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Network Working Group                                         J. LucianiRequest for Comments: 2336                                  Bay NetworksCategory: Informational                                        July 1998Classical IP and ARP over ATM to NHRP TransitionStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   This document describes methods and procedures for the graceful   transition from an ATMARP LIS[1] to an NHRP LIS[2] network model over   ATM.1. Introduction   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this   document, are to be interpreted as described in [6].   ATMARP defines an initial application of classical IP and ARP in an   ATM network environment configured as a LIS[1].  ATMARP only   considers application of ATM as a direct replacement for the "wires"   and local LAN segments connecting IP end-stations and routers   operating in the "classical" LAN-based paradigm.   The NBMA Next Hop Resolution Protocol (NHRP) allows a source station   (a host or router), wishing to communicate over a Non-Broadcast,   Multi-Access (NBMA) subnetwork, to determine the internetworking   layer addresses and NBMA addresses of suitable "NBMA next hops"   toward a destination station. If the destination is connected to the   NBMA subnetwork and direct communication is administratively allowed,   then the NBMA next hop is the destination station itself.  Otherwise,   the NBMA next hop is the egress router from the NBMA subnetwork that   is "nearest" to the destination station.  For the purposes of this   document, the NBMA network is of type ATM.Luciani                      Informational                      [Page 1]

RFC 2336         Classical IP and ARP over ATM to NHRP         July 1998   It is reasonable to expect that ATMARP Clients and NHRP Clients will   initially coexist within a LIS.  Thus, it is necessary to define a   graceful transition, including a period of coexistance, from the use   of ATMARP to the use of NHRP for address resolution in the LIS   [1][2]. In short, NHSs will be required to respond to ATMARP Client   queries in a fashion which will permit continued use of the ATMARP   Client within the LIS during the ATMARP to NHRP transition period.   Note that this document places no protocol requirements upon   ATMARP[1] servers.   For the following, it will be assumed that the reader is familiar   with the terminology as described in [1][2][3].2. Service Requirements   If NHRP is to be used in a LIS then only NHSs will be used in the   LIS; that is, there will not be a mixture of NHSs and ATMARP servers   within the same LIS.  Since ATMARP servers will not be able to   understand NHCs and since, as described below, NHSs will respond to   ATMARP Clients, this is a reasonable simplifying restriction.   This document will only address SVC based environments and will not   address PVC environments.  This document will refer only to ATM AAL5   as the NBMA and IP as the protocol layer since ATMARP only addresses   these protocols.2.1 NHRP Server Requirements   If NHRP Servers (NHS) are to be deployed in a LIS which contains both   ATMARP Clients and NHRP Clients then NHSs MUST respond to   ATMARP_Requests sent by ATMARP Clients in the same fashion that an   ATMARP Server would respond as described in [1].  To do this, the NHS   MUST first recognize the LLC/SNAP ATMARP code point with LLC=0xAA-   AA-03, OUI=0x00-00-00, and ethertype=0x08-06.  Further, the NHS MUST   recognize the packet formats described in Section 8.7 of [1].   However, since this document does not extend to PVC environments,   NHSs MUST only receive/respond to values of ar$op of 1,2,10   (Decimal).  If an NHS receives an ATMARP message with ar$op values   other than those previously noted then the NHS MUST discard the   packet and MUST NOT take any further action.   When an NHS receives a valid (as defined in the previous paragraph)   ATMARP_Request packet, the NHS MUST follow the rules described in   Section 8.4 of [1] with the following additional processing:Luciani                      Informational                      [Page 2]

RFC 2336         Classical IP and ARP over ATM to NHRP         July 1998     1) When an ATMARP_Request causes a new table entry in the NHS for        an ATMARP Client, that table entry MUST be marked as being of        type "ATMARP" so that it can be differentiated from an NHRP        sourced entry.     2) An ATMARP_Request MUST NOT cause an ATMARP_Reply to be sent if        that ATMARP_Request contains an off-LIS protocol address.  This        should never happen because the IP stack on the requesting        machine should automatically send the packet to the default        router.  If this does occur then the ATMARP_Request MUST cause        an ATMARP_NAK to be sent to the originator.   In [1], an ATMARP_Request packet also serves as a   registraion/registration-update packet which would cause a server to   add an entry to a server's cache or to update a previously existing   entry.  When an NHS receives an ATMARP_Request which causes the   creation of a new cache entry in the NHS or updates an existing entry   then that cache entry will have a holding time of 20 minutes (this is   the default value in [1]).   An NHS receiving an NHRP Resolution Request MUST NOT send a positive   NHRP Resolution Reply for a station which registered via ATMARP if   the station sending the NHRP Resolution Request is outside the LIS of   the station which registered itself via ATMARP.  This is because the   station which registered via ATMARP is almost certainly not prepared   to accept a cut-through.   When this occurs, the replying NHS must   send NHRP Resolution Reply which contains a CIE code of "4 -   Administratively Prohibited" as described in [2].  This type of reply   does not preclude the station sending the NHRP Resolution Request   from sending its data packets along the routed path but it does   preclude that station from setting up a cut-through VC.2.2 Multi-server environments   Since NHRP servers may work in a multi-server environment on a per   LIS basis during the transition, it is necessary to know how cache   synchronization occurs. These rules may be found in [5].3. Security Considerations   Not all of the security issues relating to IP over ATM are clearly   understood at this time, due to the fluid state of ATM   specifications, newness of the technology, and other factors.Luciani                      Informational                      [Page 3]

RFC 2336         Classical IP and ARP over ATM to NHRP         July 1998   It is believed that ATM and IP facilities for authenticated call   management, authenticated end-to-end communications, and data   encryption will be needed in globally connected ATM networks.  Such   future security facilities and their use by IP networks are beyond   the scope of this memo.   There are known security issues relating to host impersonation via   the address resolution protocols used in the Internet [4].  No   special security mechanisms have been added to ATMARP.  While NHRP   supplies some mechanisms for authentication, ATMARP does not.  Since   any security mechanism is only as good as its weakest link, it should   be assumed that when NHRP and ATMARP exist with a given LIS, the   security of a combination is only as good as that supplied by ATMARP.References   [1] Laubach, M. and J. Halpern, "Classical IP and ARP over ATM",RFC2225, April 1998.   [2] Luciani, J., Katz, D., Piscitello, D., Cole, B. and N. Doraswamy,   "NBMA Next Hop Resolution Protocol (NHRP)",RFC 2332, April 1998.   [3] Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy, "Server   Cache Synchronization Protocol (SCSP)",RFC 2334, April 1998.   [4] Security Problems in the TCP/IP Protocol Suite, Bellovin, ACM   Computer Communications Review, Vol. 19, Issue 2, pp. 32-48, 1989.   [5] Luciani, J., "A Distributed NHRP Service Using SCSP",RFC 2335,   April 1998.   [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement   Levels",RFC 2119, March 1997.Acknowledgments   Thanks to Andy Malis for his input on this draft.Author's Addresses   James V. Luciani   Bay Networks   3 Federal Street   Mail Stop: BL3-03   Billerica, MA 01821   Phone:  +1 978 916 4734   Email:  luciani@baynetworks.comLuciani                      Informational                      [Page 4]

RFC 2336         Classical IP and ARP over ATM to NHRP         July 1998Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS 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.Luciani                      Informational                      [Page 5]