Ethernet - Network protocol

Enhanced Definition

Ethernet is a widely adopted family of computer networking technologies that define the physical and data link layers of the OSI model. In the context of IBM mainframes and z/OS, Ethernet provides the primary means for z/OS logical partitions (LPARs) to connect to IP -based networks, enabling high-speed communication with distributed systems, client applications, and the internet. It serves as the underlying transport for the z/OS TCP/IP stack.

Key Characteristics

- Standardized Protocol: Adheres to the IEEE 802.3 standards, ensuring interoperability with a vast array of network devices.
- Layer 1 & 2 Operation: Operates at the physical layer (cabling, electrical signals) and the data link layer (framing, MAC addresses) of the OSI model.
- Media Flexibility: Supports various physical media, including twisted-pair copper cables (e.g., Cat5e, Cat6) and fiber optic cables, allowing for different distances and environments.
- Scalable Speeds: Available in various speed grades, commonly 1 Gbps, 10 Gbps, 25 Gbps, 100 Gbps, 200 Gbps, and 400 Gbps, with higher speeds continuously evolving to meet enterprise demands.
- MAC Addressing: Each Ethernet interface has a unique 48-bit Media Access Control (MAC) address, used for local network communication.
- Packet-based Communication: Data is transmitted in frames (packets), each containing source and destination MAC addresses, data payload, and error-checking information.

Use Cases

- External IP Connectivity: Connecting z/OS LPARs to corporate LANs and WANs, allowing z/OS applications (e.g., CICS, IMS, DB2) to communicate with distributed applications, web servers, and client workstations.
- Application Front-ending: Hosting web servers (e.g., IBM HTTP Server for z/OS) or application servers that serve content and interact with backend mainframe data over IP.
- Data Transfer and Integration: Facilitating high-speed data transfer between z/OS and other platforms using protocols like FTP, SFTP, or custom applications over TCP/IP.
- Remote Management: Enabling remote administration and monitoring of z/OS systems via secure shell (SSH), TN3270, or other IP-based management tools.
- Sysplex Distributor: Used by Sysplex Distributor to distribute incoming TCP/IP connection requests across multiple target z/OS LPARs within a sysplex, leveraging OSA adapters for external network access.

Related Concepts

Ethernet is fundamental to modern z/OS networking, primarily serving as the physical and data link layer for the TCP/IP for z/OS stack. It requires Open Systems Adapter (OSA) hardware cards on the mainframe to provide the physical interface to the external network. While HiperSockets provides an internal, high-speed IP network within a mainframe CPC, Ethernet is crucial for connecting z/OS to the outside world. Enterprise Extender (EE) leverages IP over Ethernet to transport SNA traffic, bridging traditional mainframe networking with modern IP infrastructure.

Best Practices:

Redundancy: Implement redundant OSA adapters and network paths (e.g., using IP Takeover or Sysplex Distributor) to ensure high availability and fault tolerance.
Performance Tuning: Optimize TCP/IP profile parameters, MTU sizes, and OSA configuration settings (e.g., QDIO mode) to maximize throughput and minimize latency.
Security Segmentation: Utilize VLANs and firewalls to logically segment mainframe network traffic, isolating sensitive applications and enforcing strict access controls.
Capacity Planning: Regularly monitor OSA port utilization and network bandwidth to ensure sufficient capacity for current and projected workload demands.
Network Monitoring: Implement comprehensive network monitoring tools to track OSA port statistics, TCP/IP stack performance, and overall network health, proactively identifying bottlenecks or issues.