DLSw and Logical Link Control 2 (LLC2)

How an LLC2 connection is established over a LAN
When a LAN-attached station must establish an SNA session with a peer LAN-connected station, it sends an LLC2 broadcast message called TEST. TEST carries the MAC address of the destination station and originating station. More data is carried in the TEST message, but this topic concentrates on the MAC address.

Data link switching (DLSw)
Data link switching carries LAN traffic over the wide area network by encapsulating the LAN traffic in TCP packets. Data link switching was first developed by IBM to provide SNA support within multi-protocol routers. The DLSw formats and protocol were then made available to the wider community and published as RFC 1434. The RFC was then later enhanced and republished as RFC 1795.

How SDLC devices are connected using DLSw
DLSw routers were installed in remote branches. The DLSw router enabled the connection of TCP/IP and SNA LAN-attached workstations to the mainframe. Many remote branches still have SDLC devices like IBM 3174 controllers, banking, or retail controllers. Using the DLSw branch router eliminates the need to connect the SDLC device using a dedicated communication link.

DLSw configuration
From a z/OS perspective, the DLSw configuration and definitions reside on the router. As a network administrator, you normally would not get involved with these definitions, because the group responsible for the WAN does them. You need to interact with this group to get MAC addresses of SNA devices and especially the SDLC virtual MAC addresses that the mainframe uses to initiate the LLC2 connection.