Internet-Draft Ali Sajassi L2VPN Working Group Samer Salam Intended status: Standards Cisco Nabil Bitar Verizon Dinesh Mohan Nortel Expires: January 2009 July 2008 Provider Backbone Bridges in H-VPLS with MPLS Access draft-sajassi-l2vpn-pbb-vpls-mpls-access-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire in May 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Sajassi, et. al. Expires: January 2009 [Page 1] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 Abstract Provider Backbone Bridge (PBB) functionality, under standardization in IEEE 802.1ah, can be employed to enhance the scalability of H- VPLS with MPLS access. This document describes how PBB technology can be used in H-VPLS with MPLS access networks to improve the scalability of customer MAC addresses and number of service instances that can be supported. The document also describes the migration mechanisms and scenarios by which PBB functionality can be incorporated into H-VPLS with existing MPLS access. Conventions used in this document 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 Status of this Memo................................................1 Conventions used in this document..................................2 1. Introduction.........................Error! Bookmark not defined. 2. Terminology..........................Error! Bookmark not defined. 3. H-VPLS with MPLS Access..............Error! Bookmark not defined. 3.1 H-VPLS with MPLS Access: PBB U-PE..............................5 3.1.1 PBB U-PEs in Single I-SID Domain.............................7 3.1.2 PBB U-PEs in Multiple I-SID Domains..........................8 3.2 H-VPLS with MPLS Access: PBB N-PE..............................8 3.2.1 PBB N-PEs in Single I-SID Domain.............................9 3.2.2 PBB N-PEs in Multiple I-SID Domains..........................9 4. Migration Scenarios..................Error! Bookmark not defined. 4.1 802.1ad Service Frames over VPLS Core....................10 4.2 PBB Service Frames over VPLS Core........................11 4.3 Mixed 802.1ad and PBB over VPLS Core.....................12 6. IANA Considerations............................................13 7. Security Considerations..............Error! Bookmark not defined. 8. References...........................Error! Bookmark not defined. 8.1 Normative References..........................................13 8.2 Informative References........................................14 Appendix A: Provider Backbone Bridges - Primer....................14 A.1 S-Tagged Service Interface....................................16 A.2 I-Tagged Service Interface....................................16 A.3 B-Tagged Service Interface....................................17 Authors' Addresses................................................17 Full Copyright Statement..........................................17 Intellectual Property.............................................18 Sajassi, et. al. Expires: January 2009 [Page 2] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 1. Introduction The scalability of H-VPLS (with either MPLS or Ethernet access network) can be improved by incorporating Provider Backbone Bridge (PBB) functionality in the VPLS access. PBB is under standardization as IEEE 802.1ah, which is an amendment to IEEE 802.1Q to address large-scale Ethernet provider network requirements. [VPLS-PBB] explores the interoperability of PBB with H-VPLS in the case of native Ethernet access network. Whereas, this document focuses on PBB interoperability with H-VPLS in the case of MPLS access network. It describes how IEEE 802.1ah functionality can be used in the H-VPLS MPLS access network to attain better scalability in terms of number of customer MAC addresses and number of service instances that can be supported. The document also describes the migration mechanisms and scenarios by which PBB functionality can be incorporated into H-VPLS with existing MPLS access. [RFC4762] describes a two-tier hierarchical solution for VPLS for the purpose of improved Pseudo Wire (PW) scalability. This improvement is achieved by reducing the number of PE devices connected in a full-mesh topology through connecting CE devices via the lower-tier access network which in turn is connected to the top- tier core network. [RFC4762] describes two types of H-VPLS network topologies - one with MPLS access network and another with IEEE 802.1ad (QinQ) Ethernet access network. In both types of H-VPLS, MAC address learning and forwarding are done based on customer MAC addresses (C-MACs) which poses scalability issues as the number of VPLS instances (and thus customer MAC addresses) increases. Furthermore, since a set of PWs is maintained on a per customer service instance, the number of PWs that need to be maintained at N- PE devices is proportional to the number of customer service instances multiplied by the number of N-PE devices in the full-mesh set. This can result in scalability issues (in terms of PWs manageability and troubleshooting) as the number of customer service instances grows. This document describes how IEEE 802.1ah (aka Provider Backbone Bridges) can be integrated with H-VPLS with MPLS access to address these scalability issues. PBB functionality can be used at the U-PE or N-PE which results in reduction of customer MAC addresses and number of PWs in the VPLS core network. This document also explores the scenarios by which an operator can gradually migrate an existing H-VPLS network to PBB over VPLS. Section 2 gives a quick terminology reference. Section 3 describes the use of PBB functionality in H-VPLS with MPLS access including PBB on U-PE and PBB on N-PE variants. Section 4 describes gradual migration scenarios from existing H-VPLS to PBB over H-VPLS. Appendix A provides a brief primer on PBB technology, for the reader's quick reference. Sajassi, et. al. Expires: January 2009 [Page 3] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 2. Terminology 802.1ad: IEEE specification for "QinQ" encapsulation and bridging of Ethernet frames 802.1ah: IEEE specification for "MAC tunneling" encapsulation and bridging of frames across a provider backbone bridged network. B-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains a B-component that supports bridging in the provider backbone based on B-MAC and B-TAG information B-MAC: The backbone source or destination MAC address fields defined in the 802.1ah provider MAC encapsulation header. BCB: A backbone core bridge running in the core of a provider backbone bridged network. It bridges frames based on B-TAG information just as an 802.1ad provider bridge will bridge frames based on a VLAN identifier (S-VLAN) BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It can contain an I-component, B-component or both I and B components. B-TAG: field defined in the 802.1ah provider MAC encapsulation header that conveys the backbone VLAN identifier information. The format of the B-TAG field is the same as that of an 802.1ad S-TAG field. B-Tagged Service Interface: This is the interface between a BEB and BCB in a provider backbone bridged network. Frames passed through this interface contain a B-TAG field. B-VID: The specific VLAN identifier carried inside a B-TAG I-component: A bridging component contained in a backbone edge bridge that bridges in the customer space (customer MAC addresses, S-VLAN) IB-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, service VLAN IDs) and a B-component for bridging the provider's backbone space (B-MAC, B- TAG). I-BEB: A backbone edge bridged positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, service VLAN IDs). Sajassi, et. al. Expires: January 2009 [Page 4] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 I-SID: The 24-bit service instance field carried inside the I-TAG. I-SID defines the service instance that the frame should be "mapped to". I-SID Domain: A network administrative boundary under which all the PBB BEBs and VPLS PE devices use the same I-SID space, i.e. the I- SID assignment is carried out by the same administration. This effectively means that a given service instance has the same I-SID designation on all devices within an I-SID Domain. I-TAG: A field defined in the 802.1ah provider MAC encapsulation header that conveys the service instance information (I-SID) associated with the frame. I-Tagged Service Interface: This the interface defined between the I and B components inside an IB-BEB or between two B-BEB. Frames passed through this interface contain an I-TAG field PBB: Provider Backbone Bridge PBBN: Provider Backbone Bridged Network S-TAG: A field defined in the 802.1ad QinQ encapsulation header that conveys the service VLAN identifier information (S-VLAN). S-Tagged Service Interface: This the interface defined between the customer (CE) and the I-BEB or IB-BEB components. Frames passed through this interface contain an S-TAG field. S-VLAN: The specific service VLAN identifier carried inside an S-TAG 3. H-VPLS with MPLS Access In this section, the case of H-VPLS with MPLS access network is discussed. The integration of PBB functionality into VPLS-PE for such access networks is described to improve the scalability of the network in terms of the number of MAC addresses and service instances that are supported. For this topology, it is possible to embed PBB functionality in either the U-PE or the N-PE. Both of these cases are described in the following sub-sections. 3.1 H-VPLS with MPLS Access: PBB U-PE As stated earlier, the objective for incorporating PBB function at the U-PE is to improve the scalability of H-VPLS networks in terms of the number of MAC addresses and service instances that are supported. Sajassi, et. al. Expires: January 2009 [Page 5] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 In current H-VPLS, the N-PE must learn customer MAC addresses (C- MACs) of all VPLS instances that it participates in. This can easily add-up to hundreds of thousands or even millions of C-MACs at the N- PE. When the U-PE performs PBB encapsulation, the N-PE only needs to learn the MAC addresses of the U-PEs, which is a significant reduction. Furthermore, when PBB encapsulation is used, many I-SIDs are multiplexed within a single bridge domain (e.g., B-VLAN). If the VPLS instance is set up per B-VLAN, then one can also achieve a significant reduction in the number of full-mesh PWs. It should be noted that this reduction in full-mesh PWs comes at the cost of potentially increased replication over the full-mesh of PWs: A given customer multicast and/or broadcast frames are effectively broadcasted within the B-VLAN. This may result in additional frame replication because the full-mesh PWs corresponding to a B-VLAN is most likely bigger than the full-mesh PWs corresponding to a single I-SID. However, multicast pruning as described in [PBB-VPLS-MCAST] can be used to remedy this drawback and have multicast traffic replicated efficiently for each customer (i.e. for each I-SID). Figure 1 below illustrates the scenario for H-VPLS with MPLS access. As it can be seen, customer networks or hosts (CE) connect into the U-PE nodes using standard Ethernet interfaces [802.1D], [802.1Q], or [802.1ad]. The U-PE is connected upstream to one or more VPLS N-PE nodes by MPLS PWs (per VPLS instance). These, in turn, are connected via a full-mesh of PWs (per VPLS instance) traversing the IP/MPLS core. The U-PE is outfitted with PBB Backbone Edge Bridge (BEB) functions where it can encapsulate/de-encapsulate customer MAC frames in provider B-MAC addresses and perform I-SID translation if needed. PBB PBB BEB +----------+ BEB | | | | | +-----------+ | IP | +-----------+ | | | MPLS | | MPLS | | MPLS | | V | Access +----+ | Core | +----+ Access | V +--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+ |CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE| +--+ +----+ +----+ | | +----+ +----+ +--+ | | | | | | +-----------+ +----------+ +-----------+ Figure 1: H-VPLS with MPLS Access Network and PBB U-PE The U-PE still provides the same type of services toward its customers as before and they are: Sajassi, et. al. Expires: January 2009 [Page 6] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 - Port mode (either 802.1D, 802.1Q, or 802.1ad) - VLAN mode (either 802.1Q or 802.1ad) - VLAN-bundling mode (either 802.1Q or 802.1ad) By incorporating PBB function, the U-PE maps each of these services (for a given customer) onto a single I-SID based on the configuration at the U-PE. Many I-SIDs are multiplexed within a single bridge domain (e.g. B-VLAN). The U-PE can, then, either map a single I-SID into a VPLS instance or it can map a bridge-domain onto a VPLS instance, according to its configuration. Next, the encapsulated frames are sent over the PW associated with that VPLS instance. If the bridge domain is mapped to a VPLS instance, then a B-VID can be used as the service delimiter and the entire Ethernet bridging operation over VPLS network is performed as defined in [RFC4762]. In other words, MAC forwarding is based on the B-MAC address space and service delimiter is based on VLAN ID, which is B-VID in this case. There is no need to inspect or deal with I-SID values. If the I-SID is used as the service delimiter, then the single and multiple I-SID Domain cases must be considered as described in the following sections. In summary, the ingress U-PE receives a customer MAC frame. It applies the appropriate PBB header and then performs standard bridge-capable U-PE processing functions, including switching the frame locally or forwarding it to the N-PE. The egress U-PE will remove the PW label, perform any relevant processing of the PBB header (e.g. I-SID translation if required) and then hand the frame to the PBB bridge component for local C-MAC processing. 3.1.1 PBB U-PEs in Single I-SID Domain In this scenario, I-SID assignment is performed globally across all MPLS access networks and therefore there is no need for I-SID translation. Both I-SID mode and I-SID bundling mode are supported in this scenario. I-SID to VPLS mapping is congruent on all U-PEs. In case of the I-SID bundling mode, a bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type as defined in [RFC4447] [RFC4448], can be used with the corresponding B-VID rewrite or translation performed at the various N-PE and egress U-PE nodes. This assumes that I-SID bundling is congruent on the associated U-PEs and N-PEs. In case of the I-SID mode, an I-SID is mapped to a VPLS instance and the new PW type described in [VPLS-PBB] is utilized without the need for I-SID translation. Sajassi, et. al. Expires: January 2009 [Page 7] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 3.1.2 PBB U-PEs in Multiple I-SID Domains In this scenario, I-SID assignment is performed on a per MPLS access network basis and thus I-SID bundling is no longer viable because I- SID values differ among different domains. In this scenario, only I- SID mode is supported. The U-PE nodes are the only nodes that are I- SID aware; so, it will be up to them to perform the translation as frames are forwarded between different service domains. At the ingress U-PE, during the PBBN encapsulation process, an I-SID value is added. A new PW type (described in [VPLS-PBB]) will be required to transport I-SID tagged payloads between the U-PE and N- PE. The one-to-one mapping between this I-SID value and the PW enables the receiving N-PE and U-PE to infer which VPLS instance the frame belongs to. When the encapsulated PBBN frames reach the egress U-PE, the PW label is removed and then the appropriate I-SID translation is performed. In this case, it is taking the I-SID originally assigned and imposed by the U-PE nodes (in MPLS access network #1) and translating it to the I-SID value assigned to MPLS access network #2. Once this is completed, the frame is handed off to the PBBN BEB for normal processing. 3.2 H-VPLS with MPLS Access: PBB N-PE In this case, the PBB function is incorporated at the N-PE to improve the scalability of H-VPLS networks in terms of the numbers of MAC addresses and service instances that are supported. Customer networks or hosts (CE) connect into the U-PE nodes using standard Ethernet interfaces [802.1D], [802.1Q], or [802.1ad]. The U-PE is connected upstream to one or more VPLS N-PE nodes by MPLS PWs (per customer). These, in turn, are connected via a full-mesh of PWs (per customer or group of customers) traversing the IP/MPLS core. The U-PE still provides the same type of services toward its customers as before and they are: - Port mode (either 802.1D, 802.1Q, or 802.1ad) - VLAN mode (either 802.1Q or 802.1ad) - VLAN-bundling mode (either 802.1Q or 802.1ad) Spoke PW from U-PE to N-PE is not service multiplexed i.e. one service per PW. The spoke PW cannot be multiplexed because of the potential for having overlapping Customer MAC addresses. PBB PBB Sajassi, et. al. Expires: January 2009 [Page 8] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 BEB +----------+ BEB | | | | +-----------+ | | IP | | +-----------+ | MPLS | V | MPLS | V | MPLS | | Access +----+ | Core | +----+ Access | +--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+ |CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE| +--+ +----+ +----+ | | +----+ +----+ +--+ | | | | | | +-----------+ +----------+ +-----------+ Figure 2: H-VPLS with MPLS Access Network and PBB N-PE By incorporating PBB function, the N-PE maps each of these services (for a given customer) onto a single I-SID based on the configuration at the N-PE. Many I-SIDs can be multiplexed within a single bridge domain (e.g. B-VLAN). The N-PE can, then, either map a single I-SID into a VPLS instance or it can map a bridge domain (e.g. B-VLAN) onto a VPLS instance, according to its configuration. Next, the encapsulated frames are sent over the set of PWs associated with that VPLS instance. If the VPLS instance is set up per bridge domain (e.g. B-VID), only one I-SID Domain is allowed. However if VPLS instance is set up per I-SID, single I-SID Domain and multiple I-SID Domain scenarios have to considered, which are covered next. 3.2.1 PBB N-PEs in Single I-SID Domain In this scenario, I-SID assignment is performed globally across all MPLS access networks and therefore there is no need for I-SID translation. Both I-SID mode and I-SID bundling mode are supported in this scenario. I-SID to VPLS mapping is congruent on all N-PEs. In case of the I-SID bundling mode, a bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type as defined in [RFC4447] [RFC4448], can be used with the corresponding B-VID rewrite or translation performed at the various N-PE nodes. This assumes that I-SID bundling is congruent on both N-PEs. In case of the I-SID mode, an I-SID is mapped to a VPLS instance and the new PW type described in [VPLS-PBB] is utilized without the need for I-SID translation. 3.2.2 PBB N-PEs in Multiple I-SID Domains In this scenario, I-SID assignment is performed on a per MPLS access network basis and thus I-SID bundling is no longer viable because I- SIDs value differ among different domains. In this scenario, only I- Sajassi, et. al. Expires: January 2009 [Page 9] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 SID mode is supported and the N-PE nodes perform the translation as frames are forwarded between different service domains. To perform this translation, the new PW type (described in [VPLS- PBB]) is used. The Ethernet frame that is carried over this PW has I-tagged format. The receiving N-PE, upon receiving this frame, will translate the I-SID to the value associated with the service instance of the PW and will append a B-VID associated for the local grouping of the I-SID. After the proper translation of I-SID and insertion of B-VID, the processing of the frame is exactly the same as the current VPLS. 4. Migration Scenarios Operators and service providers that have deployed H-VPLS with either MPLS or Ethernet are unlikely to migrate to PBB technology overnight because of obvious cost implications. Thus, it is imperative to outline migration strategies that will allow operators to protect investments in their installed base while still taking advantage of the scalability benefits of PBB technology. In the following sub-sections, we explore three different migration scenarios which allow a mix of existing H-VPLS access networks to co-exist with newer PBB-based access networks. The scenarios differ in whether the Ethernet service frames passing over the VPLS core are PBB-encapsulated or not. The first scenario in section 4.1 involves passing only non PBB-encapsulated frames over the core. The second scenario in section 4.2 stipulates passing only PBB- encapsulated frames over the core. Whereas, the final scenario in section 4.3 depicts a core that supports a mix of PBB-encapsulated and non PBB-encapsulated frames. The advantages and disadvantages of each scenario will be discussed in its respective section. 4.1 802.1ad Service Frames over VPLS Core In this scenario, existing access networks are left unchanged. All N-PEs would forward frames based on C-MAC addresses. In other words, Ethernet frames which are traversing the VPLS core (within PWs) would use the 802.1ad frame format, as in current VPLS. Hence, the N-PEs in existing access networks do not require any modification. For new MPLS access networks that have PBB functions on the U-PE, the corresponding N-PE must incorporate built-in IB-BEB functions in order to terminate the PBB encapsulation before the frames enter the core. A key point here is that while both the U-PE and N-PE nodes implement PBB IB-BEB functionality, the former has the I-Component facing the customer (CE) and the B-Component facing the core; whereas the latter has the I-Component facing the core and the B- Component facing the customer (i.e. access network). Sajassi, et. al. Expires: January 2009 [Page 10] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 PBB PBB +----------+ IB-BEB IB-BEB | | | | +-----------+ | IP | | +-----------+ | | MPLS | | MPLS | V | MPLS | | | Access +----+ | Core | +----+ Access | V +--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+ |CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE| +--+ +----+ +----+ | | +----+ +----+ +--+ | (Existing)| | | | (New) | +-----------+ +----------+ +-----------+ Figure 3: Migration with 802.1ad Service Frames over VPLS Core The main advantage of this approach is that it requires no change to existing access networks or existing VPLS N-PEs. The main disadvantage is that these N-PEs will not leverage the advantages of PBB in terms of MAC address and PW scalability. It is worth noting that this migration scenario is an optimal option for an H-VPLS deployment with a single PBB-capable access network. When multiple PBB-capable access networks are required, then the scenario in Section 4.3 is preferred, as it provides a more scalable and optimal interconnect amongst the PBB-capable networks. 4.2 PBB Service Frames over VPLS Core This scenario requires that the VPLS N-PE connecting to existing MPLS access networks be upgraded to incorporate IB-BEB functions. All Ethernet service frames passing over the VPLS core would be PBB- encapsulated. The PBB over MPLS access networks would require no special requirements beyond what is captured in section 3 of this document. In this case, both the U-PE and N-PE which implement IB-BEB functionality have the I-Component facing the customer and the B- Component facing the core. PBB PBB IB-BEB +----------+ IB-BEB | | | | +-----------+ | | IP | +-----------+ | | MPLS | V | MPLS | | MPLS | | | Access +----+ | Core | +----+ Access | V +--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+ |CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE| +--+ +----+ +----+ | | +----+ +----+ +--+ | (Existing)| | | | (New) | +-----------+ +----------+ +-----------+ Figure 4: Migration with PBB Service Frames over VPLS Core The main advantage of this approach is that it allows better scalability of the VPLS N-PEs in terms of MAC address and pseudowire Sajassi, et. al. Expires: January 2009 [Page 11] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 counts. The disadvantage is that it requires upgrading the VPLS N- PEs of all existing MPLS access networks. 4.3 Mixed 802.1ad and PBB over VPLS Core In this scenario, existing access networks are left unchanged, and exchange Ethernet frames with 802.1ad format over the PWs in the core. The newly added access networks, which incorporate PBB functionality exchange Ethernet frames that are PBB-encapsulated amongst each other over core PWs. For service connectivity between existing access network (non PBB capable) and new access network (PBB based), the VPLS N-PE of the latter network employs IB-BEB functionality to de-capsulate the PBB header from frames outbound to the core, and encapsulate the PBB header for frames inbound from the core. As a result, a mix of PBB-encapsulated and 802.1ad Ethernet service frames are exchanged over the VPLS core. This mode of operation requires new functionality on the VPLS N-PE of the PBB-capable access network, so that the PE can send frames in 802.1ad format or PBB format, on a per PW basis, depending on the capability of the destination access network. Effectively, the PE would have to incorporate B-BEB as well as IB-BEB functions. The frame format to be used over a given PW will depend on the negotiated PW type: - PBB incapable access network to PBB incapable access network: Existing raw mode (0x0005) or tagged mode (0x0004) PW types can be used. - PBB incapable access network to PBB capable access network: Existing raw mode (0x0005) or tagged mode (0x0004) PW types can be used. - PBB capable access network to PBB capable access network: new PW type discussed in [VPLS-PBB] must be used. A given PE needs to be aware of the capability of its remote peer in order to determine the right type of PW to negotiate with that peer. This can be achieved either via static configuration, or by extending the VPLS BGP-based auto-discovery mechanism discussed in [RFC4761]. The latter approach is preferred, and the details of the extensions required will be covered in future revision of this document. PBB B-BEB PBB +----------+ IB-BEB IB-BEB Sajassi, et. al. Expires: January 2009 [Page 12] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 | | | | +-----------+ | IP | | +-----------+ | | MPLS | | MPLS | V | MPLS | | | Access +----+ | Core | +----+ Access | V +--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+ |CE|--|U-PE| |N-PE| | | |N-PE| |U-PE|--|CE| +--+ +----+ +----+ | | +----+ +----+ +--+ | (Existing)| | | | (New) | +-----------+ +----------+ +-----------+ Figure 5: Migration with Mixed 802.1ad &PBB Service Frames over VPLS Core The U-PE and N-PE of the PBB-capable access network both employ BEB functionality: The U-PE implements IB-BEB function where the I- Component faces the customer (CE) and the B-Component faces the core. The N-PE, on the other hand, implements IB-BEB functionality with the I-Component facing the core and the B-Component facing the customer (access network). In addition, the N-PE implements stand- alone B-BEB functionality. This scenario combines the advantages of both previous scenarios without any of their shortcomings, namely: it does not require any changes to existing access networks and it allows the N-PE to leverage the scalability benefits of 802.1ah for PBB to PBB access network connectivity. The disadvantage of this option is that it requires new functionality on the N-PE of the PBB-capable access network. 5. IANA Considerations This document has no actions for IANA. 6. Security Considerations This document does not introduce any additional security aspects beyond those applicable to VPLS/H-VPLS. VPLS/H-VPLS security considerations are already covered in [RFC4762]. 7. References 7.1 Normative References [802.1ad] "Virtual Bridged Local Area Networks: Provider Bridges", IEEE 802.1ad/D8.1, December 2005 [802.1ag] "Connectivity Fault Management", IEEE 802.1ag/D8.1, Jul 2007 Sajassi, et. al. Expires: January 2009 [Page 13] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 [RFC4447] "Pseudowire Setup and Maintenance using LDP", RFC4447, April 2006 [RFC4448] "Encapsulation Methods for Transport of Ethernet over MPLS Networks", RFC4448, April 2006 [RFC4762] "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC4762, January 2007 [RFC4761] "Virtual Private LAN Service (VPLS) Using BGP for Auto- Discovery and Signaling", RFC4761, January 2007 7.2 Informative References [802.1Q] "Virtual Bridged Local Area Networks", IEEE Std. 802.1Q- 2005 [802.1D-REV] "Media Access Control (MAC) Bridges", IEEE Std. 802.1D- 2003 [VPLS-PBB] "VPLS Interoperability with Provider Backbone Bridges", draft-sajassi-l2vpn-vpls-pbb-interop-02.txt, Work in progress, November 2007 [VPLS-Bridge] "VPLS Interoperability with CE Bridges", draft-ietf- l2vpn-vpls-bridge-interop-02.txt, Work in progress, November 2007 [PBB-PW] "802.1ah Ethernet Pseudowire", draft-martini-pwe3-802-1ah- pw-00.txt, Work in progress, May 2007 [VPLS-MCAST] "Multicast in VPLS", draft-ietf-l2vpn-vpls-mcast- 03.txt, Work in progress, November 2007 [PBB-VPLS-MCAST] "Multicast Pruning in Provider Backbone Bridged VPLS", draft-sajassi-l2vpn-pbb-vpls-mcast-pruning-00.txt, Work in progress, July 2008 Appendix A: Provider Backbone Bridges - Primer Provider Backbone Bridges (PBBs), as currently being defined in IEEE 802.1ah, offer a scalable solution for service providers to build large bridged networks. The focus of PBB is primarily on improving two main areas with provider Ethernet bridged networks: - MAC-address table scalability: in current provider networks that employ IEEE 802.1Q or IEEE 802.1ad bridging, the service provider equipment operating at the Ethernet MAC layer is forced to learn all customer edge device MAC addresses (when the CE is a router) and all customer end-station MAC addresses (when the CE is a bridge). This clearly does not scale well as the number of customers and customer equipment, served by a Sajassi, et. al. Expires: January 2009 [Page 14] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 given provider, increases. The service providers are often limited by the size of the hardware MAC tables as they attempt to scale their networks. - Service instance scalability: when building networks using IEEE 802.1Q or IEEE 802.1ad technologies, a service provider is limited to 4094 service instances per 802.1Q or 802.1ad network. This limitation is due to the fact that the VLAN identifier is 12-bits in width which translates to 4096 possible values (and VLAN identifier values 0 and 4095 are reserved). To obviate the above two limitations, PBB introduces a hierarchical network architecture with associated new frame formats which extend the work completed by Provider Bridges (IEEE 802.1ad). In the PBB architecture, customer networks (using IEEE 802.1Q bridging) are aggregated into provider bridge networks (using IEEE 802.1ad). These, in turn, are aggregated into Provider Backbone Bridge Networks (PBBNs) which utilize the IEEE 802.1ah frame format. The frame format employs a MAC tunneling encapsulation scheme for tunneling customer Ethernet frames within provider Ethernet frames across the PBBN. A VLAN identifier (B-VID) is used to segregate the backbone into broadcast domains and a new 24-bit service identifier (I-SID) is defined and used to associate a given customer MAC frame with a provider service instance (also called the service delimiter). It should be noted that in 802.1ah there is a clear segregation between provider service instances (represented by I- SIDs) and provider VLANs (represented by B-VIDs) which was not the case for 802.1ad. As such, the network designer for an 802.1ah network has the freedom to define the number of VLANs which is optimum for network operation without any dependency on the number of service instances. PBBN bridges utilize existing IEEE control protocols (e.g. IEEE 802.1s MST) to create a loop free topology for frame forwarding. A PBBN bridge can be categorized as either a Backbone Core Bridge (BCB) or Backbone Edge Bridge (BEB). A BCB is a plain IEEE 802.1ad Provider Bridge. A BEB is responsible for encapsulation and de- encapsulation of customer Ethernet frames to/from PBB (802.1ah) frame format. As shown in the following figure A.1, a Backbone Edge Bridge (BEB) may consist of a single B-component and one or more I-components. In simple terms, the B-component provides bridging in provider space (B-MAC, B-VLAN) and the I-component provides bridging in customer space (C-MAC, S-VLAN). The customer frame is first encapsulated with the provider backbone header (B-MAC, B-tag, I-tag); then, the bridging is performed in the provider backbone space (B-MAC, B-VLAN) through the network till the frame arrives at the destination BEB where it gets de-encapsulated and passed to the CE. If a PBB bridge consists of both I & B components, then it is called IB-BEB and if Sajassi, et. al. Expires: January 2009 [Page 15] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 it only consists of either B-component or I-component, then it is called B-BEB or I-BEB respectively. The interface between an I-BEB or IB-BEB and a CE is called S-tagged service interface and the interface between an I-BEB and a B-BEB (or between two B-BEBs) is called I-tagged service interface. The interface between a B-BEB or IB-BEB and a Backbone Core Bridge (BCB) is called B-Tagged service interface. These service interfaces, for Provider Backbone Bridges, are described next. +-------------------------------+ | 802.1ah Bridge Model | | | +---+ | +------+ +-----------+ | |CE |---------|I-Comp|------| | | +---+ | | | | |-------- | +------+ | | | | o | B-Comp | | | o | |-------- | o | | | +---+ | +------+ | | | |CE |---------|I-Comp|------| |-------- +---+ ^ | | | ^ | | | ^ | | +------+ | +-----------+ | | | +------------|------------------+ | | | | | | | S-tagged I-tagged B-tagged Service I/F Service I/F Service I/F Figure A1: 802.1ah Bridge Model A.1 S-Tagged Service Interface This service interface connects a customer 802.1ad Provider Bridge to an I-BEB or IB-BEB. Three modes are supported: - Port Mode. In this mode, traffic on all S-VLANs is mapped to the same I-SID. - S-Tag Mode. In this mode, traffic associated with each S-VLAN is mapped to a single I-SID. - S-Tag Bundling Mode. In this mode, traffic associated with a group or range of S-VLANs is mapped to a single I-SID. A.2 I-Tagged Service Interface This service interface connects an I-BEB to a B-BEB or it connects two B-BEBs together. Although, in figure A.1, this interface is shown as an internal interface between I-component and B-component within an IB-BEB, in practice this service interface is an external Sajassi, et. al. Expires: January 2009 [Page 16] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 interface connecting a customer I-BEB with a provider B-BEB or connecting two different providers B-BEBs across different administrative domains. A.3 B-Tagged Service Interface This service interface connects a B-BEB or an IB-BEB with a provider Backbone Core Bridge (BCB). Authors' Addresses Ali Sajassi Cisco 170 West Tasman Drive San Jose, CA 95134, U.S. 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 Dinesh Mohan Nortel 3500 Carling Ave Ottawa, ON K2H8E9, Canada Email: mohand@nortel.com Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Sajassi, et. al. Expires: January 2009 [Page 17] Internet-Draft PBB in H-VPLS with MPLS Access July 2008 Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Sajassi, et. al. Expires: January 2009 [Page 18]