Network Working Group Luca Martini Internet Draft Chris Metz Expiration Date: August 2007 Thomas D. Nadeau Cisco Systems Inc. Vasile Radoaca Mike Duckett Matthew Bocci Bellsouth Florin Balus Mustapha Aissaoui Alcatel-Lucent February 2007 Segmented Pseudo Wire draft-ietf-pwe3-segmented-pw-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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes how to connect pseudo wires (PW) between two distinct PW control planes or PSN domains. The PW control planes may belong to independent autonomous systems, or the PSN technology is heterogeneous, or a PW might need to be aggregated at a specific PSN Martini, et al. [Page 1] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 point. The PW packet data units are simply switched from one PW to another without changing the PW payload. Martini, et al. [Page 2] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 Table of Contents 1 Specification of Requirements ........................ 4 2 Terminology .......................................... 4 3 Introduction ......................................... 5 4 General Description .................................. 7 5 PW Switching and Attachment Circuit Type ............. 10 6 Applicability ........................................ 10 7 PW-MPLS to PW-MPLS Control Plane Switching ........... 11 7.1 Static Control plane switching ....................... 11 7.2 Two LDP control planes using the same FEC type ....... 12 7.2.1 FEC 129 Active/Passive T-PE Election Procedure ....... 12 7.3 LDP FEC 128 to LDP using the generalized FEC 129 ..... 12 7.4 LDP PW switching point TLV ........................... 13 7.4.1 PW Switching Point Sub-TLVs .......................... 14 7.4.2 Adaptation of Interface Parameters ................... 15 7.5 Group ID ............................................. 16 7.6 PW Loop Detection .................................... 16 8 PW-MPLS to PW-L2TPv3 Control Plane Switching ......... 16 8.1 Static MPLS and L2TPv3 PWs ........................... 16 8.2 Static MPLS PW and Dynamic L2TPv3 PW ................. 17 8.3 Static L2TPv3 PW and Dynamic LDP/MPLS PW ............. 17 8.4 Dynamic LDP/MPLS and L2TPv3 PWs ...................... 17 8.4.1 Session Establishment ................................ 17 8.4.2 Adaptation of PW Status message ...................... 18 8.4.3 Session Tear Down .................................... 18 8.5 Adaptation of LDP/L2TPv3 AVPs to Interface Parameters ....19 8.6 Switching Point TLV in L2TPv3 ........................ 20 8.7 L2TPv3 and MPLS PW Data Plane ........................ 20 8.7.1 PWE3 Payload Convergence and Sequencing .............. 20 8.7.2 Mapping .............................................. 21 9 Operation And Management ............................. 22 9.1 Extensions to VCCV to Support Switched PWs ........... 22 9.2 PW-MPLS to PW-MPLS OAM Data Plane Indication ......... 22 9.2.1 PW Label TTL Method .................................. 22 9.2.2 MH-VCCV CW Method .................................... 23 9.3 Signaling OAM Capabilities for Switched Pseudo Wires . 23 9.3.1 OAM Capability for MH PWs Demultiplexed using MPLS ... 24 9.3.2 OAM Capability for MH PWs Demultiplexed using L2TPv3 . 24 9.4 Detailed MH-VCCV Procedures .......................... 24 9.4.1 PW Label TTL Method .................................. 25 9.4.2 MH-VCCV CW Method .................................... 25 9.5 Tracing Switched PW Switch Points Using MH-VCCV ...... 26 9.6 Mapping Switched Pseudo Wire Status .................. 26 9.6.1 S-PE initiated PW status messages .................... 28 9.6.1.1 Local PW2 reverse direction fault .................... 29 Martini, et al. [Page 3] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 9.6.1.2 Local PW1 reverse direction fault .................... 29 9.6.1.3 Local PW2 forward direction fault .................... 29 9.6.1.4 Local PW1 forward direction fault .................... 30 9.6.1.5 Clearing Faults ...................................... 30 9.6.2 PW status messages and S-PE TLV processing ........... 30 9.6.3 T-PE processing of PW status messages ................ 30 9.7 Pseudowire Status Negotiation Procedures ............. 31 9.8 Status Dampening ..................................... 31 10 Peering Between Autonomous Systems ................... 31 11 Security Considerations .............................. 31 11.1 Data Plane Security .................................. 31 11.2 Control Protocol Security ............................ 32 12 IANA Considerations .................................. 33 12.1 Channel Type ......................................... 33 12.2 L2TPv3 AVP ........................................... 33 12.3 LDP TLV TYPE ......................................... 33 12.4 LDP Status Codes ..................................... 33 12.5 L2TPv3 Result Codes .................................. 34 12.6 New IANA Registries .................................. 34 13 Intellectual Property Statement ...................... 34 14 Full Copyright Statement ............................. 35 15 Acknowledgments ...................................... 35 16 Normative References ................................. 35 17 Informative References ............................... 36 18 Author Information ................................... 37 1. Specification of Requirements The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Terminology - 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 [RFC3985]. Martini, et al. [Page 4] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 - Single-Segment Pseudo Wire (SS-PW). A PW setup directly between two T-PE devices. Each PW in one direction of a SS-PW traverses one PSN tunnel that connects the two T-PEs. - Multi-Segment Pseudo Wire (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 of 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. 3. Introduction PWE3 defines the signaling and encapsulation techniques for establishing SS-PWs between a pair of ultimate PEs and in the vast majority of cases this will be sufficient. MS-PWs come into play in two general cases: -i. When it is not possible, desirable or feasible to establish a PW control channel between the ultimate source and destination PEs. At a minimum PW control channel establishment requires knowledge of and reachability to the remote (ultimate) PE IP address. The local (ultimate) PE may not have access to this information related to topology, operational or security constraints. An example is the inter-AS L2VPN scenario where the ultimate PEs reside in different provider networks (ASes) and it is the practice to MD5-key all control traffic exchanged between two networks. Technically a SS-PW could be used but this would require MD5-keying on ALL ultimate source and destination PE nodes. An MS-PW allows the providers to confine MD5 key administration to just the PW switching points connecting the two domains. A second example might involve a single AS where the PW Martini, et al. [Page 5] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 setup path between the ultimate PEs is computed by an external entity (i.e. client-layer routing protocol). Assume a full mesh of PWE3 control channels established between PE-A, PE-B and PE-C. A client-layer L2 connection tunneled through a PW is required between ultimate PE-A and PE-C. The external entity computes a PW setup path that passes through PE-B. This results in two discrete PW segments being built: one between PE-A and PE-B and one between PE-B and PE-C. The successful client-layer L2 connection between ultimate PE-A and ultimate PE-C requires that PE-B performs the PWE3 switching process. A third example involves the use of PWs in hierarchical IP/MPLS networks. Access networks connected to a backbone use PWs to transport customer payloads between customer sites serviced by the same access network and up to the edge of the backbone where they can be terminated or switched onto a succeeding PW segment crossing the backbone. The use of PWE3 switching between the access and backbone networks can potentially reduce the PWE3 control channels and routing information processed by the access network T-PEs. It should be noted that PWE3 switching does not help in any way to reduce the amount of PW state supported by each access network T-PE. -ii. PWE3 signaling and encapsulation protocols are different. The ultimate PEs are connected to networks employing different PW signaling and encapsulation 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 ultimate PEs in this scenario. There are four different signaling protocols that are defined to signal PWs: -i. Static configuration of the PW (MPLS or L2TPv3). -ii. LDP using FEC 128 -iii. LDP using the generalized FEC 129 -iv. L2TPv3 Martini, et al. [Page 6] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 4. General Description A pseudo-wire (PW) is a tunnel established between two provider edge (PE) nodes to transport L2 PDUs across a packet switched network (PSN) as described in Figure 1 and in [PWE3-ARCH]. Many providers are looking at PWs as a means of migrating existing (or building new) L2VPN services (i.e. Frame-Relay, ATM, Ethernet) on top of a PSN by using PWs. PWs may span multiple autonomous systems of the same or different provider networks. In these scenarios PW control channels (i.e. targeted LDP, L2TPv3) and PWs will cross AS boundaries. Inter-AS L2VPN functionality is currently supported and several techniques employing MPLS encapsulation and LDP signaling have been documented [2547BIS]. It is also straightforward to support the same inter-AS L2VPN functionality employing L2TPv3. In this document we define methodology to switch a PW between two PW control planes. |<-------------- Emulated Service ---------------->| | | | |<------- Pseudo Wire ------>| | | | | | | | |<-- PSN Tunnel -->| | | | V V V V | V AC +----+ +----+ AC V +-----+ | | PE1|==================| PE2| | +-----+ | |----------|............PW1.............|----------| | | CE1 | | | | | | | | CE2 | | |----------|............PW2.............|----------| | +-----+ ^ | | |==================| | | ^ +-----+ ^ | +----+ +----+ | | ^ | | Provider Edge 1 Provider Edge 2 | | | | | | Customer | | Customer Edge 1 | | Edge 2 | | native service native service Figure 1: PWE3 Reference Model There are two methods for switching a PW between two PW control planes. In the first method (Figure 2), the two control planes terminate on different PEs. Martini, et al. [Page 7] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 |<------------Emulated Service---------->| | PSN PSN | AC | |<-1->| |<-2->| | AC | V V V V V V | | +----+ +-----+ +----+ +----+ | +----+ | | |=====| | | |=====| | | +----+ | |-------|......PW1.......|--AC1--|......PW2......|-------| | | CE1| | | | | | | | | | | |CE2 | | |-------|......PW3.......|--AC2--|......PW4......|-------| | +----+ | | |=====| | | |=====| | | +----+ ^ +----+ +-----+ +----+ +----+ ^ | PE1 PE2 PE3 PE4 | | ^ ^ | | | | | | PW stitching points | | | | | |<-------------------- Emulated Service ---------------->| Figure 2: PW Switching using ACs Reference Model In Figure 2, pseudo wires in two separate PSNs are stitched together using native service attachment circuits. PE2 and PE3 only run the control plane for the PSN to which they are directly attached. At PE2 and PE3, PW1 and PW2 are connected using attachment circuit AC1, while PW3 and PW4 are connected using attachment circuit AC2. Native |<-----------Pseudo Wire----------->| Native Layer2 | | Layer2 Service | |<-PSN1-->| |<--PSN2->| | Service (AC) V V V V V V (AC) | +----+ +-----+ +----+ | +----+ | | PE1|=========| PE2 |=========| PE3| | +----+ | |----------|........PW1.........|...PW3........|----------| | | CE1| | | | | | | | | |CE2 | | |----------|........PW2.........|...PW4........|----------| | +----+ | | |=========| |=========| | | +----+ ^ +----+ +-----+ +----+ | ^ | Provider Edge 1 ^ Provider Edge 3 | | (Ultimate PE) | (Ultimate PE) | | | | | PW switching point | | (Optional PW adaptation function) | | | |<------------------- Emulated Service ------------------>| Figure 3: PW Control Plane Switching Reference Model Martini, et al. [Page 8] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 In Figure 3 PE2 runs two separate control planes: one toward PE1, and one Toward PE3. The PW switching point is at PE2 which is configured to connect PW1 and PW3 together to complete the multi-hop PW between PE1 and PE3. PW1 and PW3 MUST be of the same PW type, but PSN1 and PSN2 need not be the same technology. In the latter case, if the PW is switched to a different technology, the PEs must adapt the PDU encapsulation between the different PSN technologies. In the case where PSN1 and PSN2 are the same technology the PW PDU does not need to be modified, and PDUs are then switched between the pseudo-wires at the PW label level. It should be noted that it is possible to adapt one PSN technology to a different one, for example MPLS over an IP or GRE [RFC4023] encapsulation, but this is outside the scope of this document. Further, one could perform an interworking function on the PWs themselves at the PW switching point, allowing conversion from one PW type to another, but this is also outside the scope of this document. The pseudowire switching methodology described in this document assumes manual configuration of the switching point at PE2. It should also be noted that a PW can traverse multiple PW switching points along it's path, and the edge PEs will not require any specific knowledge of how many PW switching points the PW has traversed (though this may be reported for troubleshooting purposes). In general the approach taken is to connect the individual control planes by passing along any signaling information immediately upon reception. First the PW switching point is configured to switch a SS-PW from a specific peer to another SS-PW destined for a different peer. No control messages are exchanged yet as the PW switching point PE does not have enough information to actually initiate the PW setup messages. However, if a session does not already exist, a control protocol (LDP/L2TP) session is setup. In this model the MS-PW setup is starting from the T-PE devices. Next once the T-PE is configured it sends the PW control setup messages. These messages are received, and immediately used to form the PW setup messages for the next SS-PW of the MS-PW. If one of the Switching PEs doesn't accept an LDP Label Mapping message then a Label Release message is sent back to the originator T-PE. A MS-PW is declared UP when all the constituent SS- PWs are UP. Martini, et al. [Page 9] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 5. PW Switching and Attachment Circuit Type The PWs in each PSN are established independently, with each PSN being treated as a separate PWE3 domain. For example, in Figure 2 for case of MPLS PSNs, PW1 is setup between PE1 and PE2 using the LDP targeted session as described in [RFC4447], and at the same time a separate pseudo wire, PW2, is setup between PE3 and PE4. The ACs for PW1 and PW2 at PE2 and PE3 MUST be configured such that they are the same PW type e.g. ATM VCC, Ethernet VLAN, etc. 6. Applicability When using a PSN to transport a PW, the performance of the PW is equal to the performance of the PSN plus any impairments introduced by the PW layer itself. Therefore it is not possible for the PW to provide better performance than the PSN over which it is transported. Therefore, it is necessary to carefully consider the order in which different layer networks are stacked upon each other within a 'network stack' in order to provide the topmost service with the performance that it requires. This performance inheritance within a PW/PSN relationship is vertical because the PW is vertically stacked upon its PSN. Note: Due to this vertical performance inheritance and the different performance provided by, and the characteristics of, each networking mode it is generally advisable to stack modes that less efficiently provide dedicated bandwidth/performance on top of modes that more efficiently provide dedicated bandwidth/performance. When performing peer partition interworking the PW inherits the performance of the PSN partition that provides the worst performance of all the peered PSN partitions over which the PW is transported. Therefore it is not possible for the PW to receive (or provide) better performance than the worst performing of the peered PSN partitions over which it is transported. Therefore, it is necessary to carefully consider which PSN modes (and/or technologies) it is appropriate to peer with one another in order to provide the service with the performance that it requires. This is a horizontal performance relationship because the server layer partitions are peered with each other horizontally. Martini, et al. [Page 10] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 7. PW-MPLS to PW-MPLS Control Plane Switching Referencing Figure 3, PE2 sets up a PW1 using the LDP targeted session as described in [RFC4447], at the same time a separate pseudo wire PW3 is setup to PE3. Each PW is configured independently on the PEs, but on PE2 pseudo wire PW1 is connected to pseudo wire PW3. PDUs are then switched between the pseudo-wires at the PW label level. Hence the data plane does not need any special knowledge of the specific pseudo wire type. A simple standard MPLS label swap operation is sufficient to connect the two PWs, and in this case the PW adaptation function is not used. This process can be repeated as many times as necessary, the only limitation to the number of PW switching points traversed is imposed by the TTL field of the PW MPLS Label. The setting of the TTL is a matter of local policy on the originating PE, but SHOULD be set to 255. There are three MPLS to MPLS PW control planes: -i. Static configuration of the PW. -ii. LDP using FEC 128 -iii. LDP using the generalized FEC 129 This results in four distinct PW switching situations that are significantly different, and must be considered in detail: -i. PW Switching between two static control planes. -ii. Static Control plane switching to LDP dynamic control plane. -iii. Two LDP control planes using the same FEC type -iv. LDP using FEC 128, to LDP using the generalized FEC 129 7.1. Static Control plane switching In the case of two static control planes the PW switching point MUST be configured to direct the MPLS packets from one PW into the other. There is no control protocol involved in this case. When one of the control planes is a simple static PW configuration and the other control plane is a dynamic LDP FEC 128 or generalized PW FEC, then the static control plane should be considered identical to an attachment circuit (AC) in the reference model of Figure 1. The switching point PE SHOULD signal the proper PW status if it detects a failure in sending or receiving packets over the static PW. Because the PW is statically configured, the status communicated to the dynamic LDP PW will be limited to local interface failures. In this case, the PW switching point PE behaves in a very similar manner to a T-PE, assuming an active role. This means that the S-PE will immediately send the LDP Label Mapping message if the static PW is deemed to be UP. Martini, et al. [Page 11] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 7.2. Two LDP control planes using the same FEC type As stated in a section above, the PW switching point PE should assume an initial passive role. This means that once independent PWs are configured on the switching point, the LSR does not advertise the LDP PW FEC mapping until it has received at least one of the two PW LDP FECs from a remote PE. This is necessary because the switching point LSR does not know a priory what the interface parameter field in the initial FEC advertisement will contain. The PWID is a unique number between each pair of PEs. Hence Each SS- PW that forms an MS-PW may have a different PWID. In the case of The Generalized PW FEC, the AGI/SAI/TAI may have to also be different for some, or sometimes all, SS-PWs. 7.2.1. FEC 129 Active/Passive T-PE Election Procedure When a MS-PW is signaled using FEC 129, each T-PE might independently start signaling the MS-PW. If the MS-PW path is not statically configured, in certain cases the signaling procedure could result in an attempt to setup each direction of the MS-PW through different paths. To avoid this situation one of the T-PE MUST start the PW signaling (active role), while the other waits to receive the LDP label mapping before sending the respective PW LDP label mapping message. (passive role). When the MS-PW path not statically configured, the Active T-PE (the ST-PE) and the passive T-PE (the TT-PE) MUST be identified before signaling is initiated for a given MS-PW. The determination of which T-PE assume the active role SHOULD be done as follows: the SAII and TAII are compared as unsigned integers, if the SAII is bigger then the T-PE assumes the active role. The selection process to determine which T-PE assumes the active role MAY be superseded by manual provisioning. 7.3. LDP FEC 128 to LDP using the generalized FEC 129 When a PE is using the generalized FEC 129, there are two distinct roles that a PE can assume: active and passive. A PE that assumes the active role will send the LDP PW setup message, while a passive role PE will simply reply to an incoming LDP PW setup message. The PW switching point PE, will always remain passive until a PWID FEC 128 LDP message is received, which will cause the corresponding Martini, et al. [Page 12] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 generalized PW FEC LDP message to be formed and sent. If a generalized FEC PW LDP message is received while the switching point PE is in a passive role, the corresponding PW FEC 128 LDP message will be formed and sent. PWIDs need to be mapped to the corresponding AGI/TAI/SAI and vice versa. This can be accomplished by local PW switching point configuration, or by some other means, such as some form of auto discovery. Such other means are outside the scope of this document. 7.4. LDP PW switching point TLV The edge to edge PW might traverse several switching points, in separate administrative domains. For management and troubleshooting reasons it is useful to record all the switching points that the PW traverses. This is accomplished by using a PW switching point TLV. Note that sending the PW switching point TLV is OPTIONAL, however the PE or SPE MUST process the TLV upon reception. The PW switching point TLV is appended to the PW FEC at each switching point and is encoded as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| PW sw TLV (0x096D) | PW sw TLV Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Variable Length Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Variable Length Value | | " | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [note] LDP TLV type is pending IANA approval. - PW sw TLV Length Specifies the total length of all the following PW switching point TLV fields in octets - Type Encodes how the Value field is to be interpreted. Martini, et al. [Page 13] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 - Length Specifies the length of the Value field in octets. - Value Octet string of Length octets that encodes information to be interpreted as specified by the Type field. PW Switching point TLV Types are assigned by IANA according the the process defined in the "IANA Allocations" section below. The PW switching Point TLV is an OPTIONAL TLV that can appear once for each switching point traversed. 7.4.1. PW Switching Point Sub-TLVs Below are details specific to PW Switching Point Sub-TLVs described in this document: - PW ID of last PW segment traversed. This sub-TLV type contains a PW ID in the format of the PWID described in [RFC4447] - PW Switching Point description string. An optional description string of text up to 80 characters long. - IP address of PW Switching Point. The IP V4 or V6 address of the PW Switching Point. This is an OPTIONAL Sub-TLV. - MH VCCV Capability Indication. - The FEC of last PW segment traversed. The Attachment Identifier of the last PW segment traversed. This is coded in the following format: Martini, et al. [Page 14] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AGI Type | Length | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ AGI Value (contd.) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AII Type | Length | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ SAII Value (contd.) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AII Type | Length | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ TAII Value (contd.) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - L2 PW address of PW Switching Point (recommended format) This sub-TLV type contains a L2 PW address of PW Switching Point in the format described in [PW-ADDR]. This includes the AII type field , and length, as well as the L2 PW address without the AC ID portion (if applicable). 7.4.2. Adaptation of Interface Parameters [RFC4447] defines several interface parameters, which are used by the Network Service Processing (NSP) to adapt the PW to the Attachment Circuit (AC). The interface parameters are only used at the end points, and MUST be passed unchanged across the PW switching point. However the following interface parameters MAY be modified as follows: - 0x03 Optional Interface Description string This Interface parameter MAY be modified, or altogether removed from the FEC element depending on local configuration policies. - 0x09 Fragmentation indicator This parameter MAY be inserted in the FEC by the switching point if it is capable of re-assembly of fragmented PW frames according to [PWE3-FRAG]. Martini, et al. [Page 15] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 - 0x0C VCCV parameter The switching point MAY not be able to inspect the VCCV control channel. If the new MH-VCCV sub-TLV is present, the VCCV parameter MUST be ignored in order to avoid conflicts with the new TLV. 7.5. Group ID The Group ID (GR ID) is used to reduce the number of status messages that need to be sent by the PE advertising the PW FEC. The GR ID has local significance only, and therefore MUST be mapped to a unique GR ID allocated by the PW switching point PE. 7.6. PW Loop Detection A switching point PE SHOULD check the OPTIONAL PW switching Point TLV, to verify if it's own IP address appears in it. If it's IP address appears in a received PW switching Point TLV, the PE SHOULD break the loop, and send a label release message with the following error code: Assignment E Description 0x0000003A 0 "PW Loop Detected" [ note: error code pending IANA allocation ] 8. PW-MPLS to PW-L2TPv3 Control Plane Switching Both MPLS and L2TPv3 PWs may be static or dynamic. This results in four possibilities when switching between L2TPv3 and MPLS. -i. Switching between MPLS and L2TPv3 static control planes. -ii. Switching between a static MPLS PW and a dynamic L2TPv3 PW. -iii. Switching between a static L2TPv3 PW and a dynamic MPLS PW. -iv. Switching between a dynamic MPLS PW and a dynamic L2TPv3 PW. 8.1. Static MPLS and L2TPv3 PWs In the case of two static control planes, the PW switching point MUST be configured to direct packets from one PW into the other. There is no control protocol involved in this case. The configuration MUST include which MPLS VC Label maps to which L2TPv3 Session ID (and associated Cookie, if present) as well as which MPLS Tunnel Label maps to which PE destination IP address. Martini, et al. [Page 16] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 8.2. Static MPLS PW and Dynamic L2TPv3 PW When a statically configured MPLS PW is switched to a dynamic L2TPv3 PW, the static control plane should be considered identical to an attachment circuit (AC) in the reference model of Figure 1. The switching point PE SHOULD signal the proper PW status if it detects a failure in sending or receiving packets over the static PW. Because the PW is statically configured, the status communicated to the dynamic L2TPv3 PW will be limited to local interface failures. In this case, the PW switching point PE behaves in a very similar manner to a T-PE, assuming an active role. 8.3. Static L2TPv3 PW and Dynamic LDP/MPLS PW When a statically configured L2TPv3 PW is switched to a dynamic LDP/MPLS PW, then the static control plane should be considered identical to an attachment circuit (AC) in the reference model of Figure 1. The switching point PE SHOULD signal the proper PW status (via an L2TPv3 SLI message) if it detects a failure in sending or receiving packets over the static PW. Because the PW is statically configured, the status communicated to the dynamic LDP/MPLS PW will be limited to local interface failures. In this case, the PW switching point PE behaves in a very similar manner to a T-PE, assuming an active role. 8.4. Dynamic LDP/MPLS and L2TPv3 PWs When switching between dynamic PWs, the switching point always assumes an initial passive role. Thus, it does not initiate an LDP/MPLS or L2TPv3 PW until it has received a connection request (Label Mapping or ICRQ) from one side of the node. Note that while MPLS PWs are made up of two unidirectional LSPs bonded together by FEC identifiers, L2TPv3 PWs are bidirectional in nature, setup via a 3-message exchange (ICRQ, ICRP and ICCN). Details of Session Establishment, Tear Down, and PW Status signaling are detailed below. 8.4.1. Session Establishment When the PW switching point receives an L2TPv3 ICRQ message, the identifying AVPs included in the message are mapped to FEC identifiers and sent in an LDP label mapping message. Conversely, if an LDP Label Mapping message is received, it is either mapped to an ICRP message or causes an L2TPv3 session to be initiated by sending Martini, et al. [Page 17] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 an ICRQ. Following are two example exchanges of messages between LDP and L2TPv3. The first is a case where an L2TPv3 T-PE initiates an MS-PW, the second is a case where an MPLS T-PE initiates an MS-PW. PE 1 (L2TPv3) PW Switching Node PE3 (MPLS/LDP) AC "Up" L2TPv3 ICRQ ---> LDP Label Mapping ---> AC "UP" <--- LDP Label Mapping <--- L2TPv3 ICRP L2TPv3 ICCN ---> <-------------------- MH PW Established ------------------> PE 1 (MPLS/LDP) PW Switching Node PE3 (L2TPv3) AC "Up" LDP Label Mapping ---> L2TPv3 ICRQ ---> <--- L2TPv3 ICRP <--- LDP Label Mapping L2TPv3 ICCN ---> AC "Up" <-------------------- MH PW Established ------------------> 8.4.2. Adaptation of PW Status message L2TPv3 uses the SLI message to indicate a interface status change (such as the interface transitioning from "Up" or "Down"). MPLS/LDP PWs either signal this via an LDP Label Withdraw or the PW Status Notification message defined in section 4.4 of [RFC4447]. 8.4.3. Session Tear Down L2TPv3 uses a single message, CDN, to tear down a pseudowire. The CDN message translates to a Label Withdraw message in LDP. Following are two example exchanges of messages between LDP and L2TPv3. The first is a case where an L2TPv3 T-PE initiates the termination of an MS-PW, the second is a case where an MPLS T-PE initiates the termination of an MS-PW. Martini, et al. [Page 18] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 PE 1 (L2TPv3) PW Switching Node PE3 (MPLS/LDP) AC "Down" L2TPv3 CDN ---> LDP Label Withdraw ---> AC "Down" <-- LDP Label Release <--------------- MH PW Data Path Down ------------------> PE 1 (MPLS LDP) PW Switching Node PE3 (L2TPv3) AC "Down" LDP Label Withdraw ---> L2TPv3 CDN --> <-- LDP Label Release AC "Down" <---------------- MH PW Data Path Down ------------------> 8.5. Adaptation of LDP/L2TPv3 AVPs to Interface Parameters [RFC4447] defines several interface parameters which MUST be mapped to the equivalent AVPs in L2TPv3 setup messages. * Interface MTU The Interface MTU parameter is mapped directly to the L2TP Interface MTU AVP defined in [L2TP-L2VPN] * Max Number of Concatenated ATM cells This interface parameter is mapped directly to the L2TP "ATM Maximum Concatenated Cells AVP" described in section 6 of [L2TP- ATM]. * Optional Interface Description String This string may be carried as the "Call-Information AVP" described in section 2.2 of [L2TP-INFOMSG] * PW Type The PW Type defined in [RFC4446] is mapped to the L2TPv3 "PW Type" AVP defined in [L2TPv3]. Martini, et al. [Page 19] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 * PW ID (FEC 128) For FEC 128, the PW ID is mapped directly to the L2TPv3 "Remote End ID" AVP defined in [L2TPv3]. * Generalized FEC 129 SAI/TAI Section 4.3 of [L2TP-L2VPN] defines how to encode the SAI and TAI parameters. These can be mapped directly. Other interface parameter mappings will either be defined in a future version of this document, or are unsupported when switching between LDP/MPLS and L2TPv3 PWs. 8.6. Switching Point TLV in L2TPv3 When translating between LDP and L2TPv3 control messages, the PW Switching Point TLV described earlier in this document is carried in a single variable length L2TP AVP present in the ICRQ, ICRP messages, and optionally in the ICCN message. The L2TP "Switching Point AVP" is Attribute Type TBA-L2TP-AVP-1. The AVP MAY be hidden (the L2TP AVP H-bit may be 0 or 1), the length of the AVP is 6 plus the length of the series of Switching Point sub- TLVs included in the AVP, and the AVP MUST NOT be marked Mandatory (the L2TP AVP M-bit MUST be 0). 8.7. L2TPv3 and MPLS PW Data Plane When switching between an MPLS and L2TP PW, packets are sent in their entirety from one PW to the other, replacing the MPLS label stack with the L2TPv3 and IP header or vice versa. There are some situations where an additional amount of interworking must be provided between the two data planes at the PW switching node. 8.7.1. PWE3 Payload Convergence and Sequencing Section 5.4 of [PWE3-ARCH] discusses the purpose of the various shim headers necessary for enabling a pseudowire over an IP or MPLS PSN. For L2TPv3, the Payload Convergence and Sequencing function is carried out via the Default L2-Specific Sublayer defined in [L2TPv3]. For MPLS, these two functions (together with PSN Convergence) are carried out via the MPLS Control Word. Since these functions are different between MPLS and L2TPv3, interworking between the two may be necessary. Martini, et al. [Page 20] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 The L2TP L2-Specific Sublayer and MPLS Control Word are shim headers which in some cases are not necessary to be present at all. For example, an Ethernet PW with sequencing disabled will generally not require an MPLS Control Word or L2TP Default L2-Specific Sublayer to be present at all. In this case, Ethernet frames are simply sent from one PW to the other without any modification beyond the MPLS and L2TP/IP encapsulation and decapsulation. The following section offers guidelines for how to interwork between L2TP and MPLS for those cases where the Payload Convergence, Sequencing, or PSN Convergence functions are necessary on one or both sides of the switching node. 8.7.2. Mapping The MPLS Control Word consists of (from left to right): -i. These bits are always zero in MPLS are not necessary to be mapped to L2TP. -ii. These six bits may be used for Payload Convergence depending on the PW type. For ATM, the first four of these bits are defined in [PWE3-ATM]. These map directly to the bits defined in [L2TP-ATM]. For Frame Relay, these bits indicate how to set the bits in the Frame Relay header which must be regenerated for L2TP as it carries the Frame Relay header intact. -iii. L2TP determines its payload length from IP. Thus, this Length field need not be carried directly to L2TP. This Length field will have to be calculated and inserted for MPLS when necessary. -iv. The Default L2-Specific Sublayer has a sequence number with different semantics than that of the MPLS Control Word. This difference eliminates the possibility of supporting sequencing across the MS-PW by simply carrying the sequence number through the switching point transparently. As such, sequence numbers MAY be supported by checking the sequence numbers of packets arriving at the switching point and regenerating a new sequence number in the proper format for the PW on egress. If this type of sequence interworking at the switching node is not supported, and a T-PE requests sequencing of all packets via the L2TP control channel during session setup, the switching node SHOULD NOT allow the session to be established by sending a CDN message with Result Code set to 17 "sequencing not supported" (subject to Martini, et al. [Page 21] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 IANA Assignment). 9. Operation And Management 9.1. Extensions to VCCV to Support Switched PWs Single-hop pseudowires are signaled using the VCCV parameter included in the interface parameter field of the PW ID FEC TLV or the sub-TLV interface parameter of the Generalized PW ID FEC TLV as described in [VCCV]. When a switching point exist between PE nodes, it is required to be able to continue operating VCCV end-to-end across a switching point and to provide the ability to trace the path of the MS-PW over any number of segments. This document provides a couple of methods for achieving these two objectives. The first method is based on re-using the existing VCCV CW and decrementing the TTL of the PW label at each hop in the path of the MS-PW. This method is suitable to deployments where T-PE nodes continue to use the SS-PW control word and where S-PE nodes are capable of decrementing the TTL field for all PW packets without overwriting it. The second method is based on using a new MH-VCCV control word and decrementing the TTL field in the control word. This method is suitable to deployments where S-PE nodes cannot rely the TTL in the PW label to identify if a VCCV packet is destined to this node or not. 9.2. PW-MPLS to PW-MPLS OAM Data Plane Indication 9.2.1. PW Label TTL Method This method reuses the SS-PW control word as described in [VCCV]. VCCV control packets are indicated using the following CW in the packet header: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1|Version| Reserved = 0 | Channel Type = 0x21 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Martini, et al. [Page 22] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 9.2.2. MH-VCCV CW Method The VCCV control packets are indicated using a new Multi-hop pseudowire CW in the packets header: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1| 0x00 | Reserved = 0 | Channel Type = TBD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MH-TTL | MH-VCCV sub-TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 9.3. Signaling OAM Capabilities for Switched Pseudo Wires Like in SS-PW, MS-PW VCCV capabilities are signaled using the VCCV parameter included in the interface parameter field of the PW ID FEC TLV or the sub-TLV interface parameter of the Generalized PW ID FEC TLV as described in [VCCV]. The new MH-VCCV CW is indicated using a new CC type in the VCCV capability parameter field. In Figure 1 T-PE1 uses the VCCV parameter included in the interface parameter field of the PW ID FEC TLV or the sub-TLV interface parameter of the Generalized PW ID FEC TLV to indicate to the far end T-PE2 what VCCV capabilities T-PE1 supports. This is the same VCCV parameter as would be used if T-PE1 and T-PE2 were connected directly by T-LDP. S-PE2, which is a PW switching point, as part of the adaptation function for interface parameters, processes locally the VCCV parameter then passes it to T-PE2. If there were multiple S-PEs on the path between T-PE1 and T-PE2, each would carry out the same processing, passing along the VCCV parameter. The local processing of the VCCV parameter removes CC Types specified by the originating T- PE, except PWE3 Control Word and the new MH-VCCV Control Word that are passed unchanged. For example, if T-PE1 indicates as supported CC Types both Control Word and Router Alert then the S-PE removes the Router Alert CC Type, leaving Control Word unchanged and then passes the modified VCCV parameter to the next S-PE along the path. The far end T-PE (T-PE2) receives the VCCV parameter indicating that one or both Control Word CC types only if they are supported by the initial T-PE (T-PE1) and all S-PEs along the PW path. If the VCCV parameter indicates both the CW CC type and the new MH-VCCV CW CC types are supported, then the T-PE1 is indicating it can receive both types. If T-PE2 also supports both types, T-PE2 uses the CW CC type Martini, et al. [Page 23] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 in preference. 9.3.1. OAM Capability for MH PWs Demultiplexed using MPLS The MH-VCCV parameter ID is defined as follows in [RFC4446]: Parameter ID Length Description 0x0c 4 VCCV The format of the VCCV parameter field is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0c | 0x04 | CC Types | CV Types | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0x01 Type 1: PWE3 control word with 0001b as first nibble as defined in [RFC4385]. 0x02 Type 2: MPLS Router Alert Label. 0x04 Type 3: MPLS PW Demultiplexor Label TTL = 1 (Type 3). 0x08 Type 4: MH-VCCV Control Word When using the PW label TTL method, the T-PE signals CC type 1. When using the MH-VCCV CW method, the T-PE signal CC type 4. 9.3.2. OAM Capability for MH PWs Demultiplexed using L2TPv3 TBD 9.4. Detailed MH-VCCV Procedures In order to test the end-to-end connectivity of the multi-segment PW, a T-PE must include the FEC used in the last segment to the destination T-PE. This information is either configured at the sending T-PE or is obtained by processing the corresponding sub-TLV's of the PW switching point TLV. Martini, et al. [Page 24] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 9.4.1. PW Label TTL Method In Figure 1, if T-PE1, S-PE and T-PE2 support Control Word for VCCV, then as described in Section 9.3 the control plane negotiates the common use of Control Word for VCCV end to end. At the S-PE the data path operations include an outer label pop, inner label swap and new outer label push. Note that there is no requirement for the S-PE to inspect the CW. Thus, the end-to-end connectivity of the multi-segment pseudowire can be verified by performing all of the following steps: -i. T-PE forms a VCCV-ping echo request message with the FEC matching that of the last segment PW to the destination T- PE. -ii. T-PE sets the inner PW label TTL to a large enough value to allow the packet to reach the far end T-PE. -iii. T-PE sends a VCCV packet that will follow the exact same data path at each S-PE as that taken by data packets. -iv. S-PE performs an outer label pop, an inner label swap with TTL decrement, and new outer label push. -v. There is no requirement for the S-PE to inspect the CW. -vi. The VCCV packet is diverted to VCCV control processing at the destination T-PE. -vii. Destination T-PE replies using the specified reply mode, i.e., reverse PW path or IP path. 9.4.2. MH-VCCV CW Method TBD Martini, et al. [Page 25] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 9.5. Tracing Switched PW Switch Points Using MH-VCCV Although the signaling of switched PWs includes functionality to record all switch points traversed by a particular switched pseudowire, this information is limited to the control plane. Specifically, this is the information which is then used to program the actual switching hardware. In an effort to provide explicit diagnostic capability of the data plane used by the switched pseudowire, it is necessary in some cases to compare the control and data planes used by a particular switched pseudowire. In these cases, it is possible to trace the pseudowire switch points by sending single-hop VCCV messages with TTL described above in the MH VCCV header, and increasing TTL values. This algorithm can be used to "walk" across the network of switching points until the ultimate PE is reached. Details of the operation for both methods will be provided in a future version of the document 9.6. Mapping Switched Pseudo Wire Status In the PW switching with attachment circuits case (Figure 2), PW status messages indicating PW or attachment circuit faults SHOULD be mapped to fault indications or OAM messages on the connecting AC as defined in [PW-MSG-MAP]. If the AC connecting two PWs crosses an administrative boundary, then the manner in which those OAM messages are treated at the boundary is out of scope of this draft. In the PW control plane switching case (Figure 3), there is no attachment circuit at the PW switching point, but the two PWs are connected together. Similarly, the status of the PWs are forwarded unchanged from one PW to the other by the control plane switching function. However, it may sometimes be necessary to communicate status of one of the locally attached SS-PW at a PW switching point. For LDP this can be accomplished by sending an LDP notification message containing the PW status TLV, as well as an OPTIONAL PW switching point TLV as follows: Martini, et al. [Page 26] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Notification (0x0001) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|1| Status (0x0300) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|1| Status Code=0x00000028 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type=0 | PW Status TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PW Status TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PW Status TLV | PWId FEC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | PWId FEC or Generalized ID FEC | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| PW sw TLV (0x096D) | PW sw TLV Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Variable Length Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Only one PW switching point TLV can be present in this message. This message is then relayed by each PW switching point unchanged. The T- PE decodes the status message and the included PW switching point TLV to detect exactly where the fault occurred. At the T-PE if there is no PW switching point TLV included in the LDP status notification then the status message can be assumed to have originated at the remote T-PE. The merging of the received T-LDP status and the local status for the PW segments at an S-PE can be summarized as follows: -i. When the local status for both PW segments is UP, the S-PE passes any received AC or PW status bits unchanged, i.e., the status notification TLV is unchanged but the VCid in the case of a FEC 128 TLV is set to value of the PW segment to the next hop. Martini, et al. [Page 27] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 -ii. When the local status for any of the PW segments is Down, the S-PE always sends "PW Down" status bits regardless if the received status bits from the remote node indicated AC UP/Down or PW UP/Down." 9.6.1. S-PE initiated PW status messages The PW fault directions are defined as follows: +-------+ ---PW1 forward---->| |-----PW2 reverse----> S-PE1 | S-PE2 | S-PE3 <--PW1 reverse-----| |<----PW2 forward----- +-------+ When a local fault is detected by the S-PE, a PW status message is sent in both directions along the PW. Since there are no attachment circuits on an S-PE, only the following status messages are relevant: 0x00000008 - Local PSN-facing PW (ingress) Receive Fault 0x00000010 - Local PSN-facing PW (egress) Transmit Fault Each S-PE needs to store only two 32-bit PW status words for each SS-PW: One for local failures , and one for remote failures (normally received from another PE). The first failure will set the appropriate bit in the 32-bit status word, and each subsequent failure will be ORed to the appropriate PW status word. In the case of the PW status word storing remote failures, this rule has the effect of a logical OR operation with the first failure received on the particular SS-PW. It should be noted that remote failures received on an S-PE are just passed along the MS-PW unchanged while local failures detected an an S-PE are signalled on both SS-PWs. A T-PE can receive multiple failures from S-PEs along the MH-PW, however only the failure from the remote closest S-PE will be stored. The PW status word received are just ORed to any existing remote PW status already stored on the T-PE. Given that there are two SS-PW at a particular S-PE for a particular MH-PW, there are for possible failure cases as follows: Martini, et al. [Page 28] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 -i. PW2 reverse direction fault -ii. PW1 reverse direction fault -iii. PW2 forward direction fault -iv. PW1 forward direction fault It should also be noted that once a PW status notification message is initiated at a PW switching point for a partucular pw status bit any further status message, for the same status bit, received from an upstream neighbor is processed locally and not forwarded until the PW switching point original status error state is cleared. Each S-PE along the MS-PW MUST store any PW status messages transiting it. If more then one status message with the same pw status bit set is received by a T-PE only the last PW status message is stored. 9.6.1.1. Local PW2 reverse direction fault When this failure occurs the S-PE will take the following actions: * Send a PW status message to S-PE3 containing "0x00000010 - Local PSN-facing PW (egress) Transmit Fault" * Send a PW status message to S-PE1 containing "0x00000008 - Local PSN-facing PW (ingress) Receive Fault" * Store 0x00000010 in the local PW status word for the SS-PW toward S-PE3. 9.6.1.2. Local PW1 reverse direction fault When this failure occurs the S-PE will take the following actions: * Send a PW status message to S-PE1 containing "0x00000010 - Local PSN-facing PW (egress) Transmit Fault" * Send a PW status message to S-PE3 containing "0x00000008 - Local PSN-facing PW (ingress) Receive Fault" * Store 0x00000010 in the local PW status word for the SS-PW toward S-PE1. 9.6.1.3. Local PW2 forward direction fault When this failure occurs the S-PE will take the following actions: * Send a PW status message to S-PE3 containing "0x00000008 - Local PSN-facing PW (ingress) Receive Fault" Martini, et al. [Page 29] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 * Send a PW status message to S-PE1 containing "0x00000010 - Local PSN-facing PW (egress) Transmit Fault" * Store 0x00000008 in the local PW status word for the SS-PW toward S-PE3. 9.6.1.4. Local PW1 forward direction fault When this failure occurs the S-PE will take the following actions: * Send a PW status message to S-PE1 containing "0x00000008 - Local PSN-facing PW (ingress) Receive Fault" * Send a PW status message to S-PE3 containing "0x00000010 - Local PSN-facing PW (egress) Transmit Fault" * Store 0x00000008 in the local PW status word for the SS-PW toward S-PE1. 9.6.1.5. Clearing Faults Remote PW status fault clearing messages received by an S-PE will only be forwarded if there are no corresponding local faults on the S-PE. ( local faults always supersede remote faults ) Once the local fault has cleared, and there is no corresponding ( same PW status bit set ) remote fault, a PW status messages is sent out to the adjacent PEs clearing the fault. 9.6.2. PW status messages and S-PE TLV processing When a PW status message is received that includes a S-PE TLV, the S-PE TLV information MAY be stored, along with the contents of the PW status Word according to the procedures described above. If susequent PW status message for the same pw status bit are received the S-PE TLV will overwrite the previously stored S-PE TLV. 9.6.3. T-PE processing of PW status messages The PW switching architecture is based on the concept that the T-PE should process the PW LDP messages in the same manner as if it was participating in the setup of a SS-PW. However T-PE participating a MS-PW, SHOULD be able to process the PW switching point TLV. Otherwise the processing of PW status messages , and other PW setup messages is exactly as described in [RFC4447]. Martini, et al. [Page 30] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 9.7. Pseudowire Status Negotiation Procedures Pseudowire Status signaling methodology, defined in [RFC4447], SHOULD be transparent to the switching point. 9.8. Status Dampening When the PW control plane switching methodology is used to cross an administrative boundary it might be necessary to prevent excessive status signaling changes from being propagated across the administrative boundary. This can be achieved by using a similar method as commonly employed for the BGP protocol route advertisement dampening. The details of this OPTIONAL algorithm are a matter of implementation, and are outside the scope of this document. 10. Peering Between Autonomous Systems The procedures outlined in this document can be employed to provision and manage MS-PWs crossing AS boundaries. The use of more advanced mechanisms involving auto-discovery and ordered PWE3 MS-PW signaling will be covered in a separate document. 11. Security Considerations This document specifies the LDP and L2TPv3 extensions that are needed for setting up and maintaining Pseudowires. The purpose of setting up Pseudowires is to enable layer 2 frames to be encapsulated and transmitted from one end of a Pseudowire to the other. Therefore we treat the security considerations for both the data plane and the control plane. 11.1. Data Plane Security Data plane security consideration as discussed in [RFC4447], [L2TPv3], and [PWE3-ARCH] apply to this extension without any changes. Martini, et al. [Page 31] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 11.2. Control Protocol Security General security considerations with regard to the use of LDP are specified in section 5 of RFC 3036. Security considerations with regard to the L2TPv3 control plane are specified in [L2TPv3]. These considerations apply as well to the case where LDP or L2TPv3 is used to set up PWs. A Pseudowire connects two attachment circuits. It is important to make sure that LDP connections are not arbitrarily accepted from anywhere, or else a local attachment circuit might get connected to an arbitrary remote attachment circuit. Therefore an incoming session request MUST NOT be accepted unless its IP source address is known to be the source of an "eligible" peer. The set of eligible peers could be pre-configured (either as a list of IP addresses, or as a list of address/mask combinations), or it could be discovered dynamically via an auto-discovery protocol which is itself trusted. (Obviously if the auto-discovery protocol were not trusted, the set of "eligible peers" it produces could not be trusted.) 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 all the 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, the LDP MD5 authentication key option, as described in section 2.9 of RFC 3036, or the Control Message Authentication option of [L2TPv3] MAY be used. This provides integrity and authentication for the control messages, and eliminates the possibility of source address spoofing. Use of the message authentication option does not provide privacy, but privacy of control messages are not usually considered to be highly urgent. Both the LDP and L2TPv3 message authentication options rely on the configuration of pre-shared keys, making it difficult to deploy when the set of eligible neighbors is determined by an auto-configuration protocol. When the Generalized ID FEC Element is used, it is possible that a particular peer may be one of the eligible peers, but may not be the right one to connect to the particular attachment circuit identified by the particular instance of the Generalized ID FEC element. However, given that the peer is known to be one of the eligible peers (as discussed above), this would be the result of a configuration error, rather than a security problem. Nevertheless, it may be advisable for a PE to associate each of its local attachment circuits with a set of eligible peers, rather than having just a single set of Martini, et al. [Page 32] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 eligible peers associated with the PE as a whole. 12. IANA Considerations 12.1. Channel Type The Channel Type code point is defined in [RFC4385], and an IANA registry was requested in [VCCV]. This draft further requests the following code point to be assigned to that registry. 0x01 OAM Indication For Multi Segment Pseudowires (MH-VCCV) 12.2. L2TPv3 AVP This document uses a ne L2TP parameter, IANA already maintains a registry of name "Control Message Attribute Value Pair" defined by [RFC3438]. The following new values are required: TBA-L2TP-AVP-1 - PW Switching Point AVP 12.3. LDP TLV TYPE This document uses several new LDP TLV types, IANA already maintains a registry of name "TLV TYPE NAME SPACE" defined by RFC3036. The following value is suggested for assignment: TLV type Description 0x096D Pseudo Wire Switching TLV 12.4. LDP Status Codes This document uses several new LDP status codes, IANA already maintains a registry of name "STATUS CODE NAME SPACE" defined by RFC3036. The following value is suggested for assignment: Assignment E Description 0x0000003A 0 "PW Loop Detected" Martini, et al. [Page 33] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 12.5. L2TPv3 Result Codes This document uses several new LDP status codes, IANA already maintains a registry of name "L2TPv3 Result Codes" defined by RFCxxxx. The following value is suggested for assignment: Assignment Description 17 "sequencing not supported" 12.6. New IANA Registries IANA needs to set up a registry of "PW Switching Point TLV Type". These are 8-bit values. Types value 1 through 3 are defined in this document. Type values 4 through 64 are to be assigned by IANA using the "Expert Review" policy defined in RFC2434. Type values 65 through 127, 0 and 255 are to be allocated using the IETF consensus policy defined in [RFC2434]. Types values 128 through 254 are reserved for vendor proprietary extensions and are to be assigned by IANA, using the "First Come First Served" policy defined in RFC2434. The Type Values are assigned as follows: Type Length Description 0x01 4 PW ID of last PW segment traversed 0x02 variable PW Switching Point description string 0x03 4/16 IP address of PW Switching Point 0x04 variable MH VCCV Capability Indication 0x05 variable AI of last PW segment traversed 0x06 variable L2 PW address of PW Switching Point 13. 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 Martini, et al. [Page 34] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 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. 14. Full Copyright Statement Copyright (C) The IETF Trust (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, 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. 15. Acknowledgments The authors wish to acknowledge the contributions of Wei Luo, Skip Booth, Neil Hart, Michael Hua, and Tiberiu Grigoriu. 16. Normative References [RFC4385] " Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", S. Bryant, et al., RFC4385, February 2006. [RFC4446] "IANA Allocations for Pseudowire Edge to Edge mulation (PWE3)", L. Martini, RFC4446, April 2006. [RFC4447] "Transport of Layer 2 Frames Over MPLS", Martini, L., et al., rfc4447 April 20065. [RFC3985] Stewart Bryant, et al., PWE3 Architecture, RFC3985 Martini, et al. [Page 35] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 [2547BIS] "BGP/MPLS IP VPNs", Rosen, E, Rekhter, Y. draft-ietf-l3vpn-rfc2547bis-03.txt ( work in progress ), October 2004. [L2TPv3] "Layer Two Tunneling Protocol (Version 3)", J. Lau, M. Townsley, I. Goyret, RFC3931 [VCCV] Nadeau, T., et al."Pseudo Wire Virtual Circuit Connection Verification (VCCV)", Internet Draft , October 2005. (work in progress) [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [PW-ADDR] C. Metz, L. Martini, F. Balus, J. Sugimoto, "AII Types for Aggregation" draft-ietf-pwe3-aii-aggregate-02.txt, (work in progress), February 2007. 17. Informative References [RFC4023] "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", Rosen, E, Rekhter, Y. RFC4023, March 2005. [PWE3-ARCH] "PWE3 Architecture" Bryant, et al., draft-ietf-pwe3-arch-07.txt ( work in progress ), June 2003. [PWE3-FRAG] "PWE3 Fragmentation and Reassembly", A. Malis, W. M. Townsley, draft-ietf-pwe3-fragmentation-05.txt ( work in progress ) February 2004 [L2TP-L2VPN] "L2VPN Extensions for L2TP", Luo, Wei, draft-ietf-l2tpext-l2vpn-00.txt, ( work in progress ), Jan 2004 [L2TP-INFOMSG] "L2TP Call Information Messages", Mistretta, Goyret, McGill, Townsley, draft-mistretta-l2tp-infomsg-02.txt, ( work in progress ), July 2004 [L2TP-ATM] "ATM Pseudo-Wire Extensions for L2TP", Singh, Townsley, Lau, draft-ietf-l2tpext-pwe3-atm-00.txt, ( work in progress ), March 2004. Martini, et al. [Page 36] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 [PWE3-ATM] "Encapsulation Methods for Transport of ATM Over IP and MPLS Networks", Martini, Rosen, Bocci, "draft-ietf-pwe3-atm-encap-05.txt", ( work in progress ), April 2004. [RFC3438] W. M. Townsley, "Layer Two Tunneling Protocol (L2TP) Internet" [PW-MSG-MAP] "Pseudo Wire (PW) OAM Message Mapping", Nadeau et al, draft-ietf-pwe3-oam-msg-map-02.txt, ( work in progress ), February 2005 18. Author Information Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112 e-mail: lmartini@cisco.com Thomas D. Nadeau Cisco Systems, Inc. 300 Beaver Brook Road Boxborough, MA 01719 e-mail: tnadeau@cisco.com Chris Metz Cisco Systems, Inc. e-mail: chmetz@cisco.com Mike Duckett Bellsouth Lindbergh Center D481 575 Morosgo Dr Atlanta, GA 30324 e-mail: mduckett@bellsouth.net Vasile Radoaca Alcatel-Lucent Optics Divison, Westford, MA, USA email: vasile.radoaca@alcatel-lucent.com Martini, et al. [Page 37] Internet Draft draft-ietf-pwe3-segmented-pw-04.txt February 2007 Matthew Bocci Alcatel-Lucent Grove House, Waltham Road Rd White Waltham, Berks, UK. SL6 3TN e-mail: matthew.bocci@alcatel-lucent.co.uk Florin Balus Alcatel-Lucent 701 East Middlefield Rd. Mountain View, CA 94043 e-mail: florin.balus@alcatel-lucent.com Mustapha Aissaoui Alcatel-Lucent 600, March Road, Kanata, ON, Canada e-mail: mustapha.aissaoui@alcatel-lucent.com Martini, et al. [Page 38]