IBM eServer zSeries 900 Technical Guide

Chapter 3. Connectivity 161

The HiperSockets LIC supports:

򐂰 Up to four independent HiperSockets

򐂰 Up to 3072 I/O devices across all four HiperSockets

z/OS allows the operation of multiple TCP/IP stacks within a single image. The read

control and write control I/O devices are required only once per image, and are controlled

by VTAM. Each TCP/IP stack within the same z/OS image requires one I/O device for data

exchange.

Running one TCP/IP stack per LPAR, z/OS requires three I/O devices (as do z/VM and

Linux). Each additional TCP/IP stack in a z/OS LPAR requires only one additional I/O

device for data exchange. The I/O device addresses can be shared between z/OS

systems running in different LPARs. Therefore, the number of I/O devices will not be a

limitation for z/OS.

򐂰 Up to 4000 IP addresses across all four HiperSockets

A total of 4000 IP addresses can be kept for the four possible IP address lookup tables.

These IP addresses include the HiperSockets interface, as well as Virtual IP addresses

(VIPA) and dynamic Virtual IP Addresses (DVIPA) that are defined to the TCP/IP stack.

An IP address is registered with its HiperSockets interface by the TCP/IP stack at the time

the TCP/IP device is started. IP addresses are removed from an IP address lookup table

when a HiperSockets device is stopped. Under operating system control, IP addresses

can be reassigned to other HiperSockets interfaces on the same HiperSockets. This

allows flexible backup of TCP/IP stacks.

Note: Reassignment is only possible within the same HiperSockets. A HiperSockets is one

network

or subnetwork. Reassignment is only possible for the same operating system

type.

For example, an IP address originally assigned to a Linux TCP/IP stack can only be

reassigned to another Linux TCP/IP stack, a z/OS dynamic VIPA can only be reassigned

to another z/OS TCP/IP stack, or a z/VM TCP/IP VIPA can only be reassigned to another

z/VM TCP/IP stack. The LIC performs the reassignment in force mode. It is up to the

operating system’s TCP/IP stack to control this change.

3.10.1 Connectivity

HiperSockets has no external components or external network. There is no internal or

external cabling. The HiperSockets data path does not go outside the z900 server platform.

z900 supports up to four HiperSockets being defined. Enabling HiperSockets requires the

definition of a CHPID defined as type=IQD using HCD and IOCP. This CHPID is treated like

any other CHPID and is counted as one of the available 256 real channels of the z900 server.

HiperSockets is not allocated a CHPID until it is defined. It also does not take an I/O cage

slot. Customers who have used all of the 256 CHPIDs on the z900 server can not enable

HiperSockets; therefore, HiperSockets must be included in the customer’s overall channel I/O

planning.

We recommend assigning the CHPID addresses starting at the high end of the CHPID

addressing range (x"FF, FE, FD and FC") to minimize possible addressing conflicts with real

channels. This is similar to the approach when defining other internal channels.

The virtual server operating systems each define their specific connection to each

HiperSockets defined in the HCD. HiperSockets supports up to 3072 devices and 4,000 IP

addresses across the four CHPIDs or “virtual networks.” For z/OS, z/VM, and Linux, the

maximum number of TCP/IP stacks or HiperSockets connections which can concurrently