Network Working Group J. Renwick Request for Comments: 2067 NetStar, Inc. Category: Standards Track January 1997 Obsoletes: 1374 IP over HIPPI Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract ANSI Standard X3.218-1993 (HIPPI-LE[3]) defines the encapsulation of IEEE 802.2 LLC PDUs and, by implication, IP on HIPPI. ANSI X3.222- 1993 (HIPPI-SC[4]) describes the operation of HIPPI physical switches. The ANSI committee responsible for these standards chose to leave HIPPI networking issues largely outside the scope of their standards; this document describes the use of HIPPI switches as IP local area networks. This memo is a revision of RFC 1374, "IP and ARP on HIPPI", and is intended to replace it in the Standards Track. RFC 1374 has been a Proposed Standard since November, 1992, with at least 10 implementations of IP encapsulation and HIPPI switch discipline. No major changes to it are required. However, the ARP part of RFC 1374 has not had sufficient implementation experience to be advanced to Draft Standard. The present document contains all of RFC 1374 except for the description ARP, which has been moved into a separate document. TABLE OF CONTENTS 1 Introduction............................................. 2 2 Scope.................................................... 3 2.1 Changes from RFC 1374.............................. 3 2.2 Terminology........................................ 4 3 Definitions.............................................. 4 4 Equipment................................................ 5 5 Protocol ................................................ 7 5.1 Packet Format...................................... 7 5.2 48 bit Universal LAN MAC addresses................. 11 5.3 I-Field Format..................................... 12 Renwick Standards Track [Page 1] RFC 2067 IP over HIPPI January 1997 5.4 Rules For Connections.............................. 13 5.5 MTU................................................ 15 6 Camp-on ................................................. 16 7 Path MTU Discovery....................................... 17 8 Channel Data Rate Discovery.............................. 17 9 Performance.............................................. 18 10 Sharing the Switch....................................... 20 11 References............................................... 21 12 Security Considerations.................................. 21 13 Author's Address......................................... 21 14 Appendix A -- HIPPI Basics............................... 22 15 Appendix B -- How to Build a Practical HIPPI LAN......... 27 1 Introduction The ANSI High-Performance Parallel Interface (HIPPI) is a simplex data channel. Configured in pairs, HIPPI can send and receive data simultaneously at nearly 800 megabits per second. (HIPPI has an equally applicable 1600 megabit/second option.) Between 1987 and 1991, the ANSI X3T9.3 HIPPI working group drafted four documents that bear on the use of HIPPI as a network interface. They cover the physical and electrical specification (HIPPI-PH [1]), the framing of a stream of bytes (HIPPI-FP [2]), encapsulation of IEEE 802.2 LLC (HIPPI-LE [3]), and the behavior of a standard physical layer switch (HIPPI-SC [4]). HIPPI-LE also implies the encapsulation of Internet Protocol[5]. The reader should be familiar with the ANSI HIPPI documents, copies of which are archived at the site "ftp.network.com" in the directory "hippi", and may be obtained via anonymous FTP. HIPPI switches can be used to connect a variety of computers and peripheral equipment for many purposes, but the working group stopped short of describing their use as Local Area Networks. This memo takes up where the working group left off, using the guiding principle that except for length and hardware header, Internet datagrams sent on HIPPI should be identical to the same datagrams sent on a conventional network, and that any datagram sent on a conventional 802 network[6] should be valid on HIPPI. Renwick Standards Track [Page 2] RFC 2067 IP over HIPPI January 1997 2 Scope This memo describes the HIPPI interface between a host and a crosspoint switch that complies with the HIPPI-SC draft standard. Issues that have no impact on host implementations are outside the scope of this memo. Host implementations that comply with this memo are believed to be interoperable on a network composed of a single HIPPI-SC switch. They are also interoperable on a simple point-to- point, two-way HIPPI connection with no switch between them. They may be interoperable on more complex networks as well, depending on the internals of the switches and how they are interconnected; however, these details are implementation dependent and outside the scope of this memo. Within the scope of this memo are: 1. Packet format and header contents, including HIPPI-FP, HIPPI- LE, IEEE 802.2 LLC[7] and SNAP. 2. I-Field contents 3. Rules for the use of connections. Outside of the scope are 1. Address Resolution (ARP) 2. Network configuration and management 3. Host internal optimizations 4. The interface between a host and an outboard protocol processor. 2.1 Changes from RFC 1374 RFC 1374 described the use of ARP on HIPPI, but because of insufficient implementation experience, the description of ARP has been separated from IP encapsulation and moved to an Informational memo. It may be returned to the standards track in the future if interest and implementations warrant it. Renwick Standards Track [Page 3] RFC 2067 IP over HIPPI January 1997 RFC 1374's specification of IP over HIPPI has been changed in this document. Certain packet format options, permitted in RFC 1374, are no longer allowed: 1. Optional short burst first; 2. D1 fill bytes; 3. Nonzero D2 offset. That is, the header format is no longer variable and is required to be that which is recommended by RFC 1374. With these changes, it is possible to send packets which conform to the ANSI standards but not to this memo. Because there are no RFC 1374 implementations in use that used these options, we believe that all existing RFC 1374 implementations are compliant with the requirements of this memo, and there should be no interoperability problems associated with these changes. 2.2 Terminology In this document the use of the word SHALL in capital letters indicates mandatory points of compliance. 3 Definitions Conventional Used with respect to networks, this refers to Ethernet, FDDI and 802 LAN types, as distinct from HIPPI-SC LANs. Destination The HIPPI implementation that receives data from a HIPPI Source. Node An entity consisting of one HIPPI Source/Destination pair that is connected by parallel or serial HIPPI to a HIPPI-SC switch and that transmits and receives IP datagrams. A node may be an Internet host, bridge, router or gateway. This memo uses the term node in place of the usual "host" to indicate that a host might be connected to the HIPPI LAN not directly, but through an external adaptor that does some of the protocol processing for the host. Renwick Standards Track [Page 4] RFC 2067 IP over HIPPI January 1997 Serial HIPPI An implementation of HIPPI in serial fashion on coaxial cable or optical fiber, informally standardized by implementor's agreement in the Spring of 1991. Switch Address A value used as the address of a node on a HIPPI-SC network. It is transmitted in the I-field. HIPPI-SC switches may map Switch Addresses to physical port numbers. Source The HIPPI implementation that generates data to send to a HIPPI Destination. Universal LAN Address (ULA) A 48 bit globally unique address, administered by the IEEE, assigned to each node on an Ethernet, FDDI, 802 network or HIPPI- SC LAN. 4 Equipment A HIPPI network can be composed of nodes with HIPPI interfaces, HIPPI cables or serial links, HIPPI-SC switches, gateways to other networks. Each HIPPI interconnection between a node and a switch SHALL consist of a pair of HIPPI links, one in each direction. If a link between a node and the switch is capable of the 1600 Megabit/second data rate option (i.e. Cable B installed for 64 bit wide operation) in either direction, the node's HIPPI-PH implementation SHALL also be capable of 32 bit operation (Cable B data suppressed) and SHALL be able to select or deselect the 1600Mb/s data rate option at the establishment of each new connection. Renwick Standards Track [Page 5] RFC 2067 IP over HIPPI January 1997 The following figure shows a sample HIPPI switch configuration. +-----+ | H 4 | | +--+--+ | +----+ +----+ +----+ | | | H1 | | H2 | | H3 | +-++ | +--+ +-++-+ +-++-+ +-++-+ |PP| +---+H5| || || || ++++ | +--+ || || || || | +---++--------++--------++------++----+ | | | | +----+ | HIPPI-SC | +---+ G1 +--------+ | | | +--------+ Switch | | +----+ | | | +---++--------++--------++------++----+ | +--+ || || || || +---+H6| || ++++ | +--+ +-++-+ |PP| | | | +-++ | | G2 | | | | | +--+--+ | +--+-+ | H 7 | | | +-----+ | -----+------------+-------+-----------+-------------+------ | | | | | | | | +--+--+ +--+--+ +--+--+ +--+--+ | H 8 | | H 9 | | H10 | | H11 | +-----+ +-----+ +-----+ +-----+ Legend: ---+---+---+-- = 802 network, Ethernet or FDDI || = Paired HIPPI link H = Host computer PP = Outboard Protocol Processor G = Gateway A possible HIPPI configuration Renwick Standards Track [Page 6] RFC 2067 IP over HIPPI January 1997 A single HIPPI-SC switch has a "non-blocking" characteristic, which means there is always a path available from any Source to any Destination. If the network consists of more than one switch, the path from a Source to a Destination may include a HIPPI link between switches. If this link is used by more than one Source/Destination pair, a "blocking" network is created: one Source may be blocked from access to a Destination because another Source is using the link it shares. Strategies for establishing connections may be more complicated on blocking networks than on non-blocking ones. This memo does not take blocking issues into account, assuming that the HIPPI LAN consists of one HIPPI-SC switch or, if the network is more complex than that, it presents no additional problems that a node must be aware of. 5 Protocol 5.1 Packet Format The HIPPI packet format for Internet datagrams SHALL conform to the HIPPI-FP and HIPPI-LE draft standards, with further restrictions as imposed by this memo. Because this memo is more restrictive than the ANSI standards, it is possible to send encapsulated IP datagrams that conform to the ANSI standards, but are illegal according to this memo. Destinations may either accept or ignore such datagrams. To summarize the additional restrictions on ANSI standards found here: Any short burst must be the last burst of the packet. Leading short bursts are not permitted. Nonzero values for the HIPPI-FP D2_Offset field are not permitted. The D1_AreaSize SHALL be 3 (64-bit words). No D1 Fill is permitted. Note: Although this document is for IP over HIPPI, the encapsulation described below accommodates ARP as well. The HIPPI-FP D1_Area SHALL contain the HIPPI-LE header. The HIPPI-FP D2_Area, when present, SHALL contain one IEEE 802.2 Type 1 LLC Unnumbered Information (UI) PDU. Support of IEEE 802.2 XID, TEST and Type 2 PDUs is not required on HIPPI, and Destinations that receive these PDUs may either ignore them or respond correctly according to IEEE 802.2 requirements. Renwick Standards Track [Page 7] RFC 2067 IP over HIPPI January 1997 The length of a HIPPI packet, including trailing fill, SHALL be a multiple of eight bytes as required by HIPPI-LE. +----------+-----------+---------------------+----------- ------+ | | | | 0 - 7 | | HIPPI-FP | HIPPI-LE | IEEE 802.2 LLC/SNAP | IP . . . bytes | |(8 bytes) |(24 bytes) | (8 bytes) | fill | +----------+-----------+---------------------+----------- ------+ HIPPI Packet Structure ULP-id (8 bits) SHALL contain 4. D1_Data_Set_Present (1 bit) SHALL be set. Start_D2_on_Burst_Boundary (1 bit) SHALL be zero. Reserved (11 bits) SHALL contain zero. D1_Area_Size (8 bits) SHALL be sent as 3. D2_Offset (3 bits) SHALL be zero. D2_Size (32 bits) Shall contain the number of bytes in the IEEE 802.2 LLC Type 1 PDU, or zero if no PDU is present. It SHALL NOT exceed 65,288. This value includes the IEEE 802.2 LLC/SNAP header and the IP datagram. It does not include trailing fill bytes. (See "MTU", below.) HIPPI-LE Header FC (3 bits) SHALL contain zero unless otherwise defined by local administration. Double_Wide (1 bit) SHALL contain one if the Destination associated with the sending Source supports 64 bit HIPPI operation. Otherwise it SHALL contain zero. Message_Type (4 bits) contains a code identifying the type of HIPPI- LE PDU. Defined values are: 0 Data PDU 1 Address Resolution Request PDU (AR_Request) 2 Address Re