Linux-SNA for accessing mainframes

UNIX servers are not the only servers available today, nor is TCP/IP the only networking protocol. Another very important, and much used protocol suite, is Systems Network Architecture (SNA) developed by IBM in the 1970s and very widely used even today in IBM mainframe environments. In particular, although SNA is described as “legacy” and “old” (in fact, SNA and TCP/IP were both developed at roughly the same time) the real importance of SNA is that the large majority of “mission critical” mainframe applications still rely on SNA. One of the challenges of today’s networks is in combining the reliability of SNA networking with the availability and widespread adoption of TCP/IP networking and the Internet.

Linux-SNA allows Linux to implement an SNA protocol stack. This means that Linux machines can be included in an existing SNA environment and, because Linux already uses TCP/IP, Linux can act as a gateway between the SNA mainframe legacy world and the TCP/IP Internet.

Core PC Network Program 1.0 Core Plus Microsoft Networks 1.03

LAN Manager 1.0 Support for OS/2 multitasking (and opportunistic locks) LANManager 2.0 Enhanced support for OS/2 (long file names)

NT LM 0.12 New commands to support Windows NT CIFS 1.0 Essentially a Microsoft version of NFS

Linux-SNA supports APPN End Node and Network Node functions over token-ring and Ethernet LAN connections. The APPN support is a subset of all the defined option sets and, today, does not include high performance routing (HPR), dependent LU requestor (DLUR), border node (PBN or EBN) or parallel TG support. Indeed, the APPN NN implementation does not support many of the directory and topology options (registration of end nodes, broadcast/directed searches, topology exchanges) or transport options, such as intermediate session routing (ISR). As it stands today, Linux-SNA is not an APPN router.

On the other hand, there are many related SNA functions which Linux-SNA can support, and perhaps the most important role Linux-SNA can perform is to act as a gateway between TCP/IP clients and SNA servers. Linux-SNA is currently being developed, but the first full and stable release (1.0) should include TN3270 and TN5250 client and server support and the ability to use SNA over LAN connections, S/390 host channel connections, and SDLC connections; at the time of writing, the channel and SDLC datalink controls have not been completed.

Linux-SNA is a project led by Jay Schulist of TurboLinux to implement SNA support into Linux. It consists of the parts shown in Table 10.

Table 10. Linux-SNA components

Linux-SNA currently requires a relatively recent Linux kernel (2.2.x) to which a patch must be applied so that additional SNA options can be added. Once the new kernel has been loaded and configuration files have been edited,

Component name Functionality

net-fun kernel patch to get SNA kernel support libsna SNA support libraries

sna-tools base set of SNA networking tools asuite APPC tools, like aftp, aping etc.

etc-sna contains the SNA config files going into /etc

llcping LLC test program

tn5250 TN5250 client

tn5250d TN5250 server

tn3270 TN3270 client

Linux-SNA should be up and running. An overview of the planned and supported devices, protocols, and APIs is shown in Table 11.

Table 11. Linux-SNA supported devices, protocols, and APIs

Note, that at the time of writing, this code is under development and test, and that support is only currently available for Ethernet and token-ring devices. Linux-SNA provides a low-cost entry point into SNA networking from the Linux world. Of course there are existing commercial solutions, not least of which is the IBM Communications Server, which runs on IBM UNIX (AIX on RS/6000) as well as on Windows NT on Netfinity hardware, and which provides many more features and functions than Linux-SNA does.

Furthermore, SNA servers, such as the IBM S/390 and AS/400, both provide native TCP/IP access to their applications and services, allowing TCP/IP clients to connect to them directly and obviating the need for a gateway such as Linux-SNA. However, there are still places where it would be convenient to have Linux-SNA support and, in due course, Linux-SNA will be able to implement:

• TCP/IP - SNA gateways:Opening routes from one network world to the other. This is a Linux-SNA implementation of AnyNet, allowing IP traffic to be transported over SNA networks or vice versa.

• TN3270/5250 gateways:Enabling today’s clients to connect to your mainframe and pull and push data.

• SNA protocol converters:Providing your new applications a way to talk your applications on the mainframe.

There are more solutions to fit your needs and to bring the mainframe worlds and the Linux worlds together, combining the advantages from both sides, such as the following:

• Using existing applications to obtain new interfaces to the fast growing Linux world.

Devices Protocols APIs

Ethernet, token-ring APPN CPI-C V2 ATM, FIDDI, SDLC LU 6.2 APPC ESCON, Bus/Tag Channel LU API 5250 Twinaxial, 3270 Coax HILLAPI

• Adding cheap commodity access servers to your installed business backbone.

• Customizing Open Source solutions to fit your needs and implement up-to-date software.

• Building stable and affordable bridges between formerly separated architectures.

Bottom line, Linux-SNA proves once again that Linux is business ready, flexible, and easily integrated in today’s computing environments, in an affordable manner.