Network Working Group S. Chiang
Request for Comments: 2114 J. Lee
Category: Informational Cisco Systems, Inc.
Obsoletes: 2106 H. Yasuda
Mitsubishi Electric Corp.
February 1997
Data Link Switching Client Access Protocol
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This memo describes the Data Link Switching Client Access Protocol
that is used between workstations and routers to transport SNA/
NetBIOS traffic over TCP sessions. Any questions or comments should
be sent to dcap@cisco.com.
Table of Contents
1. Introduction ............................................ 2
2. Overview ................................................ 2
2.1 DCAP Client/Server Model ............................... 2
2.2 Dynamic Address Resolution ............................. 3
2.3 TCP Connection ......................................... 4
2.4 Multicast and Unicast (UDP) ............................ 4
3. DCAP Format ............................................. 6
3.1 General Frame Format ................................... 6
3.2 Header Format .......................................... 6
3.3 DCAP Messages .......................................... 7
3.4 DCAP Data formats ...................................... 8
3.4.1 CAN_U_REACH, I_CAN_REACH, and I_CANNOT_REACH Frames .. 8
3.4.2 START_DL, DL_STARTED, and START_DL_FAILED Frames ..... 9
3.4.3 HALT_DL, HALT_DL_NOACK, and DL_HALTED Frames ......... 13
3.4.4 XID_FRAME, CONTACT_STN, STN_CONTACTED, INFO_FRAME,
FCM_FRAME, and DGRM_FRAME ............................ 14
3.4.5 DATA_FRAME ........................................... 15
3.4.6 CAP_XCHANGE Frame .................................... 16
3.4.7 CLOSE_PEER_REQ Frames ................................ 19
3.4.8 CLOSE_PEER_RSP, PEER_TEST_REQ, and PEER_TEST_RSP Frames 20
4. Protocol Flow Diagram ................................... 20
5. Acknowledgments ......................................... 22
6. References .............................................. 22
Chiang, et. al. Informational [Page 1]
RFC 2114 DCAP February 1997
1. Introduction
Since the Data Link Switching Protocol, RFC 1795, was published, some
software vendors have begun implementing DLSw on workstations. The
implementation of DLSw on a large number of workstations raises
several important issues that must be addressed. Scalability is the
major concern. For example, the number of TCP sessions to the DLSw
router increases in direct proportion to the number of workstations
added. Another concern is efficiency. Since DLSw is a switch-to-
switch protocol, it is not efficient when implemented on
workstations.
DCAP addresses the above issues. It introduces a hierarchical
structure to resolve the scalability problems. All workstations are
clients to the router (server) rather than peers to the router. This
creates a client/server model. It also provides a more efficient
protocol between the workstation (client) and the router (server).
2. Overview
2.1. DCAP Client/Server Model
+-----------+ +-----------+ +---------+
| Mainframe | | IP Router +- ppp -+ DLSw |
+--+--------+ +-----+-----+ | Work |
| | | Station |
| | +---------+
+--+--+ +-------------+ |
| FEP +- TR -+ DLSw Router +-- IP Backbone
+-----+ +-------------+ |
|
|
+-----------+ +---------+
| IP Router +- ppp -+ DLSw |
+-----+-----+ | Work |
| Station |
+---------+
| DLSw Session |
+-------------------------------+
Figure 2-1. Running DLSw on a large number of workstations creates a
scalability problem.
Figure 2-1 shows a typical DLSw implementation on a workstation. The
datatracker.ietf.org