Network Working Group R. Dixon Request for Comments: 1434 D. Kushi IBM March 1993 Data Link Switching: Switch-to-Switch Protocol Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard. Distribution of this memo is unlimited. Abstract This RFC describes IBM's support of Data Link Switching over TCP/IP. The RFC is being distributed to members of the Internet community in order to solicit their reactions to the proposals contained in it. While the issues discussed may not be directly relevant to the research problems of the Internet, they may be interesting to a number of researchers and implementors. Any questions or comments relative to the contents of this RFC should be sent to the following Internet address: dlsw@ralvma.vnet.ibm.com. Table of Contents 1. Introduction 2 2. Overview 2 3. Transport Connection 4 3.1. SSP Frame Formats 5 3.2. Address Parameters 8 3.3. Message Types 10 4. Protocol Specification 11 4.1. Protocol Flow Diagrams 11 4.1.1. Connect Protocols 11 4.1.2. Link Restart Protocols 13 4.1.3. Disconnect Protocols 15 4.2. DLS State Machine 16 4.2.1 Data Link Switch States 16 IMK[}LAXǾI:=EFCIC:75544455557J]e]84>»UMA:9:<>>=<@HNTT]i_VJ@=<<<>AGVoo}}`Xja-! %/FϸuRHGNOJC>>>C?;=DMX_keTNOQRWWV\\QKHKTXdʺ8,+1?¹qK@<96569=AK]þVLFAD>;98:<>EM^{lcraRGBFI:,'',:fwYNIJMLDBCEGNcYJEDEKV_sjTMLINZ`k{rb`lznQ@:89Djȹ|VONHDA@EMUkiULHFECHO^`NZrhXOQafI<3//19C_ǾaRIGDBCBDFKMPW`rgfaTLGFFDCABB@BFIP_pƿeND?==CPlxjic]XW^j_\eu^k¿i]VMHDBCEIP]_SFA>=?CEJS_ykmiifpfYKIJEC?:;<;<=?Lw½`KCBFKLU_bfYVZ_Xlzto_VC:̷nn-&5C°RPIB[F?BTdFPT@{`A?ƳZ?91.,-/=G77;ZT^ɴZKU[OD6,*)(' '3I<3I>:HkA>=8+($,* 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&/6Z^9PA:6F3,EbI6=PcAFӶV?6,)(&%%'(1F727MlȲLQ[C953.)*("$/4++175/:_ǾM942+( *,-36.5JXuͿĿZ9Hyʿ}C1,)+8?Mo`NNr]SüĹfN@?O/!#-/+6L˲ZfRGJ==VY`zL>gN03EtʬuQ\?;I]P>LiIhIXJLKAJIA?=z@,%*0Xµ=44:;8DE;;8GlKEL>;32@ߵ}<6:LضG:Ltu\J5+.9B>@=6;FRTĨijl??=H緵[I?9;79\hzT8-,7:-.=UǰkI>:3-.@KVμ=++0>JOƲϺS94DίxO' )(*4JXD?DB-*,5=Ioҿķ?>UȴWB549><9G|LIշJAINX@Ro:--,9H*):VgɾSMEP>;ຮ?9@>87W^9-8{ʴZҿd957==9=KO>:R޻qj>,+/?̳WZOG=B:8B94:CӺ[VRZ[TG3("#(9湫N;=LeN<006EqӺD:57CLOOJOaƽwWWSY}NNJNA:Y;:;2.98?~ŹN:7O94=>VüRI=;[S@KWD_ɽ¹F;=OɱB=A/*/-),8JlϾJPSm@NN>?OvUoXC<.&+9cGITuW>8;ZvXLfVQvHALLzOajD39N.,(1=HѵX3+043BJBCD_n<9F^NLns using Data Link Switching. It is identified by a Data Link ID (14 bytes) consisting of the pair of attachment addresses associated with each end system. Each attachment address is represented by the concatenation of the MAC address (6 bytes) and the LLC address (1 byte). DATA LINK ID (14 Bytes) +-----------------------------------------------------------------+ |Target MAC Address ----> . | | . . | | . . | |Origin MAC Address ----> . | | . . | | . . | |Origin Link SAP Target Link SAP | +-----------------------------------------------------------------+ An end-to-end circuit is identified by a pair of Circuit ID's. A Circuit ID is a 64 bit number that identifies the DLC circuit within a single DLS. It consists of a DLC Port ID (4 bytes), and a Data Link Correlator (4 bytes). This value is unique in a single DLS and is assigned locally. The pair of Circuit ID's along with the identifiers of the Data Link Switches, uniquely identify a single end-to-end circuit. Each DLS must keep a table of these Circuit ID pairs, one for the local end of the circuit and the other for the remote end of the circuit. In order to identify which Data Link Switch originated the establishment of a circuit, the terms, origin DLS and target DLS, will be employed in this document. CIRCUIT ID (8 Bytes) +-----------------------------------------------------------------+ |DLC Port ID ----> . | | . . | |Data Link Correlator ----> . | | . . | +-----------------------------------------------------------------+ The Origin Transport ID and the Target Transport ID fields in the message header are used to identify the individual TCP/IP port on a Data Link Switch. The values have only local significance. However, each Data Link Switch is required to reflect the values contained in these two fields, along with the associated values for DLC Port ID Dixon & Kushi [Page 8] RFC 1434 DLS: Switch-to-Switch Protocol March 1993 and the Data Link Correlator, when returning a message to the other Data Link Switch. The following figure shows the use of the addressing parameters during the establishment of an end-to-end connection. The CANUREACH, ICANREACH, and REACH_ACK messages all carry the Data Link ID, consisting of the MAC and Link SAP addresses associated with the two end stations. Upon receipt of a CANUREACH message, the target DLS starts a data link for each port, thereby obtaining a Data Link Correlator. If the target station can be reached, an ICANREACH message is returned to the origin DLS containing the Target Circuit ID parameter. Upon receipt, the origin DLS starts a data link and returns the Origin Circuit ID to the target DLS within the REACH_ACK message. If the REACH_ACK message is not successfully received, the target Data Link Switch can obtain the Origin Circuit ID from a subsequent message (i.e., CONTACT, XIDFRAME, or DGRMFRAME). +------------+ +------------+ |Disconnected| |Disconnected| +------------+ CANUREACH (Data Link ID) +------------+ -------------------------------------------------> ICANREACH (Data Link ID, Target Circuit ID) <------------------------------------------------ REACH_ACK (Data Link ID, Origin Cir ID, Target Cir ID) -------------------------------------------------> +------------+ +------------+ |Circuit Est.| |Circuit Est.| +------------+ +------------+ XIDFRAME (Data Link ID, Origin Cir ID, Target Cir ID) <------------------------------------------------> CONTACT (Data Link ID, Origin Cir ID, Target Cir ID) -------------------------------------------------> CONTACTED (Data Link ID, Origin Cir ID, Target Cir ID) <------------------------------------------------- +------------+ +------------+ | Connected | | Connected | +------------+ +------------+ INFOFRAME (Remote Circuit ID = Target Circuit ID) -------------------------------------------------> INFOFRAME (Remote Circuit ID = Origin Circuit ID) <------------------------------------------------- Figure 3. DLS Circuits and Connections During the exchange of the XIDFRAME, CONTACT, and CONTACTED messages, the pair of Circuit ID parameters is included in the message format along with the DATA LINK ID parameter. Once the connection has been established, the INFOFRAME messages are exchanged with the shorter Dixon & Kushi [Page 9] RFC 1434 DLS: Switch-to-Switch Protocol March 1993 header. This header contains only the Circuit ID associated with the remote DLS. The Remote Data Link Correlator and the Remote DLC Port ID are set equal to the Data Link Correlator and the DLC Port ID that are associated with the origin or target Data Link Switch, dependent upon the direction of the packet. 3.3. Message Types The following table lists the protocol data units that are exchanged between Data Link Switches. All values not listed are reserved for potential use in follow-on releases. Command Function Hex Value ------- -------- --------- CANUREACH Can U Reach Station x'03' ICANREACH I Can Reach Station x'04' REACH_ACK Reach Acknowledgment x'05' DGRMFRAME Datagram Frame (See note) x'06' XIDFRAME XID Frame x'07' CONTACT Contact Remote Station x'08' CONTACTED Remote Station Contacted x'09' RESTART_DL Restart Data Link x'10' DL_RESTARTED Data Link Restarted x'11' INFOFRAME Information (I) Frame x'0A' HALT_DL Halt Data Link x'0E' DL_HALTED Data Link Halted x'0F' NETBIOS_NQ NetBIOS Name Query x'12' NETBIOS_NR NetBIOS Name Recognized x'13' DATAFRAME Data Frame (See note) x'14' NETBIOS_ANQ NetBIOS Add Name Query x'1A' NETBIOS_ANR NetBIOS Add Name Response x'1B' Table 1. SSP Message Types Note: Both the DGRMFRAME and DATAFRAME messages are used to carry information received by the DLC entity within UI frames. As will be explained below, the DGRMFRAME message is addressed according to a pair of Circuit IDs, while the DATAFRAME message is addressed according to a Data Link ID, being composed of a pair of MAC addresses and a pair of link SAP addresses. The latter is employed prior to the establishment of an end-to-end circuit when Circuit IDs have yet to be established. For the exchange of NetBIOS control messages, the entire DLC header is carried as part of the message unit. This includes the MAC header, with the routing information field padded to 18 bytes, and the LLC header. The following message types are affected: NETBIOS_NQ, NETBIOS_NR, NETBIOS_ANQ, NETBIOS_ANR, and DATAFRAME when Dixon & Kushi [Page 10] RFC 1434 DLS: Switch-to-Switch Protocol March 1993 being used by NetBIOS systems. The routing information in the DLC header is not used by the remote Data Link Switch upon receiving the above five messages. 4. Protocol Specification This section provides a description of the Switch-to-Switch Protocols. Included is a set of high-level protocol flows and a detail set of state transition tables. The states and the protocols are described in terms that are intended to be generic to different platforms. Emphasis of the technical details is to ensure operability of the IBM 6611 with another vendor's implementation. Notes are inserted at points where the IBM 6611 performs local actions that are specific to the AIX platform upon which it operates. 4.1. Protocol Flow Diagrams The switch-to-switch protocols are used to setup and take down circuits between a pair of Data Link Switches. Once a circuit is established, the end stations on the local networks can employ LLC Type 1 (connectionless) protocols. In addition, the end systems can establish an end-to-end connection for support of LLC Type 2 (connection oriented) protocols. The term, Data Link, is used in this document to refer to both a "logical data link" when supporting Type 1 LLC services, and a "data link connection" when supporting Type 2 LLC services. In both cases, the Data Link in defined by the concatenation of the destination MAC address (DA), the source MAC address (SA), the destination link SAP (DSAP) and source link SAP (SSAP). 4.1.1. Connect Protocols The following figure depicts the protocol flows that are used for the establishment of a circuit between a pair of Data Link Switches, followed by the establishment of a connection between the pair of end systems. The figure is drawn assuming that the two end systems are SNA (the protocol flow for NetBIOS systems is described in a later paragraph). Dixon & Kushi [Page 11] RFC 1434 DLS: Switch-to-Switch Protocol March 1993 Data Link Data Link Data Link Data Link Control Switch Switch Control -------------------- -------------------- +------------+ +------------+ |Disconnected| |Disconnected| +------------+ +------------+ Test Command CANUREACH Test Comd. ----------> ---------------------------------------> -------> (DSAP=Null) (DSAP=SSAP) Test Response ICANREACH <--------- Test Response <--------------------------------------- <---------- REACH ACK ---------------------------------------> +------------+ +------------+ |Circuit Est.| |Circuit Est.| +------------+ +------------+ SABME CONTACT ----------> ---------------------------------------> SABME UA -------> <---------- RNR UA <---------- CONTACTED <------- <--------------------------------------- +------------+ +------------+ | Connected | | Connected | +------------+ +------------+ RR <--------- Figure 4. DLS Connect Message Protocols Upon receipt of a Test command from the origin station, the origin DLS will send a CANUREACH (i.e., can you reach) message to the target DLS. If the target DLS is not known to the origin DLS, the CANUREACH message is sent to all remote Data Link Switches defined to the origin DLS. The receipt of the CANUREACH message causes the target DLS to send a Test command searching for the target station. The target station will return a Test response, causing the target DLS to return an ICANREACH (i.e., I can reach) message to the origin DLS. If multiple Data Link Switches can reach the target station, the origin DLS will receive multiple ICANREACH messages. The origin DLS will select the first message and send a REACH_ACK (i.e., reach acknowledgment) message to the selected Data Link Switch. During this exchange of messages, both Data Link Switches change states from the Disconected state to the Circuit Established state. Once the circuit is established, Type-1 frames, such as XID, may be exchanged between the origin and target stations. Dixon & Kushi [Page 12] RFC 1434 DLS: Switch-to-Switch Protocol March 1993 To establish a connection, the origin station sends a SABME command. Upon receipt of this command, the origin DLS will send a CONTACT message to the target DLS and return a UA response to the origin station. To inhibit traffic flow until the connection is established to the remote station, a RNR supervisory frame is sent to the origin station. The CONTACT message will cause the target DLS to send a SABME command to the target station, which in return will reply with a UA response. Upon receipt of the UA response, the target DLS will send a CONTACTED message to the origin DLS. The origin DLS will now send an RR supervisory frame to the origin station. 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