Host Name

Enhanced Definition

In the context of IBM mainframe systems and z/OS, a Host Name is a human-readable label assigned to a specific z/OS instance (typically an LPAR) within a TCP/IP network. It serves as a symbolic identifier that maps to one or more IP addresses, enabling users and applications to refer to the z/OS system by a memorable name rather than its numerical IP address.

Key Characteristics

- Symbolic Identification: Provides a user-friendly name (e.g., ZOSPROD.MYCORP.COM) for a z/OS system, abstracting its underlying IP address.
- DNS Resolution: Primarily resolved to an IP address using the Domain Name System (DNS) or, less commonly, through local host tables (/etc/hosts in z/OS UNIX System Services).
- Uniqueness: Must be unique within its specified domain to prevent network addressing conflicts and ensure proper routing.
- Hierarchical Structure: Often follows a Fully Qualified Domain Name (FQDN) structure, indicating its position within a hierarchical domain namespace.
- Configurable: Defined within the z/OS TCP/IP stack configuration, typically in the PROFILE.TCPIP dataset using parameters like HOSTNAME.
- Network Addressing: Essential for any network-enabled service on z/OS, including FTP, Telnet (TN3270), SSH, HTTP servers, and distributed database access.

Use Cases

- Application Connectivity: Client applications (e.g., 3270 emulators, web browsers, custom distributed applications) connect to z/OS services by specifying the z/OS host name.
- Inter-LPAR Communication: z/OS applications on one LPAR communicate with services running on another z/OS LPAR or other network-attached systems using their respective host names.
- System Management & Monitoring: Network operations and system management tools identify and interact with z/OS systems using their host names for logging, alerts, and performance monitoring.
- Security Configuration: Used in firewall rules, network access control lists, and digital certificates to identify and authenticate z/OS systems securely.
- DNS Registration: The host name of a z/OS system is registered in the corporate DNS infrastructure to allow for both internal and external resolution.

Related Concepts

A Host Name is intrinsically linked to TCP/IP networking on z/OS, serving as the symbolic counterpart to an IP Address. It relies heavily on the Domain Name System (DNS) for translating the human-readable name into a machine-readable IP address, which is crucial for network communication. Each LPAR (Logical Partition) running z/OS typically has its own unique host name and associated IP address configuration. The definition of the host name and other network parameters is managed within the PROFILE.TCPIP dataset, which configures the z/OS TCP/IP stack.

Best Practices:

Standardized Naming Conventions: Implement and enforce clear, consistent naming conventions for z/OS host names across all environments (e.g., SYSID.ENV.DOMAIN) to improve manageability and clarity.
Maintain Accurate DNS Records: Ensure that z/OS host names are accurately registered and regularly updated in the corporate DNS to guarantee reliable name resolution.
Use Fully Qualified Domain Names (FQDNs): Always use FQDNs (e.g., zosdev.mycorp.com) in configurations and applications to avoid ambiguity and ensure proper resolution across different network segments.
Consider ETC.HOSTS for Critical Systems: For mission-critical internal connections or as a fallback during DNS issues, maintain relevant entries in the z/OS UNIX /etc/hosts file.
Security and Audit: Regularly audit host name configurations and DNS entries to prevent unauthorized changes or spoofing, which could lead to security vulnerabilities.