L2VPN Working Group Himanshu Shah Ciena
NetworksCorp Intended Status: Proposed Standard Eric Rosen Cisco System Internet Draft Giles Heron TellabsBT Vach Kompella AlcatelAlcatel/lucent February 2008 Expires: JanuaryAugust 2008 ARP Mediation for IP Interworking of Layer 2 VPN draft-ietf-l2vpn-arp-mediation-08.txtdraft-ietf-l2vpn-arp-mediation-09.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on JanuaryAugust 2008. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt Abstract The VPWS service [L2VPN-FRM] provides point-to-point connections between pairs of Customer Edge (CE) devices. It does so by binding two Attachment Circuits (each connecting a CE device with a Provider Edge, PE, device) to a pseudowire (connecting the two PEs). In general, the Attachment Circuits must be of the same technology (e.g., both Ethernet, both ATM), and the pseudowire must carry the frames of that technology. However, if it is known that the frames' payload consists solely of IP datagrams, it is possible to provide a point-to-point connection in which the pseudowire connects Attachment Circuits of different technologies. This requires the PEs to perform a function known as "ARP Mediation". ARP Mediation refers to the process of resolving Layer 2 addresses when different resolution protocols are used on either Attachment Circuit. The methods described in this document are applicable even when the CEs run a routing protocol between them, as long as the routing protocol runs over IP. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119]. Table of Contents 1. Contributing Authors........................................3 2. Introduction................................................4 3. ARP Mediation (AM) function.................................5 4. IP Layer 2 Interworking Circuit.............................6 5. IP Address Discovery Mechanisms.............................6 5.1. Discovery of IP Addresses of Locally Attached IPv4 CE Devices.....................................................7 5.1.1. Monitoring Local Traffic..........................7 5.1.2. CE Devices Using ARP..............................7 5.1.3. CE Devices Using Inverse ARP......................8 5.1.4. CE Devices Using PPP..............................9 5.1.5. Router Discovery method..........................10 5.1.6. Manual Configuration.............................10 5.2. How a CE Learns the IPv4 address of a remote CE.......10 Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 5.2.1. CE Devices Using ARP.............................10 5.2.2. CE Devices Using Inverse ARP.....................11 5.2.3. CE Devices Using PPP.............................11 5.3. Discovery of IP Addresses of Locally Attached IPv6 CE Devices [RFC 2461].........................................11 5.3.1. Monitoring Local Traffic.........................11 5.3.2. CE Devices Using Neighbor Discovery..............12 5.3.3. CE Devices Using Inverse Neighbor Discovery......13 5.3.4. Manual Configuration.............................13 5.4. How a CE Learns the IPv6 address of a remote CE.......13 5.4.1. CE Devices Using Neighbor Discovery..............14 5.4.2. CE Devices Using Inverse Neighbor Discovery......14 6. CE IP Address Signaling between PEs........................15 6.1. When to Signal an IP address of a CE..................15 6.2. LDP Based Distribution................................15 7. IANA Considerations........................................18 7.1. LDP Status messages...................................18 8. Use of IGPs with IP L2 Interworking L2VPNs.................18 8.1. OSPF..................................................19 8.2. RIP...................................................19 8.3. IS-IS.................................................19 9. Multi-domain considerations................................20 10. Security Considerations...................................21 10.1. Control plane security...............................21 10.2. Data plane security..................................22 11. Acknowledgements..........................................22 12. References................................................22 12.1. Normative References.................................22 12.2. Informative References...............................23 13. Authors' Addresses........................................23 Full Copyright Statement......................................24 Intellectual Property.........................................25 1. Contributing Authors This document is the combined effort of the following individuals and many others who have carefully reviewed the document and provided the technical clarifications. W. Augustyn consultant T. Smith Laurel NetworksNetwork Appliances A. Moranganti Big Band Networks S. Khandekar Alcatel Draft-ietf-l2vpn-arp-mediation-08.txtAlcatel/Lucent Draft-ietf-l2vpn-arp-mediation-09.txt A. Malis TellabsVerizon S. Wright Bell South V. Radoaca consultant A. Vishwanathan Force10 Networks T. Grigoriu AlcatelAlcatel/Lucent N. Hart AlcatelAlcatel/Lucent S. Amante Level3 2. Introduction Layer 2 Virtual Private Networks (L2VPN) are constructed over a Service Provider IP backbone but are presented to the Customer Edge (CE) devices as Layer 2 networks. In theory, L2VPNs can carry any Layer 3 protocol, but in many cases, the Layer 3 protocol is IP. Thus it makes sense to consider procedures that are optimized for IP. In a typical implementation, illustrated in the diagram below, the CE devices are connected to the Provider Edge (PE) devices via Attachment Circuits (AC). The ACs are Layer 2 links. In a pure L2VPN, if traffic sent from CE1 via AC1 reaches CE2 via AC2, both ACs would have to be of the same type (i.e., both Ethernet, both FR, etc.). However, if it is known that only IP traffic will be carried, the ACs can be of different technologies, provided that the PEs provide the appropriate procedures to allow the proper transfer of IP packets. +-----+ +------------| CE3 | | +-----+ +-----+ ......| PE3 |........... . +-----+ . . | . . | . +-----+ AC1 +-----+ Service +-----+ AC2 +-----+ | CE1 |-----| PE1 |--- Provider ----| PE2 |-----| CE2 | +-----+ +-----+ Backbone +-----+ +-----+ . . ........................ A CE, which is connected via a given type of AC, may use an IP Address Resolution procedure that is specific to that type of AC. For example, an Ethernet-attached IPv4 CE would use ARP Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt [ARP] and a FR-attached CE might use Inverse ARP [INVARP]. If we are to allow the two CEs to have a Layer 2 connection between them, even though each AC uses a different Layer 2 technology, the PEs must intercept and "mediate" the Layer 2 specific address resolution procedures. In this draft, we specify the procedures for VPWS services, which the PEs must implement in order to mediate the IP address resolution mechanism. We call these procedures "ARP Mediation". Consider a Virtual Private Wire Service (VPWS) constructed between CE1 and CE2 in the diagram above. If AC1 and AC2 are of different technologies, e.g. AC1 is Ethernet and AC2 is Frame Relay (FR), then ARP requests coming from CE1 cannot be passed transparently to CE2. PE1 must interpret the meaning of the ARP requests and mediate the necessary information with PE2 before responding. 3. ARP Mediation (AM) function The ARP Mediation (AM) function is an element of a PE node that deals with the IP address resolution for CE devices connected via an VPWS L2VPN. By placing this function in the PE node, ARP Mediation is transparent to the CE devices. For a given point-to-point connection between a pair of CEs, a PE must perform the following logical steps as part of the ARP Mediation procedure: 1. Discover the IP address of the locally attached CE device 2. Terminate, do not distribute ARP, Inverse ARP, Neighbor Discovery and Inverse Neighbor Discovery requests from CE device at local PE. 3. Distribute those IP Addresses to the remote PE 4. Notify the locally attached CE of the IP address of the remote CE. 5. Respond appropriately to ARP, Inverse ARP, Neighbor Discovery and Inverse Neighbor Discovery requests from local CE device, using IP address of remote CE and hardware address of local PE. This information is gathered using the mechanisms described in the following sections. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 4. IP Layer 2 Interworking Circuit The IP Layer 2 interworking Circuit refers to interconnection of the Attachment Circuit with the IP Layer 2 Transport pseudowire that carries IP datagrams as the payload. The ingress PE removes the data link header of its local Attachment Circuit and transmits the payload (an IP packet) over the pseudowire with or without the optional control word. In some cases, multiple data link headers may exist, such as bridged Ethernet PDU on ATM Attachment Circuit. In this case, ATM header as well as the Ethernet header is removed to expose the IP packet at the ingress. The egress PE encapsulates the IP packet with the data link header used on its local Attachment Circuit. The encapsulation for the IP Layer 2 Transport pseudowire is described in [RFC4447]. 5. IP Address Discovery Mechanisms An IP Layer 2 Interworking Circuit enters monitoring state immediately after the configuration. During this state it performs two functions. - Discovery of locally attached CE IP device - Establishment of the PW The establishment of the PW occurs independently from local CE IP address discovery. During the period when the PW has been established but the local CE IP device has not been discovered, only broadcast/multicast IP frames are propagated between the Attachment Circuit and pseudowire; unicast IP datagrams are dropped. The IP destination address is used to classify unicast/multicast packets. The unicast IP frames are propagated between AC and pseudowire only when CE IP devices on both Attachment Circuits have been discovered, notified and proxy functions have completed. 5.1. Discovery of IP Addresses of Locally Attached IPv4 CE Devices Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 5.1.1. Monitoring Local Traffic The PE devices may learn the IP addresses of the locally attached CEs from any IP traffic, such as link local multicast packets (e.g., destined to 224.0.0.x), and are not restricted to the operations below. 5.1.2. CE Devices Using ARP If a CE device uses ARP to determine the IP address to MAC address binding of its neighbor, the PE processes the ARP requests to learn the IP address of local CE for the local Attachment Circuit. This document mandates that there MUST be only one CE per Attachment Circuit. However, customer facing access topologies may exist whereby more than one CE appears to be connected to the PE on a single Attachment Circuit. For example this could be the case when CEs are connected to a shared LAN that connects to the PE. In such case, the PE MUST select one local CE. The selection could be based on manual configuration or the PE may optionally use following selection criteria. In either case, manual configuration of IP address of the local CE (and its MAC address) MUST be supported. o Wait to learn the IP address of the remote CE (through PW signaling) and then select the local CE that is sending the request for IP address of the remote CE. o Augment cross checking with the local IP address learned through listening of link local multicast packets (as per section 5.1.1 above) o Augment cross checking with the local IP address learned through the Router Discovery protocol (as described below in section 5.1.5). Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt o There is still a possibility that the local PE may not receive an IP address advertisement from the remote PE and there may exist multiple local IP routers that attempt to 'connect' to remote CEs. In this situation, the local PE may use some other criteria to select one IP device from many (such as "the first ARP received"), or an operator may configure the IP address of local CE. Note that the operator does not have to configure the IP address of the remote CE (as that would be learned through pseudowire signaling). Once the local and remote CEs has been discovered for the given Attachment Circuit, the local PE responds with its own MAC address to any subsequent ARP requests from the local CE with a destination IP address matching the IP address of the remote CE. The local PE signals IP address of the CE to the remote PE and may initiate an unsolicited ARP response to notify the IP address to MAC address binding for the remote CE to local CE (again using its own MAC address). Once the ARP mediation function is completed (i.e. the PE device knows both the local and remote CE IP addresses), unicast IP frames are propagated between the AC and the established PW. The PE may periodically generate ARP request messages for the IP address of the CE as a means of verifying the continued existence of the address and its MAC address binding. The absence of a response from the CE device for a given number of retries could be used as a trigger for withdrawal of the IP address advertisement to the remote PE. The local PE would then re-enter the address resolution phase to rediscover the IP address of the attached CE. Note that this "heartbeat" scheme is needed only for broadcast links (such as Ethernet AC), where the failure of a CE device may otherwise be undetectable. 5.1.3. CE Devices Using Inverse ARP If a CE device uses Inverse ARP to determine the IP address of its neighbor, the attached PE processes the Inverse ARP request from the Attachment Circuit and responds with an Inverse ARP reply containing the IP address of the remote CE, if the address is known. If the PE does not yet have the IP address of the remote CE, it does not respond, but notes the IP address of the local CE and the circuit information. Subsequently, when the IP Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt address of the remote CE becomes available, the PE may initiate the Inverse ARP request as a means of notifying the IP address of the remote CE to the local CE. This is the typical mode of operation for Frame Relay and ATM Attachment Circuits. If the CE does not use Inverse ARP, the PE can still discover the IP address of local CE using the mechanisms described in section 5.1.1 and 5.1.5 5.1.4. CE Devices Using PPP The IP Control Protocol [PPP-IPCP] describes a procedure to establish and configure IP on a point-to-point connection, including the negotiation of IP addresses. When using IP (Routed) mode L2VPN interworking, PPP negotiation is not performed end-to-end between CE devices. In this case, PPP negotiation takes place between the CE device and its local PE device (on the PPP attachment circuit). The PE device performs proxy PPP negotiation, and informs the local CE device of the IP address of the remote CE device during IPCP negotiation using the IP-Address option (0x03). When a PPP link completes LCP negotiations, the local PE MAY perform the following IPCP actions: o The PE learns the IP address of the local CE from the Configure-Request received with the IP-Address option (0x03). The PE verifies that the IP address present in the IP-Address option is non-zero. If the IP address is zero, PE responds with Configure-Reject (as this is a request from CE to assign it an IP address). Also, the Configure- Reject copies the IP-Address option with a zero value to instruct the CE to not include that option in new Configure-Request. If the IP address is non-zero, PE responds with Configure-Ack. o If the PE receives Configure-Request without the IP- Address option, it responds with a Configure-Ack. In this case the PE is unable to learn the IP address of the local CE using IPCP and hence must rely on other means as described in sections 5.1.1 and 5.1.5. Note that in order to employ other learning mechanisms, the IPCP negotiations must have reached the open state. o If the PE does not know the IP address of the remote CE, it sends a Configure-Request without the IP-Address option. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt o If the PE knows the IP address of the remote CE, it sends a Configure-Request with the IP-Address option containing the IP address of the remote CE. The IPCP IP-Address option MAY be negotiated between the PE and the local CE device. Configuration of other IPCP options MAY be rejected. Other NCPs, with the exception of the Compression Control Protocol (CCP) and Encryption Control Protocol (ECP), MUST be rejected. The PE device MAY reject configuration of the CCP and ECP. 5.1.5. Router Discovery method In order to learn the IP address of the CE device for a given Attachment Circuit, the PE device may execute Router Discovery Protocol [RFC 1256] whereby a Router Discovery Request (ICMP - router solicitation) message is sent using a source IP address of zero. The IP address of the CE device is extracted from the Router Discovery Response (ICMP - router advertisement) message from the CE. It is possible that the response contains more than one router addresses with the same preference level; in which case, some heuristics (such as first on the list) is necessary. The use of the Router Discovery method by the PE is optional. 5.1.6. Manual Configuration In some cases, it may not be possible to discover the IP address of the local CE device using the mechanisms described in section 5.1 above. In such cases manual configuration MAY be used. All implementations of this draft MUST support manual configuration of the IP address of the local CE. 5.2. How a CE Learns the IPv4 address of a remote CE Once the local PE has received the IP address information of the remote CE from the remote PE, it will either initiate an address resolution request or respond to an outstanding request from the attached CE device. 5.2.1. CE Devices Using ARP When the PE learns IP address of the remote CE as described in section 6.1 and 6.2, it may or may not already know IP address Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt of the local CE. If the IP address is not known, the PE must wait until it is acquired through one of the methods described in sections 5.1.1, 5.1.2 and 5.1.5. If IP address of the local CE is known, the PE may choose to generate an unsolicited ARP message to notify the local CE about the binding of the IP address of the remote CE with the PE's own MAC address. When the local CE generates an ARP request, the PE must proxy the ARP response [PROXY-ARP] using its own MAC address as the source hardware address and IP address of remote CE as the source protocol address. The PE must respond only to those ARP requests whose destination protocol address matches the IP address of the remote CE. 5.2.2. CE Devices Using Inverse ARP When the PE learns the IP address of the remote CE, it should generate an Inverse ARP request. If the Attachment Circuit requires activation (e.g. Frame Relay) the PE should activate it first before the Inverse ARP request. It should be noted, that PE might never receive the response to its own request, nor see any Inverse ARP request from the CE, in cases where CE is pre- configured with IP address of the remote CE or where the use of Inverse ARP has not been enabled. In either case the CE has used other means to learn the IP address of his neighbor. 5.2.3. CE Devices Using PPP When the PE learns the IP address of the remote CE, it should initiate a Configure-Request and set the IP-Address option to the IP address of the remote CE to notify the IP address of the remote CE to the local CE. 5.3. Discovery of IP Addresses of Locally Attached IPv6 CE Devices [RFC 2461] 5.3.1. Monitoring Local Traffic The PE devices may learn the IP addresses of the locally attached CEs from any IP traffic, such as link local multicast packets (e.g., destined to FF02::x), and are not restricted to the operations below. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 5.3.2. CE Devices Using Neighbor Discovery If a CE device uses Neighbor Discovery to determine the IP address to MAC address binding of its neighbor, the PE processes the messages to learn the IP address of local CE for the local Attachment Circuit. If the PE receives a Neighbor Solicitation message, and the source IP address of the message is not the unspecified address, the PE saves the CE address and may communicate it to the remote PE (see section 6. ). It also saves the source link-layer address. If the PE has received remote CE IP addresses, and the destination address in the message matches one of the remote CE IP addresses, the PE replies with a Neighbor Advertisement specifying its own link-layer address as the source link-layer address and the remote CE IP address as source address. If the PE receives an unsolicited Neighbor Advertisement message, the PE saves the CE address (the source IP address) and may communicate it to the other PE. It also saves the source link-layer address. If the PE receives a Router Solicitation, and the source IP address of the message is not the unspecified address, the PE saves the CE address and may communicate it to the other PE. It also saves the source link-layer address. If the PE has received remote CE IP addresses from the other PE, it may reply with a Router Advertisement, specifying its own source link-layer address and specify remote CE IP addresses in prefix information option. If the PE receives a Router Advertisement, it may communicate the source IP address and the on-link addresses to the other PE. It also saves the source link-layer address. Once the local and remote CE IP addresses have been discovered for the given Attachment Circuit, the local PE responds with its own link-layer address to any subsequent Neighbor Solicitation and Router Solicitation requests from the local CE with a destination IP address matching the IP address of the remote CE. The local PE signals the IP addresses of the CE to the remote PE and may initiate an unsolicited Router Advertisment to notify the IP address to link-layer address binding for the remote CE to local CE (again using its own link-layer address). Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt Once the ARP mediation function is completed (i.e. the PE device knows both the local and remote CE IP addresses), unicast IP frames are propagated between the AC and the established PW. The PE will periodically generate Neighbor Solicitation messages for the IP address of the CE as a means of verifying the continued existence of the address and its MAC address binding. The absence of a response from the CE device for a given number of retries could be used as a trigger for withdrawal of the IP address advertisement to the remote PE. The local PE would then re-enter the address resolution phase to rediscover the IP address of the attached CE. 5.3.3. CE Devices Using Inverse Neighbor Discovery If a CE device uses Inverse Neighbor Discovery to determine the IP address of its neighbor, the attached PE processes the Inverse Neighbor Discovery Solicitation from the Attachment Circuit and responds with an Inverse Neighbor Discovery Advertisement containing the IP address of the remote CE, if the address is known. If the PE does not yet have the IP address of the remote CE, it does not respond, but notes the IP address of the local CE and the circuit information. Subsequently, when the IP address of the remote CE becomes available, the PE may initiate the Inverse Neighbor Discovery Solicitation as a means of notifying the IP address of the remote CE to the local CE. This is the typical mode of operation for Frame Relay and ATM Attachment Circuits. 5.3.4. Manual Configuration In some cases, it may not be possible to discover the IP address of the local CE device using the mechanisms described in section 5.3. above. In such cases manual configuration MAY be used. All implementations of this draft MUST support manual configuration of the IP address of the local CE. 5.4. How a CE Learns the IPv6 address of a remote CE Once the local PE has received the IP address information of the remote CE from the remote PE, it will either initiate an address resolution request or respond to an outstanding request from the attached CE device. The PE uses the Address List TLV to Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt communicate the IP addresses. If the PE has received no Router Advertisements from its local CE, it should specify the single CE IP address it has received. If the PE has received a Router Advertisement, it should specify an Address List in which the first entry is the source interface address and the remaining entries are taken from the list of on-link addresses. 5.4.1. CE Devices Using Neighbor Discovery When the PE learns the IP address of the remote CE as described in section 6.1 and 6.2, it may or may not already know the IP address of the local CE. If the IP address is not known, the PE must wait until it is acquired through one of the methods described in section 5.3. above. If the IP address of the local CE is known, the PE may choose to generate an unsolicited Neighbor Advertisement message to notify the local CE about the binding of the IP address of the remote CE with the PE's own link-layer address. It may also generate a Router Advertisement in which the source IP address is the first address from the Address List TLV and the on-link addresses are the remaining entries in the TLV. When the local CE generates a Neighbor Solicitation request, the PE must proxy the response using its own link-layer address as the source hardware address and IP address of remote CE as the source protocol address. The PE must respond only to those requests whose target address matches the IP address of the remote CE. 5.4.2. CE Devices Using Inverse Neighbor Discovery When the PE learns the IP address of the remote CE, it should generate an Inverse Neighbor Discovery Solicitation. If the Attachment Circuit requires activation (e.g. Frame Relay) the PE should activate it first before the Inverse Neighbor Discovery Solicitation. It should be noted, that the PE might never receive the response to its own solicitation, nor see any Inverse Neighbor Discovery Solicitation from the CE, in cases where the CE is pre-configured with the IP address of the remote CE or where the use of Inverse Neighbor Discovery has not been enabled. In either case the CE has used other means to learn the IP address of his neighbor. The PE may also generate a Router Advertisement message in the same way as specified in section 5.4.1. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 6. CE IP Address Signaling between PEs 6.1. When to Signal an IP address of a CE A PE device advertises the IP address of the attached CE only when the encapsulation type of the pseudowire is IP Layer2 Transport (the value 0x0000B, as defined in [PWE3-IANA]). It is quite possible that the IP address of a CE device is not available at the time the PW labels are signaled. For example, in Frame Relay the CE device sends an inverse ARP request only when the DLCI is active. If the PE signals the DLCI to be active only when it has received the IP address along with the PW FEC from the remote PE, a chicken and egg situation arises. In order to avoid such problems, the PE must be prepared to advertise the PW FEC before the IP address of the CE is known and hence uses IP address value zero. When the IP address of the CE device does become available, the PE re-advertises the PW FEC along with the IP address of the CE. Similarly, if the PE detects that an IP address of a CE is no longer valid (by methods described above), the PE must re- advertise the PW FEC with null IP address to denote the withdrawal of IP address of the CE. The receiving PE then waits for notification of the remote IP address. During this period, propagation of unicast IP traffic is suspended, but multicast IP traffic can continue to flow between the AC and the pseudowire. If two CE devices are locally attached to the PE where one CE is connected to an Ethernet port and the other to a Frame Relay port, for example, the IP addresses are learned in the same manner described above. However, since the CE devices are local, the distribution of IP addresses for these CE devices is a local step. 6.2. LDP Based Distribution [RFC4447] uses Label Distribution Protocol (LDP) transport to exchange PW FECs in the Label Mapping message in the Downstream Unsolicited (DU) mode. The PW FEC comes in two flavors; PWid and Generalized ID FEC elements and has some common fields between them. The discussions below refer to these common fields for IP L2 Interworking encapsulation. In addition to PW-FEC, this document defines an IP address list TLV that must be included in the optional parameter field of the Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt Label Mapping message when advertising the PW FEC for the IP Layer2 Transport. The use of optional parameters in the Label Mapping message to extend the attributes of the PW FEC is specified in the [RFC4447]. As defined in [RFC4447], when processing a received PW FEC, the PE matches the PW ID and PW type with the locally configured PW ID and PW Type. If there is a match, and if the PW Type is IP Layer2 Transport the PE further checks for the presence of an Address List TLV (as specified in [RFC 3036]) in the optional parameter TLVs. If absent, a Label Release message is issued with a Status Code meaning "IP Address of the CE is absent" [note: Status Code 0x0000002D is pending IANA allocation] to reject the PW establishment. The Address Family Type value further augments the meaning of type of IP traffic (IPv4 or IPv6) that PW will carry. If there is a mismatch between the received Address Family value and the configured Address Family value, the PE must issue a Label Release message with a Status Code meaning "IP Address type mismatch" [note: Status Code 0x0000002E is pending IANA allocation] to reject the PW establishment. We use the Address List TLV as defined in [RFC 3036] to signal the IP address(es) of the local CE. This IP address list TLV must be included in the optional parameter field of the Label Mapping message, and MUST contain exactly one address of family IPv4 or one or more addresses of family IPv6. If the message contains multiple IPv6 addresses, it is assumed that the PE received a Router Advertisement and the first address in the list was the source address of the Router Advertisement packet, while the remaining addresses are taken from the on-link address list of the Rourter Advertisement packet. Encoding of the IP Address List TLV is: 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| Address List (0x0101) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Family | IP Address of CE ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ IP Address of CE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt Length When Address Family is IPV4, Length is equal to 6 bytes; 2 bytes for address family and 4 bytes of IP address. When Address Family is IPV6, Length is equal to (2 + (n * 16)); 2 bytes for address family and 16 bytes for each IPv6 address. Address Family Two octet quantity containing a value from the ADDRESS FAMILY NUMBERS from ADDRESS FAMILY NUMBERS in [RFC 3232] that encodes the address contained in the Address field. IP Address of CE IP address of the CE attached to the advertising PE. The encoding of the individual address depends on the Address Family. The following address encodings are defined by this version of the protocol: Address Family Address Encoding IPv4 (1) 4 octet full IPv4 address IPv6 (2) 16 octet full IPv6 address The IP address field is set to all zeroes to denote that advertising PE has not learned the IP address of its local CE device. Any non-zero value of the IP address field denotes the IP address of advertising PE's attached CE device. The IP address of the CE is also supplied in the optional parameters field of the LDP Notification message along with the PW FEC. The LDP Notification message is used to signal any change in the status of the CE's IP address. The encoding of the LDP Notification message is as follows. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status (TLV) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Address List TLV (as defined above) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PWId FEC or Generalized ID FEC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Status TLV status code is set to 0x0000002C "IP address of CE", to indicate that IP Address update follows. Since this notification does not refer to any particular message the Message Id, and Message Type fields are set to 0. [note: Status Code 0x0000002C is pending IANA allocation]. The PW FEC TLV SHOULD not include the interface parameters as they are ignored in the context of this message. 7. IANA Considerations 7.1. LDP Status messages This document uses new LDP status codes, IANA already maintains a registry of name "STATUS CODE NAME SPACE" defined by [RFC 3036]. The following values are suggested for assignment: 0x0000002C "IP Address of CE" 0x0000002D "IP Address of the CE is absent" 0x0000002E "IP Address type mismatch" 8. Use of IGPs with IP L2 Interworking L2VPNs In an IP L2 interworking L2VPN, when an IGP on a CE connected to a broadcast link is cross-connected with an IGP on a CE connected to a point-to-point link, there are routing protocol related issues that must be addressed. The link state routing protocols are cognizant of the underlying link characteristics Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt and behave accordingly when establishing neighbor adjacencies, representing the network topology, and passing protocol packets. 8.1. OSPF The OSPF protocol treats a broadcast link type with a special procedure that engages in neighbor discovery to elect a designated and a backup designated router (DR and BDR respectively) with which each other router on the link forms adjacencies. However, these procedures are neither applicable nor understood by OSPF running on a point-to-point link. By cross-connecting two neighbors with disparate link types, an IP L2 interworking L2VPN may experience connectivity issues. Additionally, the link type specified in the router LSA will not match for the two cross-connected routers. Finally, each OSPF router generates network LSAs when connected to a broadcast link such as Ethernet, receipt of which by an OSPF router which believes itself to be connected to a point-to- point link further adds to the confusion. Fortunately, the OSPF protocol provides a configuration option (ospfIfType), whereby OSPF will treat the underlying physical broadcast link as a point-to-point link. It is strongly recommended that all OSPF protocols on CE devices connected to Ethernet interfaces use this configuration option when attached to a PE that is participating in an IP L2 Interworking VPN. 8.2. RIP RIP protocol broadcasts RIP advertisements every 30 seconds. If the multicast/broadcast traffic snooping mechanism is used as described in section 5.1, the attached PE can learn the local CE router's IP address from the IP header of its advertisements. No special configuration is required for RIP in this type of Layer 2 IP Interworking L2VPN. 8.3. IS-IS Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt The IS-IS protocol does not encapsulate its PDUs in IP, and hence cannot be supported in IP L2 Interworking L2VPNs. 9. Multi-domain considerations In a back-to-back configuration, when two PEs are connected with Ethernet, the ARP proxy function has limited application as there is no local CE. | Network A | Network B CE-1 <---> PE-1 <---> PE-2 <===> PE-3 <---> PE-4 <---> CE-2 ATM LDP ETH LDP ETH PW-1 PW-2 Consider a Multi-domain network topology as shown above where PW segment 1 (PE1<->PE2) is in network A and PW segment 2 (PE3<- >PE4) is in network B. In this configuration CE1 is connected to PE1 and CE2 is connected to PE4. PE2 on network A is directly connected to PE3 in network B with Ethernet. In this configuration there needs to be a mechanism for PE2 and PE3 to learn IP addresses of the CEs present in each otherísother's network. The two options to do this are as follows. o Configure CE2ísCE2's IP address as a local CEísCE's IP address at PE2 and CE1ísCE1's IP address as local CEísCE's IP address at PE3. Additionally, PE2 and PE3 are required to generate ARP requests using their own MAC addresses as the source address. These PEs are in effect proxying for CEs present in the each otherísother's network. This is not a desirable option as it requires configuration of IP address of a CE that is present in others (possibly other service providerís)provider's) network. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt o In the second option, PE2 and PE3 use gratuitous ARP which eliminates configuration of IP addresses of the CEs. In this scheme, when PE2 learns the IP address of CE1 (through LDP signaling), PE2 sends a gratuitous ARP to PE3 with the source and destination IP address field set to CE1ísCE1's IP address and the source MAC address field set to PE2ísPE2's MAC address. When PE3 learns the IP address of CE1 (from the gratuitous ARP), PE3 notifies PE4 of the IP address of the CE1 through LDP signaling. Similarly, for the traffic in the opposite direction, when PE3 learns the IP address of CE2, it sends a gratuitous ARP to PE2. PE2 sends an IP address notification, via LDP, of CE2ísCE2's IP address to PE1 using the same procedures described above. This allows PE2 and PE3 to dynamically learn the IP addresses of the CEs present in each otherísother's networks. This is the preferred mode of operation as compared to the option 1 above. 10. Security Considerations The security aspect of this solution is addressed for two planes; control plane and data plane. 10.1. Control plane security Control plane security pertains to establishing the LDP connection, and to pseudowire signaling and CE IP address distribution over that LDP connection. The LDP connection between two trusted PEs can be achieved by each PE verifying the incoming connection against the configured address of the peer and authenticating the LDP messages using MD5 authentication. Pseudowire signaling between two secure LDP peers do not pose security issue but mis-wiring could occur due to configuration error. Some checks, such as, proper pseudowire type and other pseudowire options may prevent mis-wiring due to configuration errors. Learning the IP address of the appropriate CE can be a security issue. It is expected that the Attachment Circuit to the local CE will be physically secured. If this is a concern, the PE must be configured with IP and MAC address of the CE when connected with Ethernet or IP and virtual circuit information (DLCI or VPI/VCI when connected over Frame Relay or ATM and IP address only when connected over PPP). During each ARP/inARP frame Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt processing, the PE must verify the received information against local configuration before forwarding the information to the remote PE to protect against hijacking the connection. 10.2. Data plane security The data traffic between CE and PE is not encrypted and it is possible that in an insecure environment, a malicious user may tap into the CE to PE connection and generate traffic using the spoofed destination MAC address on the Ethernet Attachment Circuit. In order to avoid such hijacking, local PE may verify the source MAC address of the received frame against the MAC address of the admitted connection. The frame is forwarded to PW only when authenticity is verified. When spoofing is detected, PE must sever the connection with the local CE, tear down the PW and start over. 11. Acknowledgements The authors would like to thank Yetik Serbest, Prabhu Kavi, Bruce Lasley, Mark Lewis, Carlos Pignataro, Shane Amante and other folks who participated in the discussions related to this draft. 12. References 12.1. Normative References [ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Addresses for Transmission on Ethernet Hardware". [INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution Protocol". [RFC4447] L. Martini et al., "Pseudowire Setup and Maintenance using LDP", RFC 4447. [PWE3-IANA] L. Martini et al,. "IANA Allocations for pseudo Wire Edge to Edge Emulation (PWE3)", RFC 4446. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt [RFC 2119] S. Bradner, "Key words for use in RFCs to indicate requirement levels" [RFC 3036] L.Anderssen et al., "LDP Specification" [RFC 2461] Narten, T., Nordmark, E. and W.Simpson, "Neighbor Discovery for IP Version(IPv6)", RFC 2461, December, 1998. 12.2. Informative References [L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", June 2004, work in progress. [PPP-IPCP] RFC 1332, G. McGregor, "The PPP Internet Protocol Control Protocol (IPCP)". [PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution". [RFC 1256] S.Deering, "ICMP Router Discovery Messages". [RFC 3232] Reynolds and Postel, "Assigned Numbers". 13. Authors' Addresses Himanshu Shah 35 Nagog Park, Acton, MA 01720 Email: firstname.lastname@example.org Eric Rosen Cisco Systems 1414 Massachusetts Avenue, Boxborough, MA 01719 Email: email@example.com Waldemar Augustyn Email: firstname.lastname@example.org Giles Heron Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt Tellabs 24-28 Easton Steet High Wycombe Bucks HP11 1NT UK Email: email@example.com Sunil Khandekar and Vach Kompella Email: firstname.lastname@example.org Email: email@example.com Toby Smith Network Appliance, Inc. 800 Cranberry Woods Drive Suite 300 Cranberry Township, PA 16066 EMail: firstname.lastname@example.org Arun Vishwanathan Force10 Networks 1440 McCarthy Blvd., Milpitas, CA 95035 Email: email@example.com Andrew G. Malis Tellabs 1415 West Diehl Road Naperville, IL 60563 EMail: Andy.Malis@tellabs.com Steven Wright Bell South Corp Email: firstname.lastname@example.org Vasile Radoaca Email: email@example.com 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. Draft-ietf-l2vpn-arp-mediation-08.txtDraft-ietf-l2vpn-arp-mediation-09.txt 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. 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