INN - Internal Network Node

Enhanced Definition

An Internal Network Node (INN) is a type 4 node within an IBM Systems Network Architecture (SNA) network, primarily responsible for routing data traffic between other nodes. It acts as a major junction point, managing network resources and facilitating session establishment across the network. In the z/OS environment, a VTAM host can function as an INN, or a dedicated communications controller (like an IBM 3745/3746) can serve this role.

Key Characteristics

- SNA Type 4 Node: INNs are classified as Type 4 nodes in SNA, indicating their capability to perform network control and routing functions.
- Routing Capabilities: They possess the intelligence and resources to route data packets based on network addresses, directing traffic between different physical units (PUs) and logical units (LUs).
- Network Control Point (NCP): When implemented on a communications controller, the INN runs the Network Control Program (NCP), which manages the attached lines, devices, and routing tables.
- VTAM Host Role: A z/OS system running VTAM can serve as an INN, managing its own local resources and participating in network-wide routing.
- Resource Management: INNs manage the status and availability of attached PUs and LUs, facilitating their activation and deactivation.
- Session Establishment: They play a crucial role in the setup and termination of SNA sessions between LUs located on different nodes.

Use Cases

- Interconnecting Mainframe Hosts: An INN can connect multiple z/OS systems (each running VTAM) within a large SNA network, enabling applications on one host to communicate with resources on another.
- Centralized Network Hub: A communications controller acting as an INN can serve as a central hub for a regional network, routing traffic from numerous peripheral nodes (e.g., 3x74 cluster controllers) to one or more mainframe hosts.
- Application-to-Application Communication: Facilitating communication between distributed applications, such as a CICS region on one z/OS LPAR needing to access a DB2 database on another.
- Remote Terminal Access: Routing user traffic from remote terminals (connected via peripheral nodes) to the appropriate mainframe application (e.g., TSO, CICS, IMS).

Related Concepts

INN is a foundational concept within SNA (Systems Network Architecture), defining a specific type of network node with routing capabilities. It works in conjunction with VTAM (Virtual Telecommunications Access Method), which is the primary access method on z/OS for SNA communications, often acting as an INN itself. INNs manage PUs (Physical Units) and LUs (Logical Units), providing the network infrastructure for these resources to communicate. They are distinct from End Nodes (ENs), which typically do not perform routing, and Peripheral Nodes (PNs), which are lower-level nodes like cluster controllers.

Best Practices:

Optimize Routing Tables: Regularly review and optimize ROUTE tables and PATH statements within VTAM and NCP configurations to ensure efficient data flow and minimize latency.
Monitor Resource Utilization: Continuously monitor INN resources, such as buffer pools, CPU utilization on communications controllers, and VTAM storage, to prevent bottlenecks and ensure stable network performance.
Implement Redundancy: For critical network paths, configure redundant INNs and backup PATH statements to provide high availability and fault tolerance.
Secure Network Access: Implement robust security measures for INN control points and associated network resources to prevent unauthorized access and maintain data integrity.
Maintain Current NCP/VTAM Versions: Keep NCP and VTAM software up-to-date with the latest maintenance levels to leverage performance enhancements, security fixes, and new features.