Himanshu Shah K.Arvind Tenor Networks PPVPN Working Group Internet Draft draft-shah-ppvpn-ipls-00.txt Eric Rosen Francois Le Faucheur October 2002 Cisco Systems Expires: March 2003 Giles Heron PacketExchange,Ltd Vasile Radoaca Nortel Networks IP over LAN Service (IPLS) 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 A Virtual Private LAN Service (VPLS) [VPLS] is used to interconnect systems across a wide-area or metropolitan-area network, making it appear to those systems as if they are interconnected on a private LAN. The systems which are interconnected in this way may themselves be LAN switches. If, however, the interconnected systems are NOT LAN switches, but rather are IP hosts or IP routers, certain simplifications are possible. We call this simplified type of virtual private LAN service an ôIP over LAN Serviceö (IPLS). In IPLS, as in VPLS, LAN interfaces are run in promiscuous mode, and frames are forwarded based on their MAC Destination Addresses. Shah, et al. Expires March 2003 1 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt However, the maintenance of the MAC forwarded tables is done via signaling, rather than via the ôMAC Address Learningö procedures of IEEE 802.1D. Further, Address Resolution Protocol (ARP) messages are proxied, rather than being carried transparently. This draft specifies the protocols and procedures for support of the IPLS service. 1.0 Boiler Plate for Sub-IP Area Drafts RELATED DOCUMENTS draft-ietf-ppvpn-l2-framework-01.txt draft-lasserre-vkompella-ppvpn-vpls-02.txt draft-rosen-ppvpn-l2-signaling-02.txt draft-ietf-pwe3-control-protocol-00.txt draft-heinanen-inarp-uni-01.txt WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK Belongs in PPVPN WHY IS IT TARGETED AT THIS WG This document describes a mechanism to assist in Provider- Provisioned Layer 2 VPNs. JUSTIFICATION This document provides a detailed description for IP over LAN Service (IPLS), which is discussed in the L2 PPVPN Framework [PPVPN- FWK]. The VPLS [VPLS] services of L2VPN require PE devices to function as MAC learning bridges. IPLS is a solution for a specific topology where MAC learning capabilities are not required for VPLS services, because user data traffic is restricted to IP, and the CE devices are not LAN switches. 2.0 Overview As emphasized in [VPLS], Ethernet has become popular as an access technology in Metropolitan and Wide Area Networks. [VPLS] describes how geographically dispersed customer LANs can be interconnected over a service providerÆs network using Layer 2 VPNs. The VPLS service is provided by Provider Edge (PE) devices, and it is provided to Customer Edge (CE) devices. The VPLS architecture provides such services by incorporating bridging functions such as MAC address learning in the PE devices. There are Provider Edge platforms, both existing and forthcoming, which have been designed primarily to be IP routers, rather than to be LAN switches. It can be fairly straightforward to add a MAC address lookup capability to these platforms, and to run their LAN interfaces in promiscuous mode, so that they can forward frames Shah, et al. Expires March 2003 2 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt based on the MAC Destination Address of the frame. It is less straightforward to add the IEEE 802.1D MAC Address learning capability to these platforms. However, in scenarios where the CE devices are NOT LAN switches, but rather are IP hosts or IP routers, it is possible to provide the virtual private LAN service without requiring IEEE 802.1D MAC address learning/aging on the PE. Due to these restrictions, we dub such a service an ôIP LAN Serviceö, or IPLS. The purpose of this draft is to specify the IPLS. Consequently, IPLS allows a service provider to provide a VPLS-like service by using PE routers that are not designed to perform general LAN bridging functions. However one must be willing to accept the restriction that the Virtual LAN service be used for IP traffic only, and not used to interconnect CE devices that are themselves LAN switches. This seems like an acceptable restriction in many environments, given that IP is the predominant type of traffic in today's networks. In IPLS, a PE device implements multi-point LAN connectivity for IP traffic using the following key functions: 1. Discovery: Each Provider Edge (PE) device discovers IP/MAC address associations for the locally attached Customer Edge (CE) devices, for each IPLS instance configured on the PE device. 2. Pseudowires (PW) for Unicast Traffic: For each locally attached CE device in a given IPLS instance, a PE device sets up a pseudo-wire (VC-LSP) to each of the other PEs that supports the same IPLS instance. For instance, if PEx and PEy both support IPLS I, and PEy is locally attached to CEw and CEz, PEy will initiate the setup of two pseudowires between itself and PEx. One of these will be used to carry unicast traffic from any of PExÆs CE devices to CEw. The other will be used to carry unicast traffic from any of PExÆs CE devices to CEz. Note that these pseudowires carry traffic only in one direction. Further, while the pseudowire implicitly identifies the destination CE of the traffic, it does not identify the source CE; packets from many CEs may be freely intermixed on a given pseudowire. 3. Pseudowires for Multicast Traffic: In addition, every PE supporting a given IPLS instance will set up a special ômulticast pseudowireö to every other PE in that IPLS instance. If, in the above example, one of PExÆs CE devices sends a multicast packet, PEx would forward the multicast packet to PEy on the special multicast pseudowire. PEy would then send a copy of that packet to CEw and a copy to CEz. Shah, et al. Expires March 2003 3 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt Thus when a PE sends a multicast packet across the network, it sends one copy to each remote PE (supporting the given IPLS instance). If a particular remote PE has more than one CE device in that IPLS instance, the remote PE must replicate the packet and send one copy to each of its local CEs. As with the pseudowires that are used for unicast traffic, packets travel in only one direction on these pseudowires, and packets from different sources may be freely intermixed. 4. Signaling: The necessary pseudowires can be set up and maintained using the LDP-based signaling procedures described in [PWE3-CONTROL] and/or [ROSEN-SIG]. Use of other signaling procedures is for further study. A PE may assign the same label to each of the unicast pseudowires that leads to a given CE device, in effect creating a multipoint-to-point pseudowire. Similarly, a PE may assign the same label to each of the multicast pseudowires for a given IPLS instances, in effect creating a multipoint-to-point pseudowire. When setting up a pseudowire to be used for unicast traffic, the PE must also signal the IP address and the MAC address of the corresponding CE device. 5. Proxy ARP: Distribution of IP/MAC address associations to remote PE devices via PW signaling enables each PE device to function as a proxy ARP server for CE devices attached to other PE devices. This makes it possible for any CE device to ARP for the MAC addresses of remote CE devices. 6. Forwarding: A PE device programs its Forwarding Information Base using the CE MAC addresses and VC labels signaled through the PW signaling. Unicast IP traffic from the local CEs is then switched to the proper VC-LSP based on the destination MAC address. Multicast IP traffic from the local CEs is replicated by the local PE over all the multicast VC-LSPs for that IPLS instance and is then replicated by each remote PE onto all its Attachment Circuits for that IPLS instance. Both VPLS [VPLS] and IPLS require the ingress PE to forward a frame based on its destination MAC address. However, two key differences between VPLS and IPLS can already be noted from the above description: . In VPLS, MAC entries are placed in the FIB of the ingress PE as a result of IEEE 802.1D MAC address learning (which occurs in the data plane) while in IPLS MAC entries are placed in the FIB as a result of pseudowire signaling operations (control plane). Shah, et al. Expires March 2003 4 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt . In VPLS, the egress PE looks up a frameÆs MAC destination address to determine the customer-facing interface out which the frame must be sent; in IPLS, the choice of interface is based entirely on the VC-label. The following sections describe the details of the IPLS scheme. 2.1 Terminology IPLS IP over LAN service (class of VPLS for IP only). IPLS network A collection of PE nodes supporting the IPLS service and the mechanisms described in this document, including the Extended LDP based PW signaling between them. IPLS Service A single service instance of IPLS emulating a LAN segment for IP data traffic. MPt-Pt PW Multipoint-to-Point Pseudowire. A pseudowire that carries traffic from remote PE devices to a PE device that signals the pseudowire. The signaling PE device advertises the same VC- label to all remote PE devices that participate in the IPLS service instance. In IPLS, for a given IPLS instance, a MPt-Pt PW used for IP unicast traffic is established by a PE for each CE device locally attached to that PE. It is a unidirectional tree whose leaves consist of the remote PE peers (which connect at least one Attachment Circuit associated with the same IPLS instance) and whose root is the signaling PE. Traffic flows from the leaves towards the root. Multicast PW Multicast Pseudowire. A special kind of MPt-Pt PW that carries only IP multicast/broadcast traffic. In the IPLS architecture, for each IPLS instance supported by a PE, that PE device establishes exactly one Multicast PW. CE Customer Edge device. In this document, a CE is any IP node (host or router) connected to the IPLS LAN service. Replication Tree The collection of all pseudowires and attachment circuits that are members of an IPLS service instance on a given PE. When a multicast/broadcast packet is received by the PE on an attachment circuit, the PE device sends a copy of the packet to every pseudowire Shah, et al. Expires March 2003 5 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt and attachment circuit of the replication tree, excluding the attachment circuit on which the packet was received. 3.0 Topology The Customer Edge (CE) devices are IP nodes (hosts or routers) that are connected to PE devices either directly, or via an Ethernet network. We assume that the PE/CE connection may be regarded by the PE as an ôinterfaceö to which one or more CEs are attached. This interface may be the physical LAN interface or a VLAN. The Provider Edge (PE) routers are MPLS Label Edge Routers (LERs) that serve as pseudowire endpoints. +----+ +----+ + S1 +---+ ........................... +---| S2 | +----+ | | . . | +----+ IPa | | +----+ +----+ | IPe + +---| PE1|---MPLS and/or IP---| PE2|---+ / \ +----+ |Network +----+ | +----+ +---+ . | . | +----+ + S1 + | S1| . +----+ . +---| S2 | +----+ +---+ ..........| PE3|........... +----+ IPb IPc +----+ IPf | | +----+ | S3 | +----+ IPd In the above diagram, an IPLS instance is shown with three sites: site S1, site S2 and site S3. In site S3, the CE device is directly connected to its PE. In the other two sites, there are multiple CEs connected to a single PE. More precisely, the CEs at these sites are on an Ethernet network (or VLAN), and the PE is attached to that same Ethernet network or VLAN). We impose the following restriction: if one or more CEs attach to a PE by virtue of being on a common LAN or VLAN, there MUST NOT be more than one PE on that LAN or VLAN. PE1, PE2 and PE3 are shown to be connected via an MPLS network; however, other tunneling technologies, such as GRE, L2TP, etc., could also be used to carry the pseudowires. An IPLS instance is a single broadcast domain, such that each IP end station (e.g., IPa) appears to be co-located with other IP end stations (e.g., IPb though IPf) on the same subnet. The IPLS service is transparent to the CE devices and requires no changes to them. 4.0 Configuration Shah, et al. Expires March 2003 6 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt Each PE router is configured with one or more IPLS service instances, and each IPLS service instance is associated with a unique VPN-Id. For a given IPLS service instance, a set of Attachment Circuits is identified. Each Attachment Circuit can be associated with only one IPLS instance. An Attachment Circuit, in this document, is either a customer-facing Ethernet port, or a particular VLAN (identified by an IEEE 802.1Q VLAN ID) on a customer-facing Ethernet port. The PE router can optionally be configured with a local MAC address to be used as source MAC address when packets are forwarded from a pseudowire to an Attachment Circuit. By default, a PE uses the MAC address of the customer-facing Ethernet interface for this purpose. 5.0 Discovery The discovery process includes: . Remote PE discovery . VPN (i.e., IPLS) membership discovery . IP CE end station discovery This draft does not discuss the remote PE discovery or VPN membership discovery. This information can either be user configured or can be obtained using auto-discovery techniques described in [DNS-Discovery] or [BGP-Discovery]. However, the discovery of the CE is an important operational step in the IPLS model and is described below. 5.1 CE discovery Each PE actively detects the presence of local CEs by snooping IP and ARP frames received over the Attachment Circuits. During the discovery phase, the PE examines each broadcast/multicast Ethernet frame. For IP frames (for example IGP discovery/multicast/broadcast packets), the CEÆs (source) MAC address is extracted from the Ethernet header and the (source) IP address is obtained from the IP header. For ARP frames, the source MAC and IP address are determined from the ARP PDU. For each CE, the PE maintains a tuple. Once discovered, the presence/liveness of a CE is monitored continuously by examining the received ARP frames and by periodically generating ARP requests. The absence of an ARP response from a CE after a configurable number of such ARP requests, is interpreted as a loss of connectivity with the CE. 6.0 Pseudowire Creation 6.1 Receive Unicast Multipoint-to-point Pseudowire Shah, et al. Expires March 2003 7 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt As the PE discovers each locally attached CE, a unicast Multipoint- to-point Pseudowire (MPt-Pt PW) associated exclusively with that CE is created by distributing the CEÆs IP address and MAC address along with a VC-Label to all the remote PE peers that participate in the same IPLS instance. Note that the same value of a VC-label should be distributed to all the remote PE peers for a given CE. The MP-Pt PW thus created is used by remote PEs to send unicast IP traffic to a specific CE. (The same functionality can be provided by a set of point-to-point PWs, so the PE is not required to send the same VC-label to all the other PEs. For convenience however, we will speak in the following only of multipoint-to-point PWs, without pointing out each time that a set of point-to-point PWs could be used instead.) The PE forwards a frame received over this MPt-Pt PW to the associated attachment circuit. 6.2 Receive Replication Multipoint-to-point PseudoWire When a PE is configured to participate in an IPLS instance, it advertises a "multicast" VC-label to every other PE that is a member of the same IPLS. The advertised VC-label value is the same for each PE, which creates a multipoint-to-point pseudowire for IP multicast traffic. There is only one multicast MPt-Pt PW per PE for each IPLS instance and this pseudowire is used exclusively to carry multicast/broadcast IP traffic from the remote PEs to this PE for this IPLS instance. Note that no special functionality is expected from this pseudowire. We sometimes call it a ômulticast pseudowireö because we use it only to carry multicast traffic. The pseudowire itself need not provide any different service than any of the unicast pseudowires. In particular, the Receive multicast MPt-PT PW does not perform any replication of frames itself. Rather, it is there to signify to the PE that the PE needs to replicate a copy of a frame received over this MPt-Pt PW onto all the attachment circuits that are associated with the IPLS instance of the MPt-Pt PW. The use of pseudowires, which are specially optimized for multicast, is for further study. 6.3 Send Multicast Replication tree The PE creates a send replication tree for each IPLS instance, which consists of the collection of all attachment circuits and all the ômulticastö pseudowires of this IPLS instance. Any broadcast/multicast frame received over an attachment circuit is replicated to all the other attachment circuits and all pseudowires of the send replication tree of the IPLS instance of the incoming Attachment Circuit. Shah, et al. Expires March 2003 8 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt 7.0 Proxy ARP As part of the signaling of the unicast multipoint-to-point pseudo- wire (See Section 8), each PE distributes to its remote PE peers the CE IP address/MAC address associations that it has discovered. The remote PE peers then build and maintain a database of these associations. When a PE receives an ARP request from a local CE for a remote CE, it searches for the destination IP address in the database associated with the CEÆs IPLS instance. If a match is found, the PE sends an ARP response with the MAC address of the remote CE. This enables the local CE to send unicast IP frames addressed directly to the MAC address of the remote CE. 8.0 Signaling IPLS uses PW signaling based on LDP as specified in [PWE3-CONTROL] and [ROSEN-SIG] to exchange layer-2 cross-connect information for a given VPN. The cross-connect information is represented as a new LDP FEC element (VC-FEC in [PWE3-CONTROL] with a FEC element type of 128, new FEC element in [ROSEN-SIG] with a FEC element type of 129), which LDP then distributes to remote peers in downstream-unsolicited mode. This document proposes extensions to the new FEC element to support the IPLS as a new circuit type and to include the IP address and MAC address information. 8.1 IPLS PW Signaling The IPLS VPN type is advertised in the VC-Type field of the VC FEC as the value 0x000D. The ôinterface parameterö field in the VC FEC is defined in [PWE3- CONTROL] and [ROSEN-SIG] 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Parameter ID | Length | Variable Length Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Variable Length Value | | " | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following parameters of the VC FEC are already defined: 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. Shah, et al. Expires March 2003 9 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt 0x05 4 CEM options. The Length field is defined as the length of the interface parameter including the parameter id and length field itself. We propose the following additional parameters for the VC FEC: 0x06 4 IP address of CE 0x07 6 MAC address of CE 0x08 1 Multicast Label Flag These parameters are used to transport CE IP address/MAC address associations when establishing the MPt-Pt unicast PWs and to establish the multicast multipoint-to-point pseudowire label. The IP address and MAC address interface parameter denotes the IP and MAC address of a CE. The Multicast Label Flag value of 1 indicates that the advertised VC-Label represents a ômulticastö PW. The Multicast Label Flag value of 0 indicates that advertised VC-label represents a ôunicastö PW. As explained earlier, the term ômulticast PWö only means that the PW carries IP broadcast/multicast traffic and does not refer to a multicast LSP in the traditional sense. The Multicast Label flag must be zero, if present, when the IP and MAC address parameters are present (and their value is non-zero). We recommend two options that are currently present as the interface parameter field in the VC FEC, for signaling such ôVC associated informationö. 1. The entire ôinterface parameterö field is either removed or duplicated from the VC FEC to the ôoptional parameterö field of the LDPÆs Label Mapping Message. 2. A new VC Status FEC is introduced that accompanies the VC FEC in the LDPÆs Label Mapping Message. The ôinterface parameterö field of the VC FEC is then either removed or duplicated from the VC FEC to the VC Status FEC. We intend to work with authors of [PWE3-Control] and [ROSEN-SIG] to find the most suitable solution for extensions (such as IP address, IP address and MAC address, interface status, etc.) that are generic, in a backward-compatible fashion. The new FEC specified in [ROSEN-SIG] contains an Attachment Group Identifier (AGI) field, a Source Attachment Individual Identifier field (SAII) and a Target Attachment Individual Identifier field (TAII). The VPN-Id configured on the advertising PE to identify the IPLS instance is advertised in the AGI field. The SAII and TAAI fields are set to the null value. 8.2 Signaling Advertisement Processing Shah, et al. Expires March 2003 10 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt A PE should process a received [PWE3-CONTROL] advertisement with VC- type of IPLS as follows, - Verify the IPLS VPN membership by matching the VPN-Id signaled in the AGI field with the all the VPN-Ids configured on the PE. Discard and release the VC label if VPN-Id is not found. - Distribute the received IP address-to-MAC address binding by sending a gratuitous ARP response on all the attachment circuits associated with the VPN-Id. - Program the Forwarding Information Base (FIB) such that when a packet is received from an attachment circuit with its destination MAC address matching the advertised MAC address, the packet is forwarded out over the tunnel to the advertising PE with the advertised VC-label as the inner label. - When the advertised VC-label is ômulticastö, add the VC-label to the multicast replication tree for the VPN-Id. This enables sending a copy of a multicast/broadcast IP frame from the attachment circuit to this Pseudowire. 8.3 Requesting for IP to MAC binding It is possible that in some cases, some CEs may remain undetected in the absence of any multicast/broadcast IP or ARP packet generation. If another CE needs to converse with a CE in this undetected set, it will proceed to generate ARP requests. The Proxy ARP scheme described so far will be unable to resolve the ARP request, since the address to be resolved would not have been discovered yet. In order to address such situations, an optional Address Resolution Request TLV is included in the Label Mapping message. This TLV contains an IP address parameter that represents the destination IP address that needs to be resolved. The PE may use some intelligent mechanisms (e.g., the number of ARP requests received for unknown IP destination within a certain interval exceeds a threshold) to detect the need for such advertisement. When the need is detected, the PE generates Label Mapping Messages to all remote PEs in the IPLS, with the IP address parameter in the Address Resolution Request TLV set to the destination IP address to be resolved. A PE that supports the Address Resolution Request TLV must, on receiving a Label Mapping message with this TLV, generate an ARP request message using the received IP address as the destination, and some already known IP and MAC address as the source (in the ARP PDU) on all Attachment Circuits associated with the IPLS instance. In essence, this is a request to remote PEs to generate an ARP request on their Attachment Circuits to locate a specific CE and advertise a Label Mapping message back to the requesting PE. This can be seen as reverting to the usual full broadcasting of ARP messages throughout the Emulated LAN in case Proxy ARP fails. Shah, et al. Expires March 2003 11 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt 9 Forwarding 9.1 Non-IP traffic In an IPLS VPN, only IP traffic is forwarded by a PE. ARP frames are directed to the control plane in the PE and the rest of the frames are dropped silently. If the CEs must pass non-IP traffic to each other, they must do so through IP tunnels that terminate at the CEs themselves. 9.2 Unicast IP Traffic In IPLS, IP traffic is forwarded based on the destination MAC address of the layer 2 frame (and not based on the IP Header). To do so, the PE uses a Forwarding Information Base (FIB), which is programmed for the considered IPLS instance, in the following manner: - Whenever a CE (and its MAC address) is discovered locally by the PE on an Attachment Circuit, the PE programs its FIB such that frames received on other attachment circuits with a destination address equal to the CE MAC address, are forwarded onto the corresponding attachment circuit. - When advertising the corresponding unicast PW, the PE programs the FIB such that packets received onto the advertised unicast pseudo-wire are forwarded onto the attachment circuit associated with the CE corresponding to the advertised MAC and IP addresses. - As discussed in section 8.2, on receipt of a PW signaling advertisement, the FIB is programmed by the PE receiving the advertisement such that frames received on an Attachment Circuit with a destination address equal to the advertised MAC address, are forwarded onto the advertised unicast pseudowire. Using the FIB of the IPLS instance to which the attachment circuit belongs, the PE forwards a unicast IP frame to the Attachment Circuit or pseudowire based on the destination MAC address information, if received from an Attachment Circuit, or to the Attachment Circuit based on the VC label, if received from a pseudowire. When a unicast destination MAC address is not recognized in the FIB, the IP frame is dropped. 9.3 Broadcasts and Multicast forwarding When the destination MAC address is either a broadcast or multicast, a copy of the frame is sent to the control plane for CE discovery purposes (see section 5.1). Shah, et al. Expires March 2003 12 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt When a multicast/broadcast IP frame is received from an Attachment Circuit, a PE replicates it onto the Send Multicast Replication Tree (See section 6.3). When a multicast/broadcast IP frame is received from a pseudowire, the PE forwards it to all attachment circuits associated with the IPLS VPN instance involved. It is important to note that PEs participating in an IPLS VPN are responsible for translating a multicast IP address to a multicast Ethernet MAC address when forwarding frames from a ômulticastö pseudowire to the Attachment Circuits. (The translation consists of recognizing the multicast IP address (224.x1.x2.x3) and appending the least significant three bytes of the IP address to 0x01-00-05 to construct the MAC address, e.g., 0x01-00-5E-x1-x2-x3 [RFC-1112]). All other IP packets received over the ômulticastö MPt-Pt PW (such as directed broadcasts, subnet broadcasts, etc) are forwarded over Attachment Circuits using a broadcast MAC address. 9.4 Encapsulation The Ethernet MAC header of a frame received from an Attachment Circuit is stripped before forwarding the frame to the appropriate pseudowire. However, the MAC header is retained when a unicast or broadcast IP frame is directed to one or more Attachment Circuit(s). An IP frame received over a pseudowire is prepended with a MAC header before transmitting it on the appropriate Attachment Circuit(s). The fields in the MAC header are filled in as follows: - The destination MAC address is the MAC address associated with the VC label in the FIB when the pseudowire is unicast - The destination MAC address is a multicast MAC address derived from the IP multicast address or the broadcast MAC address when the VC label is ômulticastö - The source MAC address is the PEÆs own local MAC address or a MAC address which has been specially configured on the PE for this use. - The Ethernet Type field is 0x0800 - The frame may get IEEE802.1Q tagged based on the VLAN information associated with the Attachment Circuit. An FCS field is appended to the frame. 10.0 Attaching to IPLS via ATM or FR In addition to (i) an Ethernet port and a (ii) combination of Ethernet port and a VLAN ID, an Attachment Circuit to IPLS may also be (iii) an ATM or FR VC carrying encapsulated bridged Ethernet frames or (iv) the combination of an ATM or FR VC and a VLAN ID. The ATM/FR VC is just used as a way to transport Ethernet frames between a customer site and the PE. The PE terminates the ATM/FR VC and operates on the encapsulated Ethernet frames exactly as if those were received on a local Ethernet interface. Operation of an IPLS over ATM/FR VC is exactly as described above, with the exception Shah, et al. Expires March 2003 13 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt that the attachment circuit is then identified via the ATM VCI/VPI or Frame Relay DLCI (instead of via a local Ethernet port ID), or a combination of those with a VLAN ID. 11.0 VPLS vs IPLS The VPLS approach proposed in [VPLS] provides VPN services for IP as well as other protocols. The IPLS approach described in this draft is similar to VPLS in many respects: - It provides a Provider Provisioned Virtual LAN service with multipoint capability where a CE connected via a single attachment circuit can reach many remote CEs - It appears as a broadcast domain and a single subnet - forwarding is based on destination MAC addresses However, unlike VPLS, IPLS is restricted to IP traffic only. By restricting the scope of the service to the predominant type of traffic in today's environment, IPLS eliminates the need for service provider edge routers to implement some bridging functions such as MAC address learning in the data path (by, instead, distributing MAC information in the control plane). Thus this solution offers a number of benefits: - Facilitates Virtual LAN services in instances where PE devices cannot or cannot efficiently (or are specifically configured not to) perform MAC address learning. - Does not require flooding of ARP frames. - Encapsulation is more efficient (MAC header is stripped) while traversing the backbone network. - PE devices are not burdened with the processing overhead associated with traditional bridging (e.g., STP processing, etc.). Note however that some of these overheads (e.g., STP processing) could optionally be turned-off with a VPLS solution in the case where it is known that only IP devices are interconnected. - Loops (perhaps through backdoor links) are minimized since a PE could easily reject (via label release) a duplicate IP to MAC address advertisement. 12.0 Acknowledgements Authors would like to thank Nigel Burmeister and others at Tenor Networks for their valuable comments. 13.0 Security Considerations The security aspects of this solution will be discussed at a later time. 14.0 References Shah, et al. Expires March 2003 14 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt [L2VPN-FMWK] Andersson, draft-ietf-ppvpn-l2-framework-01.txt, PPVPN L2 Framework, August 2002, (work in progress). [PWE3-CONTROL] Martini et. Al., ôTransport of Layer 2 Frames Over MPLSö, draft-ietf-pwe3-control-protocol-00.txt, August 2002 (work in progress) [PWE3-ETH-ENCAP] Martini et. Al., ôEncapsulation Methods for Transport of Ethernet Frames over IP/MPLS Networksö, draft-ietf- pwe3-ethernet-encap-00.txt, August 2002 (work in progress) [ROSEN-SIG] Rosen, ôLDP-based Signaling for L2VPNsö, draft-rosen- ppvpn-l2-signaling-02.txt. September 2002. (work in progress). [VPLS] Lasserre et al, ôVirtual Private LN Service over MPLSö, draft-lasserre-vkompella-ppvpn-vpls-02.txt, June 2002 (work in progress). [DNS-Discovery] "DNS/LDP Based VPLS", Heinanen, draft-heinanen-dns- ldp-vpls-00.txt, June 2002 [BGP-Discovery] ôUsing BGP as an Auto-Discovery Mechanism for Network Based VPNsö, Ould-Brahim et al., draft-ietf-ppvpn-bgpvpn- auto-02.txt, February 2002, (work in progress). [ARP] Plummer, D., "An Ethernet Address Resolution Protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Addresses for Transmission on Ethernet Hardware", STD 37, RFC 826, November 1982. [PROXY-ARP] Postel, J., "Multi-LAN Address Resolution", RFC 925, October 1984. [RFC-1112] Deering, S., ôHost Extensions for IP Multicastingö, RFC 1112, August, 1989. 15.0. Intellectual Property Considerations Tenor Networks may seek patent or other intellectual property protection for some or all of the technologies disclosed in this document. If any standards arising from this document are or become protected by one or more patents assigned to Tenor Networks, Tenor intends to disclose those patents and license them on reasonable and non-discriminatory terms. Author's Address Himanshu Shah K.Arvind Tenor Networks 100 Nagog Park Shah, et al. Expires March 2003 15 Internet Draft draft-shah-rosen-heron-ppvpn-IPLS-00.txt Acton, MA 01720 Email: hshah@tenornetworks.com Email: arvind@tenornetworks.com Eric Rosen Cisco Systems 300 Apollo Drive, Chelmsford, MA 01824 Email: erosen@cisco.com Giles Heron PacketExchange Ltd. The Truman Brewery 91 Brick Lane LONDON E1 6QL United Kingdom Email: giles@packetexchange.net Francois Le Faucheur Cisco Systems, Inc. Village d'Entreprise Green Side - Batiment T3 400, Avenue de Roumanille 06410 Biot-Sophia Antipolis France Email: flefauch@cisco.com Vasile Radoaca Nortel Networks Email: vasile@nortelnetworks.com Shah, et al. Expires March 2003 16