Network Working Group Nabil Bitar (Editor) Internet Draft Verizon Expiration Date: July 2007 Luca Martini (Editor) Matthew Bocci (Editor) Cisco Systems Inc. Alcatel January 2007 Requirements for Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3) draft-ietf-pwe3-ms-pw-requirements-04.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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes the necessary requirements to allow a service provider to extend the reach of pseudowires across multiple domains. These domains can be autonomous systems under one provider administrative control, IGP areas in one autonomous system, different autonomous systems under the administrative control of two or more Bitar, et al. [Page 1] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 service providers, or administratively established pseudowire domains. Bitar, et al. [Page 2] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 Table of Contents 1 Specification of Requirements ........................ 4 2 Acknowledgments ...................................... 4 3 Introduction ......................................... 4 3.1 Scope ................................................ 4 3.2 Architecture ......................................... 4 4 Terminology .......................................... 7 5 Use Cases ............................................ 8 5.1 Multi-Segment Pseudowire Placement Mechanisms ........ 11 6 Multi-Segment Pseudowire Requirements ................ 11 6.1 All Mechanisms ....................................... 11 6.1.1 Architecture ......................................... 11 6.1.2 Resiliency ........................................... 12 6.1.3 Quality Of Service ................................... 13 6.2 Generic Requirements for MS-PW Setup Mechanisms ...... 14 6.2.1 Routing .............................................. 15 6.3 Statically configured MS-PWs ......................... 16 6.3.1 Architecture ......................................... 16 6.3.2 MPLS-PWs ............................................. 16 6.3.3 Resiliency ........................................... 16 6.3.4 Quality of service ................................... 17 6.4 Signaled PW-segments ................................. 17 6.4.1 Architecture ......................................... 17 6.4.2 Resiliency ........................................... 17 6.4.3 Quality of Service ................................... 18 6.4.4 Routing .............................................. 18 6.5 Signaled PW / Dynamic Route .......................... 19 6.5.1 Architecture ......................................... 19 6.5.2 Resiliency ........................................... 19 6.5.3 Quality of Service ................................... 19 6.5.4 Routing .............................................. 20 7 Operations and Maintenance (OAM) ..................... 20 8 Security Considerations .............................. 21 8.1 Data-plane Security Requirements ..................... 22 8.2 Control-plane Security Requirements .................. 23 9 Full Copyright Statement ............................. 24 10 Intellectual Property Statement ...................... 24 11 IANA Considerations .................................. 25 12 Normative References ................................. 25 13 Informative References ............................... 25 14 Author Information ................................... 25 Bitar, et al. [Page 3] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 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 RFC 2119. 2. Acknowledgments The editors gratefully acknowledge the following contributors: Dimitri Papadimitriou (Alcatel), Peter Busschbach (Lucent), Sasha Vainshtein (Axerra), Richard Spencer (British Telecom), Simon Delord (France Telecom), Deborah Brungard (AT&T), David McDyson, Rahul Aggawal (Juniper), Du Ke (ZTE), Cagatay Buyukkoc (ZTE). 3. Introduction 3.1. Scope This document specifies requirements for extending pseudowires across more than one packet switched network (PSN) domain and/or more than one PSN tunnel. These pseudowires are called multi-segment pseudowires (MS-PW). Requirements for single-segment pseudowires (SS-PW) that extend edge to edge across only one PSN domain are specified in [RFC3916]. This document specifies additional requirements that apply to MS-PWs. These requirements do not apply to PSNs that only support SS-PWs. 3.2. Architecture The following three figures describe the reference models which are derived from [RFC3985] to support PW emulated services. Bitar, et al. [Page 4] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 |<-------------- Emulated Service ---------------->| | | | |<------- Pseudowire ------->| | | | | | | | |<-- PSN Tunnel -->| | | | PW End V V V V PW End | V Service +----+ +----+ Service V +-----+ | | PE1|==================| PE2| | +-----+ | |----------|............PW1.............|----------| | | CE1 | | | | | | | | CE2 | | |----------|............PW2.............|----------| | +-----+ ^ | | |==================| | | ^ +-----+ ^ | +----+ +----+ | | ^ | | Provider Edge 1 Provider Edge 2 | | | | | | Customer | | Customer Edge 1 | | Edge 2 | | | | Attachment Circuit (AC) Attachment Circuit (AC) Native service Native service Figure 1: PWE3 Reference Configuration Figure 1 shows the PWE3 reference architecture [RFC3985]. This architecture applies to the case where a PSN tunnel extends between two edges of a single PSN domain to transport a PW with endpoints at these edges. Bitar, et al. [Page 5] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 Native |<--------Multi-Segment Pseudowire----->| Native Service | PSN PSN | Service (AC) | |<-Tunnel->| |<-Tunnel->| | (AC) | V V 1 V V 2 V V | | +-----+ +-----+ +---- + | +---+ | |T-PE1|==========|S-PE1|==========|T-PE2| | +---+ | |---------|........PW1.......... |...PW3..........|---|----| | |CE1| | | | | | | | | |CE2| | |---------|........PW2...........|...PW4..........|--------| | +---+ | | |==========| |==========| | | +---+ ^ +-----+ +-----+ +-----+ ^ | Provider Edge 1 ^ Provider Edge 3 | | | | | | | | PW switching point | | | | | |<------------------- Emulated Service ------------------->| Figure 2: PW switching Reference Model Figure 2 extends this architecture to show a multi-segment case. Terminating PE1 (T-PE1) and Terminating PE3 (T-PE3) provide PWE3 service to CE1 and CE2. These PEs terminate different PSN tunnels, PSN Tunnel 1 and PSN Tunnel 2, and may reside in different PSN or pseudowire domains. One PSN tunnel extends from T-PE1 to S-PE1 across PSN1, and a second PSN tunnel extends from S-PE1 to T-PE2 across PSN2. PWs are used to connect the Attachment circuits (ACs) attached to T- PE1 to the corresponding ACs attached to T-PE2. Each PW on PSN tunnel 1 is switched to a PW in the tunnel across PSN2 at S-PE2 to complete the multi-segment PW (MS-PW) between T-PE1 and T-PE2. S-PE1 is therefore the PW switching point and will be referred to as the PW switching provider edge (S-PE). PW1 and PW3 are segments of the same MS-PW while PW2 and PW4 are segments of another pseudowire. PW segments of the same MS-PW (e.g., PW1 and PW3) MAY be of the same PW type or different type, and PSN tunnels (e.g., PSN Tunnel 1 and PSN Tunnel 2) can be the same or different technology. This document requires support for MS-PWs with segments of the same PW type. An S- PE switches a MS-PW from one segment to another based on the PW identifiers (e.g., PW label in case of MPLS PWs). In Figure 2, the domains that PSN Tunnel 1 and PSN Tunnel 2 traverse could beIGP areas in the same IGP network, or simply PWE3 domains in a single flat IGP network for instance. Bitar, et al. [Page 6] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 |<------Multi-Segment Pseudowire------>| | AS AS | AC | |<----1---->| |<----2--->| | AC | V V V V V V | | +----+ +-----+ +----+ +----+ | +----+ | | |=====| |=====| |=====| | | +----+ | |-------|.....PW1..........PW2.........PW3.....|-------| | | CE1| | | | | | | | | | | |CE2 | +----+ | | |=====| |=====| |=====| | | +----+ ^ +----+ +-----+ +----+ +----+ ^ | T-PE1 S-PE2 S-PE3 T-PE4 | | ^ ^ | | | | | | PW switching points | | | | | |<------------------- Emulated Service --------------->| Figure 3: PW switching inter provider Reference Model Note that although Figure 2 only shows a single S-PE, a PW may transit more than one S-PE along its path. For instance, in the multi-AS case shown in Figure 3, there can be an S-PE (S-PE2), at the border of one AS (AS1) and another S-PE (S-PE3) at the border of the other AS (AS2). A MS-PW that extends from the edge of one AS (T-PE1) to the edge of the other AS (T-PE4) is composed of three segments: (1) PW1, a segment in AS1, (2) PW2, a segment between the two border routers (S-PE2 and S-PE3) that are switching PEs, and (3) PWE3, a segment in AS2. AS1 and AS2 could be belong to the same provider (e.g., AS1 could be an access network or metro transport network, and AS2 could be an MPLS core network) or to two different providers (e.g., AS1 for Provider 1 and AS2 for Provider2). 4. Terminology RFC 3985 [RFC3985] provides terminology for PWE3. The following additional terminology is defined for multi-segment pseudowires: - PW Terminating Provider Edge (T-PE). A PE where the customer- facing attachment circuits (ACs) are bound to a PW forwarder. A Terminating PE is present in the first and last segments of a MS-PW. This incorporates the functionality of a PE as defined in RFC 3985. Bitar, et al. [Page 7] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 - Single-Segment Pseudowire (SS-PW). A PW setup directly between two T-PE devices. Each direction of a SS-PW traverses one PSN tunnel that connects the two T-PEs. - Multi-Segment Pseudowire (MS-PW). A static or dynamically configured set of two or more contiguous PW segments that behave and function as a single point-to-point PW. Each end of a MS-PW by definition MUST terminate on a T-PE. - PW Segment. A part of a single-segment or multi-segment PW, which is set up between two PE devices, T-PEs and/or S-PEs. - PW Switching Provider Edge (S-PE). A PE capable of switching the control and data planes of the preceding and succeeding PW segments in a MS-PW. The S-PE terminates the PSN tunnels transporting the preceding and succeeding segments of the MS-PW. It is therefore a PW switching point for a MS-PW. A PW Switching Point is never the S-PE and the T-PE for the same MS-PW. A PW switching point runs necessary protocols to setup and manage PW segments with other PW switching points and terminating PEs. 5. Use Cases PWE3 defines the signaling and encapsulation techniques for establishing SS-PWs between a pair of terminating PEs (T-PEs) and in the vast majority of cases this will be sufficient. MS-PWs may be useful in the following situations: -i. Inter-Provider PWs: An Inter-Provider PW is a PW that extends from a T-PE in one provider domain to a T-PE in another provider domain. -ii. It may not be possible, desirable or feasible to establish a direct PW control channel between the T-PEs, residing in different provider networks, to setup and maintain PWs. At a minimum, a direct PW control channel establishment (e.g., targeted LDP session) requires knowledge of and reachability to the remote T-PE IP address. The local T-PE may not have access to this information due to operational or security constraints. Moreover, a SS-PW would require the existence of a PSN tunnel between the local T-PE and the remote T-PE. It may not be feasible or desirable to extend single, contiguous PSN tunnels between T-PEs in one domain and T-PEs in another domain for security and/or scalability reasons or because the two domains may be using different PSN technologies. Bitar, et al. [Page 8] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -iii. MS-PW setup, maintenance and forwarding procedures must satisfy requirements placed by the constraints of a multi- provider environment. An example is the inter-AS L2VPN scenario where the T-PEs reside in different provider networks (ASs) and it is the current practice to MD5-key all control traffic exchanged between two networks. A MS-PW allows the providers to confine MD5 key administration for the LDP session to just the PW switching points connecting the two domains. -iv. PSN Interworking: PWE3 signaling protocols and PSN types may differ in different provider networks. The terminating PEs may be connected to networks employing different PW signaling and /or PSN protocols. In this case it is not possible to use a SS-PW. A MS-PW with the appropriate interworking performed at the PW switching points can enable PW connectivity between the terminating PEs in this scenario. -v. Traffic Engineered PSN Tunnels and bandwidth-managed PWs: There is a requirement to deploy PWs edge to edge in large service provider networks. Such networks typically encompass hundreds or thousands of aggregation devices at the edge, each of which would be a PE. Furthermore, there is a requirement that these PWs have explicit bandwidth guarantees. To satisfy these requirements, the PWs will be tunneled over PSN TE-tunnels with bandwidth constraints. A single segment pseudowire architecture would require that a full mesh of PSN TE-tunnels be provisioned to allow PWs to be established between all PEs. Inter-provider PWs riding traffic engineered tunnels further add to the number of tunnels that would have to be supported by the PEs and the core network as the total number of PEs increases. In this environment, there is a requirement either to support a sparse mesh of PSN TE-tunnels and PW signaling adjacencies, or to partition the network into a number of smaller PWE3 domains. In either case, a PW would have to pass through more than one PSN tunnel hop along its path. An objective is to reduce the number of tunnels that must be supported, and thus the complexity and scalability problem that may arise. -vi. Pseudowires in access/metro metworks: Service providers wish to extend PW technology to access and metro networks in order to reduce maintenance complexity and operational costs. Today's access and metro networks are either legacy (TDM, SONET/SDH, or Frame Relay/ATM), Ethernet or IP based. Bitar, et al. [Page 9] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 Due to these architectures, circuits (e.g., Ethernet VCs, ATM VCs, TDM circuits) in the access/metro are traditionally handled as attachment circuits, in their native format, to the edge of the IP-MPLS network where the PW starts. This combination requires multiple separate access networks and complicates end-to-end control, provisioning, and maintenance. In addition, when a TDM or SONET/SDH access network is replaced with a packet-based infrastructure, expenses may be lowered due to moving statistical multiplexing closer to the end-user and converging multiple services onto a single access network. Access networks have a number of properties that impact the application of PWs. For example, there exist access mechanisms where the PSN is not of an IETF specified type, but uses mechanisms compatible with those of PWE3 at the PW layer. Here, use case (iv) may apply. In addition, many networks consist of hundreds or thousands of access devices. There is therefore a desire to support a sparse mesh of PW signaling adjacencies and PSN tunnels. Use case (v) may therefore apply. Finally, Access networks also tend to differ from core networks in that the access PW setup and maintenance mechanism may only be a subset of that used in the core. Using the MS-PWs, access and metro network elements need only maintain PW signaling adjacencies with the PEs to which they directly connect. They do not need PW signaling adjacencies with every other access and metro network device. PEs in the PSN backbone in turn maintain PW signaling adjacencies among each other. In addition, a PSN tunnel is setup between an access element and the PE to which it connects. Another PSN tunnel needs to be established between every PE pair in the PSN backbone. A MS-PW may be setup from one access network element to another another access element with three segments: (1) access-element - PSN-PE, (2) PSN-PE to PSN-PE, and (3) PSN- PE to access element. In this MS-PW setup, access elements are T-PEs while PSN-PEs are S-PEs. It should be noted that the PSN backbone can be also segmented into PWE3 domains resulting in more segments per PW. Bitar, et al. [Page 10] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 5.1. Multi-Segment Pseudowire Placement Mechanisms This requirements document assumes that the above use cases are realized using one or more of the following mechanisms: -i. Static Configuration: The switching points (S-PEs), in addition to the T-PEs, are manually provisioned for each segment. -ii. Pre-determined Route: The PW is established along an administratively determined route using an end-to-end signaling protocol with automated stitching at the S-PEs. -iii. Signaled Dynamic Route: The PW is established along a dynamically determined route using an end-to-end signaling protocol with automated stitching at the S-PEs. The route is selected with the aid of one or more dynamic routing protocols. Note that we define the PW route to be the set of S-PEs through which a MS-PW will pass between a given pair of T-PEs. PSN tunnels along that route can be explicitly specified or locally selected at the S- PEs and T-PEs. The routing of the PSN tunnels themselves is outside the scope of the requirements specified in this document. 6. Multi-Segment Pseudowire Requirements The following sections detail the requirements that the above use cases put on the MS-PW setup mechanisms. 6.1. All Mechanisms The following generic requirements apply to the three MS-PW setup mechanisms defined in the previous section. 6.1.1. Architecture -i. If MS-PWs are tunneled, across a PSN that only supports SS- PWs, then only the requirements of [RFC3916] apply to that PSN. The fact that the overlay is carrying MS-PWs MUST be transparent to the routers in the PSN. Bitar, et al. [Page 11] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -ii. The PWs MUST remain transparent to the P-routers. A P-router is not an S-PE or an T-PE from the MS-PW architecture viewpoint. P-routers provide transparent PSN transport for PWs and MUST not have any knowledge of the PWs traversing them. -iii. The MS-PWs MUST use the same encapsulation modes specified for SS-PWs. -iv. The MS-PWs MUST be composed of SS-PWs. -v. A MS-PW MUST be able to pass across PSNs of all technologies specified by PWE3 for SS-PWs. When crossing from one PSN technology to another, an S-PE must provide the necessary PSN interworking functions in that case. -vi. Both directions of a PW segment MUST terminate on the same S-PE/T-PE. -vii. S-PEs MAY only support switching PWs of the same PW type. In this case, the PW type is transparent to the S-PE in the forwarding plane, except for functions needed to provide for interworking between different PSN technologies. -viii. Solutions MAY provide a way to prioritize the setup and maintenance process among PWs. 6.1.2. Resiliency Mechanisms to protect a MS-PW when an element on the existing path of a MS-PW fails MUST be provided. These mechanisms will depend on the MS-PW setup. Following are the generic resiliency requirements that apply to all MS-PW setup mechanisms: -i. Configuration and establishment of a backup PW to a primary PW SHOULD be supported. Mechanisms to perform a switchover from a primary PW to a backup PW upon failure detection SHOULD be provided. -ii. The ability to configure an end-to-end backup PW path for a primary PW path SHOULD be supported. The primary and backup paths may be statically configured, statically specified for signaling or dynamically selected via dynamic routing depending on the MS-PW establishment mechanism. Backup and primary paths should have the ability to traverse separate S-PEs. The backup path MAY be signaled at configuration time or after failure. Bitar, et al. [Page 12] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -iii. The ability to configure a primary PW and a backup PW with a different T-PE from the primary SHOULD be supported. -iv. Automatic Mechanisms to perform a fast switchover from a primary PW to a backup PW upon failure detection SHOULD be provided. -v. A mechanism to automatically revert to a primary PW from a backup PW MAY be provided. When provided, it MUST be configurable. 6.1.3. Quality Of Service Pseudowires are intended to support emulated services (e.g., TDM and ATM) which may have strict per-connection quality of service requirements. This may include either absolute or relative guarantees on packet loss, delay, and jitter. These guarantees are in part delivered by reserving sufficient network resources (e.g. bandwidth), and by providing appropriate per-packet treatment (e.g. scheduling priority and drop precedence) throughout the network. For SS-PWs, a traffic engineered PSN tunnel (i.e., MPLS-TE) may be used to ensure that sufficient resources are reserved in the P- routers to provide QoS to PWs on the tunnel. In this case, T-PEs MUST have the ability to automatically manage PSN tunnel resources in the traffic direction (e.g. admission control of PWs onto the PSN tunnel and accounting for reserved bandwidth and available bandwidth on the tunnel). In cases where the tunnel supports multiple classes of service (CoS) (e.g., E-LSP), bandwidth management is required per CoS. For MS-PWs, each S-PE maps a PW segment to a PSN tunnel. Solutions Must enable S-PEs and T-PEs to automatically bind a PW segment to a PSN-tunnel based on CoS and bandwidth requirements when these attributes are specified for a PW. Solutions SHOULD also provide the capability of binding a PW segment to a tunnel as a matter of policy configuration. S-PEs and T-PEs must be capable of automatically managing PSN-tunnel resources per CoS. S-PEs and T-PEs MUST be able to associate a CoS marking (e.g., EXP field value for MPLS PWs) with PW PDUs. CoS marking in the PW PDUs affects packet treatment. The CoS marking depends on the PSN technology. Thus, solutions must enable the configuration of necessary mapping for CoS marking when the MS-PW crosses from one PSN technology to another. Similarly, different administrative domains may use different CoS values to imply the same CoS treatment. Solutions MUST provide the ability to define CoS marking maps on S- Bitar, et al. [Page 13] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 PEs at administrative domain boundaries to translate from one CoS value to another as a a PW PDU crosses from one domain to the next. Solutions MUST enable S-PEs and T-PEs on the path of a MS-PW to notify other S-PEs and T-PEs on that path of congestion when it occurs. Congestion may be indicated by queue length, packet loss rate, or bandwidth measurement (among others) crossing a respective threshold. The action taken by a T-PE that receives a notification of congestion along the path of one of its PWs could be to reroute the MS-PW to an alternative path, including an alternative T-PE if available. Some PW types, such as TDM PWs, are more sensitive to congestion than others. The reaction to a congestion notification MAY vary per PW type. 6.2. Generic Requirements for MS-PW Setup Mechanisms The MS-PW setup mechanisms MUST accommodate Service Provider's practices, especially in relation to security, confidentiality and traffic engineering. Security and confidentiality are especially important when the MS-PWs are setup across Autonomous Systems in different administrative domains. Following are generic requirements that apply to the three MS-PW setup mechanisms defined earlier: -i. The ability to statically select S-PEs and PSN tunnels on a PW path MUST be provided. Static selection of S-PEs is by definition a requirement for the static configuration and signaled/static route setup mechanisms. This requirement satisfies the need for forcing a MS-PW to traverse specific S-PEs to enforce service provider security and administrative policies. -ii. Solutions SHOULD minimize the amount of configuration needed to setup a MS-PW. -iii. Solutions should support different PW setup mechanisms on the same T-PE, S-PE and PSN network. -iv. Solutions MUST allow T-PEs to simultaneously support use of SS-PW signaling mechanisms as specified in [RFC4447] as well as MS-PW signaling mechanisms. -v. Solutions MUST ensure that a MS-PW will be setup when a path that satisfies the PW constraints for bandwidth, CoS and other possible attributes does exist in the network. Bitar, et al. [Page 14] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -vi. Solutions must clearly define the setup procedures for each mechanism so that a MS-PW setup on T-PEs can be interpreted as successful only when all PW segments are successfully setup. -vii. Admission control to the PSN tunnel needs to be performed against available resources, when applicable. This process MUST be performed at each PW segment comprising the MS-PW. PW admission control into a PSN tunnel MUST be configurable. -viii. In case the PSN tunnel lacks the resources necessary to accommodate the new PW, an attempt to signal a new PSN tunnel, or increase the capacity of the existing PSN tunnel MAY be made. If the expanded PSN tunnel fails to setup the PW MUST fail to setup. -ix. The setup mechanisms must allow the setup of a PW segment between two directly connected S-PEs without the existence of a PSN tunnel. This requirement allows a PW segment to be setup between two (Autonomous System Border Routers (ASBRs) when the MS-PW crosses AS boundaries without the need for configuring and setting up a PSN tunnel. In this case, admission control must be done, when enabled, on the link between the S-PEs. 6.2.1. Routing An objective of MS-PWs is to provide support for the following connectivity: -i. MS-PWs MUST be able to traverse multiple Service Provider administrative domains. -ii. MS-PWs MUST be able to traverse multiple Autonomous Systems within the same administrative domain. -iii. MS-PWs MUST be able to traverse multiple Autonomous Systems belonging to different administrative domains. -iv. MS-PWs MUST be able to support any hybrid combination of the aforementioned connectivity scenarios, including both PW transit, and termination in a domain. Bitar, et al. [Page 15] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 6.3. Statically configured MS-PWs When the MS-PW segments are statically configured the following requirements apply in addition to the generic requirements previously defined. 6.3.1. Architecture There are no additional requirements on the architecture. 6.3.2. MPLS-PWs Solutions should allow for the static configuration of MPLS labels for MPLS-PW segments and the cross-connection of these labels to preceding and succeeding segments. This is especially useful when a MS-PW crosses provider boundaries and two providers do not want to run any PW signaling protocol between them. A T-PE or S-PE that allows the configuration of static labels for MS-PW segments should also simultaneously allow for dynamic label assignments for other MS-PW segments. It should be noted that when two interconnected S-PEs do not have signaling peering for the purpose of setting up MS-PW segments, they should have in-band PW OAM capabilities that relay PW or attachment circuit defect notifications between the adjacent S- PEs. 6.3.3. Resiliency The solution should allow for the protection of a PW-segment, a contiguous set of PW-segments, as well as the end-end path. The primary and protection segments paths must share the same segments endpoints. Solutions should allow for having the backup paths setup prior to the failure or as a result of failure. The choice should be made by configuration. When resources are limited and cannot satisfy all PWs, the PWs with the higher setup priorities should be given preference when compared with the setup priorities of other PWs being setup or the holding priorities of existing PWs. Solutions should strive to minimize traffic loss between T-PEs. Bitar, et al. [Page 16] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 6.3.4. Quality of service The CoS and bandwidth of the MS-PW must be configurable at T-PEs and S-PEs. 6.4. Signaled PW-segments When the MS-PW segments are dynamically signaled the following requirements apply in addition to the generic requirements previously defined. These signaled MS-PW segments can be on the path of a statically configured MS-PW, signaled/statically routed MS-PW or signaled/dynamically routed MS-PW. There are four different SS-PW signaling protocols that are defined to signal PWs: -i. Static setup of the SS-PW (MPLS or L2TPv3 forwarding). -ii. LDP using PWid FEC 128 -iii. LDP using the generalized PW FEC 129 -iv. L2TPv3 The MS-PW setup mechanism MUST be able to support PW segments signaled with any of the above protocols, however the specification of which combinations of SS-PW signaling protocols is supported by a specific implementation is outside the scope of this document. For the signaled/statically routed and signaled/dynamically routed MS-PW setup mechanisms the following requirements apply in addition to the generic requirements previously defined. 6.4.1. Architecture There are no additional requirements on the architecture. 6.4.2. Resiliency Solutions should allow for the signaling of a protection path for a PW segment, sequence of segments or end-to-end path. The protection and primary paths for the protected segment(s) share the same respective segments endpoints. When admission control is enabled, Bitar, et al. [Page 17] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 systems must be careful not to double account for bandwidth allocation at merged points (e.g., tunnels). Solutions should allow for having the backup paths setup prior to the failure or as a result of failure. The choice should be made by configuration at the endpoints of the protected path. When resources are limited and cannot satisfy all PWs, the PWs with the higher setup priorities should be given preference when compared with the setup priorities of other PWs being setup or the holding priorities of existing PWs. Procedures must allow for the primary and backup paths to be diversified 6.4.3. Quality of Service When the T-PE attempts to signal a MS-PW the following capability is required: -i. Signaling must be able to identify the CoS associated with a MS-PW -ii. Signaling must be able to carry the traffic parameters for a MS-PW per CoS. Traffic parameters should be based on existing INTSERV definitions and must be used for admission control when admission control is enabled. -iii. The PW signaling MUST enable separate traffic parameter values to be specified for the forward and reverse directions of the PW. -iv. PW traffic parameter representations MUST be the same for all types of MS-PWs. -v. The signaling protocol must be able to accommodate a method to prioritize the PW setup and maintenance process among PWs. 6.4.4. Routing See the requirements for "Resiliency" above. Following are further requirements on signaled MS-PW setup mechanisms: -i. The signaling procedures MUST be defined such that the setup of a MS-PW is considered successful if all segments of the MS-PW are successfully setup. Bitar, et al. [Page 18] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -ii. The MS-PW path MUST have the ability to be dynamically setup between the T-PEs by provisioning only the T-PEs. -iii. Dynamic MS-PW setup requires that a unique identifier be associated with a PW and be carried in the signaling message. That identifier must contain sufficient information to determine the path to the remote T-PE through intermediate S-PEs. -iv. In a single-provider domain it is natural to have the T-PE identified by one of its IP addresses. This may also apply when a MS-PW is setup across multiple domains operated by the same provider. However, some service providers have security and confidentiality policies that prevent them from advertising reachability to routers in their networks to other providers (reachability to an ASBR is an exception). Thus, procedures MUST be provided to allow dynamic setup of MS-PWs under these conditions. 6.5. Signaled PW / Dynamic Route The following requirements apply, in addition to those in Section 6.1 and Section 6.2, when both dynamic signaling and dynamic routing are used. 6.5.1. Architecture There are no additional architectural requirements. 6.5.2. Resiliency The PW Routing function MUST support dynamic re-routing around failure points when segments are setup using the dynamic setup method. 6.5.3. Quality of Service There are no additional QoS requirements. Bitar, et al. [Page 19] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 6.5.4. Routing Following are requirements associated with dynamic route selection for a MS-PW: -i. Routing must enable S-PEs and T-PEs to discover S-PEs on the path to a destination T-PE. -ii. The MS-PW routing function MUST have the ability to automatically select the S-PEs along the MS-PW path. Some of the S-PEs MAY be statically selected and carried in the signaling to constrain the route selection process. -iii. The PW Routing function MUST support re-routing around failures that occur between the statically configured segment endpoints. This may be done by choosing another PSN tunnel between the two segment endpoints or setting up an alternative tunnel. -iv. Routing protocols must be able to advertise reachability information to attachment circuit (AC) endpoints. This reachability information must be consistent with the AC identifiers carried in signaling. 7. Operations and Maintenance (OAM) OAM mechanisms for the attachment circuits are defined in the specifications for PW emulated specific technologies (e.g., ITU-T I.610 for ATM). These mechanisms enable, among other things, defects in the network to be detected, localized and diagnosed. They also enable communication of PW defect states on the PW attachment circuit. The interworking of OAM mechanisms for SS-PWs between ACs and PWs is defined in [PWE3-OAM]. These enable defect states to be propagated across a PWE3 network following the failure and recovery from faults. OAM mechanisms for MS-PWs MUST provide at least the same capabilities as those for SS-PWs. In addition, it should be possible to support both segment and end- to-end OAM mechanisms for both defect notifications and connectivity verification in order to allow defects to be localized in a multi- segment network. That is, PW OAM segments can be T-PE to T-PE, T-PE to S-PE, or S-PE to S-PE. The following requirements apply to OAM for MS-PWs: Bitar, et al. [Page 20] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 -i. Mechanisms for PW segment failure detection and notification to other segments of a MS-PW MUST be provided. -ii. MS-PW OAM SHOULD be supported end-to-end across the network. -iii. Single ended monitoring SHOULD be supported for both directions of the MS-PW. -iv. MS-PW OAM SHOULD support switch over between 1:1 protected LSPs end-to-end. -v. SS-PW OAM mechanisms (e.g., [VCCV]) SHOULD be extended to support MS-PWs on both end-end basis and segment basis. -vi. All PE routers along the MS-PW MUST agree on a common PW OAM mechanism to use for the MS-PW. -vii. At the S-PE, defects on an PSN tunnel MUST be propagated to all PWs that utilize that particular PSN tunnel. -viii. The directionality of defect notifications MUST be maintained across the S-PE. -ix. The S-PE SHOULD be able to behave as a segment endpoint for PW OAM mechanisms. -x. The S-PE MUST be able to pass T-PE to T-PE PW OAM messages transparently. -xi. Performance OAM, is required for both MS-PWs and SS-PWs to measure round-trip delay, one-way delay, jitter, and packet loss ratio. 8. Security Considerations This document specifies the requirements for MS-PWs that can be setup across domain boundaries administered by one ore more service providers. The security requirements for MS-PW setup across domains administered by one service provider are the same as those described under security considerations in [RFC4447]. These requirements also apply to interprovider MS-PWs. In addition, [RFC4111] identifies user and provider requirements for L2 VPNs that apply to MS-PWs described in this document. In this section, the focus is on the additional security requirements for interprovider operation of MS-PWs in both the control plane and data plane,and some of these requirements may overlap with those in [RFC4111]. Bitar, et al. [Page 21] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 8.1. Data-plane Security Requirements MS-PWs that cross SP domain boundaries may connect one T-PE in a SP domain to a T-PE in another SP-domain. They may also transit other SP domains even if the two T-PEs are under the control of one SP. Under these scenarios, there is a chance that one or more PDUs could be falsely inserted into a MS-PW at any of the originating, terminating or transit domains. Such false injection can be the result of a malicious attack or fault in the MS-PW cross-connects. Solutions MAY provide mechanisms for ensuring the end-to-end authenticity of MS-PW PDUs. One of the crossed domains may decide to selectively mirror the PDUs of a MS-PW for eavesdropping purposes. It may also decide to selectively hijack the PDUs of a MS-PW by directing the PDUs away from their destination. In either case, the privacy of a MS-PDU can be violated. This document does not place any requirements on protecting the privacy of a MS-PW PDU via encryption for instance. Encryption may be performed at a higher layer in the protocol stack, based on the application or network requirements. The data plane of an S-PE at a domain boundary MUST be able to police an incoming MS-PW traffic to the MS-PW traffic parameters or to an administratively configured profile. The option to enable/disable policing MUST be provided to the network administrator. This is to ensure that a MS-PW or a group of MS-PWs do not grab more resources than they are allocated. In addition, the data plane of an S-PE MUST be able to police OAM messages to a pre-configured traffic profile or to filter out these messages upon administrative configuration. An ingress S-PE MUST ensure that a MS-PW receive the CoS treatment configured or signaled for that MS-PW at the S-PE. Specifically, an S-PE MUST guard against packets marked in the exp bits or IP-header DS field (depending on the PSN) for a better CoS than they should receive. An ingress S-PE MUST be able to define per-interface or interface- group (a group may correspond to interfaces to a peer-provider) label space for MPLS-PWs. An S-PE MUST be configurable not to accept labeled packets from another provider unless the bottom label is a PW-label assigned by the S-PE on the interface on which the packet arrived. Bitar, et al. [Page 22] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 8.2. Control-plane Security Requirements A MS-PW connects two attachment circuits. It is important to make sure that PW connections are not arbitrarily accepted from anywhere, or else a local attachment circuit might get connected to an arbitrary remote attachment circuit. The fault in the connection can start at a remote T-PE or an S-PE. An incoming MS-PW request/reply MUST NOT be accepted unless its IP source address is known to be the source of an "eligible" peer. If a peering adjacency has to be established prior to exchanging setup requests/responses, peering MUST only be done with eligible peers. The set of eligible peers could be pre-configured (either as a list of IP addresses, or as a list of address/mask combinations). Furthermore, the restriction of peering sessions to specific interfaces SHOULD also be provided. The S-PE and T-PE SHOULD drop the unaccepted signaling messages in the data path to avoid a DoS attack on the control plane. Even if a connection request appears to come from an eligible peer, its source address may have been spoofed. So some means of preventing source address spoofing must be in place. For example, if eligible peers are in the same network, source address filtering at the border routers of that network could eliminate the possibility of source address spoofing. For a greater degree of security, an authentication mechanism that is suitable to the associated protocol MUST be available. Furthermore authentication using a signature for each individual MS-PW setup messages MUST be available, in addition to an overall control protocol session authentication , and message validation. Peer authentication protects against IP address spoofing but does not prevent one peer (S-PE or T-PE) from connecting to the wrong attachment circuit. Under a single administrative authority, this may be the result of a misconfiguration. When the MS-PW crosses multiple provider domains, this may be the result of a malicious act by a service provider or a security hole in that provider network. Static manual configuration of MS-PWs at S-PEs and T-PEs provide a greater degree of security. If an identification of both ends of a MS-PW is configured and carried in the signaling message, an S-PE can verify the signaling message against the configuration. To support dynamic signaling of MS-PWs, whereby only endpoints are provisioned and S-PEs are dynamically discovered, mechanisms SHOULD be provided to configure such information on a server and to use that information during a connection attempt for validation. S-PEs that connect one provider domain to another provider domain Bitar, et al. [Page 23] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 MUST have the capability to rate-limit signaling traffic in order to prevent DoS attacks on the control plane. Furthermore, detection and disposition of malformed packets and defense against various forms of attacks that can be protocol-specific MUST be provided. 9. Full Copyright Statement Copyright (C) The Internet Society (2007). 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 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. 10. Intellectual Property Statement 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. Bitar, et al. [Page 24] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 11. IANA Considerations This document has no IANA Actions. 12. Normative References [RFC3916] "Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3)", X. Xiao, D. McPherson, P. Pate, September 2004 [RFC3985] "PWE3 Architecture" Bryant, et al., RFC3985. 13. Informative References [VCCV] Nadeau, T., et al."Pseudo Wire Virtual Circuit Connection Verification (VCCV)", Internet Draft , October 2006. (work in progress) [RFC4447] L. Martini, Ed, et al., "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC4447, April 2006 [RFC4111] "Security Framework for Provider-Provisioned Virtual Private Networks (PPVPNs)," Fang. L., et al., RFC 4111, July 2005 [PWE3-OAM] "Pseudo Wire (PW) OAM Message Mapping" Nadeau et al., draft-ietf-pwe3-oam-msg-map-02.txt (work in progress), February 2005 14. Author Information Nabil Bitar Verizon 40 Sylvan Road Waltham, MA 02145 e-mail: nabil.bitar@verizon.com Bitar, et al. [Page 25] Internet Draft draft-ietf-pwe3-ms-pw-requirements-04.txt January 2007 Matthew Bocci Alcatel Telecom Ltd, Voyager Place Shoppenhangers Road Maidenhead Berks, UK e-mail: matthew.bocci@alcatel.co.uk Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112 e-mail: lmartini@cisco.com Bitar, et al. [Page 26]