . . . 17 9.3 Operation: . . . . . . . . . . . . . . . . . . . . . . . . . 17 10. Solution Advantages . . . . . . . . . . . . . . . . . . . . . 17 10.1. MAC Advertisement Route Scalability . . . . . . . . . . . 18 10.2. C-MAC Mobility with MAC Sub-netting . . . . . . . . . . . 18 10.3. C-MAC Address Learning and Confinement . . . . . . . . . 18 10.4. Seamless Interworking with TRILL and 802.1aq Access Networks . . . . . . . . . . . . . . . . . . . . . . . . 19 10.5. Per Site Policy Support . . . . . . . . . . . . . . . . . 19 10.6. Avoiding C-MAC Address Flushing . . . . . . . . . . . . . 19 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 12. Security Considerations . . . . . . . . . . . . . . . . . . . 20 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 14. Intellectual Property Considerations . . . . . . . . . . . . 20 15. Normative References . . . . . . . . . . . . . . . . . . . . 20 16. Informative References . . . . . . . . . . . . . . . . . . . 20 17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 21 Sajassi et al. Expires December 18, 2014 [Page 3] INTERNET DRAFT PBB-EVPN June 18, 2014 1. Introduction [EVPN] introduces a solution for multipoint L2VPN services, with advanced multi-homing capabilities, using BGP for distributing customer/client MAC address reach-ability information over the core MPLS/IP network. [PBB] defines an architecture for Ethernet Provider Backbone Bridging (PBB), where MAC tunneling is employed to improve service instance and MAC address scalability in Ethernet as well as VPLS networks [PBB-VPLS]. In this document, we discuss how PBB can be combined with EVPN in order to: reduce the number of BGP MAC advertisement routes by aggregating Customer/Client MAC (C-MAC) addresses via Provider Backbone MAC address (B-MAC), provide client MAC address mobility using C-MAC aggregation and B-MAC sub-netting, confine the scope of C-MAC learning to only active flows, offer per site policies and avoid C-MAC address flushing on topology changes. The combined solution is referred to as PBB-EVPN. 2. Contributors In addition to the authors listed above, the following individuals also contributed to this document. Sami Boutros, Cisco Dennis Cai, Cisco Keyur Patel, Cisco Clarence Filsfils, Cisco Sam Aldrin, Huawei Himanshu Shah, Ciena Florin Balus, ALU 3. Terminology BEB: Backbone Edge Bridge B-MAC: Backbone MAC Address CE: Customer Edge C-MAC: Customer/Client MAC Address DHD: Dual-homed Device DHN: Dual-homed Network LACP: Link Aggregation Control Protocol LSM: Label Switched Multicast MDT: Multicast Delivery Tree MP2MP: Multipoint to Multipoint P2MP: Point to Multipoint P2P: Point to Point PE: Provider Edge PoA: Point of Attachment Sajassi et al. Expires December 18, 2014 [Page 4] INTERNET DRAFT PBB-EVPN June 18, 2014 PW: Pseudowire EVPN: Ethernet VPN Single-Active Redundancy Mode: When only a single PE, among a group of PEs attached to an Ethernet segment, is allowed to forward traffic to/from that Ethernet Segment, then the Ethernet segment is defined to be operating in Single-Active redundancy mode. All-Active Redundancy Mode: When all PEs attached to an Ethernet segment are allowed to forward traffic to/from that Ethernet Segment, then the Ethernet segment is defined to be operating in All-Active redundancy mode. 4. Requirements The requirements for PBB-EVPN include all the requirements for EVPN that were described in [EVPN-REQ], in addition to the following: 4.1. MAC Advertisement Route Scalability In typical operation, an [EVPN] PE sends a BGP MAC Advertisement Route per customer/client MAC (C-MAC) address. In certain applications, this poses scalability challenges, as is the case in data center interconnect (DCI) scenarios where the number of virtual machines (VMs), and hence the number of C-MAC addresses, can be in the millions. In such scenarios, it is required to reduce the number of BGP MAC Advertisement routes by relying on a 'MAC summarization' scheme, as is provided by PBB. 4.2. C-MAC Mobility with MAC Summarization Certain applications, such as virtual machine mobility, require support for fast C-MAC address mobility. For these applications, the exact virtual machine MAC address needs to be transmitted in BGP MAC Advertisement route. Otherwise, traffic would be forwarded to the wrong segment when a virtual machine moves from one Ethernet segment to another. This means MAC address prefixes cannot be used in data center applications. In order to support C-MAC address mobility, while retaining the scalability benefits of MAC summarization, PBB technology is used. It defines a Backbone MAC (B-MAC) address space that is independent of the C-MAC address space, and aggregate C-MAC addresses via a B-MAC address and then apply summarization to B-MAC addresses. 4.3. C-MAC Address Learning and Confinement In EVPN, all the PE nodes participating in the same EVPN instance are Sajassi et al. Expires December 18, 2014 [Page 5] INTERNET DRAFT PBB-EVPN June 18, 2014 exposed to all the C-MAC addresses learnt by any one of these PE nodes because a C-MAC learned by one of the PE nodes is advertise in BGP to other PE nodes in that EVPN instance. This is the case even if some of the PE nodes for that EVPN instance are not involved in forwarding traffic to, or from, these C-MAC addresses. Even if an implementation does not install hardware forwarding entries for C-MAC addresses that are not part of active traffic flows on that PE, the device memory is still consumed by keeping record of the C-MAC addresses in the routing table (RIB). In network applications with millions of C-MAC addresses, this introduces a non-trivial waste of PE resources. As such, it is required to confine the scope of visibility of C-MAC addresses only to those PE nodes that are actively involved in forwarding traffic to, or from, these addresses. 4.4. Per Site Policy Support In many applications, it is required to be able to enforce connectivity policy rules at the granularity of a site (or segment). This includes the ability to control which PE nodes in the network can forward traffic to, or from, a given site. PBB-EVPN is capable of providing this granularity of policy control. In the case where per C-MAC address granularity is required, the EVI can always continue to operate in EVPN mode. 4.5. Avoiding C-MAC Address Flushing It is required to avoid C-MAC address flushing upon link, port or node failure for All-Active multi-homed devices and networks. This is in order to speed up re-convergence upon failure. 5. Solution Overview The solution involves incorporating IEEE Backbone Edge Bridge (BEB) functionality on the EVPN PE nodes similar to PBB-VPLS, where BEB functionality is incorporated in the VPLS PE nodes. The PE devices would then receive 802.1Q Ethernet frames from their attachment circuits, encapsulate them in the PBB header and forward the frames over the IP/MPLS core. On the egress EVPN PE, the PBB header is removed following the MPLS disposition, and the original 802.1Q Ethernet frame is delivered to the customer equipment. Sajassi et al. Expires December 18, 2014 [Page 6] INTERNET DRAFT PBB-EVPN June 18, 2014 BEB +--------------+ BEB || | | || \/ | | \/ +----+ AC1 +----+ | | +----+ +----+ | CE1|-----| | | | | |---| CE2| +----+\ | PE1| | IP/MPLS | | PE3| +----+ \ +----+ | Network | +----+ \ | | AC2\ +----+ | | \| | | | | PE2| | | +----+ | | /\ +--------------+ || BEB <-802.1Q-> <------PBB over MPLS------> <-802.1Q-> Figure 1: PBB-EVPN Network The PE nodes perform the following functions:- Learn customer/client MAC addresses (C-MACs) over the attachment circuits in the data- plane, per normal bridge operation. - Learn remote C-MAC to B-MAC bindings in the data-plane for traffic received from the core per [PBB] bridging operation. - Advertise local B-MAC address reach-ability information in BGP to all other PE nodes in the same set of service instances. Note that every PE has a set of local B-MAC addresses that uniquely identify the device. More on the PE addressing in section 5. - Build a forwarding table from remote BGP advertisements received associating remote B-MAC addresses with remote PE IP addresses and the associated MPLS label(s). 6. BGP Encoding PBB-EVPN leverages the same BGP Routes and Attributes defined in [EVPN], adapted as follows: 6.1. Ethernet Auto-Discovery Route This route and all of its associated modes are not needed in PBB- EVPN. The receiving PE knows that it need not wait for the receipt of the Ethernet A-D route for route resolution by means of the reserved ESI Sajassi et al. Expires December 18, 2014 [Page 7] INTERNET DRAFT PBB-EVPN June 18, 2014 encoded in the MAC Advertisement route: the ESI values of 0 and MAX- ESI indicate that the receiving PE can resolve the path without an Ethernet A-D route. 6.2. BGP MAC Advertisement Route The EVPN MAC Advertisement Route is used to distribute B-MAC addresses of the PE nodes instead of the C-MAC addresses of end- stations/hosts. This is because the C-MAC addresses are learnt in the data-plane for traffic arriving from the core. The MAC Advertisement Route is encoded as follows: - The MAC address field contains the B-MAC address. - The Ethernet Tag field is set to 0. - The Ethernet Segment Identifier field must be set either to 0 (for single-homed Segments or multi-homed Segments with per-ISID load- balancing) or to MAX-ESI (for multi-homed Segments with per-flow load-balancing). All other values are not permitted. - All other fields are set as defined in [EVPN]. This route is tagged with the RT corresponding to its EVI. This EVI is analogous to a B-VID. 6.3. Inclusive Multicast Ethernet Tag Route This route is used for multicast pruning per I-SID. It is used for auto-discovery of PEs participating in a given I-SID so that a multicast tunnel (MP2P, P2P, P2MP, or MP2MP LSP) can be setup for that I-SID . [PBB-VPLS] uses multicast pruning per I-SID based on [MMRP] which is a soft-state protocol. The advantages of multicast pruning using this BGP route over [MMRP] are that a) it scales very well for large number of PEs and b) it works with any type of LSP (MP2P, P2P, P2MP, or MP2MP); whereas, [MMRP] only works over P2P PWs. The Inclusive Multicast Ethernet Tag Route is encoded as follow: - The Ethernet Tag field is set with the appropriate I-SID value. - All other fields are set as defined in [EVPN]. This route is tagged with an RT. This RT SHOULD be set to a value corresponding to its EVI (which is analogous to a B-VID). The RT for this route MAY also be auto-derived from the corresponding Ethernet Tag (I-SID) based on the procedure specified in section 9.4.1.1.1 of [EVPN]. 6.4. Ethernet Segment Route Sajassi et al. Expires December 18, 2014 [Page 8] INTERNET DRAFT PBB-EVPN June 18, 2014 This route is used as defined in [EVPN]. 6.5. ESI Label Extended Community This extended community is not used in PBB-EVPN. In [EVPN], this extended community is used along with the Ethernet AD route to advertise an MPLS label for the purpose of split-horizon filtering. Since in PBB-EVPN, the split-horizon filtering is performed natively using B-MAC SA, there is no need for this extended community. 6.6. ES-Import Route Target This RT is used as defined in [EVPN]. 6.7. MAC Mobility Extended Community This extended community is defined in [EVPN] and it is used with a MAC route (B-MAC route in case of PBB-EVPN). The B-MAC route is tagged with the RT corresponding to its EVI (which is analogous to a B-VID). When this extended community is used along with a B-MAC route in PBB-EVPN, it indicates that all C-MAC addresses associated with that B-MAC address across all corresponding I-SIDs must be flushed. 6.8. Default Gateway Extended Community This extended community is not used in PBB-EVPN. 7. Operation This section discusses the operation of PBB-EVPN, specifically in areas where it differs from [EVPN]. 7.1. MAC Address Distribution over Core In PBB-EVPN, host MAC addresses (i.e. C-MAC addresses) need not be distributed in BGP. Rather, every PE independently learns the C-MAC addresses in the data-plane via normal bridging operation. Every PE has a set of one or more unicast B-MAC addresses associated with it, and those are the addresses distributed over the core in MAC Advertisement routes. 7.2. Device Multi-homing Sajassi et al. Expires December 18, 2014 [Page 9] INTERNET DRAFT PBB-EVPN June 18, 2014 7.2.1 Flow-based Load-balancing This section describes the procedures for supporting device multi- homing in an All-Active redundancy mode (i.e., flow-based load- balancing). 7.2.1.1 PE B-MAC Address Assignment In [PBB] every BEB is uniquely identified by one or more B-MAC addresses. These addresses are usually locally administered by the Service Provider. For PBB-EVPN, the choice of B-MAC address(es) for the PE nodes must be examined carefully as it has implications on the proper operation of multi-homing. In particular, for the scenario where a CE is multi-homed to a number of PE nodes with All-Active redundancy mode, a given C-MAC address would be reachable via multiple PE nodes concurrently. Given that any given remote PE will bind the C-MAC address to a single B-MAC address, then the various PE nodes connected to the same CE must share the same B-MAC address. Otherwise, the MAC address table of the remote PE nodes will keep oscillating between the B-MAC addresses of the various PE devices. For example, consider the network of Figure 1, and assume that PE1 has B-MAC BM1 and PE2 has B-MAC BM2. Also, assume that both links from CE1 to the PE nodes are part of the same Ethernet link aggregation group. If BM1 is not equal to BM2, the consequence is that the MAC address table on PE3 will keep oscillating such that the C-MAC address M1 of CE1 would flip-flop between BM1 or BM2, depending on the load-balancing decision on CE1 for traffic destined to the core. Considering that there could be multiple sites (e.g. CEs) that are multi-homed to the same set of PE nodes, then it is required for all the PE devices in a Redundancy Group to have a unique B-MAC address per site. This way, it is possible to achieve fast convergence in the case where a link or port failure impacts the attachment circuit connecting a single site to a given PE. Sajassi et al. Expires December 18, 2014 [Page 10] INTERNET DRAFT PBB-EVPN June 18, 2014 +---------+ +-------+ PE1 | IP/MPLS | / | | CE1 | Network | PEr M1 \ | | +-------+ PE2 | | /-------+ | | / | | CE2 | | M2 \ | | \ | | +------+ PE3 +---------+ Figure 2: B-MAC Address Assignment In the example network shown in Figure 2 above, two sites corresponding to CE1 and CE2 are dual-homed to PE1/PE2 and PE2/PE3, respectively. Assume that BM1 is the B-MAC used for the site corresponding to CE1. Similarly, BM2 is the B-MAC used for the site corresponding to CE2. On PE1, a single B-MAC address (BM1) is required for the site corresponding to CE1. On PE2, two B-MAC addresses (BM1 and BM2) are required, one per site. Whereas on PE3, a single B-MAC address (BM2) is required for the site corresponding to CE2. All three PE nodes would advertise their respective B-MAC addresses in BGP using the MAC Advertisement routes defined in [EVPN]. The remote PE, PEr, would learn via BGP that BM1 is reachable via PE1 and PE2, whereas BM2 is reachable via both PE2 and PE3. Furthermore, PEr establishes, via the PBB bridge learning procedure, that C-MAC M1 is reachable via BM1, and C-MAC M2 is reachable via BM2. As a result, PEr can load-balance traffic destined to M1 between PE1 and PE2, as well as traffic destined to M2 between both PE2 and PE3. In the case of a failure that causes, for example, CE1 to be isolated from PE1, the latter can withdraw the route it has advertised for BM1. This way, PEr would update its path list for BM1, and will send all traffic destined to M1 over to PE2 only. For single-homed sites, it is possible to assign a unique B-MAC address per site, or have all the single-homed sites connected to a given PE share a single B-MAC address. The advantage of the first model over the second model is the ability to avoid C-MAC destination address lookup on the disposition PE (even though source C-MAC learning is still required in the data-plane). Also, by assigning the B-MAC addresses from a contiguous range, it is possible to advertise a single B-MAC subnet for all single-homed sites, thereby rendering the number of MAC advertisement routes required at par with the second model. In summary, every PE may use a unicast B-MAC address shared by all Sajassi et al. Expires December 18, 2014 [Page 11] INTERNET DRAFT PBB-EVPN June 18, 2014 single-homed CEs or a unicast B-MAC address per single-homed CE and, in addition, a unicast B-MAC address per All-Active multi-homed CE. In the latter case, the B-MAC address MUST be the same for all PE nodes in a Redundancy Group connected to the same CE. 7.2.1.2. Automating B-MAC Address Assignment The PE B-MAC address used for single-homed sites can be automatically derived from the hardware (using for e.g. the backplane's address). However, the B-MAC address used for multi-homed sites must be coordinated among the RG members. To automate the assignment of this latter address, the PE can derive this B-MAC address from the MAC Address portion of the CE's LACP System Identifier by flipping the 'Locally Administered' bit of the CE's address. This guarantees the uniqueness of the B-MAC address within the network, and ensures that all PE nodes connected to the same multi-homed CE use the same value for the B-MAC address. Note that with this automatic provisioning of the B-MAC address associated with multi-homed CEs, it is not possible to support the uncommon scenario where a CE has multiple bundles towards the PE nodes, and the service involves hair-pinning traffic from one bundle to another. This is because the split-horizon filtering relies on B- MAC addresses rather than Site-ID Labels (as will be described in the next section). The operator must explicitly configure the B-MAC address for this fairly uncommon service scenario. Whenever a B-MAC address is provisioned on the PE, either manually or automatically (as an outcome of CE auto-discovery), the PE MUST transmit an MAC Advertisement Route for the B-MAC address with a downstream assigned MPLS label that uniquely identifies that address on the advertising PE. The route is tagged with the RTs of the associated EVIs as described above. 7.2.1.3 Split Horizon and Designated Forwarder Election [EVPN] relies on access split horizon, where the Ethernet Segment Label is used for egress filtering on the attachment circuit in order to prevent forwarding loops. In PBB-EVPN, the B-MAC source address can be used for the same purpose, as it uniquely identifies the originating site of a given frame. As such, Ethernet Segment (ES) Labels are not used in PBB-EVPN, and the egress split-horizon filtering is done based on the B-MAC source address. It is worth noting here that [PBB] defines this B-MAC address based filtering function as part of the I-Component options, hence no new functions are required to support split-horizon beyond what is already defined in [PBB]. Given that the ES label is not used in PBB-EVPN, the PE sets the Label field in the Ethernet Segment Route to 0. Sajassi et al. Expires December 18, 2014 [Page 12] INTERNET DRAFT PBB-EVPN June 18, 2014 The Designated Forwarder election procedures are defined in [EVPN]. 7.2.2 I-SID Based Load-balancing This section describes the procedures for supporting device multi- homing in a Single-Active redundancy mode with per-ISID load- balancing. 7.2.2.1 PE B-MAC Address Assignment In the case where per-ISID load-balancing is desired among the PE nodes in a given redundancy group, multiple unicast B-MAC addresses are allocated per multi-homed Ethernet Segment: Each PE connected to the multi-homed segment is assigned a unique B-MAC. Every PE then advertises its B-MAC address using the BGP MAC advertisement route. In this mode of operation, two B-MAC address assignment models are possible: - The PE may use a shared B-MAC address for multiple Ethernet Segments. This includes the single-homed segments as well as the multi-homed segments operating with per-ISID load-balancing mode. - The PE may use a dedicated B-MAC address for each Ethernet Segment operating with per-ISID load-balancing mode. All PE implementations MUST support the shared B-MAC address model and MAY support the dedicated B-MAC address model. A remote PE initially floods traffic to a destination C-MAC address, located in a given multi-homed Ethernet Segment, to all the PE nodes configured with that I-SID. Then, when reply traffic arrives at the remote PE, it learns (in the data-path) the B-MAC address and associated next-hop PE to use for said C-MAC address. 7.2.2.2 Split Horizon and Designated Forwarder Election The procedures are similar to the flow-based load-balancing case, with the only difference being that the DF filtering must be applied to unicast as well as multicast traffic, and in both core-to-segment as well as segment-to-core directions. 7.2.2.3 Handling Failure Scenarios When a PE connected to a multi-homed Ethernet Segment loses connectivity to the segment, due to link or port failure, it needs to notify the remote PEs to trigger C-MAC address flushing. This can be achieved in one of two ways, depending on the B-MAC assignment model: - If the PE uses a shared B-MAC address for multiple Ethernet Sajassi et al. Expires December 18, 2014 [Page 13] INTERNET DRAFT PBB-EVPN June 18, 2014 Segments, then the C-MAC flushing is signaled by means of having the failed PE re-advertise the MAC Advertisement route for the associated B-MAC, tagged with the MAC Mobility Extended Community attribute. The value of the Counter field in that attribute must be incremented prior to advertisement. This causes the remote PE nodes to flush all C-MAC addresses associated with the B-MAC in question. This is done across all I-SIDs that are mapped to the EVI of the withdrawn MAC route. - If the PE uses a dedicated B-MAC address for each Ethernet Segment operating under per-ISID load-balancing mode, the the failed PE simply withdraws the B-MAC route previously advertised for that segment. This causes the remote PE nodes to flush all C-MAC addresses associated with the B-MAC in question. This is done across all I-SIDs that are mapped to the EVI of the withdrawn MAC route. When a PE connected to a multi-homed Ethernet Segment fails (i.e. node failure) or when the PE becomes completely isolated from the EVPN network, the remote PEs will start purging the MAC Advertisement routes that were advertised by the failed PE. This is done either as an outcome of the remote PEs detecting that the BGP session to the failed PE has gone down, or by having a Route Reflector withdrawing all the routes that were advertised by the failed PE. The remote PEs, in this case, will perform C-MAC address flushing as an outcome of the MAC Advertisement route withdrawals. For all failure scenarios (link/port failure, node failure and PE node isolation), when the fault condition clears, the recovered PE re-advertises the associated Ethernet Segment route to other members of its Redundancy Group. This triggers the backup PE(s) in the Redundancy Group to block the I-SIDs for which the recovered PE is a DF. When a backup PE blocks the I-SIDs, it triggers a C-MAC address flush notification to the remote PEs by re-advertising the MAC Advertisement route for the associated B-MAC, with the MAC Mobility Extended Community attribute. The value of the Counter field in that attribute must be incremented prior to advertisement. This causes the remote PE nodes to flush all C-MAC addresses associated with the B- MAC in question. This is done across all I-SIDs that are mapped to the EVI of the withdrawn MAC route. 7.3. Network Multi-homing When an Ethernet network is multi-homed to a set of PE nodes running PBB-EVPN, a single-active redundancy model can be supported with per service instance (i.e. I-SID) load-balancing. In this model, DF election is performed to ensure that a single PE node in the redundancy group is responsible for forwarding traffic associated Sajassi et al. Expires December 18, 2014 [Page 14] INTERNET DRAFT PBB-EVPN June 18, 2014 with a given I-SID. This guarantees that no forwarding loops are created. Filtering based on DF state applies to both unicast and multicast traffic, and in both access-to-core as well as core-to- access directions (unlike the multi-homed device scenario where DF filtering is limited to multi-destination frames in the core-to- access direction). Similar to the multi-homed device scenario, with I-SID based load-balancing, a unique B-MAC address is assigned to each of the PE nodes connected to the multi-homed network (Segment). 7.4. Frame Forwarding The frame forwarding functions are divided in between the Bridge Module, which hosts the [PBB] Backbone Edge Bridge (BEB) functionality, and the MPLS Forwarder which handles the MPLS imposition/disposition. The details of frame forwarding for unicast and multi-destination frames are discussed next. 7.4.1. Unicast Known unicast traffic received from the AC will be PBB-encapsulated by the PE using the B-MAC source address corresponding to the originating site. The unicast B-MAC destination address is determined based on a lookup of the C-MAC destination address (the binding of the two is done via transparent learning of reverse traffic). The resulting frame is then encapsulated with an LSP tunnel label and the MPLS label which uniquely identifies the B-MAC destination address on the egress PE. If per flow load-balancing over ECMPs in the MPLS core is required, then a flow label is added as the end of stack label. For unknown unicast traffic, the PE forwards these frames over MPLS core. When these frames are to be forwarded, then the same set of options used for forwarding multicast/broadcast frames (as described in next section) are used. 7.4.2. Multicast/Broadcast Multi-destination frames received from the AC will be PBB- encapsulated by the PE using the B-MAC source address corresponding to the originating site. The multicast B-MAC destination address is selected based on the value of the I-SID as defined in [PBB]. The resulting frame is then forwarded over the MPLS core using one out of the following two options: Option 1: the MPLS Forwarder can perform ingress replication over a set of MP2P tunnel LSPs. The frame is encapsulated with a tunnel LSP label and the EVPN ingress replication label advertised in the Inclusive Multicast Route. Sajassi et al. Expires December 18, 2014 [Page 15] INTERNET DRAFT PBB-EVPN June 18, 2014 Option 2: the MPLS Forwarder can use P2MP tunnel LSP per the procedures defined in [EVPN]. This includes either the use of Inclusive or Aggregate Inclusive trees. Note that the same procedures for advertising and handling the Inclusive Multicast Route defined in [EVPN] apply here. 8. Minimizing ARP Broadcast The PE nodes implement an ARP-proxy function in order to minimize the volume of ARP traffic that is broadcasted over the MPLS network. This is achieved by having each PE node snoop on ARP request and response messages received over the access interfaces or the MPLS core. The PE builds a cache of IP / MAC address bindings from these snooped messages. The PE then uses this cache to respond to ARP requests ingress on access ports and targeting hosts that are in remote sites. If the PE finds a match for the IP address in its ARP cache, it responds back to the requesting host and drops the request. Otherwise, if it does not find a match, then the request is flooded over the MPLS network using either ingress replication or LSM. 9. Seamless Interworking with IEEE 802.1aq/802.1Qbp +--------------+ | | +---------+ | MPLS | +---------+ +----+ | | +----+ +----+ | | +----+ |SW1 |--| | | PE1| | PE2| | |--| SW3| +----+ | 802.1aq |---| | | |--| 802.1aq | +----+ +----+ | .1Qbp | +----+ +----+ | .1Qbp | +----+ |SW2 |--| | | Backbone | | |--| SW4| +----+ +---------+ +--------------+ +---------+ +----+ |<------ IS-IS -------->|<-----BGP----->|<------ IS-IS ------>| CP |<------------------------- PBB -------------------------->| DP |<----MPLS----->| Legend: CP = Control Plane View DP = Data Plane View Figure 7: Interconnecting 802.1aq/802.1Qbp Networks with PBB-EVPN 9.1 B-MAC Address Assignment For the same reasons cited in the TRILL section, the B-MAC addresses Sajassi et al. Expires December 18, 2014 [Page 16] INTERNET DRAFT PBB-EVPN June 18, 2014 need to be globally unique across all the IEEE 802.1aq / 802.1Qbp networks. The same hierarchical address assignment scheme depicted above is proposed for B-MAC addresses as well. 9.2 IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route B-MAC addresses associated with 802.1aq / 802.1Qbp switches are advertised using the BGP MAC Advertisement route already defined in [EVPN]. The encapsulation for the transport of PBB frames over MPLS is similar to that of classical Ethernet, albeit with the additional PBB header, as shown in the figure below: +------------------+ | IP/MPLS Header | +------------------+ | PBB Header | +------------------+ | Ethernet Header | +------------------+ | Ethernet Payload | +------------------+ | Ethernet FCS | +------------------+ Figure 8: PBB over MPLS Encapsulation 9.3 Operation: When a PE receives a PBB-encapsulated Ethernet frame from the access side, it performs a lookup on the B-MAC destination address to identify the next hop. If the lookup yields that the next hop is a remote PE, the local PE would then encapsulate the PBB frame in MPLS. The label stack comprises of the VPN label (advertised by the remote PE), followed by an LSP/IGP label. From that point onwards, regular MPLS forwarding is applied. On the disposition PE, assuming penultimate-hop-popping is employed, the PE receives the MPLS-encapsulated PBB frame with a single label: the VPN label. The value of the label indicates to the disposition PE that this is a PBB frame, so the label is popped, the TTL field (in the 802.1Qbp F-Tag) is reinitialized and normal PBB processing is employed from this point onwards. 10. Solution Advantages In this section, we discuss the advantages of the PBB-EVPN solution Sajassi et al. Expires December 18, 2014 [Page 17] INTERNET DRAFT PBB-EVPN June 18, 2014 in the context of the requirements set forth in section 3 above. 10.1. MAC Advertisement Route Scalability In PBB-EVPN the number of MAC Advertisement Routes is a function of the number of segments (sites), rather than the number of hosts/servers. This is because the B-MAC addresses of the PEs, rather than C-MAC addresses (of hosts/servers) are being advertised in BGP. And, as discussed above, there's a one-to-one mapping between multi- homed segments and B-MAC addresses, whereas there's a one-to-one or many-to-one mapping between single-homed segments and B-MAC addresses for a given PE. As a result, the volume of MAC Advertisement Routes in PBB-EVPN is multiple orders of magnitude less than EVPN. 10.2. C-MAC Mobility with MAC Sub-netting In PBB-EVPN, if a PE allocates its B-MAC addresses from a contiguous range, then it can advertise a MAC prefix rather than individual 48- bit addresses. It should be noted that B-MAC addresses can easily be assigned from a contiguous range because PE nodes are within the provider administrative domain; however, CE devices and hosts are typically not within the provider administrative domain. The advantage of such MAC address sub-netting can be maintained even as C-MAC addresses move from one Ethernet segment to another. This is because the C-MAC address to B-MAC address association is learnt in the data-plane and C-MAC addresses are not advertised in BGP. To illustrate how this compares to EVPN, consider the following example: If a PE running EVPN advertises reachability for a MAC subnet that spans N addresses via a particular segment, and then 50% of the MAC addresses in that subnet move to other segments (e.g. due to virtual machine mobility), then in the worst case, N/2 additional MAC Advertisement routes need to be sent for the MAC addresses that have moved. This defeats the purpose of the sub-netting. With PBB-EVPN, on the other hand, the sub-netting applies to the B-MAC addresses which are statically associated with PE nodes and are not subject to mobility. As C-MAC addresses move from one segment to another, the binding of C-MAC to B-MAC addresses is updated via data-plane learning. 10.3. C-MAC Address Learning and Confinement In PBB-EVPN, C-MAC address reachability information is built via data-plane learning. As such, PE nodes not participating in active conversations involving a particular C-MAC address will purge that address from their forwarding tables. Furthermore, since C-MAC addresses are not distributed in BGP, PE nodes will not maintain any record of them in control-plane routing table. Sajassi et al. Expires December 18, 2014 [Page 18] INTERNET DRAFT PBB-EVPN June 18, 2014 10.4. Seamless Interworking with TRILL and 802.1aq Access Networks Consider the scenario where two access networks, one running MPLS and the other running 802.1aq, are interconnected via an MPLS backbone network. The figure below shows such an example network. +--------------+ | | +---------+ | MPLS | +---------+ +----+ | | +----+ +----+ | | +----+ | CE |--| | | PE1| | PE2| | |--| CE | +----+ | 802.1aq |---| | | |--| MPLS | +----+ +----+ | | +----+ +----+ | | +----+ | CE |--| | | Backbone | | |--| CE | +----+ +---------+ +--------------+ +---------+ +----+ Figure 9: Interoperability with 802.1aq If the MPLS backbone network employs EVPN, then the 802.1aq data- plane encapsulation must be terminated on PE1 or the edge device connecting to PE1. Either way, all the PE nodes that are part of the associated service instances will be exposed to all the C-MAC addresses of all hosts/servers connected to the access networks. However, if the MPLS backbone network employs PBB-EVPN, then the 802.1aq encapsulation can be extended over the MPLS backbone, thereby maintaining C-MAC address transparency on PE1. If PBB-EVPN is also extended over the MPLS access network on the right, then C-MAC addresses would be transparent to PE2 as well. Interoperability with TRILL access network will be described in future revision of this draft. 10.5. Per Site Policy Support In PBB-EVPN, a unique B-MAC address can be associated with every site (single-homed or multi-homed). Given that the B-MAC addresses are sent in BGP MAC Advertisement routes, it is possible to define per site (i.e. B-MAC) forwarding policies including policies for E-TREE service. 10.6. Avoiding C-MAC Address Flushing With PBB-EVPN, it is possible to avoid C-MAC address flushing upon topology change affecting a multi-homed device. To illustrate this, consider the example network of Figure 1. Both PE1 and PE2 advertize the same B-MAC address (BM1) to PE3. PE3 then learns the C-MAC addresses of the servers/hosts behind CE1 via data-plane learning. If Sajassi et al. Expires December 18, 2014 [Page 19] INTERNET DRAFT PBB-EVPN June 18, 2014 AC1 fails, then PE3 does not need to flush any of the C-MAC addresses learnt and associated with BM1. This is because PE1 will withdraw the MAC Advertisement routes associated with BM1, thereby leading PE3 to have a single adjacency (to PE2) for this B-MAC address. Therefore, the topology change is communicated to PE3 and no C-MAC address flushing is required. 11. Acknowledgements The authors would like to thank Jose Liste and Patrice Brissette for their reviews and comments of this document. 12. Security Considerations There are no additional security aspects beyond those of VPLS/H-VPLS that need to be discussed here. 13. IANA Considerations This document requires IANA to assign a new SAFI value for L2VPN_MAC SAFI. 14. Intellectual Property Considerations This document is being submitted for use in IETF standards discussions. 15. Normative References [PBB] Clauses 25 and 26 of "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q, 2013. 16. Informative References [PBB-VPLS] Sajassi, et al., "VPLS Interoperability with Provider Backbone Bridges", draft-ietf-l2vpn-pbb-vpls-interop- 05.txt, work in progress, October, 2013. [EVPN-REQ] Sajassi, et al., "Requirements for Ethernet VPN (EVPN)", draft-ietf-l2vpn-evpn-req-05.txt, work in progress, October, 2013. [EVPN] Sajassi, et al., "BGP MPLS Based Ethernet VPN", draft-ietf- l2vpn-evpn-04.txt, work in progress, July, 2013. [MMRP] Clause 10 of "IEEE Standard for Local and metropolitan area Sajassi et al. Expires December 18, 2014 [Page 20] INTERNET DRAFT PBB-EVPN June 18, 2014 networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q, 2013. 17. Authors' Addresses Ali Sajassi Cisco 170 West Tasman Drive San Jose, CA 95134, US Email: sajassi@cisco.com Samer Salam Cisco 595 Burrard Street, Suite # 2123 Vancouver, BC V7X 1J1, Canada Email: ssalam@cisco.com Nabil Bitar Verizon Communications Email : nabil.n.bitar@verizon.com Aldrin Isaac Bloomberg Email: aisaac71@bloomberg.net Wim Henderickx Alcatel-Lucent Email: wim.henderickx@alcatel-lucent.be Lizhong Jin ZTE Corporation 889, Bibo Road Shanghai, 201203, China Email: lizhong.jin@zte.com.cn Sajassi et al. Expires December 18, 2014 [Page 21]