With the introduction of MVS/ESA Version 4.3 in 1993, the IBM Mainframe included the major foundations for meaningful Distributed Systems connectivity, including the first steps of POSIX compliance via OpenEdition functionality. However, even before this timeframe, the TCP/IP protocol was available in the first release of MVS/ESA Version 4 (4.1), although in a very limited fashion. In this instance, MVS was benefitting from the path already trodden by the VM Operating System and the TCP for VM software product. Put another way, even when TCP/IP was in its early stages, being deployed and evolved in universities and scientific laboratories (E.g. CERN), its foundation was being embedded into the IBM Mainframe.
Early IBM Mainframe TCP/IP usage allowed for RS/6000 (AIX) connectivity, LAN integration via Novell NetWare, typically via the 3172 Interconnect Controller, Sockets Interface (E.g. CICS), et al. In 1994, IBM introduced the Open Systems Adapter (OSA) processor feature for S/390 Parallel Enterprise Servers. The OSA provided native Open Systems connectivity to the Local Area Network (LAN), directly via the Mainframe processor. The OSA feature supported the Fiber Distributed Data Interface (FDDI), Token-Ring & Ethernet LANs, arguably making the 3172 controller obsolete.
So, since the early-mid 1990’s, even before pervasive usage of the Internet, the Mainframe was already a fully functioning and efficient user of IP networking.
How is the TCP/IP function being utilized by the IBM Mainframe today?
TCP/IP on z/OS supports all of the well-known server and client applications. The TCP/IP started task is the engine that drives all IP-based activity on z/OS. Even though z/OS is an EBCDIC host, communication with ASCII-based IP applications is seamless.
IP applications running on z/OS use a resolver configuration file for environmental values. Locating a resolver configuration file is somewhat complicated by the dual operating system nature of z/OS (UNIX and MVS). Nearly each and every z/OS customer deploys the following core TCP/IP services:
TCP/IP Daemon: The single entity that handles, and is required for, all IP-based communications in a z/OS environment is the TCP/IP daemon itself. The TCP/IP daemon implements the IP protocol stack and runs a huge number of IP applications to the same specifications as any other operating system.
TCP/IP Profile: Is loaded by TCP/IP when started. If a change needs to be made to the TCP/IP configuration after it has been started, TCP/IP can be made to reload the profile dynamically (or read a new profile altogether).
FTP Server: Like some other IP applications, FTP is actually a z/OS UNIX System Services (USS) application. It can be started within an MVS environment, but it does not remain active in z/OS. It immediately forks itself into the z/OS UNIX environment and tells the parent task to kill itself.
Telnet Daemon: There are two telnet servers available in the z/OS operating environment. One is the TN3270 server, which supports line mode telnet, but it is seldom used for just that. Instead, it is primarily used to support the TN3270 Enhanced protocol. The other telnet server is a line mode server only, referred to as the z/OS UNIX Telnet server (otelnetd).
Many IBM and ISV software products exploit IP and USS functionality, most typically WebSphere (MQ).
Whether UNIX System Services (USS) or TCP/IP usage, the convergence of the IBM Mainframe and UNIX technologies arguably became mandatory with the deployment of TCP/IP on the IBM Mainframe. Obviously the technical personnel that support these different platforms have their own viewpoint as to which platform might be the best, but that is somewhat of an arbitrary point. However, what is absolutely certain is recognition of how data is stored and secured in a UNIX environment and indeed the z/OS (MVS) specific environment, originally named MVS OpenEdition, but now commonly referred to as OMVS.
There are fundamental differences too numerous to mention when comparing the User and File management policies and processes, when comparing the security and data access lifecycle intricacies of z/OS and UNIX. So what you might say! This might be a cursory and lax attitude, as business critical data is probably being stored in OMVS file systems, if only for FTP purposes, but more than likely for other more pervasive and user based access (E.g. Database, Messaging, Data Mining, Data Exchange, et al).
So, which technical party is managing the security of Unix System Services (USS) file systems for the OMVS Mainframe deployment? Is it the Mainframe Systems Programmer, the Unix System Admin or the Mainframe Security Team, or somebody else? To date, some people might have thought it didn’t matter, but of course, seasoned security professionals knew that this was never the case. However, the migration to z/OS 2.1 is a tangible juncture for each and every IBM Mainframe installation to review their USS and thus OMVS security deployment. Why?
The BPX.DEFAULT.USER facility was introduced with OS/390 2.4 and was a commonly used process for implementing USS (OMVS) security. However, with z/OS 2.1, the BPX.DEFAULT.USER facility is withdrawn, meaning that the Mainframe user must perform some migration actions. IBM provide some generic assistance with this challenge via APAR OA42554 and APAR OA37164. However, maybe this is an ideal juncture to perform a thorough review of USS (OMVS) security, vis-à-vis a comprehensive and dispassionate audit, highlighting issues, implementing standards and securing exposures. For example, use of UID(0) must be eradicated and certainly no human being should be allocated such privileges.
There are some useful guidelines available from security specialists such as Vanguard, where the process can be simplified using their Identity & Access Management (IAM) toolset. Similarly, recent user conferences have included presentations on this subject matter.
In conclusion, the IBM Mainframe can be classified as just another node on the IP (TCP/IP) network. However, as always, no matter how secure the Mainframe platform might be, the biggest threat is typically the human being, and for USS, the migration to z/OS 2.1 forces us to review OMVS security settings. Therefore, let’s do a good job and eradicate any security exposures we might have inadvertently implemented over the years. As we all know, passing an external security audit process doesn’t necessarily mean our IT systems and processes are secure, while sometimes the internal security people are better qualified or more knowledgeable than external auditors. Arguably most external auditors will do a good job of auditing UNIX platforms, yet their Mainframe knowledge and abilities are typically limited. It is therefore somewhat of a paradox that in this particular area of z/OS USS, the typical UNIX exposures are not highlighted in the typical Mainframe security audit process…
One must draw one’s own conclusions as to the merits of engaging 3rd Mainframe security specialists to perform such an audit, coinciding with this z/OS 2.1 migration activity, safeguarding that OMVS security and processes are as good and secure as they can be. Put another way, why wouldn’t a Mainframe organization go that extra mile to safeguard their most valuable of assets, namely business critical data, engaging a 3rd party specialist to review and provide guidance on this subject matter.