Network Working Group Luca Martini Internet Draft Nasser El-Aawar Expiration Date: May 2003 Level 3 Communications, LLC. Toby Smith Eric C. Rosen Laurel Networks, Inc. Cisco Systems, Inc. Giles Heron PacketExchange Ltd. November 2002 Transport of Layer 2 Frames Over MPLS draft-ietf-pwe3-control-protocol-01.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 methods for transporting the Protocol Data Units (PDUs) of layer 2 protocols such as Frame Relay, ATM AAL5, Ethernet, and providing a SONET circuit emulation service across an MPLS network. Martini, et al. [Page 1] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 Table of Contents 1 Specification of Requirements .......................... 2 2 Introduction ........................................... 3 3 PSN Tunnel Labels and PW Labels ........................ 4 4 Protocol-Specific Details .............................. 6 4.1 Frame Relay ............................................ 6 4.2 ATM .................................................... 6 4.2.1 ATM AAL5 VCC Transport ................................. 6 4.2.2 ATM Transparent Cell Transport ......................... 6 4.2.3 ATM VCC and VPC Cell Transport ......................... 6 4.2.4 OAM Cell Support ....................................... 7 4.2.5 ILMI Support ........................................... 8 4.3 Ethernet VLAN .......................................... 8 4.4 Ethernet ............................................... 8 4.5 HDLC and PPP ........................................... 8 5 LDP .................................................... 9 5.1 Interface Parameters Field ............................. 10 5.1.1 PW types for which the control word is REQUIRED ........ 12 5.1.2 PW types for which the control word is NOT mandatory ... 13 5.1.3 Status codes ........................................... 14 5.2 LDP label Withdrawal procedures ........................ 15 5.3 Sequencing Considerations .............................. 15 5.3.1 Label Mapping Advertisements ........................... 15 5.3.2 Label Mapping Release .................................. 16 6 IANA Considerations .................................... 16 7 Security Considerations ................................ 16 8 References ............................................. 17 9 Author Information ..................................... 18 10 Appendix A - C-bit Handling Procedures Diagram ......... 21 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. Martini, et al. [Page 2] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 2. Introduction In an MPLS network, it is possible to carry the Protocol Data Units (PDUs) of layer 2 protocols by prepending an MPLS label stack to these PDUs. This document specifies the necessary label distribution procedures for accomplishing this using the encapsulation methods in [7],[10],[12]. We restrict discussion to the case of point-to-point transport. QoS related issues are not discussed in this draft. This document describes methods for transporting a number of protocols; in some cases, transporting a particular protocol may have several modes of operation, though a default mode of operation which MUST be supported is identified for each. Each of these protocols and/or modes may be implemented independently. An accompanying document [8] also describes a method for transporting time division multiplexed (TDM) digital signals (TDM circuit emulation) over a packet-oriented MPLS network. The transmission system for circuit-oriented TDM signals is the Synchronous Optical Network (SONET)[5]/Synchronous Digital Hierarchy (SDH) [6]. To support TDM traffic, which includes voice, data, and private leased line service, the MPLS network must emulate the circuit characteristics of SONET/SDH payloads. MPLS labels and a new circuit emulation header are used to encapsulate TDM signals and provide the Circuit Emulation Service over MPLS (CEM). The following two figures describe the reference models which are derived from [PWE3-FRAME] to support the Ethernet PW emulated services. Native |<----- Pseudo Wire ---->| Native Layer2 | | Layer2 Service | |<-- PSN Tunnel -->| | Service | V V V V | | +----+ +----+ | +----+ | | PE1|==================| PE2| | +----+ | |----------|............PW1.............|----------| | | CE1| | | | | | | |CE2 | | |----------|............PW2.............|----------| | +----+ | | |==================| | | +----+ ^ +----+ +----+ | ^ | Provider Edge 1 Provider Edge 2 | | | |<-------------- Emulated Service ---------------->| Figure 1: PWE3 Ethernet/VLAN Interface Reference Configuration Martini, et al. [Page 3] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 +-------------+ +-------------+ | Layer2 | | Layer2 | | Emulated | | Emulated | | Services | Emulated Service | Services | | |<==============================>| | +-------------+ Pseudo Wire +-------------+ |Demultiplexer|<==============================>|Demultiplexor| +-------------+ +-------------+ | PSN | PSN Tunnel | PSN | | MPLS |<==============================>| MPLS | +-------------+ +-------------+ | Physical | | Physical | +-----+-------+ +-----+-------+ Figure 2: Ethernet PWE3 Protocol Stack Reference Model For the purpose of this document, PE1 will be defined as the ingress router, and PE2 as the egress router. A layer 2 PDU will be received at PE1, encapsulated at PE1, transported, decapsulated at PE2, and transmitted out of PE2. 3. PSN Tunnel Labels and PW Labels Suppose it is desired to transport layer 2 PDUs from ingress LSR PE1 to egress LSR PE2, across an intervening MPLS network. We assume that there is an LSP ( PSN tunnel ) from PE1 to PE2. That is, we assume that PE1 can cause a packet to be delivered to PE2 by pushing some label onto the packet and sending the result to one of its adjacencies. Call this label the "PSN tunnel label", and the corresponding LSP the "PSN tunnel LSP". The PSN tunnel LSP merely gets packets from PE1 to PE2, the corresponding label doesn't tell PE2 what to do with the payload, and in fact if penultimate hop popping is used, PE2 may never even see the corresponding label. (If PE1 itself is the penultimate hop, a PSN tunnel label may not even get pushed on.) Thus if the payload is not an IP packet, there must be a label, which becomes visible to PE2, that tells PE2 how to treat the received packet. Call this label the "PW label". So when PE1 sends a layer 2 PDU to PE2, it first pushes a PW label on its label stack, and then (if PE1 is not adjacent to PE2) pushes on a PSN tunnel label. The PSN tunnel label gets the MPLS packet from PE1 to PE2; the PW label is not visible until the MPLS packet reaches PE2. PE2's disposition of the packet is based on the PW label. Martini, et al. [Page 4] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 Note that the tunnel could be a GRE encapsulated MPLS tunnel between PE1 and PE2. In this case PE1 would be adjacent to PE2, and only the PW label would be used, and the intervening network need only carry IP packets. If the payload of the MPLS packet is, for example, an ATM AAL5 PDU, the VC label will generally correspond to a particular ATM VC at PE2. That is, PE2 needs to be able to infer from the PW label the outgoing interface and the VPI/VCI value for the AAL5 PDU. If the payload is a Frame Relay PDU, then PE2 needs to be able to infer from the PW label the outgoing interface and the DLCI value. If the payload is an Ethernet frame, then PE2 needs to be able to infer from the PW label the outgoing interface, and perhaps the VLAN identifier. This process is uni-directional, and will be repeated independently for bi- directional operation. It is REQUIRED to assign the same PW ID, and PW type for a given circuit in both directions. The group ID (see below) MUST NOT be required to match in both directions. The transported frame MAY be modified when it reaches the egress router. If the header of the transported layer 2 frame is modified, this MUST be done at the egress LSR only. Note that the PW label must always be at the bottom of the label stack, and the PSN tunnel label, if present, must be immediately above the PW label. Of course, as the packet is transported across the MPLS network, additional labels may be pushed on (and then popped off) as needed. Even PE1 itself may push on additional labels above the PSN tunnel label. If PE1 and PE2 are directly adjacent LSRs, then it may not be necessary to use a PSN tunnel label at all. This document does not specify a method for distributing the PSN tunnel label or any other labels that may appear above the PW label on the stack. Any acceptable method of MPLS label distribution will do. This document does specify a method for assigning and distributing the PW label. Static label assignment MAY be used, and implementations SHOULD provide support for this. When signaling is used, the PW label MUST be distributed from PE2 to PE1 using LDP in the downstream unsolicited mode; this requires that an LDP session be created between PE1 and PE2. It should be noted that this LDP session is not necessarily transported along the same path as the Layer 2 PDUs. [1] In addition, when using LDP to distribute the PW label, liberal label retention mode SHOULD be used. Note that this technique allows an unbounded number of layer 2 "PWs" to be carried together in a single "tunnel". Thus it scales quite well in the network backbone. Martini, et al. [Page 5] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 While this document currently defines the emulation of Frame Relay and ATM PVC services, it specifically does not preclude future enhancements to support switched service (SVC and SPVC) emulation. 4. Protocol-Specific Details 4.1. Frame Relay The Frame Relay PDUs are encapsulated according to the procedures defined in [7]. The MPLS edge LSR MUST provide Frame Relay PVC status signaling to the Frame Relay network. If the MPLS edge LSR detects a service affecting condition as defined in [2] Q.933 Annex A.5 sited in IA FRF1.1, it MUST withdraw the label that corresponds to the frame relay DLCI. The Egress LSR SHOULD generate the corresponding errors and alarms as defined in [2] on the egress Frame relay VC. 4.2. ATM 4.2.1. ATM AAL5 VCC Transport ATM AAL5 CSPS-SDUs are encapsulated according to [10] ATM AAL5 CPCS- SDU mode. This mode allows the transport of ATM AAL5 CSPS-SDUs traveling on a particular ATM PVC across the MPLS network to another ATM PVC. 4.2.2. ATM Transparent Cell Transport This mode is similar to the Ethernet port mode. Every cell that is received at the ingress ATM port on the ingress LSR, PE1, is encapsulated according to [10], ATM cell mode n-to-one, and sent across the PW to the egress LSR, PE2. This mode allows an ATM port to be connected to only one other ATM port. [10] ATM cell n-to-one mode allows for grouping of multiple cells into a single MPLS frame. Grouping of ATM cells is OPTIONAL for transmission at the ingress LSR, PE1. If the Egress LSR PE2 supports cell concatenation the ingress LSR, PE1, should only concatenate cells up to the "Maximum Number of concatenated ATM cells" parameter received as part of the FEC element. 4.2.3. ATM VCC and VPC Cell Transport This mode is similar to the ATM AAL5 VCC transport except that cells are transported. Every cell that is received on a pre-defined ATM PVC, or ATM PVP, at the ingress ATM port on the ingress LSR, PE1, is encapsulated according to [10], ATM cell mode, and sent across the Martini, et al. [Page 6] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 LSP to the egress LSR PE2. Grouping of ATM cells is OPTIONAL for transmission at the ingress LSR, PE1. If the Egress LSR PE2 supports cell concatenation the ingress LSR, PE1, MUST only concatenate cells up to the "Maximum Number of concatenated ATM cells in a frame" parameter received as part of the FEC element. 4.2.4. OAM Cell Support OAM cells MAY be transported on the VC LSP. When the LSR is operating in AAL5 CPCS-SDU transport mode if it does not support transport of ATM cells, the LSR MUST discard incoming MPLS frames on an ATM VC LSP that contain a VC label with the T bit set [10]. When operating in AAL5 SDU transport mode an LSR that supports transport of OAM cells using the T bit defined in [7], or an LSR operating in any of the three cell transport modes MUST follow the procedures outlined in [9] section 8 for mode 0 only, in addition to the applicable procedures specified in [6]. 4.2.4.1. OAM Cell Emulation Mode AN LSR that does not support transport of OAM cells across an LSP MAY provide OAM support on ATM PVCs using the following procedures: A pair of LSRs MAY emulate a bi-directional ATM VC by two uni- directional LSPs. If an F5 end-to-end OAM cell is received from a ATM VC, by either LSR that is transporting this ATM VC, with a loopback indication value of 1, and the LSR has a label mapping for the ATM VC, then the LSR MUST decrement the loopback indication value and loop back the cell on the ATM VC. Otherwise the loopback cell MUST be discarded by the LSR. The ingress LSR, PE1, may also optionally be configured to periodically generate F5 end-to-end loopback OAM cells on a VC. If the LSR fails to receive a response to an F5 end-to-end loopback OAM cell for a pre-defined period of time it MUST withdraw the label mapping for the VC. If an ingress LSR, PE1, receives an AIS F5 OAM cell, fails to receive a pre-defined number of the End-to-End loop OAM cells, or a physical interface goes down, it MUST withdraw the label mappings for all VCs associated with the failure. When a PW label mapping is withdrawn, the egress LSR, PE2, MUST generate AIS F5 OAM cells on the VC associated with the withdrawn label mapping. In this mode it is very useful to apply a unique group ID to each interface. In the case where a physical interface goes down, a wild card label withdraw can be sent to all LDP neighbors, greatly reducing the signaling response Martini, et al. [Page 7] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 time. 4.2.5. ILMI Support An MPLS edge LSR MAY provide an ATM ILMI to the ATM edge switch. If an ingress LSR receives an ILMI message indicating that the ATM edge switch has deleted a VC, or if the physical interface goes down, it MUST withdraw the label mappings for all VCs associated with the failure. When a PW label mapping is withdrawn, the egress LSR SHOULD notify its client of this failure by deleting the VC using ILMI. 4.3. Ethernet VLAN The Ethernet frame will be encapsulated according to the procedures in [12] tagged mode. It should be noted that if the VLAN identifier is modified by the egress LSR, according to the procedures outlined above, the Ethernet spanning tree protocol might fail to work properly. If the LSR detects a failure on the Ethernet physical port, or the port is administratively disabled, it MUST withdraw the label mappings for all PWs associated with the port. 4.4. Ethernet The Ethernet frame will be encapsulated according to the procedures in [12]. If the LSR detects a failure on the Ethernet physical port, or the port is administratively disabled, the corresponding PW label mapping MUST be withdrawn. 4.5. HDLC and PPP HDLC and PPP frames are encapsulated according to the procedures in [11]. If the MPLS edge LSR detects that the physical link has failed, or the port is administratively disabled, it MUST withdraw the label mapping that corresponds to the HDLC or PPP link. Martini, et al. [Page 8] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 5. LDP The PW label bindings are distributed using the LDP downstream unsolicited mode described in [1]. The LSRs will establish an LDP session using the Extended Discovery mechanism described in [1, section 2.4.2 and 2.5], for this purpose a new type of FEC element is defined. The FEC element type is 128. [note1] Only a single PW FEC element MUST be advertised per LDP PW label. The pseudo wire FEC element, is defined as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VC tlv |C| PW type |VC info Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PW ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface parameters | | " | | " | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - PW type A 15 bit quantity containing a value which represents the type of VC. Assigned Values are: PW type Description 0x0001 Frame Relay DLCI 0x0002 ATM AAL5 VCC transport 0x0003 ATM transparent cell transport 0x0004 Ethernet VLAN 0x0005 Ethernet 0x0006 HDLC 0x0007 PPP 0x8008 CEM [8] 0x0009 ATM VCC cell transport 0x000A ATM VPC cell transport - Control word bit (C) The highest order bit (C) of the PW type is used to flag the presence of a control word ( defined in [7] ) as follows: Martini, et al. [Page 9] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 bit 15 = 1 control word present on this VC. bit 15 = 0 no control word present on this VC. Please see the section "C-Bit Handling Procedures" for further explanation. - VC information length Length of the PW ID field and the interface parameters field in octets. If this value is 0, then it references all PWs using the specified group ID and there is no PW ID present, nor any interface parameters. - Group ID An arbitrary 32 bit value which represents a group of PWs that is used to create groups in the VC space. The group ID is intended to be used as a port index, or a virtual tunnel index. To simplify configuration a particular PW ID at ingress could be part of the virtual tunnel for transport to the egress router. The Group ID is very useful to send wild card label withdrawals to remote LSRs upon physical port failure. - PW ID A non-zero 32-bit connection ID that together with the PW type, identifies a particular PW. - Interface parameters This variable length field is used to provide interface specific parameters, such as interface MTU. 5.1. Interface Parameters Field This field specifies interface specific parameters. When applicable, it MUST be used to validate that the LSRs, and the ingress and egress ports at the edges of the circuit, have the necessary capabilities to interoperate with each other. The field structure is defined as follows: Martini, et al. [Page 10] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Parameter ID | Length | Variable Length Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Variable Length Value | | " | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The parameter ID is defined as follows: Parameter ID Length Description 0x01 4 Interface MTU in octets. 0x02 4 Maximum Number of concatenated ATM cells. 0x03 up to 82 Optional Interface Description string. 0x04 4 CEM [8] Payload Bytes. 0x05 2 CEM options. 0x06 2 Requested VLAN ID The Length field is defined as the length of the interface parameter including the parameter id and length field itself. Processing of the interface parameters should continue when encountering unknown interface parameters and they MUST be silently ignored. - Interface MTU A 2 octet value indicating the MTU in octets. This is the Maximum Transmission Unit, excluding encapsulation overhead, of the egress packet interface that will be transmitting the decapsulated PDU that is received from the MPLS network. This parameter is applicable only to PW types 1, 2, 4, 5, 6, and 7, and is REQUIRED for these PW types. If this parameter does not match in both directions of a specific PW, that PW MUST NOT be enabled. - Maximum Number of concatenated ATM cells A 2 octet value specifying the maximum number of concatenated ATM cells that can be processed as a single PDU by the egress LSR. An ingress LSR transmitting concatenated cells on this VC can concatenate a number of cells up to the value of this parameter, but MUST NOT exceed it. This parameter is applicable only to PW types 3, 9, and 0x0a, and is REQUIRED for these VC types. This parameter does not need to match in both directions of a specific VC. Martini, et al. [Page 11] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 - Optional Interface Description string This arbitrary, OPTIONAL, interface description string is used to send a human-readable administrative string describing the interface to the remote. This parameter is OPTIONAL, and is applicable to all PW types. The interface description parameter string length is variable, and can be from 0 to 80 octets. Human-readable text MUST be provided in the UTF-8 charset using the Default Language [RFC2277]. - Payload Bytes A 2 octet value indicating the number of TDM payload octets contained in all packets on the CEM stream, from 48 to 1,023 octets. All of the packets in a given CEM stream have the same number of payload bytes. Note that there is a possibility that the packet size may exceed the SPE size in the case of an STS-1 SPE, which could cause two pointers to be needed in the CEM header, since the payload may contain two J1 bytes for consecutive SPEs. For this reason, the number of payload bytes must be less than or equal to 783 for STS-1 SPEs. - CEM Options. An optional 16 Bit value of CEM Flags. See [8] for the definition of the bit values. - Requested VLAN ID. An Optional 16 bit value indicating the requested VLAN ID. This parameter MAY be used by an LSR that is incapable of rewriting the 802.1Q ethernet VLAN tag on output. If the ingress LSR receives this request it MAY rewrite the VLAN ID tag in input to match the requested VLAN ID. If this is not possible, and the VLAN ID does not already match configured ingress VLAN ID the PW should not be enabled.This parameter is applicable only to PW type 4. 5.1.1. PW types for which the control word is REQUIRED The Label Mapping messages which are sent in order to set up these PWs MUST have c=1. When a Label Mapping message for a VC of one of these types is received, and c=0, a Label Release MUST be sent, with an "Illegal C-bit" status code. In this case, the VC will not come up. Martini, et al. [Page 12] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 5.1.2. PW types for which the control word is NOT mandatory If a system is capable of sending and receiving the control word on PW types for which the control word is not mandatory, then each such PW endpoint MUST be configurable with a parameter that specifies whether the use of the control word is PREFERRED or NOT PREFERRED. For each PW, there MUST be a default value of this parameter. This specification does NOT state what the default value should be. If a system is NOT capable of sending and receiving the control word on VC types for which the control word is not mandatory, then it behaves as exactly as if it were configured for the use of the control word to be NOT PREFERRED. If a Label Mapping message for the PW has already been received, but no Label Mapping message for the PW has yet been sent, then the procedure is the following: -i. If the received Label Mapping message has c=0, send a Label Mapping message with c=0, and the control word is not used. -ii. If the received Label Mapping message has c=1, and the PW is locally configured such that the use of the control word is preferred, then send a Label Mapping message with c=1, and the control word is used. -iii. If the received Label Mapping message has c=1, and the PW is locally configured such that the use of the control word is not preferred or the control word is not supported, then act as if no Label Mapping message for the PW had been received (i.e., proceed to the next paragraph). If a Label Mapping message for the PW has not already been received (or if the received Label Mapping message had c=1 and either local configuration says that the use of the control word is not preferred or the control word is not supported), then send a Label Mapping message in which the c bit is set to correspond to the locally configured preference for use of the control word. (I.e., set c=1 if locally configured to prefer the control word, set c=0 if locally configured to prefer not to use the control word or if the control word is not supported). The next action depends on what control message is next received for that PW. The possibilities are: -i. A Label Mapping message with the same c bit value as specified in the Label Mapping message that was sent. PW setup is now complete, and the control word is used if c=1 but not used if c=0. Martini, et al. [Page 13] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 -ii. A Label Mapping message with c=1, but the Label Mapping message that was sent has c=0. In this case, ignore the received Label Mapping message, and continue to wait for the next control message for the PW. -iii. A Label Mapping message with c=0, but the Label Mapping message that was sent has c=1. In this case, send a Label Withdraw message with a "Wrong c-bit" status code, followed by a Label Mapping message that has c=0. PW setup is now complete, and the control word is not used. -iv. A Label Withdraw message with the "Wrong c-bit" status code. Treat as a normal Label Withdraw, but do not respond. Continue to wait for the next control message for the PW. If at any time after a Label Mapping message has been received, a corresponding Label Withdraw or Release is received, the action taken is the same as for any Label Withdraw or Release that might be received at any time. Note that receiving a Label Withdraw should not cause a corresponding Label Release to be sent. If both endpoints prefer the use of the control word, this procedure will cause it to be used. If either endpoint prefers not to use the control word, or does not support the control word, this procedure will cause it not to be used. If one endpoint prefers to use the control word but the other does not, the one that prefers not to use it is has no extra protocol to execute, it just waits for a Label Mapping message that has c=0. The diagram in Appendix A illustrates the above procedure. 5.1.3. Status codes RFC 3036 has a range of Status Code values which are assigned by IANA on a First Come, First Served basis. These are in the range 0x20000000-0x3effffff [note2]. The following new status codes are defined: 0x20000001 "Illegal C-Bit" 0x20000002 "Wrong C-Bit" Martini, et al. [Page 14] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 5.2. LDP label Withdrawal procedures As mentioned above the Group ID field can be used to withdraw all PW labels associated with a particular group ID. This procedure is OPTIONAL, and if it is implemented the LDP label withdraw message should be as follows: the PW information length field is set to 0, the PW ID field is not present, and the interface parameters field is not present. For the purpose of this document this is called the "wild card withdraw procedure", and all LSRs implementing this design are REQUIRED to accept such a withdraw message, but are not required to send it. The interface parameters field MUST NOT be present in any LDP PW label withdrawal message or release message. A wildcard release message MUST include only the group ID. A Label Release message initiated from the imposition router must always include the PW ID. 5.3. Sequencing Considerations In the case where the router considers the sequence number field in the control word, it is important to note the following when advertising labels 5.3.1. Label Mapping Advertisements After a label has been withdrawn by the disposition router and/or released by the imposition router, care must be taken to not re- advertise (re-use) the released label until the disposition router can be reasonably certain that old packets containing the released label no longer persist in the MPLS network. This precaution is required to prevent the imposition router from restarting packet forwarding with sequence number of 1 when it receives the same label mapping if there are still older packets persisting in the network with sequence number between 1 and 32768. For example, if there is a packet with sequence number=n where n is in the interval[1,32768] traveling through the network, it would be possible for the disposition router to receive that packet after it re-advertises the label. Since the label has been released by the imposition router, the disposition router SHOULD be expecting the next packet to arrive with sequence number to be 1. Receipt of a packet with sequence number equal to n will result in n packets potentially being rejected by the disposition router until the imposition router imposes a sequence number of n+1 into a packet. Possible methods to avoid this is for the disposition router to always advertise a different PW label, or for the disposition router Martini, et al. [Page 15] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 to wait for a sufficient time before attempting to re-advertised a recently released label. This is only an issue when sequence number processing at the disposition router is enabled. 5.3.2. Label Mapping Release In situations where the imposition router wants to restart forwarding of packets with sequence number 1, the router shall 1) Send to disposition router a label mapping release, and 2) Send to disposition router a label mapping request. When sequencing is supported, advertisement of a PW label in response to a label mapping request MUST also consider the issues discussed in the section on Label Mapping Advertisements. 6. IANA Considerations As specified in this document, a Virtual Circuit FEC element contains the PW Type field. PW type value 0 is reserved. PW type values 1 through 10 are defined in this document. PW type values 11 through 63 are to be assigned by IANA using the "IETF Consensus" policy defined in [RFC2434]. PW type values 64 through 127 are to be assigned by IANA, using the "First Come First Served" policy defined in [RFC 2434]. PW type values 128 through 32767 are vendor-specific, and values in this range are not to be assigned by IANA. As specified in this document, a Pseudo Wire FEC element contains the Interface Parameters field, which is a list of one or more parameters, and each parameter is identified by the Parameter ID field. Parameter ID value 0 is reserved. Parameter ID values 1 through 6 are defined in this document. Parameter ID values 7 through 63 are to be assigned by IANA using the "IETF Consensus" policy defined in RFC2434. Parameter ID values 64 through 127 are to be assigned by IANA, using the "First Come First Served" policy defined in RFC2434. Parameter ID values 128 through 255 are vendor- specific, and values in this range are not to be assigned by IANA. 7. Security Considerations This document does not affect the underlying security issues of MPLS. Martini, et al. [Page 16] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 8. References [1] "LDP Specification." L. Andersson, P. Doolan, N. Feldman, A. Fredette, B. Thomas. January 2001. RFC3036 [2] ITU-T Recommendation Q.933, and Q.922 Specification for Frame Mode Basic call control, ITU Geneva 1995 [3] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, D. Tappan, G. Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032 [4] "IEEE 802.3ac-1998" IEEE standard specification. [5] American National Standards Institute, "Synchronous Optical Network Formats," ANSI T1.105-1995. [6] ITU Recommendation G.707, "Network Node Interface For The Synchronous Digital Hierarchy", 1996. [7] "Encapsulation Methods for Transport of Frame-Relay Over IP and MPLS Networks", draft-ietf-pwe3-frame-encap-01.txt. ( work in progress ) [8] "SONET/SDH Circuit Emulation Service Over MPLS (CEM) Encapsulation", draft-malis-sonet-ces-mpls-05.txt ( Work in progress ) [9] ATM Forum Specification fb-fbatm-0151.000 (2000) ,Frame Based ATM over SONET/SDH Transport (FAST) [10] "Encapsulation Methods for Transport of ATM Cells/Frame Over IP and MPLS Networks", draft-ietf-pwe3-atm-encap-00.txt ( work in progress ) [11] "Encapsulation Methods for Transport of PPP/HDLC Frames Over IP and MPLS Networks", draft-martini-ppp-hdlc-encap-mpls-00.txt. ( work in progress ) [12] "Encapsulation Methods for Transport of Ethernet Frames Over IP/MPLS Networks", draft-ietf-pwe3-ethernet-encap-01.txt. ( work in progress ) [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998. Martini, et al. [Page 17] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 [note1] FEC element type 128 is pending IANA approval. [note2] Status codes assigment is pending IANA approval. 9. Author Information Luca Martini Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021 e-mail: luca@level3.net Nasser El-Aawar Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021 e-mail: nna@level3.net Giles Heron PacketExchange Ltd. The Truman Brewery 91 Brick Lane LONDON E1 6QL United Kingdom e-mail: giles@packetexchange.net Dimitri Stratton Vlachos Mazu Networks, Inc. 125 Cambridgepark Drive Cambridge, MA 02140 e-mail: d@mazunetworks.com Dan Tappan Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: tappan@cisco.com Martini, et al. [Page 18] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 Jayakumar Jayakumar, Cisco Systems Inc. 225, E.Tasman, MS-SJ3/3, San Jose, CA, 95134 e-mail: jjayakum@cisco.com Alex Hamilton, Cisco Systems Inc. 285 W. Tasman, MS-SJCI/3/4, San Jose, CA, 95134 e-mail: tahamilt@cisco.com Eric Rosen Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: erosen@cisco.com Steve Vogelsang Laurel Networks, Inc. Omega Corporate Center 1300 Omega Drive Pittsburgh, PA 15205 e-mail: sjv@laurelnetworks.com John Shirron Omega Corporate Center 1300 Omega Drive Pittsburgh, PA 15205 Laurel Networks, Inc. e-mail: jshirron@laurelnetworks.com Toby Smith Omega Corporate Center 1300 Omega Drive Pittsburgh, PA 15205 Laurel Networks, Inc. e-mail: tob@laurelnetworks.com Martini, et al. [Page 19] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 Andrew G. Malis Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 Phone: +1 408 383 7223 Email: Andy.Malis@vivacenetworks.com Vinai Sirkay Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 e-mail: sirkay@technologist.com Vasile Radoaca Nortel Networks 600 Technology Park Billerica MA 01821 e-mail: vasile@nortelnetworks.com Chris Liljenstolpe Cable & Wireless 11700 Plaza America Drive Reston, VA 20190 e-mail: chris@cw.net Dave Cooper Global Crossing 960 Hamlin Court Sunnyvale, CA 94089 e-mail: dcooper@gblx.net Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave Sunnyvale, CA 94089 e-mail: kireeti@juniper.net Martini, et al. [Page 20] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 10. Appendix A - C-bit Handling Procedures Diagram ------------------ Y | Received Label | N -------| Mapping Msg? |-------------- | ------------------ | -------------- | | | | ------- ------- | | C=0 | | C=1 | | ------- ------- | | | | | ---------------- | | | Control Word | N | | | Capable? |----------- | | ---------------- | | | Y | | | | | | | | ---------------- | | | | Control Word | N | | | | Preferred? |---- | | | ---------------- | | | | Y | | | | | | | | ---------------- | | | | | Control Word | | | | | | Preferred? | | | | | ---------------- | | | | N | Y | | | | | | | Send Send Send Send Send Send C=0 C=1 C=0 C=0 C=0 C=1 | | | | ---------------------------------- | If receive the same as sent, | | PW setup is complete. If not: | ---------------------------------- | | | | ------------------- ----------- | Receive | | Receive | | C=1 | | C=0 | ------------------- ----------- | | Wait for the Send next message Wrong C-Bit | Send Label Mapping Message Martini, et al. [Page 21] Internet Draft draft-ietf-pwe3-control-protocol-01.txt November 2002 Martini, et al. [Page 22]