RFC 2114 (rfc2114) - Page 3 of 22
Data Link Switching Client Access Protocol
Alternative Format: Original Text Document
RFC 2114 DCAP February 1997
+-----------+ +--------+
| Mainframe | | DCAP |
+--+--------+ +-----+ Client |
| | +--------+
| ppp
| |
+--+--+ +--------+ +------+------+
| FEP +- TR -+ DLSw +-- IP Backbone --+ DLSw Router |
+-----+ | Router | | DCAP Server |
+--------+ +------+------+
|
ppp
| +--------+
+-----+ DCAP |
| Client |
+--------+
| DLSw Session | | DCAP Session |
+----------------------+ +--------------+
Figure 2-2. DLSw Client Access Protocol solves the scalability
problem.
In a large network, DCAP addresses the scalability problem by
significantly reducing the number of peers that connect to the
central site router. The workstations (DCAP clients) and the router
(DCAP server) behave in a Client/Server relationship. Workstations
are attached to a DCAP server. A DCAP server has a single peer
connection to the central site router.
2.2. Dynamic Address Resolution
In a DLSw network, each workstation needs a MAC address to
communicate with a FEP attached to a LAN. When DLSw is implemented on
a workstation, it does not always have a MAC address defined. For
example, when a workstation connects to a router through a modem via
PPP, it only consists of an IP address. In this case, the user must
define a virtual MAC address. This is administratively intensive
since each workstation must have an unique MAC address.
DCAP uses the Dynamic Address Resolution protocol to solve this
problem. The Dynamic Address Resolution protocol permits the server
to dynamically assign a MAC address to a client without complex
configuration.
For a client to initiate a session to a server, the workstation sends
a direct request to the server. The request contains the destination
MAC address and the destination SAP. The workstation can either
specify its own MAC address, or request the server to assign one to
Chiang, et. al. Informational
