Mainframe System Programmer – Network Final Master Concept & Interview Explanation Bank

A comprehensive set of practice flashcards covering z/OS networking, TCP/IP fundamentals, SNA/VTAM, and Sysplex architecture concepts suitable for a Mainframe System Programmer review.

What is the core function of a network?

A network allows two or more systems to communicate and exchange data using a communication method called a protocol.

What is a protocol in networking?

A protocol is a set of rules for communication that dictates how systems format, send, and understand data, such as TCP, IP, DNS, and HTTP.

How many bits are used in IPv4 and IPv6 addresses respectively?

IPv4 uses $32$ bits and IPv6 uses $128$ bits.

In an IPv4 address like $192.168.1.10$, how is the address normally written?

As four decimal numbers separated by dots.

What is the purpose of a subnet mask?

It identifies which part of an IPv4 address represents the network and which part represents the host, such as $255.255.255.0$ where the first three parts identify the network.

What is the role of a default gateway?

The default gateway is the router used to forward traffic when the destination is outside the local network.

What is the difference between the functions of ICMP and ARP?

ICMP is used for network control and diagnostic messages (like Ping), while ARP (Address Resolution Protocol) is used to find the MAC address for a known IP address on a local network.

How do TCP and UDP differ as transport protocols?

TCP is connection-oriented, reliable, and uses handshakes and acknowledgements, while UDP is connectionless, has less overhead, and does not guarantee delivery.

What are the three steps of the TCP three-way handshake?

$1.$ Client sends SYN, $2.$ Server replies with SYN-ACK, $3.$ Client sends ACK.

What does the TCP state 'LISTEN' indicate?

It means an application is waiting for incoming connections.

What is a socket?

A socket is a communication endpoint used by an application that is associated with an IP address and a port.

What is the function of the DNS resolver?

The resolver is the part of the system that handles name resolution by contacting DNS servers to map hostnames to IP addresses.

What is the difference between symmetric and asymmetric encryption in TLS?

Symmetric encryption uses the same secret key for encryption and decryption, while asymmetric encryption uses a public key and a private key.

What does a digital certificate bind together?

A certificate binds an identity to a public key and is signed by a Certificate Authority (CA) for verification.

How do FTPS and SFTP differ?

FTPS is the FTP protocol with TLS protection, while SFTP is the SSH File Transfer Protocol which runs over SSH.

Which two major networking worlds are supported by z/OS Communications Server?

TCP/IP (for IP-based communication) and SNA (managed through VTAM).

What is OSA and QDIO?

OSA (Open Systems Adapter) provides physical network connectivity for the mainframe, and QDIO (Queued Direct I/O) is the high-speed I/O method used to move data between the stack and the OSA adapter.

What is the difference between PROFILE.TCPIP and TCPIP.DATA?

PROFILE.TCPIP is the main stack configuration member (IP addresses, routes, ports), while TCPIP.DATA contains resolver information like hostnames and name servers.

In SNA, what is the difference between an LU and a PU?

An LU (Logical Unit) represents a logical communication endpoint for applications, while a PU (Physical Unit) represents a physical or network resource.

What is Enterprise Extender (EE)?

Enterprise Extender allows SNA traffic to travel over an IP network by encapsulating SNA HPR traffic within UDP.

What is PAGENT and its role in AT-TLS?

PAGENT (Policy Agent) manages network policies and makes the AT-TLS policy (identifying which connections use TLS) available to the TCP/IP stack.

What is the purpose of TN3270?

TN3270 allows traditional 3270 terminal sessions to travel over TCP/IP networks instead of original SNA connections.

What is the difference between Sysplex and Parallel Sysplex?

A Sysplex is a group of z/OS systems working together, while a Parallel Sysplex uses a Coupling Facility (CF) for shared structures and fast coordination.

What is XCF?

XCF (Cross-System Coupling Facility) is the component that supports communication between systems in a Sysplex.

What is a DVIPA (Dynamic Virtual IP Address)?

A DVIPA is a virtual address that can be moved or activated dynamically across systems in a Sysplex to ensure high availability.

How does Sysplex Distributor use WLM?

Sysplex Distributor uses workload information from WLM (Workload Manager) to decide which target LPAR has the capacity to handle new incoming connections.

What are HiperSockets?

HiperSockets provide high-speed, internal memory-based communication between LPARs on the same mainframe without using external network hardware.

What is the MTU (Maximum Transmission Unit)?

MTU is the largest packet size that can be sent over a network interface without fragmentation.