Endpoint - Communication terminus

Enhanced Definition

In the mainframe and z/OS context, an endpoint refers to a specific network address and port combination that uniquely identifies a communication channel or a service listener on a z/OS system. It serves as the designated termination point for network connections, enabling applications and subsystems to send and receive data over a network. In the context of IBM mainframe and z/OS, an endpoint refers to a specific, addressable location or component within a network or system that serves as a termination point for communication. It is the logical address where data originates or is consumed, representing a particular application, service, or device on the mainframe.

Key Characteristics

- IP Address and Port: An endpoint is fundamentally defined by an IP address (or a resolvable hostname) and a unique port number, forming a socket address.
- Service Listener: It is typically associated with a server process or daemon (e.g., FTPD, TN3270, CICS Listener, DB2 DDF) that actively listens for incoming connection requests on the specified port.
- Protocol Specific: Endpoints are usually bound to a specific network protocol, most commonly TCP (Transmission Control Protocol) or UDP (User Datagram Protocol).
- Network Configuration: Endpoints are configured within the z/OS TCP/IP profile or through associated network components like PAGENT for IP filtering and routing rules.
- Security Context: Access to endpoints is often controlled by z/OS security managers like RACF, which define which users, groups, or IP ranges are authorized to connect.
- Application-Bound: While the TCP/IP stack provides the underlying network services, the endpoint is ultimately utilized by a specific application, subsystem, or middleware to expose its functionality.

Use Cases

- TN3270 Terminal Access: A TN3270 server listens on a specific port (commonly port 23) to allow terminal emulation clients to connect to TSO, CICS, or IMS applications.
- File Transfer Services: The FTP daemon (FTPD) listens on port 21 (control) and other ports (data) to facilitate file transfers between z/OS datasets and remote clients.
- CICS Transaction Gateway (CTG): A CTG daemon or CICS Listener uses specific endpoints to accept client requests for CICS transactions from distributed applications.
- DB2 Distributed Data Facility (DDF): DB2 DDF utilizes endpoints to enable remote applications (e.g., Java, .NET) to connect to DB2 subsystems and execute SQL queries.
- Web Services and APIs: z/OS Connect EE or Liberty Profile servers expose RESTful APIs and web services via specific HTTP/HTTPS endpoints, allowing modern applications to interact with mainframe data and programs.

Related Concepts

Endpoints are foundational to network communication on z/OS, relying on the TCP/IP stack for their operation. They are often secured by RACF (or equivalent) access control rules and are integral to how subsystems like CICS, DB2, IMS Connect, and TSO expose their services to internal and external clients. The PAGENT (Policy Agent) can enforce IP filtering and routing policies based on endpoint definitions, while Sysplex Distributor can manage workload balancing across multiple LPARs using a single virtual endpoint.

Best Practices:

Standard Port Usage: Utilize well-known or registered port numbers for standard services (e.g., 21 for FTP, 23 for TN3270) to ensure interoperability and avoid conflicts.
Robust Security Configuration: Implement strong security measures using RACF (or equivalent) to restrict access to endpoints based on user ID, group, and source IP address. Leverage IP filtering via PAGENT to further control network access.
Proactive Monitoring: Continuously monitor endpoint availability, connection rates, and resource utilization using z/OS network monitoring tools (e.g., NetView, OMEGAMON) to detect and resolve issues promptly.
Comprehensive Documentation: Maintain clear and up-to-date documentation for all configured endpoints, including their associated services, port numbers, protocols, and security settings, for auditing and troubleshooting.
High Availability Design: For critical services, consider configuring redundant endpoints or utilizing Sysplex Distributor to provide a single, highly available virtual IP address (VIPA) that distributes connections across multiple LPARs.