Internet Engineering Task Force T. Przygienda/P.
DrozDroz/R. Haas INTERNET DRAFT Bell Labs/IBM 5 March 199815 June 1999 OSPF over ATM and Proxy PAR <draft-ietf-ospf-atm-01.txt><draft-ietf-ospf-atm-02.txt> Status of This Memo This document is an Internet Draft,Draft and can be found as draft-ietf-ospf-atm-01.txtis in any standard internet drafts repository.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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material, or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the I-D abstract listing contained in each Internet Draft directory to learn theThe list of current statusInternet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of this or any other Internet Draft.Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This draft specifes for OSPF implementors and users mechanisms describing how the protocol operates in ATM networks over PVC and SVC meshes with the presence of Proxy PAR. These recommendations do not require any protocol changes and allow for simpler, more efficient and cost-effective network designs. It is recommended that OSPF implementations should be able to support logical interfaces, each consisting of one or more virtual circuits and used either as numbered logical point-to-point links (one VC) orVC), logical NBMA networks (more than one VC) or point-to-multipoint networks (more than one VC), where a solution simulating broadcast interfaces is not appropriate. PAR can help to distribute across the ATM cloud configuration set-up and changes of such interfaces when OSPF capable routers are reconfigured on(re-)configured. Proxy-PAR can in turn be used to exchange this information between the ATM cloud and the routers connected to it. Internet Draft OSPF over ATM cloud.and Proxy PAR 15 June 1999 1. Introduction Proxy-PAR and PAR have been accepted as standards by the ATM Forum in January 1999 [Dro99 ]. A more complete overview of Proxy PAR than in the section below is given in [PD99 ]. 1.1. Introduction to Proxy PAR PNNI Augmented Routing (PAR) [For98]Proxy PAR [Dro99 ] is an extension allowing for different ATM attached devices (like routers) to PNNI [AF96b] routing to allowinteract with PAR capable switches and query information about non-ATM services to be distributedwithout executing PAR themselves. The Proxy PAR client side in anthe ATM network as partattached device is much simpler in terms of the PNNI topology. The contentimplementation complexity and format of the information is specified bymemory requirements than a complete PAR but is transparent to PNNI routing. A PAR-capable device, one that implementsprotocol stack (which includes the full PNNI [AF96b ] protocol stack) and theshould allow easy implementation in e.g. existing IP routers. Additionnaly, clients can use Proxy PAR extension, is ableto create PAR PTSEs that describe theregister different non-ATM services located on or behind that device. Because this information is flooded by PNNI routing, PAR-capable devices are also ableand protocols they support. Proxy PAR has consciously not been included as part of ILMI [AF96a ] due to examinethe complexity of PAR PTSEsinformation passed in the topology databaseprotocol and the fact that were originated by other nodes to obtain information on desired services reachable through the ATM network. An important example of how PAR can be used is provided by overlay routing on ATM backbones. If the routers are PAR-capable, they can create PTSEs to advertise the routing protocol supported on the given interface (e.g., OSPF, RIP, or BGP), along with their IP address and subnet, and other protocol-specific details. The PAR-capable routers can also automatically learn about "compatible" routers (e.g., supporting the same routing protocol, in the same IP subnet) active in the same ATM network. In this manner the overlay routing network can be established automatically on an ATM backbone. The mechanism is dynamic, and does not require configuration. One potential drawback of PAR is that a device must implement PNNI in order to participate. Therefore an additional set of optional protocols called Proxy PAR has been defined to allow a client that is not PAR-capable to interact with a server that is PAR-capable and thus obtain the PAR capabilities. The server acts as a proxy for the client in the operation of PAR. The client is able to register its own services, and query the server to obtain information on compatible services available in the ATM network. A key feature of PAR and Proxy PAR is the ability to provide VPN support in a simple yet very effective manner. All PAR information is tagged with a VPN ID and can therefore be filtered on that basis. This can be used for example, in a service provider network. Each customer can be provided with a unique VPN ID that is part of all Proxy PAR registrations and queries. Usage of the correct VPN ID can easily be enforced at the Proxy PAR server. In this way the services of a given customer will be available only to clients in that customer's network. 1.1.1. Overview of PNNI Augmented Routing (PAR) PNNI Augmented Routing (PAR) is an extension to PNNI to allow the flooding of information about non-ATM devices. PAR uses a new PTSE type to carry this non-ATM-related information. The current version of PAR specifies IGs for the flooding of IPv4-related protocol information such as OSPF or BGP. In addition PAR also allows the use of the System Capabilities IG, which can be used to carry proprietary or experimental information. PAR supports extensive filtering possibilities, which allow the implementation of virtual private networks (VPN). As PAR is a PNNI extension, it can reuse existing PNNI routing level scopes. In addition, PAR provides filtering in terms of a VPN ID, IP address, including a subnet mask, as well as protocol flags. The correct filtering according to these parameters is part of a PAR implementation. 1.1.2. Overview of Proxy PAR Proxy PAR is a protocol that allows for different ATM attached devices to interact with PAR-capable switches and obtain information about non-ATM services without executing PAR themselves. The client side is much simpler in terms of implementation complexity and memory requirements than a complete PAR instance and should allow easy implementation in, for example, existing IP routers. Clients can use Proxy PAR to register different non-ATM services and protocols they support. This protocol has deliberately not been included as part of ILMI [AF96a] owing to the complexity of PAR information passed in the protocol and the fact that it is intended for integration of non-ATM protocols andit is intended for integration of non-ATM protocols and services only. A device executing Proxy PAR does not necessarily need to execute ILMI or UNI signaling, although this willnormally will be the case. The protocol in itself does not specify how the distributed service registration and data delivered to the client areis supposed to drivebe driving other protocols. For example,protocols so e.g. OSPF routers finding themselves through Proxy PAR could use this information to formin a Classical IP over ATM [ML98 ] fashion, forming a full mesh of P2P VCs and communicate using RFC1483 [Hei93] encapsulation. In terms of the discovery ofpoint-to-point connections to interact with each other devices such as IP routers, Proxy PAR is an alternativeto simulate broadcast interfaces. For the same purpose LANE [AF95][AF95 ] or MARS [Arm96]. It is expected that the guidelines defining how[Arm96 ] could be used. As a certain protocol can make use of Proxy PAR and PAR should come from the group or standardization body that is responsible for the particular protocol. PAR andby-product, Proxy PAR have the ability tocould provide the ATM address resolution for IP attached devices,devices but such resolution can alsobe achieved by other protocols under specification inat the IETF as well, e.g. [CH97a, CH97b]. However, the main purpose of[Col98 ]. And last but not least, it should be mentioned here that the protocol coexists with and complements the ongoing work in IETF on server detection via ILMI extensions [Dav99a , Dav99b , Dav99c ]. 1.1.1. Proxy PAR Scopes Any Proxy PAR registration is carried only within a defined scope that is set during registration and is equivalent to allowthe automatic detection of devicesPNNI routing level. Since no assumptions except scope values can be made about the information distributed (e.g. IP addresses bound to NSAPs Przygienda, Droz, Haas Expires 15 December 1999 [Page 2] Internet Draft OSPF over anATM cloudand Proxy PAR 15 June 1999 are not assumed to be aligned with them in any respect such as encapsulation or functional mapping), registration information cannot be summarized. This makes a distributed fashion, not relyingcareful handling of scopes necessary to preserve the scalability. More details on a broadcast facility. Finally, it should be mentioned thatthe protocol complements and coexists with server detection via ILMI extensions.usage of scope can be found in [PD99 ]. 1.2. Introduction to OSPF OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP) and described in [Moy94, Moy97][Moy98 ] from which most of the following paragraphs has been taken almost literally. OSPF distributes routing information between routers belonging to a single Autonomous System. The OSPF protocol is based on link-state or SPF technology. It was developed by the OSPF working group of the Internet Engineering Task Force. It has been designed expressly for the TCP/IP internet environment, including explicit support for IP subnetting, and the tagging of externally-derived routing information. OSPF also utilizes IP multicast when sending/receiving the updates. In addition, much work has been done to produce a protocol that responds quickly to topology changes, yet involves small amounts of routing protocol traffic. To cope with the needs of NBMA and demand circuits capable networks such as Frame Relay or X.25, [Moy95][Moy95 ] has been made available that standardizes extensions to the protocol allowing for efficient operation over on-demand circuits. OSPF supports three types of networks today: - Point-to-point networks: A network that joins a single pair of routers. Point- to-point networks can either be numbered or unnumbered in the latter case the interfaces do not have IP addresses nor masks. Even when numbered, both sides of the link do not have to agree on the IP subnet. - Broadcast networks: Networks supporting many (more than two) attached routers, together with the capability to address a single physical message to all of the attached routers (broadcast). Neighboring routers are discovered dynamically on these netsnetworks using OSPF'sthe OSPF Hello Protocol. The Hello Protocol itself takes advantage of the broadcast capability. The protocol makes further use of multicast capabilities, if they exist. An Ethernet is an example of a broadcast network. Przygienda, Droz, Haas Expires 15 December 1999 [Page 3] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 - Non-broadcast networks: Networks supporting many (more than two) attached routers, but having no broadcast capability. Neighboring routers are maintained on these nets using OSPF's Hello Protocol. However, due to the lack of broadcast capability, some configuration information is necessary for the correct operation of the Hello Protocol. On these networks, OSPF protocol packets that are normally multicast need to be sent to each neighboring router, in turn. An X.25 Public Data Network (PDN) is an example of a non-broadcast network. OSPF runs in one of two modes over non-broadcast networks. The first mode, called non-broadcast multi-access (NBMA), simulates the operation of OSPF on a broadcast network. The second mode, called Point-to-MultiPoint, treats the non-broadcast network as a collection of point-to-point links. Non-broadcast networks are referred to as NBMA networks or Point-to-MultiPoint networks, depending on OSPF's mode of operation over the network. 2. OSPF over ATM 2.1. Model Contrary to broadcast-simulation based solutions such as LANE [AF95][AF95 ] or RFC1577 [Lau94],Classical IP over ATM [ML98 ], this RFCdocument elaborates on how to handle virtual OSPF interfaces over ATM such as NBMA, point-to-multipoint or point-to-point and allow for their auto-configuration in presence of Proxy PAR. One advantage is the circumvention of server solutions that often present single points of failure or hold large amounts of configuration information. The other main benefit is the possibility to execute OSPF on top of partially meshed VC topologies.NBMA and point-to-multpoint ATM networks, and still benefit from the automatic discovery of OSPF neighbors. As opposed to broadcast networks, broadcast-simulation based networks (like LANE or Classical IP over ATM), and point-to-point networks, where an OSPF router dynamically discovers its neighbors by sending Hello packets to the AllSPFRouters multicast address, this is not the case on NBMA and point-to-multipoint networks. On NBMA networks, the list of all other attached routers to the same NBMA network has to be manually configured or discovered by some other means: Proxy PAR allows to automate this configuration. Also on point-to-multipoint networks, the set of routers that are directly reachable must be configured: it can be dynamically discovered by Proxy PAR or through mechanisms like Inverse ATMARP. In an ATM network, (see 8.2 in [ML98 ]) Inverse ATMARP can be used to discover the Przygienda, Droz, Haas Expires 15 December 1999 [Page 4] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 IP address of the router at the remote end of a given PVC, whether or not its ATM address is known. But Inverse ATMARP does not return for instance whether the remote router is running OSPF, as opposed to Proxy PAR. Parallel to [dR94][dR94 ] that describes the recommended operation of OSPF over Frame Relay networks, a similar model is assumed where the underlying ATM network can be used to model single VCs as point-to-point interfaces or collections of VCs can be accessedas annon-broadcast interfaceinterfaces, whether in NBMA or point-to-multipoint mode. Such a VC or collection of VCs is called a logical interface and specified through its type (either point-to-point, NBMA or point-to-point), IP instance (presenting an incarnation of IP with its own address spaces),NBMA or point-to-multipoint), VPN ID (the Virtual Private Network to which interface belongs), address and mask. Layer 2 specific configuration such as address resolution method, class and quality of service of used circuits and other must be also included. As logical consequence thereof, a single, physical interface could encompass multiple IP subnets or even multiple, independent IP instances.multiple VPNs. In contrary to layer 2 and IP addressing information, when running Proxy PAR, most of the OPSFOSPF information needed to operate such a logical interface does not have to be configured into routers statically but can be provided through Proxy PAR queries. This allows for much more dynamic configuration of VC meshes in OSPF environments than e.g. in Frame Relay solutions. 2.2.Proxy PAR queries can also be issued with a subnet address set to 0.0.0.0, instead of a specific subnet address. This type of query returns information on all OSPF routers available in all subnets, within the scope specified in the query. This can be used for instance when the IP addressing information has not been configured. 2.2. Configuration Interactionof OSPF interfaces with Proxy PAR To achieve the goal of simplification of VC mesh reconfiguration, Proxy PAR allows the router to learn automatically most of the configuration that has to be provided to OSPF. Non-broadcast and point-to-point interface information can be learned across an ATM cloud as described in the ongoing sections. It is up to the implementation to possibly allow for a mixture of Proxy PAR autoconfiguration and manual configuration of neighbor information. Moreover, manual configuration could e.g. override or complement information derived from a proxyProxy PAR client. Additionally, OSPF extensions to handle on-demand circuits [Moy95][Moy95 ] can be used to allow for graceful tearing down of VCs not carrying any OSPF traffic over Przygienda, Droz, Haas Expires 15 December 1999 [Page 5] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 prolonged periods of time. The different interactions are described in sections 2.2.1, 2.2.2 and 2.2.3. Even after autoconfiguration of interfaces has been provided, the problem of VC setups in an ATM network is unsolved since none of the normally used mechanisms such as RFC1577 [Lau94]Classical IP [ML98 ] or LANE [AF95][AF95 ] are assumed to be present. Section 2.5 describes the behavior of OSPF routers necessary to allow for router connectivity necessary.connectivity. 2.2.1. Autoconfiguration of Non-Broadcast Multiple-Access (NMBA) Interfaces Proxy PAR allows to autoconfigure the list of all routers residing on the same IP network in the same IP instanceVPN by simply querying the Proxy PAR server. Each router can easily obtain the list of all OSPF routers on the same subnet with their router priorities and corresponding ATM address bindings.addresses. This is the precondition for OSPF to work properly across such logical NBMA interfaces. Note that thethis memberlist, when learned through Proxy PAR queries, can dynamically change with PNNI (in)stability and general ATM network behavior. It maybe preferable for an implementation to withdraw list membership (de-register itself as an OSPF router) e.g. much slower than detect new members.members (done by querying). Relying on OSPF mechanism to discover lack of reachability in the overlaying logical IP network could alleviate the risk of thrashing DR elections and excessive information flooding. Once the DR registration is completed and the router has not been elected DR or BDR, an implementation of [Moy95][Moy95 ] can ignore the fact that all routers on the specific NBMA subnet are available in its configuration since it only needs to maintain VCs to the DR and BDR. Traditionally, router configuration for a NBMA network provides the list of all neighboring routers to allow for proper protocol operation. For stability purposes, the user may choose to provide a list of neighbors through such static means but additionally enable the operation of Proxy PAR protocol to complete the list. It is left to specific router implementations whether the manual configuration is used in addition to the information provided by Proxy PAR, used as filter of the dynamic information or whether a concurrent mode of operation is prohibited. In any case it should be obvious that allowing for more flexibility may facilitate operation but provides more possibilities for misconfiguration as well. Przygienda, Droz, Haas Expires 15 December 1999 [Page 6] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 2.2.2. Autoconfiguration of Point-to-Multipoint Interfaces Point-to-Multipoint interfaces in ATM networks only make sense if no VCs can be dynamically set up since an SVC-capable ATM network normally presents a NBMA cloud to OSPF. This is e.g. the case if the intended use of the network is only to executeOSPF in presenceexecutes over a network composed of a partial PVC or SPVC mesh or pre-determined SVC meshes. Such a collectionnetwork could be modeled using the point-to-multipoint OSPF interface and the neighbor detection could be provided by Proxy PAR or other means. In the Proxy PAR case the router queries for all OSPF routers on the same network in the same IP instanceVPN but it installs in the interface configuration only routers that are already reachable through presetexisting PVCs. The underlying assumption is that a router understandsknows the remote NSAPATM address of a PVC and can compare it with appropriate Proxy PAR registrations. If the remote NSAPATM address of the PVC is unknown, alternative autodiscovery mechanisms have toit can be used e.g. inversediscovered by mechanisms like Inverse ARP [BB92, LH96].[TB99 ]. Proxy PAR provides a true OSPF neighbor detection mechanism, whereas a mechanism like Inverse ARP only returns addresses of directly reachable routers (which are not necessarily running OSPF), in the point-to-multipoint environment. 2.2.3. Autoconfiguration of Numbered Point-to-Point Interfaces OSPF point-to-point links do not necessarily have an IP address assigned and even when having one, the mask is undefined. As a precondition to successfully register a service with Proxy PAR, IP address and mask is required. Therefore, if a router desires to use Proxy PAR to advertise the local end of a point-to- pointpoint-to-point link to the router it intends to form an adjacency with, an IP address has to be provided and a netmask set or a default of 255.255.255.254 (this gives as the default case a subnet with 2 routers on it) assumed. To allow the discovery of the remote end of the interface, IP address of the remote side has to be provided and a netmask set or a default of 255.255.255.254 assumed. Obviously the discovery can only be successfull when both sides of the interface are configured with the same network mask and are within the same IP network. The situation where more than two possible neighbors are discovered through queries and the interface type is set to point-to-point presents a configuration error. Sending multicast Hello packets on the point-to-point links allows to automatically discover OSPF neighbors. On the other hand, using Proxy PAR instead avoids sending Hello messages to routers which are not necessarily running OSPF. Przygienda, Droz, Haas Expires 15 December 1999 [Page 7] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 2.2.4. Autoconfiguration of Unnumbered Point-to-Point Interfaces For reasons given already in [dR94][dR94 ] using unnumbered point-to-point interfaces with Proxy PAR is not a very attractive alternative since the lack of an IP address prevents efficient registration and retrieval of configuration information. Relying on the numbering method based on MIB entries generates conflicts with the dynamic nature of creation of such entries and is beyond the scope of this work. 2.3. Registration of OSPF interfaces with Proxy PAR Interaction with OSPF ConfigurationTo allow other routers to discover an OSPF interface automatically, the IP address, mask, Area ID, interface type and router priority information given must be registered with the Proxy PAR server at an appropriate scope. A change in any of these parameters has to force a reregistration with Proxy PAR. It should be emphasized here that since the registration information can be used by other routers to resolve IP addresses against NSAPs as explained in section 2.4 already, whole IP address of the router must be registered. It is not enough to just indicate the subnet up to the mask length but all address bits must be provided. 2.3.1. Registration of Non-Broadcast Multiple-Access Interfaces For an NBMA interface the appropriate parameters are available and can be registered through Proxy PAR without further complications. 2.3.2. Registration of Point-to-Multipoint Interfaces In case of a point-to-multipoint interface the router registers its information in the same fashion as in the NBMA case except that the interface type is modified accordingly. 2.3.3. Registration of Numbered Point-to-Point Interfaces In case of point-to-point numbered interfaces the address mask is not specified in the OSPF configuration. If the router has to use Proxy PAR to advertise its capability, a mask must be defined or a default value of 255.255.255.254 used. Przygienda, Droz, Haas Expires 15 December 1999 [Page 8] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 2.3.4. Registration of Unnumbered Point-to-Point Interfaces Due to the lack of a configured IP address and difficulties generated by this fact as described earlier, registration of unnumbered point-to-point interfaces is not covered in this document. 2.4. IP address to NSAP Resolution Using Proxy PAR As a byproduct of Proxy PAR presence, an OSPF implementation could use the information in registrations for the resolution of IP addresses to ATM NSAPs on a subnet without having to use static data or mechanisms such as ATMARP [LH96].[ML98 ]. This again should allow for drastic simplification of number of mechanisms involved in operation of OSPF over ATM to provide an IP overlay. 2.5. Connection Setup Mechanisms This sections describes OSPF behavior in an ATM network under different assumptions in terms of signaling capabilities and preset connectivity. 2.5.1. OSPF in PVC Environments In environments where only partial PVCs (or SPVCs) meshes are available and modeled as point-to-multipoint interfaces, the routers see reachable routers through autodiscovery provided by Proxy PAR. This leads to expected OSPF behavior. In cases where a full mesh of PVCs is present, such an interfacea network should preferably be modeled as broadcast and Proxy PAR discovery should be superfluous.NBMA. 2.5.2. OSPF in SVC Environments In SVC-capable environments the routers can initiate VCs after having discovered the appropriate neighbors, preferably driven by the need to send data such as Hello-packets. Since this can lead to race conditions where both sides can open a VC and it is desirable to minimize this valuable resource, if the router with lower Router IDrouter with lower Router ID detects that the VC initiated by the other side is bidirectional, it is free to close its own VC and use the detected one. Observe that this behavior operates correctly in case OSPF over Demand Circuits extensions are used [Moy95 ] over SVC capable interfaces. Przygienda, Droz, Haas Expires 15 December 1999 [Page 9] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 + + + | +---+ | | +--+ |---|RTA|---| +-------+ | +--+ |H1|---| +---+ | | ATM | |---|H2| +--+ | | +---+ | Cloud | +---+ | +--+ |LAN Y |---|RTB|-------------|RTC|---| + | +---+ | PPAR | +---+ | + +-------+ + Figure 1: Simple Topology with Router B and Router C operating across NBMA ATM interfaces with Proxy PAR detects that the VC initiated by the other side is bidirectional, it is free to close its own VC and use the detected one. Observe that this behavior operates correctly in case OSPF over Demand Circuits extensions are used [Moy95] over SVC capable interfaces.The existence of VCs used for OSPF exchanges is orthogonal to the number and type of VCs the router chooses to use within the logical interface to forward data to other routers. OSPF implementations are free to use any of these VCs (1) to send packets if their endpoints are adequate and must accept hello packets arriving on any of the VCs belonging to the logical interface even if OSPF operating on such an interface is not aware of their existence. An OSPF implementation may not accept or close connections being initiated by another router that has either not been discovered by Proxy PAR or whose Proxy PAR registration is indicating that it is not adjacent. As an example consider the topology in figure 2.5.2 where router RTB and RTC are connected to a common ATM cloud offering Proxy PAR services. Assuming that RTB's OSPF implementation is aware of SVCs initiated on the interface and RTC only makes minimal use of Proxy PAR information the following sequence could develop illustrating some of the cases described above: 1. RTC and RTB register with ATM cloud as Proxy PAR capable and discover each other as adjacent OSPF routers. ___________________________________________ 1. in case they are aware of their existence2. RTB sends a hello which forces it to establish a SVC connection to RTC. ___________________________________________ 1. in case they are aware of their existence Przygienda, Droz, Haas Expires 15 December 1999 [Page 10] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 3. RTC sends a hello to RTB but disregards the already existing VC and establishes a new VC to RTB to deliver the packet. 4. RTB sees a new bi-directional VC and assuming here that RTC's OSPF Id is higher, closes the VC originated in step 2. 5. Host H1 sends data to H2 and RTB establishes a new data SVC between itself and RTC. 6. RTB sends a Hello to RTC and decides to do it using the newly establish data SVC. RTC must accept the hello despite the minimal implementation. 3. Acknowledgments Comments and contributions from several sources, especially Rob Coltun, Doug Dykeman and John Moy are included in this work. 4. Security Consideration Several aspects are to be considered when talking about security of operating OSPF over ATM and/or Proxy PAR. The security of registered information handed to the ATM cloud must be guaranteed by the underlying PNNI protocol. Extensions to PNNI are available and given their implementation spoofing of registrations and/or denial-of-service issues can be addressed [PB97].[PB97 ]. The registration itself through proxy PAR is not secured and appropriate mechanisms are for further study. However, even if the security at the ATM layer is not guaranteed, OSPF security mechanisms can be used to verify that detected neighbors are authorized to interact with the entity discovering them. References [AF95] ATM-Forum. LAN Emulation over ATM 1.0. ATM Forum af-lane-0021.000, January 1995. [AF96a] ATM-Forum. Interim Local Management Interface (ILMI) Specification 4.0. ATM Forum 95-0417R8, June 1996. [AF96b] ATM-Forum. Private Network-Network Interface Specification Version 1.0. ATM Forum af-pnni-0055.000, March 1996. Przygienda, Droz, Haas Expires 15 December 1999 [Page 11] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 [Arm96] G. Armitage. Support for Multicast over UNI 3.0/3.1 based ATM Networks,networks, RFC 2022. Internet Engineering Task Force, November 1996. [BB92] T. Bradley and C. Brown. Inverse Address Resolution Protocol,[Col98] R. Coltun. The OSPF Opaque LSA Option, RFC 1293.2370. Internet Engineering Task Force, January 1992. [CH97a] R. Coltun and J. Heinanen. Opaque LSA in OSPF.July 1998. [Dav99a] M. Davison. ILMI-Based Server Discovery for ATMARP, RFC 2601. Internet Draft, 1997. [CH97b] R. Coltun and J. Heinanen. The OSPF Address Resolution Advertisement Option.Engineering Task Force, June 1999. [Dav99b] M. Davison. ILMI-Based Server Discovery for MARS, RFC 2602. Internet Draft, 1997.Engineering Task Force, June 1999. [Dav99c] M. Davison. ILMI-Based Server Discovery for NHRP, RFC 2603. Internet Engineering Task Force, June 1999. [dR94] O. deSouza and M. Rodrigues. Guidelines for Running OSPF Over Frame Relay Networks, RFC 1586. Internet Engineering Task Force, March 1994. [For98] ATM Forum.[Dro99] P. Droz. PNNI Augmented Routing (PAR) Version 1.0. ATM Forum PNNI-RA-PAR-01.04, 1998. [Hei93]af-ra-0104.000, January 1999. [ML98] J. Heinanen. Multiprotocol Encapsulation over ATM Adaptation Layer 5, RFC 1483. Internet Engineering Task Force, July 1993. [Lau94]Halpern M. Laubach. Classical IP and ARP over ATM, RFC 1577. Internet Engineering Task Force, January 1994. [LH96] M. Laubach and J. Halpern. Classical IP and ARP over ATM. Internet Draft, 1996. [Moy94] J. Moy. OSPFv2, RFC 1583.2225. Internet Engineering Task Force, March 1994.April 1998. [Moy95] J. Moy. Extending OSPF to Support Demand Circuits, RFC 1793. Internet Engineering Task Force, April 1995. [Moy97][Moy98] J. Moy. OSPFv2,OSPF Version 2 - RFC 2178.2328. Internet Engineering Task Force, July 1997.April 1998. [PB97] T. Przygienda and C. Bullard. Baseline Text for PNNI Peer Authentication and Cryptographic Data Integrity. ATM Forum 97-0472, July 1997. [PD99] T. Przygienda P. Droz. Proxy PAR. Internet Draft draft-ietf-ion-proxypar-arch-01, February 1999. [TB99] A. Malis T. Bradley, C. Brown. Inverse Address Resolution Protocol, RFC 2390. Internet Engineering Task Force, September 1999. Przygienda, Droz, Haas Expires 15 December 1999 [Page 12] Internet Draft OSPF over ATM and Proxy PAR 15 June 1999 Authors' Addresses Tony Przygienda Bell Labs, Lucent Technologies 101 Crawfords Corner Road Holmdel, NJ 07733-3030 email@example.com Patrick Droz IBM Research Division Saumerstrasse 4 8803 Ruschlikon Switzerland firstname.lastname@example.org Robert Haas IBM Research Division Saumerstrasse 4 8803 Ruschlikon Switzerland email@example.com Przygienda, Droz, Haas Expires 15 December 1999 [Page 13]