What is the SNA?

The SNA is a network architecture developed by IBM and is widely used in IBM's host environment. Generally, the SNA is primarily a major networking protocol for IBM's mainframe (es/9000, s/390, etc.) and midsize machines (as/400).
The main feature of the SNA is its closeness, which is a proprietary protocol developed by IBM. If the SNA is to be applied in other host systems, software and hardware supporting the SNA need to be added at every node of the network.
The SNA environment has the capability of COS (service classification) and security, but the security of SNA is only host-based XID (Exchange ID). XID is similar to the user's password, in the SNA session establishment process to Exchange XID to confirm the user's legality. The XID needs to be statically configured in the host, and the network LU (logical unit) needs to Exchange XID with the LU on the host while establishing the session; In the SNA environment, there is no security concern other than XID exchange. Due to the closeness of the SNA protocol, most people are unfamiliar with it and the network using the SNA protocol is less vulnerable, but for those who are familiar with it, the security mechanism of SNA is not strict. The design and development of security systems based on SNA is also uncommon. It is actually unreliable to rely on closeness alone.
Due to the openness of the SNA and the complexity of development, it is very complicated to develop the application system in the SNA environment, and the mobility of the system is weaker, which is not in line with the open trend of the industry. Maintaining a large number of experts to support the SNA network is also becoming increasingly difficult. With the development and popularization of the Internet, more and more users use the open TCP/IP protocol, IBM is no exception. The TCP/IP protocol, including es/9000 and as/400, is now supported on IBM's traditional machines that support only the SNA environment. More and more SNA users are migrating to the TCP/IP environment